Nature of salivation produced by thyrotropin-releasing hormone (TRH)

In the unanesthetized cat, TRH was injected into the cerebral ventricles (ICV) through chronically implanted cannulae and the nature of the evoked salivation was investigated. TRH injected in doses from 0.1 to 1.0 mg evoked salivation which was not dose-dependent. The antimuscarinic drug atropine as well as the ganglionic blocking agent mecamylamine injected also ICV prevented the salivation induced by ICV TRH. On the other hand, virtually no effect on the TRH-salivation was induced by the following drugs injected ICV: alpha and the beta adrenergic blocking agents, yohimbine and propranolol; dopamine antagonist, chlorpromazine; 5-hydroxytryptamine antagonist, methysergide; and the antihistamine, antazoline. Further, in cats pretreated with ICV reserpine and 6-hydroxydopamine, but not with ICV 5,6-dihydroxytryptamine and hemicholinium, the salivation caused by ICV TRH was abolished. It is concluded that central cholinoceptive and catecholaminergic mechanisms are involved in the salivation induced by ICV TRH.