Lack of expression of serotonin receptor subtype -1a, 1c, and -2 mRNAs in gonadotropin-releasing hormone producing neurons of the rat.

Serotonin is one of the neurotransmitters which participates in the regulation of gonadotropin-releasing hormone (GnRH) release from the hypothalamus. In order to test the hypothesis that serotonin acts directly on the GnRH neurons, dual in situ hybridization with 35S-labeled cRNA probes encoding for the serotonin receptor subtypes-1a, -1c, or -2 together with digoxigenin-labeled GnRH cRNA probes was applied to histological sections of the septum-diagonal band and preoptic area. The results of these studies show that many neurons in these brain regions contain the various serotonin receptor mRNAs, however, no cells were detected that contain both GnRH mRNA and serotonin receptor mRNAs. It is therefore suggested that the effects of serotonin on GnRH release are not mediated by direct actions of the neurotransmitter through serotonin-1a, -1c or -2 receptors on GnRH neurons but instead through other, yet unidentified serotonin receptor subtypes or through non-serotoninergic intermediary neurons.