Abstract
Thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH(2)) and the structurally related [Glu(2)]TRH (pGlu-Glu-Pro-NH(2)) are endogenous peptides with a plethora of actions in the central nervous system. Many centrally-mediated effects of TRH are shared with those of [Glu(2)]TRH, although the involvement of different receptors is presumed. The analeptic action is the best-known TRH-related central nervous system effect. While [Glu(2)]TRH itself is analeptic, its co-administration with TRH into mice produced a dose-dependent attenuation of TRH-evoked reversal of barbiturate-induced sleeping time. This finding is in agreement with our previous observations that [Glu(2)]TRH significantly attenuates TRH-induced hippocampal extracellular acetylcholine release. Taken together, [Glu(2)]TRH may be considered as a negative modulator for the cholinergic effect of TRH in the mouse brain.