Antidepressants: Past, Present and Future - ReadingSample

An understanding of the basic elements of neurotransmission in the brain is an important foundation for any consideration of the clinical use and future development of antidepressants. However, attempts to describe the influences of drugs on brain and neuronal function have become increasingly complex, and it is now clear that neuronal processes are complex molecular events involving multiple control factors. The brain consists of approximately 100 million neurons, which account for half of the brain s volume, with the other half being made up of glial cells. New insights into the function of glial cells, the influence of phosphorylation on neuronal functions, and the regulation of genetic functions in synthesizing neuronal proteins have enhanced our appreciation of the complexity of neural function in the brain. Glial cells play an important role in recycling and conserving the neurotransmitters glutamate and GABA and also have an important effect on neurons in the brain via glial cell line-derived neurotrophic factor (GDNF). The basic function of neurons is to convey electrical signals in a highly organized and integrated way. The dominant means of neuron-to-neuron communication or transmission occurs by means of specific chemicals (i.e., neurotransmitters). Neuronal communication is a complex process that involves neurotransmitter storage and release, neurotransmitter inactivation, receptors, G proteins, and second messengers. A number of neuronal mechanisms have been identified that are thought to play important roles in the etiology of major depressive disorder (e.g., the serotonin transporter mechanism); an increasing understanding of the neuronal mechanisms that underlie psychiatric disorders will help to guide future drug development.