*3.2.4 Sour taste*

Acidic pH and organic acids such as acetic acid evokes sour taste in the tongue. A subset of taste receptor cells in the tongue and palate epithelium that respond to acidic pH and weak organic acids with electrical activity detects the sour taste [78, 79]. PKD2L1-expressing cells respond are required for sensory response to acids [72, 78, 80] which is mediated by an unusual proton-selective ion channel [80]. Proton selectivity allows the cells to respond to acids without interference from Na+ , which may vary independently in concentration. The taste of carbonation (CO2) is also detected by PKD2L1-expressing cells. This response is

dependent on a membrane anchored carbonic anhydrase isoform 4, Car4 [81], which interconverts CO2 + H2O to H+ + HCO3 −. How Car4 contributes to the activation of sour cells is still not known.

Fruit flies reject foods that are too acidic and prefer the ones which are slightly acidic, such as carbonated water. Carbonated water triggers Ca2+ influx in the region of the SEZ innervated by taste peg GRNs, suggesting these neurons are involved in CO2 detection [82]. Fruit flies avoid many carboxylic acids with a low pH. Behavioral and physiological analysis reveals that the avoidance to carboxylic acid is mainly mediated by a subset of bitter GRNs [83]. The ionotropic receptor Ir7a has been shown for rejecting foods laced with high levels of acetic acid suggesting flies discriminate foods on the basis of acid composition rather than just pH [84].

#### *3.2.5 Amino acid receptors*

Umami (amino acid taste) is the sensation elicited by glutamate. In humans, umami is only elicited by glutamate, while mice are sensitive to a wider range of L-amino acids [1]. Addition of the nucleotides IMP or GMP potentiates the umami response, distinguishing it from a more general sensing of glutamate [85]. T1R1/ T1R3 is widely recognized as the umami receptor [1].

Fruit flies can taste amino acids too, although their preference is enhanced when raised on a food source devoid of amino acids [86]. Female fruit flies show greatest preference for cysteine, phenylalanine, threonine and tyrosine, while males prefer leucine and histidine. None of the 18 standard amino acids tested stimulates action potentials in GRNs in sugar responsive sensilla [8] raising the possibility of taste pegs in sensing amino acids. Another amino acid, L-canavanine is toxic and elicits an avoidance response in flies [87] and is sensed by GRNs in a subset of S-type sensilla [88]. Gr8a and Gr66a are both required for L-canavanine avoidance [88]. An ionotropic receptor Ir76b has been shown recently for amino acid taste in flies [89].

Activation of fly GRNs by sweet substances, bitter compounds and the amino acid, L-canavanine occur through direct activation of ion channels and G-protein signaling pathways. G proteins subunits Gγ, Goα, Gsα and Gqα are implicated in sugar signaling [90–93]. PLCβ is an effector for Gqα. Knockdown in sugar-responsive GRNs of *plc*β*21c* or any of the genes encoding TRPC channels (TRP, TRPL and TRPγ) alters the behavioral response to trehalose [92]. Role of G-protein coupled signaling pathways in sensation of bitter tastants has also been suggested for example AC78C is required for the response to caffeine [94], and the PLCβ encoded by *norpA* is required in *trpA1*-expressing GRNs for the behavioral and electrophysiological responses to the bitter compound, aristolochic acid [64] suggesting a role of Gq/PLC/TRPA1 pathway functions in the detection of aristolochic acid. Goα47A is needed for detection of L-canavanine [95]. The predicted role of G-protein coupled signaling pathways in insect taste is to enhance the responses to low concentrations of ligands, as seen for photo transduction cascade in amplifying the response to a photon of light.

#### **3.3 Taste coding**

Taste in flies and mammals use labeled line model of coding (in which each cell represents a distinct taste quality and communicates essentially without interruption to the central nervous system). Single taste neurons in flies can detect multiple taste qualities having the same valence (behavioral output) supported by the results that some GRNs are activated by sugars, and low levels of fatty acids,

**137**

be determined.

*Understanding Taste Using* Drosophila melanogaster *DOI: http://dx.doi.org/10.5772/intechopen.89643*

behaviors [77].

to behavior, as is the case in flies.

**3.4 Taste modulation in** *Drosophila*

both of which promote feeding [96] while other GRNs are activated by bitter compounds and high concentrations of salt and suppress feeding [20]. In addition, a subset of bitter GRNs is also activated by low pH carboxylic acids, which are feeding deterrents [83]. A complex model for salt coding in flies that combinatorially integrates inputs from across cell types to afford robust and flexible salt

The taste system of mice also uses a variant of the labeled line model. In mice, taste receptors are segregated into distinct populations such that bitter, sweet, sour and low concentrations of salt are detected by non-overlapping sets of cells [1, 58]. Whether this principle applies to sweet and umami is presently unclear. Recent evidence suggest that aversive high concentrations of salt are not detected by a separate subset of cells, but are instead detected by the populations of cells that detect bitter and sour [72] suggesting that the mammalian taste system is relatively hard-wired

Modulation of taste neuron activity prior to the first relay has been suggested. Presence of multiple molecular and cellular mechanisms by which tastant information is integrated in primary taste neurons has been proposed [97]. Various studies suggest that aversive tastants such as bitter compounds and acids, can inhibit the activity of appetitive taste circuits in adult flies and larvae [83, 98, 99]. The reduction of the firing rate of sweet neurons in mixtures of sucrose and the aversive tastants is independent of the activity of the deterrent neuron [83, 98, 99]. Bitter compounds suppress feeding by activating bitter—GRNs and by inhibiting sugar sensitive GRNs [11]. The suppression of sugar GRNs depends on a odorant binding proteins" (OBP), OBP49a, which is expressed in gustatory organs or indirectly via GABAergic interneurons that connect bitter taste neuron activity to that of sweet taste neurons [100, 101]. Accessory cells synthesized OBP49a and release it into endolymph fluid bathing the GRNs, which then acts non-cell autonomously on sugar activated GRNs. OBP49a binds directly to bitter compounds, and later interacts with the sugar receptor, Gr64a, on the cell surface of the GRNs to suppress its activity [101]. Such non-cell autonomous modulation of the sugar response ensures that bitter compounds in sugar-laden foods are not consumed. Low concentrations of acid tastants have also been observed to modulate detection of bitter compounds in the context of both sweet and deterrent neurons, suppressing their inhibitory effect in the former and their excitatory effect in the latter [102]. Although the mechanisms by which carboxylic acids or low pH inhibit taste neurons remains to

