Regional Dissociation of Cyclic AMP and Inositol Phosphate Formation in Response to Thyrotropin-Releasing Hormone in the Rat Brain

The present study was undertaken to define effects of thyrotropin-releasing hormone (TRH) on formation of cyclic AMP (cAMP) and inositol phosphates (IPs) in rat brain regions. The brain of male Wistar rats was dissected into seven discrete regions, and each region was sliced. The slices were incubated in Krebs-Henseleit glucose buffer containing varying doses of TRH. TRH caused a significant and consistent increase in cAMP level, but not in formation of IPs, in the hypothalamus, striatum, and midbrain. TRH stimulated formation of IPs in the cerebellum, where the tripeptide did not change the cAMP level. In contrast, formation of neither cAMP nor IPs was affected by TRH in the cortex, hippocampus, or pons-medulla. These data suggest that TRH possesses two distinct types of brain intracellular signaling systems, which vary with brain regions.