NEURONS EXPRESSING 5-HT2 RECEPTORS IN THE RAT-BRAIN - NEUROCHEMICAL IDENTIFICATION OF CELL-TYPES BY IMMUNOCYTOCHEMISTRY

The serotonin(2) (5-HT2) receptor has been implicated in a number of b ehavioral and physiological processes. It may also play a role in cell ular development and differentiation, and represents a site of action of hallucinogens and certain psychotherapeutic drugs. To better unders tand the functions and regulation of the 5-HT2 receptor, we have under taken a series of studies in which we attempted to identify the specif ic cell types that express the receptor. This was accomplished using a variety of double-labeling strategies with an antibody we raised agai nst the rat 5-HT2 receptor protein. In this review we recount of some of our previously published findings and present some new data in whic h we identify subpopulations of cholinergic neurons in the brainstem a nd gamma-aminobutynic acid (GABA)ergic interneurons in the cortex that express 5-HT2 receptor immunoreactivity. Developmentally, the appeara nce of 5-HT2 receptor immunoreactivity occurs relatively late in the o ntogeny of the cells in which it is expressed, mostly in the early pos tnatal period. This argues against a significant role for this recepto r in early development, though it may participate in some aspect of te rminal differentiation. We discuss the significance of the cell-type-s pecific and temporal expression of the 5-HT2 receptor in the context o f current hypotheses of neuropsychiatric disorders such as schizophren ia.