Internal state can change the gustatory sensitivity as well: starvation potentiates the responses of sweet GRN and suppresses bitter GRN responses; mating increases taste peg GRN sensitivity to polyamines and behavioral responses to low salt in females; and protein deprivation sensitizes taste peg GRNs to yeast and increases behavioral sensitivity to amino acids [86, 103–108]. Taste neuron sensitivity is also modulated by prior dietary experience. Response to camphor (non-toxic bitter compound) decrease after exposing flies to camphor for long [66]. An E3 ubiquitin ligase-regulated decline in the levels of Trpl caused the change in sensitivity. No calories diet also cause increase activity in the *Gr5a*+ sweet taste circuit [104, 109] and reduce sensitivity in the bitter taste circuit [105]. In the former case, dopamine signaling acting on the both primary and secondary neurons in the sweet circuit caused the change in sensitivity [104, 109]. The latter is dependent on sNPF acting via GABAergic interneurons [105]. A significant modulation of fly salt taste behav-

ior by salt deprivation has been shown recently [77].

*Understanding Taste Using* Drosophila melanogaster *DOI: http://dx.doi.org/10.5772/intechopen.89643*

*Animal Models in Medicine and Biology*

which interconverts CO2 + H2O to H+

just pH [84].

*3.2.5 Amino acid receptors*

activation of sour cells is still not known.

T1R3 is widely recognized as the umami receptor [1].

recently for amino acid taste in flies [89].

dependent on a membrane anchored carbonic anhydrase isoform 4, Car4 [81],

+ HCO3

Umami (amino acid taste) is the sensation elicited by glutamate. In humans, umami is only elicited by glutamate, while mice are sensitive to a wider range of L-amino acids [1]. Addition of the nucleotides IMP or GMP potentiates the umami response, distinguishing it from a more general sensing of glutamate [85]. T1R1/

Fruit flies can taste amino acids too, although their preference is enhanced when raised on a food source devoid of amino acids [86]. Female fruit flies show greatest preference for cysteine, phenylalanine, threonine and tyrosine, while males prefer leucine and histidine. None of the 18 standard amino acids tested stimulates action potentials in GRNs in sugar responsive sensilla [8] raising the possibility of taste pegs in sensing amino acids. Another amino acid, L-canavanine is toxic and elicits an avoidance response in flies [87] and is sensed by GRNs in a subset of S-type sensilla [88]. Gr8a and Gr66a are both required for L-canavanine avoidance [88]. An ionotropic receptor Ir76b has been shown

Activation of fly GRNs by sweet substances, bitter compounds and the amino acid, L-canavanine occur through direct activation of ion channels and G-protein signaling pathways. G proteins subunits Gγ, Goα, Gsα and Gqα are implicated in sugar signaling [90–93]. PLCβ is an effector for Gqα. Knockdown in sugar-responsive GRNs of *plc*β*21c* or any of the genes encoding TRPC channels (TRP, TRPL and TRPγ) alters the behavioral response to trehalose [92]. Role of G-protein coupled signaling pathways in sensation of bitter tastants has also been suggested for example AC78C is required for the response to caffeine [94], and the PLCβ encoded by *norpA* is required in *trpA1*-expressing GRNs for the behavioral and electrophysiological responses to the bitter compound, aristolochic acid [64] suggesting a role of Gq/PLC/TRPA1 pathway functions in the detection of aristolochic acid. Goα47A is needed for detection of L-canavanine [95]. The predicted role of G-protein coupled signaling pathways in insect taste is to enhance the responses to low concentrations of ligands, as seen for photo transduction cascade in amplifying the response to a

Taste in flies and mammals use labeled line model of coding (in which each cell represents a distinct taste quality and communicates essentially without interruption to the central nervous system). Single taste neurons in flies can detect multiple taste qualities having the same valence (behavioral output) supported by the results that some GRNs are activated by sugars, and low levels of fatty acids,

Fruit flies reject foods that are too acidic and prefer the ones which are slightly acidic, such as carbonated water. Carbonated water triggers Ca2+ influx in the region of the SEZ innervated by taste peg GRNs, suggesting these neurons are involved in CO2 detection [82]. Fruit flies avoid many carboxylic acids with a low pH. Behavioral and physiological analysis reveals that the avoidance to carboxylic acid is mainly mediated by a subset of bitter GRNs [83]. The ionotropic receptor Ir7a has been shown for rejecting foods laced with high levels of acetic acid suggesting flies discriminate foods on the basis of acid composition rather than

−. How Car4 contributes to the

**136**

photon of light.

**3.3 Taste coding**

both of which promote feeding [96] while other GRNs are activated by bitter compounds and high concentrations of salt and suppress feeding [20]. In addition, a subset of bitter GRNs is also activated by low pH carboxylic acids, which are feeding deterrents [83]. A complex model for salt coding in flies that combinatorially integrates inputs from across cell types to afford robust and flexible salt behaviors [77].

The taste system of mice also uses a variant of the labeled line model. In mice, taste receptors are segregated into distinct populations such that bitter, sweet, sour and low concentrations of salt are detected by non-overlapping sets of cells [1, 58]. Whether this principle applies to sweet and umami is presently unclear. Recent evidence suggest that aversive high concentrations of salt are not detected by a separate subset of cells, but are instead detected by the populations of cells that detect bitter and sour [72] suggesting that the mammalian taste system is relatively hard-wired to behavior, as is the case in flies.

## **3.4 Taste modulation in** *Drosophila*

Modulation of taste neuron activity prior to the first relay has been suggested. Presence of multiple molecular and cellular mechanisms by which tastant information is integrated in primary taste neurons has been proposed [97]. Various studies suggest that aversive tastants such as bitter compounds and acids, can inhibit the activity of appetitive taste circuits in adult flies and larvae [83, 98, 99]. The reduction of the firing rate of sweet neurons in mixtures of sucrose and the aversive tastants is independent of the activity of the deterrent neuron [83, 98, 99]. Bitter compounds suppress feeding by activating bitter—GRNs and by inhibiting sugar sensitive GRNs [11]. The suppression of sugar GRNs depends on a odorant binding proteins" (OBP), OBP49a, which is expressed in gustatory organs or indirectly via GABAergic interneurons that connect bitter taste neuron activity to that of sweet taste neurons [100, 101]. Accessory cells synthesized OBP49a and release it into endolymph fluid bathing the GRNs, which then acts non-cell autonomously on sugar activated GRNs. OBP49a binds directly to bitter compounds, and later interacts with the sugar receptor, Gr64a, on the cell surface of the GRNs to suppress its activity [101]. Such non-cell autonomous modulation of the sugar response ensures that bitter compounds in sugar-laden foods are not consumed. Low concentrations of acid tastants have also been observed to modulate detection of bitter compounds in the context of both sweet and deterrent neurons, suppressing their inhibitory effect in the former and their excitatory effect in the latter [102]. Although the mechanisms by which carboxylic acids or low pH inhibit taste neurons remains to be determined.

