Involvement of both opiate and catecholaminergic receptors in the behavioural excitation provoked by thyrotropin-releasing hormone: comparisons with amphetamine.

Following direct administration of thyrotropin-releasing hormone (TRH), but not thyroid-stimulating hormone (TSH) or vehicle solution, into the lateral cerebral ventricle in rats, three main categories of behaviour were provoked: activity of the normal type--stimulation of forward locomotion, head and body rearing (as shown by an enhancement in gross movements); stereotyped activity--increased grooming and head swaying (as shown by an enhancement in fine movements); abnormal behaviour--tail elevation and piloerection (as observed grossly). The behavioural excitation caused by TRH was antagonized by pretreatment of the rats with either a narcotic receptor antagonist, naloxone, an alpha-adrenergic receptor antagonists, yohimbine, or a dopaminergic receptor antagonist, haloperidol, but not with a beta-adrenergic receptor antagonist, propranolol. Intraventricular administration of amphetamine to rats caused stimulation of forward locomotion, head and body rearing, increased grooming and sniffing. Unlike TRH, amphetamine did not produce wet-dog shakes, tail elevation and piloerection. Furthermore, the amphetamine-induced excitation was antagonized by pretreatment with a dopaminergic receptor antagonist, haloperidol, but not with either naloxone, yohimbine or propranolol. The data indicate that both opiate and catecholaminergic receptors are involved in the TRH-induced behavioural excitation, whereas dopaminergic receptors are involved in amphetamine-induced excitement in the rat.