Molecular cloning and pharmacological characterization of the guinea pig 5-HT1E receptor.

The human 5-HT1E receptor gene was cloned more than a decade ago. Little is known about its function, and there have been no reports of its existence in the genome of small laboratory animals. In this study, attempts to clone the 5-HT1E gene from the rat and mouse were unsuccessful. In fact, a search of the mouse genome database revealed that the 5-HT1E receptor gene is missing from the mouse genome. However, the 5-HT1E gene was cloned from guinea pig genomic DNA and was characterized. The guinea pig 5-HT1E receptor gene encodes a protein of 365 amino acids. It shares 88% (nucleic acid) and 95% (amino acid) homology with the human receptor. The guinea pig 5-HT1E receptor showed similar pharmacology to the human 5-HT1E receptor in radioligand binding assays. Serotonin (5-hydroxytryptamine, 5-HT) dose-dependently stimulated [35S]GTPγS binding to the guinea pig 5-HT1E receptor with an EC50 of 13.6±1.92 nM, similar to that of the human 5-HT1E receptor (13.7±1.78 nM). Activation of the guinea pig 5-HT1E receptor was also achieved by ergonovine, α-methyl-5-HT, 1-naphthylpiperazine, methysergide, tryptamine, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Methiothepin exhibited antagonist activity. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that 5-HT1E mRNA was present in the guinea pig brain with the greatest abundance in the hippocampus, followed by the olfactory bulb. Lower levels were detected in the cortex, thalamus, pons, hypothalamus, midbrain, striatum, and cerebellum. Our current study marks the first identification of the 5-HT1E receptor gene in a commonly used laboratory animal species. This finding should allow the elucidation of the receptor's role(s) in the complex coordination of central serotonergic effects.