Internal state can change the gustatory sensitivity as well: starvation potentiates the responses of sweet GRN and suppresses bitter GRN responses; mating increases taste peg GRN sensitivity to polyamines and behavioral responses to low salt in females; and protein deprivation sensitizes taste peg GRNs to yeast and increases behavioral sensitivity to amino acids [86, 103–108]. Taste neuron sensitivity is also modulated by prior dietary experience. Response to camphor (non-toxic bitter compound) decrease after exposing flies to camphor for long [66]. An E3 ubiquitin ligase-regulated decline in the levels of Trpl caused the change in sensitivity. No calories diet also cause increase activity in the *Gr5a*+ sweet taste circuit [104, 109] and reduce sensitivity in the bitter taste circuit [105]. In the former case, dopamine signaling acting on the both primary and secondary neurons in the sweet circuit caused the change in sensitivity [104, 109]. The latter is dependent on sNPF acting via GABAergic interneurons [105]. A significant modulation of fly salt taste behavior by salt deprivation has been shown recently [77].

#### **3.5 Non-canonical taste qualities**

#### *3.5.1 Fats*

Vertebrates can sense a variety of other important taste qualities such as wetness and fattiness. Olfaction and somatosensation helps in the detection of fats, and they elicit post-ingestive effects that promote consumption. It has been shown that mice prefer water spiked with free fatty acids supports a role for the taste system in detecting this rich source of calories [110].  GPR120 is required for preference to fatty acids in mice [112] and is expressed in human TRCs as well [113].

In flies, sweet GRN activation requires the function of the three *Ionotropic receptor* genes *Ir25a*, *Ir76b* and *Ir56d*. *Ir25a and Ir76b* are expressed in several neurons per sensillum, while *IR56d* expression is restricted to sweet GRNs. *Ir25a* and *Ir76b* mutant flies loose appetitive behavioral responses to fatty acids. The phenotype can be rescued by expression of respective transgenes in sweet GRNs [114].

#### *3.5.2 Calcium taste*

Ca2+, an ion is required for a vast array of cellular functions. Ca2+-deprived animals show attraction and Ca2+-sated animals show rejection. The aversive response to Ca2+requires a functioning T1R3 receptor, a subunit of the umami and sweet receptor [115]. In human subjects an attenuation of the taste of Ca2+ by the T1R3 blocker lactisole has been shown [116].

Fruit flies avoids toxic levels of calcium. This repulsion is mediated by two mechanisms—activation of a specific class of GRNs that suppresses feeding, and inhibition of sugar-activated GRNs, which normally stimulates feeding. The distaste for Ca2+, and electrophysiological responses to Ca2+ require three members of the variant ionotropic receptor family Ir25a, Ir62a and Ir76b. The high concentrations of Ca2+ show decrease survival in flies [117].

#### *3.5.3 Water*

No water receptor has been identified in vertebrate so far. The somatosensory system of animals can detect wetness across their body and also contribute to the sensing of aqueous solutions in the oral cavity. Various tastes have been ascribed to distilled water, from bitter to salty and sweet. Notably, application of water after exposure to some artificial sweeteners, such as saccharin, elicits a sweet taste [118].

A member of the Degenerin/Epithelial Sodium Channel family, ppk28 (an osmosensitive ion channel) mediates the cellular and behavioral response to water in flies. *ppk28* is expressed in water-sensing neurons and loss of *ppk28* abolishes water sensitivity [119].

#### **3.6 Taste signal processing and taste sensory maps in the** *Drosophila* **brain**

In flies, after evaluation of taste input, the information translates into an appropriate behavioral response such as feeding, cessation of feeding, search for alternative food source, courtship, or egg-laying. Detection of sweet compounds by labellum GRs induces a sucking response and sugar detection by the tarsi induces extension of proboscis. It is a requirement to understand the flow of information

**139**

learning [97].

**4. Conclusions**

*Understanding Taste Using* Drosophila melanogaster *DOI: http://dx.doi.org/10.5772/intechopen.89643*

from peripheral activation of GRNs to behavioral output to gain insight into the

Unlike mammalian taste cells, fly GRNs from labellum and pharynx send projections of axons directly to the SEZ area of the brain. GRNs in the ovipositor, wings, and some leg sensilla send projections to the thoracic ganglia [24, 25]. Taste neurons send their axons to loosely defined, widely circumscribed zones in the SEZ or thoracic ganglia [32]. Labial palp *Gr5a* positive GRNs project to large areas in the lateral and anterior region of the SEZ, whereas the *Gr66a*-expressing GRNs project to the medial part of the SEZ [6, 7]. Information from GRNs of the legs activates non-overlapping areas of the SEZ than GRNs of the labial palps, suggesting different behavioral outputs of neurons responding to the same ligand but located in different taste tissues. Functional domains of taste have been mapped in the brain using live flies expressing the calcium-sensitive indicator G-CaMP [120] (G-CaMP protein is a fusion of the calmodulin-binding domain from the myosin chain kinase (M13 peptide), permutated EGFP and the calmodulin) in response to sugars and bitter compounds suggesting different taste compounds activate distinct neural ensembles in the SEZ. In terms of their taste quality, organ location, and in some cases sensillar type, at least 10 categories of patterns have been defined in the SEZ and nine in the thoracic abdominal ganglia. Each category is a unique combination

