Neurotransmitter

Interest in the neurotransmitter is based on evidence that knowledge of how they function provides insight into the cause of some diseases, the effects of certain substances, and the behavior of organisms. Myasthenia gravis, which is a disease characterized by weakness of muscles and fatigue, is caused by a disturbance in the action of acetylcholine on skeletal muscles and is now treated by drugs that enhance the effect of acetylcholine. The discovery that dopamine-containing neurons in the brain of Parkinson's disease victims degenerate, which results in the shuffling gait and trembling characteristic of the disease, led to the use of levodopa, a compound that replaces dopamine.

Impairment of the dopamine system is also implicated in schizophrenia, a mental disease marked by disturbances in thinking and emotional reactions. Drugs, such as chlorpromazine and clozapine, that block dopamine receptors in the brain have been used to alleviate the symptoms and help patients return to a normal social setting. Depression, which afflicts about 3.5% of the population, is treated with antidepressants that affect norepinephrine and serotonin in the brain. The antidepressants help correct the abnormal excess or inhibition of signals that control mood, thoughts, pain, and other sensations. A new drug, fluoxetine, is a serotonin reuptake inhibitor which appears to establish the level of serotonin required to function at a normal level.

Alzheimer disease, which affects an estimated four million Americans, is characterized by memory loss and the eventual inability for self-care. The disease seems to be caused by a loss of cells in the basal forebrain which secrete acetylcholine. Some experimental drugs to alleviate the symptoms have been developed, but presently there is no known treatment for the disease.