Excitatoty effects of TRH on medullary reticular neurones.

Thyrotropin releasing hormone (TRH) was applied iontophoretically to single neruones in the rat bulbar reticular formation. TRH excited 41 to 56 cells tested; none were inhibited. Excitation developed slowly and was prolonged, and desensitization often occurred. TRH effects were not correlated with effects of acetylcholine, noradrenaline, dopamine or serotonin on the same cells. Atropine applied to cells affected by both acetylcholine and TRH did not affect TRH responses although the acetylcholine actions were blocked. The results support a transmitter role for TRH in this brain area and may explain certain arousal effects of TRH mediated via the reticular formation.