The SEZ is a primary gustatory center, the higher brain centers where taste information is conveyed from the SEZ are unknown. Recently, sweet second order projection neurons that relay sweet taste information from the SEZ to the antennal and mechanosensory motor center (AMMC) in the deutocerebrum were described [109]. The results support the role of AMMC (generally receives input from mechanosensory and olfactory neurons) in processing multisensory information. Various other studies have identified interneurons that impinge on taste circuits and feeding behavior routines, including a feeding promoting command neuron, feeding promoting dopaminergic neurons, bitter sensitive projection interneurons, feeding restrain GABAergic neurons and neurons in the ventral nerve cord that

The taste representations in the mushroom bodies (MB) (sites for associative learning) examined recently and found that input to the main calyx continues to be segregated according to taste modality and the location that taste information originates from. The bitter and sweet stimuli activate distinct areas, and stimuli from different taste organs activate partially overlapping but distinct patterns [127]. The information about water and sweet qualities, as well as nutritive and non-nutritive sugars is also separated in MB [128, 129]. Unraveling taste circuits, therefore, will be important not only for understanding how sensory input is translated to behavioral output, but also how taste associations are formed in reward and aversive

*Drosophila* Grs, IRs, Trp, and ppk receptors underlie detection of various categories of tastants but a lot remains undetermined about the composition and response properties of taste receptors. How combinations of GRs and IRs belonging to different receptor families (e.g. Gr and IR), coordinate within the neurons that house them is a subject of investigation. Feeding behavior is root cause of metabolic disorders. A better understanding of the biology of metabolic disorders in association with GRs, IRs, Trp, and ppk receptors is a need of the hour because of the burden of metabolic disorders, high incidences of cardiovascular diseases, faster

neuronal wiring of the taste at each level of information processing.

of discrete patterns elements that define taste neurons [97].

balance feeding and locomotion [121–126].

#### *Understanding Taste Using* Drosophila melanogaster *DOI: http://dx.doi.org/10.5772/intechopen.89643*

*Animal Models in Medicine and Biology*

**3.5 Non-canonical taste qualities**

Vertebrates can sense a variety of other important taste qualities such as wetness

channels that are sensitive to polyunsaturated fatty acids [111].

and fattiness. Olfaction and somatosensation helps in the detection of fats, and they elicit post-ingestive effects that promote consumption. It has been shown that mice prefer water spiked with free fatty acids supports a role for the taste system in detecting this rich source of calories [110]. A fatty acid transporter (CD36) and two fat-sensitive GPCRs—GPR40 and GPR120 are putative receptors for fat

GPR120 is required for preference to fatty acids in mice [112] and is expressed in

be rescued by expression of respective transgenes in sweet GRNs [114].

In flies, sweet GRN activation requires the function of the three *Ionotropic receptor* genes *Ir25a*, *Ir76b* and *Ir56d*. *Ir25a and Ir76b* are expressed in several neurons per sensillum, while *IR56d* expression is restricted to sweet GRNs. *Ir25a* and *Ir76b* mutant flies loose appetitive behavioral responses to fatty acids. The phenotype can

Ca2+, an ion is required for a vast array of cellular functions. Ca2+-deprived animals show attraction and Ca2+-sated animals show rejection. The aversive response to Ca2+requires a functioning T1R3 receptor, a subunit of the umami and sweet receptor [115]. In human subjects an attenuation of the taste of Ca2+ by the T1R3

Fruit flies avoids toxic levels of calcium. This repulsion is mediated by two mechanisms—activation of a specific class of GRNs that suppresses feeding, and inhibition of sugar-activated GRNs, which normally stimulates feeding. The distaste for Ca2+, and electrophysiological responses to Ca2+ require three members of the variant ionotropic receptor family Ir25a, Ir62a and Ir76b. The high concentra-

No water receptor has been identified in vertebrate so far. The somatosensory system of animals can detect wetness across their body and also contribute to the sensing of aqueous solutions in the oral cavity. Various tastes have been ascribed to distilled water, from bitter to salty and sweet. Notably, application of water after exposure to some artificial sweeteners, such as saccharin, elicits a sweet

A member of the Degenerin/Epithelial Sodium Channel family, ppk28 (an osmosensitive ion channel) mediates the cellular and behavioral response to water in flies. *ppk28* is expressed in water-sensing neurons and loss of *ppk28* abolishes

**3.6 Taste signal processing and taste sensory maps in the** *Drosophila* **brain**

In flies, after evaluation of taste input, the information translates into an appropriate behavioral response such as feeding, cessation of feeding, search for alternative food source, courtship, or egg-laying. Detection of sweet compounds by labellum GRs induces a sucking response and sugar detection by the tarsi induces extension of proboscis. It is a requirement to understand the flow of information

*3.5.1 Fats*

taste including K+

*3.5.2 Calcium taste*

*3.5.3 Water*

taste [118].

water sensitivity [119].

human TRCs as well [113].

blocker lactisole has been shown [116].

tions of Ca2+ show decrease survival in flies [117].

**138**

from peripheral activation of GRNs to behavioral output to gain insight into the neuronal wiring of the taste at each level of information processing.

Unlike mammalian taste cells, fly GRNs from labellum and pharynx send projections of axons directly to the SEZ area of the brain. GRNs in the ovipositor, wings, and some leg sensilla send projections to the thoracic ganglia [24, 25]. Taste neurons send their axons to loosely defined, widely circumscribed zones in the SEZ or thoracic ganglia [32]. Labial palp *Gr5a* positive GRNs project to large areas in the lateral and anterior region of the SEZ, whereas the *Gr66a*-expressing GRNs project to the medial part of the SEZ [6, 7]. Information from GRNs of the legs activates non-overlapping areas of the SEZ than GRNs of the labial palps, suggesting different behavioral outputs of neurons responding to the same ligand but located in different taste tissues. Functional domains of taste have been mapped in the brain using live flies expressing the calcium-sensitive indicator G-CaMP [120] (G-CaMP protein is a fusion of the calmodulin-binding domain from the myosin chain kinase (M13 peptide), permutated EGFP and the calmodulin) in response to sugars and bitter compounds suggesting different taste compounds activate distinct neural ensembles in the SEZ. In terms of their taste quality, organ location, and in some cases sensillar type, at least 10 categories of patterns have been defined in the SEZ and nine in the thoracic abdominal ganglia. Each category is a unique combination of discrete patterns elements that define taste neurons [97].

