CLONING AND CHARACTERIZATION OF A CDNA-ENCODING A NOVEL SUBTYPE OF RAT THYROTROPIN-RELEASING-HORMONE RECEPTOR

A cDNA encoding a thyrotropin-releasing hormone (TRH) receptor express ed in the pituitary was previously cloned (De La Pena, P., Delgado, L. M., Del Camino, D., and Barros, F. (1992) Biochem. J. 284, 891-899; D e La Pena, P., Delgado, L. M., Del Camino, D., and Barros, F. (1992) J . Biol. Chem. 267, 25703-25708; Duthie, S. M., Taylor, P, L., Anderson , J,, Cook, J., and Eidne, K, A. (1993) Mol. Cell Endocrinol. 95, R11- R15). We now describe the isolation of a rat cDNA encoding a novel sub type of TRH receptor (termed TRHR2) displaying an overall homology of 50% to the pituitary TRH receptor. Introduction of TRHR2 cDNA in HEK-2 93 cells resulted in expression of high affinity TRH binding with a di fferent pharmacological profile than the pituitary TRH receptor. De no vo expressed receptors were functional and resulted in stimulation of calcium transient as assessed by fluorometric imaging plate reader ana lysis. The message for TRHR2 was exclusive to central nervous system t issues as judged by Northern blot analysis. Studies of the expression of TRHR-2 message by in situ hybridization revealed a pattern of expre ssion remarkably distinct (present in spinothalamic tract, spinal cord dorsal horn) from that of the pituitary TRH receptor (present in hypo thalamus, and ventral horn of the spinal cord, anterior pituitary). Th erefore, we have identified a novel, pharmacologically distinct recept or for thyrotropin-releasing hormone that appears to be more restricte d to the central nervous system particularly to the sensory neurons of spinothalamic tract and spinal cord dorsal horn, which may account fo r the sensory antinociceptive actions of TRH.