Rats that were trained to press a lever in order to get cocaine no longer pressed it with the same frequency after they were given mecamylamine, said Edward Levin, lead author of the study. Results were prepared for presentation Saturday by Tonya Mead and Amir Rezvani at the International Behavioral Neuroscience Society meeting. Mecamylamine is an older medication originally used to treat high blood pressure. Researchers now know it blocks some of nicotine's ability, and potentially that of other drugs, to generate feelings of pleasure in the brain. When mecamylamine blocks these receptors, nicotine can no longer exert its full action, that of stimulating the release of dopamine.
Dopamine is the primary brain chemical involved in generating pleasure.
Drugs like nicotine, alcohol and cocaine all increase available amounts of dopamine and thereby increase the pleasure sensation, said Jed Rose, chief of the Nicotine Research Program at Duke and study co-author. Eventually, the brain may prefer the drug over natural rewards like food or sex, and hence, the person can become addicted. Mecamylamine blocks the action of nicotine, and potentially cocaine, by lowering the net amount of dopamine available in the brain. While cocaine still boosts available levels of dopamine, its overall amount is decreased because mecamylamine has plugged up some of the nicotinic receptor sites where the brain would naturally be activating its own dopamine. In other words, the brain has its own chemical, acetylcholine, that stimulates the release of dopamine.