The SEZ is a primary gustatory center, the higher brain centers where taste information is conveyed from the SEZ are unknown. Recently, sweet second order projection neurons that relay sweet taste information from the SEZ to the antennal and mechanosensory motor center (AMMC) in the deutocerebrum were described [109]. The results support the role of AMMC (generally receives input from mechanosensory and olfactory neurons) in processing multisensory information. Various other studies have identified interneurons that impinge on taste circuits and feeding behavior routines, including a feeding promoting command neuron, feeding promoting dopaminergic neurons, bitter sensitive projection interneurons, feeding restrain GABAergic neurons and neurons in the ventral nerve cord that balance feeding and locomotion [121–126].

The taste representations in the mushroom bodies (MB) (sites for associative learning) examined recently and found that input to the main calyx continues to be segregated according to taste modality and the location that taste information originates from. The bitter and sweet stimuli activate distinct areas, and stimuli from different taste organs activate partially overlapping but distinct patterns [127]. The information about water and sweet qualities, as well as nutritive and non-nutritive sugars is also separated in MB [128, 129]. Unraveling taste circuits, therefore, will be important not only for understanding how sensory input is translated to behavioral output, but also how taste associations are formed in reward and aversive learning [97].


*2.2.1. Ostriches and peacocks in the donors' arena*

Individuals might have many reasons to embrace prosocial behaviors and donate to charities. While some people are altruistic, and want to maximize the benefit and well-being of others, others are moved by more egoistic reasons and want something in exchange for their good deeds. They might seek public recognition, enhance their self-esteem, create a good impression, or increase their sense of belonging [20, 24, 25]. There are donors who want to remain in anonymity, and others show a conspicuous donation behavior (i.e., they want to overtly display their support for charities with the use of merchandise or symbols) [24, 25]. For the latest, NGOs and charities usually have empathy ribbons, pins, and badges that visibly demonstrate one person's affiliations, interests, and participation with different causes.

For those NGOs that have moved to the digital world, there is also an opportunity to provide donors with virtual tokens to strengthen relationships with the different stakeholders while providing the desired visibility. Among other tools, there are "twibbons" (i.e., virtual ribbons that can be used both in Facebook and Twitter), photo frames, and badges that donors can share or embed on social media pages [25]. Some Facebook pages also allow donors to update their status and share the information with their own peers. These virtual tokens transform private actions (i.e., blood donation) into a publicly recognized behavior, which might motivate donors who seek social value and benefit from the warm-glow that comes from behaving prosocially [20].

To enhance conversation, share information about a cause, or demonstrate support, members of an OSCC can also use the hashtag symbol (#). The hashtag allows ordering and quick retrieval of information about a specific topic, but it also serves as a channel to get out a message and to attract visibility and attention from different publics. Hashtags can easily become trending topics and inspire others to follow the conversation, turning a simple character into a powerful form of digital activism [26].

the four virtual communities studied, where we observed that its members have their goal to support the causes of their interest through donations, voluntary work, or signing petitions

925,331 Greenpeace is an independent global campaigning organization that acts to

357,482 Suspended Coffees is a nonprofit organization partnering with a variety of

change attitudes and behavior, to protect and conserve the environment and

Marketing Strategies for the Social Good http://dx.doi.org/10.5772/intechopen.73683 121

businesses around the world, helping to bring communities together and change peoples' lives, by giving free coffee and meals to people in need.

revolutionizing the way people cause changes in the network. It allows anyone, anywhere, to start and win campaigns for social change.

their potential. UNICEF was created with this purpose in mind – to work with others to overcome the obstacles that poverty, violence, disease and

Upon joining the Facebook community, members see regular posts from the issue-based OSCC, published by the administrators or leaders of the community in the Facebook news feed. They can use either videos, photos, stories, or infographics to grab people's attention, strengthen the links with the community members, and invite them to take action (e.g., make a donation, share a comment, vote for certain issue, etc.). In turn, the latter demonstrate their commitment and loyalty by using the dynamic and interactive tools of the network (likes, shares, hashtags, etc.), which allow them to interact with other members, engage in conversations, viralize the contents they find more attractive and interesting, or demonstrate their

With our analysis, we found that most posts can be classified in six categories: (1) for economic purposes (e.g., raise funds, sale of promotional merchandise, etc.), (2) mobilization/ call to action (e.g., sign petitions, use hashtags, share publications, collect signatures, peaceful marches, etc.), (3) educational (i.e., provide facts and/or instructions regarding an specific issue), (4) community building (i.e., encourage dialog among followers, with publications that motivate and generate a sense of pride and belonging), (5) inspiration (i.e., share testimonials and achieved milestones, as well as uplifting and inspiring quotes), and (6) empowerment (i.e., give members of the community skills, knowledge, abilities, and the opportunity

To be able to collect funds on Facebook, the organization must set up a dedicated page to share their mission and story and then add a donate button to their page header or to specific posts and live videos. Once the button is set, visitors will be able to donate through a website or through Facebook. Of the four studied communities, three of them have an active donate button that leads potential donors to a website (Greenpeace Mexico, Change.org, and

for support, among other actions.

Source: Our elaboration with Facebook data.

**Table 1.** OSCC characteristics.

**OSCC Followers General description**

to promote peace.

Change.org 1.5 million Change.org is the largest online petitions platform in the world. It is

UNICEF 6.9 million UNICEF saves children's lives, defends their rights, and helps them fulfill

discrimination place in a child's path.

Greenpeace Mexico

USA

Suspended coffees

position before a social or ecological cause.

to make choices).


**Je** ff**rey Haynes**

School of Social Sciences, London Metropolitan University, London N7 8DB, UK<EMAIL_ADDRESS>Received: 23 April 2020; Accepted: 5 May 2020; Published: 13 May 2020

**Abstract:** Recent years have seen a growing literature on the interactions between peace, politics and religion, including their diverse and often complex relationships. Underpinning this literature is an increase, more generally, in scholarly and policy interest in connections between religion and politics. The context is that over the last three decades, religion has made a remarkable return to prominence in various academic literatures, including sociology, political science and international relations. This was a surprise to many social scientists and confounded the expectations of both secularization theorists and secularists. In addition, religion retained a strong, some say growing, significance as a core source of identity for billions of people around the world. Numerous religious leaders and faith-based organizations are important carriers and focal points of religious ideas, playing an important role in many countries, both developed and developing, as well as internationally, including at the United Nations and to a lesser, although still notable extent, in the European Union and other regional organizations. This introductory article examines interactions between religious entities in relation to peace and conflict and sets the scene for the articles comprising this volume.

