31.   Much of the current research, however, is focusing on the role of neuropeptides, or specialized brain chemicals, on appetite and cravings.

32.   Much of the research, Bigelow said, has focused on dopamine, a brain chemical that plays an important role in movement, thought, emotion and addiction.

33.   Nicotine increases the release of brain chemicals that are stimulating and relaxing as well as those that produce a mild euphoria.

34.   No one knows for certain what causes TS, but researchers believe it stems from the abnormal metabolism of at least one brain chemical, called dopamine.

35.   One hypothesis has been that lowering levels of cholesterol also lowers levels of serotonin, a brain chemical tied to depression, as well as to violence and suicide.

36.   Other big drug companies are concentrating on a brain chemical called neuropeptide-Y, the most potent stimulator of eating discovered thus far.

37.   Other studies have suggested that violence is linked to a brain chemical called serotonin, but no tie has been established between the chemical and life experiences.

38.   One such class acts on a particular brain chemical, a neuropeptide known as Substance P.

39.   Other investigators see no point in viewing depression as anything other than a malfunction of brain chemicals.

40.   Protein is allied with tryptophan, a calming amino acid that helps initiate sleep and produce serotonin, an important brain chemical.