5-Hydroxytryptamine receptors. An example for the complexity of chemical transmission of information in the brain.

Since serotoninergic axon terminals (the cell bodies of which are mainly located in the raphe nuclei of the brain stem) innervate virtually all brain regions, it is intelligible that the serotoninergic system is involved in many physiological and pathological cerebral functions. The marked heterogeneity of the serotonin (5-hydroxytryptamine, 5-HT)receptors and the differences in distribution of the various 5-HT receptor types and subtypes within the brain makes serotoninergic neurotransmission in the brain very complex. This complexity of chemical transmission of information is a prerequisite for the development of drugs which may specifically influence certain cerebral functions, but which do not mimic or block other effects of 5-HT, thus making it possible to reduce or even avoid undesired side effects. The current classification scheme of 5-HT receptors is based on the integration of results of pharmacological, biochemical, electrophysiological and molecular investigations. The multiplicity of 5-HT receptors can be incorporated into the scheme of two main receptor families, i.e. 1. the G protein receptor family, comprising, among the 5-HT receptors, the 5-HT1 and 5-HT2 subtypes and the 5-HT4 type, and 2. the ligand gated ion channels to which (at least according to the current knowledge) only one 5-HT receptor, the 5-HT3 type, belongs. The three 5-HT1 subtypes and the two 5-HT2 subtypes of the current classification scheme, but not the 5-HT3 and 5-HT4 receptors, have already been cloned.(ABSTRACT TRUNCATED AT 250 WORDS)