**Keywords:** peace; politics; conflict; religion; faith; faith-based organizations

Recent years have seen a growing literature on the interactions between peace, politics and religion, including their diverse and often complex relationships. Underpinning this literature is an increase, more generally, in scholarly and policy interest in connections between religion and politics. Sind the 1980s, there has been renewed scholarly interest in the social sciences regarding how religion affects outcomes in the discipline's various sub-disciplines, including the study of politics. Many social scientists were very surprised by this development; most at this time were adherents of the secularization thesis. This maintained that as societies modernized they would inevitably secularize. Things turned out di fferently: instead, religion has retained a strong, some say growing, significance as a core source of identity for billions of people around the world. In addition, numerous religious individuals and faith-based organizations (FBOs) are important carriers and focal points of religious ideas. They play an important role not only in numerous countries around the world, but also in some of the world's major international organizations, including the United Nations, the European Union and the Organization of Islamic Cooperation.

Why does social science now pay more attention to what religion does in terms of outcomes? It is often suggested that religion has an important, sometimes pivotal role, in conflict. Religion can either be a cause of conflict, or a key component in helping resolve conflict. In addition, once religion has established a key role in ending conflict, it may then pay a role in helping build sustained peace. That being said, it is certainly the case that when someone is asked how they regard the role of religion in various aspects of conflict, then many would suggest that it is noteable primarily for causing or exacerbating conflict, not helping resolve it. In this respect, there is much empirical evidence amassed over the last few decades to substantiate the notion that religion is more the problem than the solution to many of the world's more enduring conflicts, both within countries and between them. In the West, for example, religious hatred characterized the recently quelled conflict in Northern Ireland, while in the USA, culture wars between religionists and secularists have widened and deepening during the controversial presidency of Donald Trump. On the other hand, there is growing evidence that religious leaders and FBOs can, if so minded, play highly constructive roles in helping end societal violence and interstate conflicts. How might they do this? They can alert their followers and others to the dangers that an emerging conflict poses for societal harmony, they can do their best to help resolve conflicts when the have begun, and they can be advocates for peace and conflict resolution. They can o ffer to be mediators between conflicting parties and can seek to bring them together once peace is won. In short, contemporary discussions about the relationship between peace, politics and religion necessarily highlight that religion can both encourage conflict *and* peace, through the activities of people individually and collectively, imbued with faith-based ideas and ideals.

Given the often-messy nature of religiously-informed conflict, it is no surprise that we do not have a sole, sophisticated theoretical model enabling us to understand clearly all the applicable cases of religion's relationship with peace and politics. We can, however, note that often the involvement of religion in conflict comes in the context of what might be called "good governance" issues, which are in turn often linked to the multiple impacts of globalization both within and between countries. The impact of post-Cold War globalization—which I characterize as having four main, interactive dimensions: economic, political, cultural and technological—may highlight or exacerbate previously dormant religious tensions, often by undermining or dismantling traditional value systems, which cannot cope with the changes which globalization brings. It is often suggested that, as a result, numerous people feel increasingly bewildered and distressed, and their attentions may turn to religion to help them recover their equilibrium and sense of wellbeing. Put another way, numerous (re)turn to faith to (re)discover a lost sense of comfort, serenity, stability, as well as to uplift themselves spiritually. There is however another potential impact: (re)discovering faith may also encourage believers to experience novel or changed feelings of identity. On the one hand, this can lead to helping provide them with renewed meaning and purpose. On the other hand, it can encourage them to regard others with disfavour or distaste and the outcome can be new or heightened interreligious competition and conflict, making pursuit of peace especially problematic.

It is widely noted that post-Cold War globalization has led to greatly increased global interactions between people and communities. As a result, over the last three decades encounters between people of di ffering religious traditions have become increasingly common—although, sadly, this has not always led to increasingly harmonious outcomes. Such conflicts, involve, variously, small groups or larger sections of people, who self-identify by their and others' racial, ethnic or religious characteristics, and find reasons for tensions or conflict as a result. Such conflicts can become all-consuming and very di fficult to resolve, as they appear to many as existential struggles between "good" against "evil", with religion as a dependent variable. This development is played out in some countries, for example, in Iran and the USA, and characterized by the outbreak of "culture wars" between strongly religious and stridently secular people. Such culture wars can be seemingly endless; there may seem no room for compromise between two polarised worldviews, which encourage very di fferent allegiances and standards in certain fundamental aspects of life, including: family, law, education and politics.

We have noted that societal and political conflicts may have significant religious dimensions, whereby real or perceived related di fferences between people can drive both hatred and violence. The implication is that religious actors, including religious leaders and FBOs, can be characterized, albeit generally, predominantly as those who pursue peace avidly and those who are more concerned with triumphing in a conflict, if necessary by the sustained use of force. Religion's inconsistency in this respect stems from the fact that the world religions—Buddhism, Christianity, Hinduism, Islam and Judaism,—all have ambivalent views about peace, cooperation, violence and conflict. Such inconsistency is made clear when we think about various manifestations of religious involvement in large-scale conflicts. For example, large-scale violence in sub-Saharan Africa, Asia and other parts of the world is often associated with serious social conflicts, many of which significantly involve levels of religious, cultural and/or civilizational tensions (Haynes 2019a). Yet, in virtually all such cases, what appear to be religious tensions that erupt into conflict and violence are also intimately linked to other, non-religious, issues, including: ethnicity, gender, culture, class, power and wealth. Such strains and stresses may be played out both within countries in recent years, in, for example, Northern Ireland, Egypt, Nigeria, Fiji, Cyprus, Sri Lanka, or between them, for example, India and Pakistan, and Israel and Palestine (Haynes 2019b).

