1. the act of perceiving; observation; attention: to escape notice. 2. take notice to pay attention; attend. 3. take no notice of to ignore or disregard. 4. information about a future event; warning; announcement. 5. a displayed placard or announcement giving information.
Nicotine: A Stimulant Nicotine, the chemical that makes addicts out of cigarette smokers, is a stimulant with properties similar to those of cocaine and amphetamine (speed). Nicotine provides the pick-me-up that smokers feel.
Nicotine in Tobacco. Nicotine imitates the action of a natural neurotransmitter called acetylcholine and binds to a particular type of acetylcholine receptor, known as the nicotinic receptor. Whether it is acetylcholine or nicotine that binds to this receptor, it responds in the same way: it changes its conformation, which causes its associated ion channel to open for a few milliseconds. This channel then allows sodium ions to enter the neuron, depolarizing the membrane and exciting the cell. Then the channel closes again, and the nicotinic receptor becomes temporarily unresponsive to any neurotransmitters. It is this state of desensitization that is artificially prolonged by continual exposure to nicotine.