thus from choline), because this material is used to myelinate (insulate) nerve fibers. choline is also in demand for the production of the neurotransmitter acetylcholine, which can influence the structure and organization of brain regions, neurogenesis, myelination, and synapse formation. acetylcholine is even present in the placenta and may help control cell proliferation and differentiation (increases in cell number and changes of multiuse cells into dedicated cellular functions) and parturition. choline uptake into the brain is controlled by a low-affinity transporter located at the blood–brain barrier. transport occurs when arterial blood plasma choline concentrations increase above 14 μmol/l, which can occur during a spike in choline concentration after consuming choline-rich foods. neurons, conversely, acquire choline by both high- and low-affinity transporters. choline is stored as membrane-bound phosphatidylcholine, which can then be used for acetylcholine neurotransmitter synthesis later. acetylcholine is formed as needed, travels across the synapse, and transmits the signal to the following neuron. afterwards, acetylcholinesterase degrades it, and the free choline is taken up by a high-affinity transporter into the neuron again. uses choline chloride and choline bitartrate are used in dietary supplements. bitartrate is used more often due to its lower hygroscopicity. certain choline salts are used to supplement chicken, turkey and some other animal feeds. some salts are also used as industrial chemicals: for example, in photolithography to remove photoresist. choline theophyllinate and choline salicylate are used as medicines, as well as structural analogs, like methacholine and carbachol. radiolabeled cholines, like 11c-choline, are used in medical imaging. other commercially used salts include tricholine citrate and choline bicarbonate. antagonists and inhibitors hundreds of choline antagonists and enzyme inhibitors have been developed for research purposes. aminomethylpropanol is among the first ones used as a research tool. it inhibits choline and trimethylglycine synthesis. it is able to induce choline deficiency that in turn results in fatty liver in rodents. diethanolamine is another such compound, but also an environmental pollutant. n-cyclohexylcholine inhibits choline uptake primarily in brains. hemicholinium-3 is a more general inhibitor, but also moderately inhibits choline kinases. more specific choline kinase inhibitors have also been developed. trimethylglycine synthesis inhibitors also exist: carboxybutylhomocysteine is an example of a specific bhmt inhibitor. the cholinergic hypothesis of dementia has not only lead to medicinal acetylcholinesterase inhibitors, but also to a variety of acetylcholine inhibitors. examples of such inhibiting research chemicals include triethylcholine, homocholine and many other n-ethyl derivates of choline, which are false neurotransmitter analogs of acetylcholine. choline acetyltransferase inhibitors have also been developed. history discovery in 1849, adolph strecker was the first to isolate choline from pig bile. in 1852, l. babo and m. hirschbrunn extracted choline from white mustard seeds and named it sinkaline. in 1862, strecker repeated his experiment with pig and ox bile, calling the substance choline for the first time after the greek word for bile, chole, and identifying it with the chemical formula c5h13no. in 1850, theodore nicolas gobley extracted from the brains and roe of carps a substance he named lecithin after the greek word for egg yolk, lekithos, showing in 1874 that it was a mixture of phosphatidylcholines. in 1865, oscar liebreich isolated "neurine" from animal brains. the structural formulas of acetylcholine and liebreich's "neurine" were resolved by adolf von baeyer in 1867. later that year "neurine" and sinkaline were shown to be the same substances as strecker's choline. thus, bayer was the first to resolve the structure of choline. the compound now known as neurine is unrelated to choline. discovery as a nutrient in the early 1930s, charles best and colleagues noted that fatty liver in rats on a special diet and diabetic dogs could be prevented by feeding them lecithin, proving in 1932 that choline in lecithin was solely responsible for this preventive effect. in 1998, the us national academy of medicine reported their first recommendations for choline in the human diet.