Let me be clear: I am not suggesting that religion's involvement in societal or political interactions always leads to conflict or even challenges to peace or the status quo. What I am suggesting is that religion's inconsistency in this regard is reflected in the fact that it *can* play a significant role in attempts to resolve inter- and intra-group clashes and help build peace, or it can stimulate or exacerbate a decline of the peace. This also underlines how the traditions underpinning and informing many religious expressions, including the five world religions, contain often multiple references to conflict and division and their consequences in terms of group harmony. The world religions also have a lot to say about how their followers *should* behave in order to achieve greater intersocietal harmony and peace not only among fellow believers abut also in relation to those of a di fferent religion. These issues have provided the stimulus to numerous books, book chapters, journal articles, blogs and reports since the 1980s. Many valuable sources in relation to religion, conflict and peace are noted or analysed in the articles which make up the special issue, so I will not provide a comprehensive list here. The key point to note is that, while often di ffering greatly in terms of subject matter and conclusions, collectively they focus on how sundry religious actors can play a role in stimulating, exacerbating or helping arrive at the termination of conflicts. Seeking to summarize a huge set of findings regarding religious peacebuilding and what is often referred to as "faith-based diplomacy", we can note the following, derived from Appleby's (2006) thought provoking and influential work on this topic:

These communities are symbolically charged sources of personal as well as collective identity, which typically establish, maintain and help embed essential educational and welfare institutions, often serving the entire community and not just specified followers of a particular religious tradition (Appleby 2000, 2006).

### **Societal and Political Conflicts: Religion as a Potential Bridge towards Peace**

As we have already noted, the premise of religious involvement in both conflict and peacemaking and peacebuilding points to all five world religions. We also took in to account that interactive processes of globalization lead to greatly increased interactions between people, including those who are widely separated geographically and culturally. Finally, we have seen that as a consequence of enhanced globalization over the last 30 years, encounters between followers of various religious traditions have also increased greatly. That they are not always harmonious is obvious; we have seen that religion is often regarded by social scientists as a key cause of tensions and conflict in many parts of the world, both within and between countries. This is the case with, for examples, the decades-long Israel/Palestinians culture wars and that involving Kashmir, consistently squabbled over by successive governments in Pakistan and India, as well as in the United States today, during the Trump presidency in relation to, for example, abortion, education, and LGBTQ and women's rights (Haynes 2019b). What causes such culture-based conflicts? According to Kurtz, they surface, develop and consolidate because of conflicting cultural worldviews, very often with a pronounced religious dimension. Such issues tend to exacerbate already-present areas of tension, leading them into various fundamental areas, typically linked to societal, gender, state, territorial, and/or political topics. A result is that they "take on 'larger-than-life' proportions as the struggle of good against evil" (Kurtz 1995, p. 170). According to the eminent Roman Catholic theologian, Hans Kung,

[T]he most fanatical, the cruelest political struggles are those that have been colored, inspired, and legitimized by religion. To say this is not to reduce all political conflicts to religious ones, but to take seriously the fact that religions share in the responsibility for bringing peace to our torn and warring world.

> (Kung cited in Smock 2004)

In short, many contemporary conflicts have religious and/or cultural roots, increasing both hatred and violence and driving communities apart.

As already noted, religious leaders and FBOs can function either as core actors in the benign pursuit of peace or in the tragic development of serious and sustained conflict. What Scott Appleby (Appleby 2000) calls the *ambivalence of the sacred* is intimately linked to the fact that the relationship of the world religions to violence is itself indecisive. As Holenstein (2005, p. 10) reminds us

All great God-narratives are familiar with traditions that legitimise force in certain circumstances, claim victims in the battle for their own beliefs and demonise people of other religions. However, at the same time there are sources that proclaim the incompatibility of violence with religion, demand sacrifices for peace and insist on respect for people of other religions. If we are to assume that, for the foreseeable future, the religions of the world will continue to be a factor in political conflicts, then it is high time that we strengthened the "civilising" side of the sacred and made it more difficult for it cynically to be taken over by political interests. What is said here about the relationship of world religions to violence can be considered generally valid for religions overall.

The problem is that while most religious believers would no doubt believe that their faith is both compassionate and inspirational, the ideas underpinning a particular faith-driven view of the world are also often implicated in the eruption of violence and conflict both between and within religious groups (or at least entities with a religious component to their guiding ideology). In recent years, a massive literature has appeared on religious contributions to conflict and violence (see, for example, National Commission on Terrorist Attacks 2004). Various armed groups, such as al-Qaida, Islamic State, Boko Haram, and Al Shabaab, claim religious justification for their murderous activities (For a discussion, see Haynes 2013).

Such extremist Islamist groups are collectively informed by similar jihadi ideologies. A key component if the development of today's jihadi ideologies was the epochal event of 11 September 2001 (9/11). The al-Qaida attacks on the United States was an issue of fundamental importance to continuing jihadi conflicts with Western—especially Christian—countries. Put another way, it seems likely that without 9/11 the world would not have devoted many years and trillions of dollars fruitlessly to fighting "jihadi terrorism".

One of the tragic outcomes of 9/11 and its aftermath was that globalization clearly increased both the potential and the actualization of violence from extremist non-state actors with religious ideologies—who might be physically located almost anywhere—against states. Before 9/11, governments of powerful countries like the USA believed that their national territories were largely impervious to external attack because of their high-cost militaries and national defence plans. What the 9/11 attacks made crystal clear, at a stroke, was that geographical space—until then believed to be an impenetrable barrier to attacks from external actors except from those from nuclear weapons—no longer mattered. Having said that, al-Qaida's attacks on the Twin Towers and the Pentagon on 9/11 made the task much more difficult of seeking to understand what role religion can play in reducing conflicts and building peace. What was clear was that henceforward there was a sudden,

urgent new challenge to our understanding of global politics, including its relationship to domestic politics. Now, the state's "hard shell" was forever breached. According to Smith (2002, p. 177), this suggested an important connotation for future chances of world order, because states were "no longer, if they ever were, the key actors in major international arenas". Thus, the kind of international terrorism exemplified by al-Qaida in relation to 9/11 and more recently from the so-called Islamic State does not 'map onto state structures', but 'works in the spaces between them'. What 9/11 also illustrated regarding the relationship between peace, politics and religion was that some of the most dangerous and committed of international threats to peace—such as, from al-Qaida, Islamic State, Boko Haram, and Al Shabaab—are not inevitably focused on acquiring territory *per se*. Instead, what they want to achieve is primarily defined by their desire to spread their values and beliefs via ideologically driven methods. The obvious implication of this is that today's jihadi groups are very di fferent types of organization compared to the conventional notion of the state, both in terms of identity and structure. Their structures are the reverse of the modern state, characterized by a hierarchy of power and authority, while its identity is nebulous (Haynes 2013).

