Identification of 5-HT receptor sub-types in a homogeneous population of presumptive serotoninergic neurones

The expression of the known rat 5-HT receptor sub-types has been analyzed in a presumptive serotoninergic cell line derived from the rat raphé nuclei, using reverse transcription followed by polymerase chain reaction. By manipulating the activity of the oncogene (ts-SV40T) product used to immortalize the serotoninergic precursors, it has been possible to compare the expression of the 5-HT receptors in either replicative or differentiating cells. 5-HT1B, 5-HT1D, 5-HT3, 5-HT6 and 5-HT7 receptor gene expression were all observed in the replicating cells. However, under differentiation conditions, expression of all except the 5-HT1B receptor was lost. Only one novel amplification product appeared during early differentiation, in the 5-HT2B lane; its smaller than expected size was suggestive of a previously undescribed alternate splicing of the mRNA in brain. The curtailment of 5-HT receptor expression in differentiating neurones in vitro may reflect the normal ongoing restriction in the phenotypic potential during embryogenesis in vivo. The serotonin cells, therefore, constitute a pristine cell line in which to study the receptor pharmacology of one or more 5-HT receptor sub-types in isolation.