Rat brain 5-HT_(1C) receptors are encoded by a 5-6 kbase mRNA size class and are functionally expressed in injected Xenopus oocytes

Injection of rat brain RNA into Xenopus laevis oocytes induces synthesis of receptors that show an electrophysiological response to bath application of serotonin. While there are at least 4 pharmacologically distinct subtypes of 5-HT binding sites in the rat brain, we find that the pharmacological characteristics of the predominant electrophysiologically active receptor synthesized in Xenopus oocytes are most consistent with those of the 5-HT_(1C) subtype. Additional electrophysiologically active 5-HT receptor types could not be detected. Injection of mRNA isolated from a number of rat brain regions shows that the choroid plexus is particularly enriched for 5-HT_(1C) mRNA. Oocytes injected with RNA isolated from this region respond 16 or 8 times more strongly to serotonin than do oocytes injected with RNA isolated from cortex or substantia nigra, respectively. In addition, by fractionation of rat brain mRNA through agarose gels, we have identified a single RNA size class of about 5–6 kbase that encodes this serotonin receptor