More generally, in recent years various religious expressions have been centrally implicated in many domestic and international conflicts. This is because sustained and implacable religious conviction contains within it at least four discrete sources of danger:

In addition, those who hold religious power may also adopt the following tactics in order to bolster or strengthen their positions:

Kurtz refers to the last point as "exclusive accounts of the nature of reality". What he means by this is that followers of fundamentalist religious expressions only accept the religious beliefs that they claim are the solely *true* dogmas (Kurtz 1995, p. 238). Once again, the three Abrahamic religions are noted in this regard. This is the case because fundamentalist expressions of each of the three religions base their truth claims on each faith's recognized holy books. Such readings lead to exclusivist truth

claims which are not only undeniable but also can lead to conflict with those who do not accept their "truths". It is obvious that engaging with religious ideas without a mindset that can accept the need for compromise will likely lead to unremitting conflict with those with di fferent beliefs. This is especially the case in today's highly globalized world. "On the other hand, many religious traditions have within them beliefs that can help develop a peaceful, multicultural world. For example, from within Christianity comes the idea of nonviolence, a key attribute of Jesus, the religion's founder, who insisted that all people are children of God, and that the test of one's relationship with God is whether one loves one's enemies and brings good news to the poor. As St. Paul said, 'There is no Jew or Greek, servant or free, male or female: because you are all one in Jesus Christ' (Galatians 3: 28)" (Haynes 2013, p. 657).

It is suggested that "all religious traditions contain references in the form of didactical stories, teaching or even direct recommendation as to how the faithful should act in order to achieve harmony and peace within him/herself in the first place" (Bartoli 2005, pp. 5–6). As Bouta et al. (2005) note, when it comes to seeking to resolve inter-societal conflicts then religions—variously individuals and groups—often are noteable by their attempts to make things better. Note that such attempts are not only a product of current times. Over the last half century or so, there have been examples, albeit sometimes intermittent rather than necessarily sustained, which point to a consistent involvement of religious individuals and/or representatives of various FBOs in many such e fforts. "Examples include intermediation undertaken by the Quakers and financed by the Ford foundation in the Nigerian Civil War in 1967–1970, the work of the World Council of Churches and the All Africa Conference of Churches in mediating a cessation to the Sudan conflict in 1972, e fforts made by John Paul Lederach, Professor of International Peacebuilding at the University of Notre Dame, in Nicaragua in the 1980s, and the more recent work of the Imam of Timbuktu in seeking to end various conflicts in West Africa (Conflict and Resolution Forum 2001)" (Haynes 2013, p. 658). The conclusion to draw from this is that it is not appropriate or necessary to assess the role of religion in conflicts and draw the conclusion that religions always makes things worse. On the contrary, this would overlook the many attempts over the years of religious entities to improve conflicts and help build peace. Sadly, however, conflicts are much more newsworthy that religious leaders' often problematic attempts to end conflicts and build peace. But this does not mean that they should be summarily disregarded or dismissed. Even unsuccessful attempts can be important components in the eventual building of peace, even if in the short term such e fforts do not seem to meet with obvious success.

Appleby (2006) claims that religious peacemakers are most likely to contribute usefully to ending conflict when they: (1) seek to work internationally or transnationally, (2) consistently highlight the importance and desirability peace and point to the obvious and clear costs of conflict, and (3) pursue good inter-religious relations—even when a conflict is ongoing, as this will be an important builder of trust when trying to develop peace after conflict the key to a positive input from them. It is often noted that the three Abrahamic religions share a broadly similar set of theological and spiritual values and views and this potentially underpins their ability to provide positive contributions to conflict resolution and peacebuilding.

In conclusion, contributors to Smock's (2006) edited volume identify the following of importance when examining often complex issue of religious involvement in conflict, conflict resolution and peacebuilding:

Finally, faith-based peacebuilding initiatives "have contributed positively to peacebuilding" in four main ways. They can provide (1) "emotional and spiritual support to war-a ffected communities", (2) e ffective mobilization for "their communities and others for peace", (3) mediation "between conflicting parties", and (4) a conduit in pursuit of "reconciliation, dialogue, and disarmament, demobilization and reintegration" (Bouta et al. 2005, p. ix). We can also note the promise that religious peacemakers o ffer, while also pointing to two problems: (1) "there is often a failure of religious leaders to understand and/or enact their potential peace-building roles within the local community", and (2) many religious leaders lack the ability to "exploit their strategic capacity as transnational actors" (Appleby 2006, p. 2). Such concerns arise in a global region of apparently growing political and societal tensions: the Middle East. Escalating tensions following the Arab Uprisings of 2011 serve to underscore both the potential importance of interreligious dialogue while also highlighting the roles of local and international actors to aggravate existing tensions—for example, in relation to Israel and the Palestinians or Iran and Saudi Arabia—and makes finding common ground even harder to achieve and, by extension, pursuit of peace in the region is (even) more problematic.


(e) Search for Prey

Grey wolves mainly rely on the information of α, β, and δ to find their prey. In the process of searching for prey, keeping the search agent away from the prey can make the grey wolf perform a global search. In formula (b), the C vector composed of random values in the interval range [0, 2]. The random search behavior of grey wolves can make the optimization results more accurate and avoid falling into local optimum. C is a random value during the iteration process. This coe fficient is helpful for the algorithm to jump out of the local area, especially the algorithm is particularly important in the later stage of the iteration.

After the microgrid obtains real-time information on the system status, it begins to execute the GWO. First, it sets the number of wolves and initializes the wolves, and then calculates the fitness value of each wolf. The top three are recorded as α, β, δ each wolf updates its position by calculating the distance from α, β, δ and finally outputs the global optimal solution, according to whether the maximum number of iterations is reached. Some of the previous optimization algorithms are prone to fall into the shortcomings of local optimization, slow convergence, and optimization of the microgrid. The flow chart in Figure 4 is the microgrid dispatching process combined with the GWO.

**Figure 4.** Flowchart for microgrid dispatching process combined with the GWO.

### **6. Case Study and Simulation Results**

Sanya is located south of the Tropic of Cancer and has a tropical monsoon climate characterized by high temperature and rain. All relevant data are obtained from the official website of the local

meteorological bureau. The annual average temperature is 26.7 ◦C. The highest temperature month is June with an average of 29.7 ◦C. The lowest temperature month is January with an average of 22.4 ◦C. The sunshine time of the year is 2534 h. The average annual precipitation is 1347.5 mm. Known as the "natural greenhouse".