Jumping behavior induced by thyrotropin releasing hormone in combination with apomorphine in mice

Neuronal mechanisms involved in the jumping produced by thyrotropin releasing hormone (TRH) plus apomorphine were studied in mice. TRH (5--20 mg/kg IP) administered after apomorphine (0.25--2.0 mg/kg IP) elicited jumping behavior, the frequency of jumping being proportional to the dose of TRH but inversely related to the dose of apomorphine. Jumping behavior was also induced by TRH (20 mg/kg IP) administered after atropine (5 mg/kg IP) or clonidine (0.5 mg/kg IP). The jumping elicited by TRH (20 mg/kg IP) in combination with apomorphine (0.25 mg/kg IP) was decreased by pretreatment with haloperidol (1 mg/kg IP), physostigmine (0.2 mg/kg IP) or phentolamine (10 mg/kg IP), unaffected by propranolol (10 mg/kg IP), and markedly increased by atropine (5 mg/kg IP) or clonidine (0.5 mg/kg IP). The results suggest that TRH in combination with apomorphine, atropine or clonidine elicits jumping in which dopaminergic, cholinergic and noradrenergic functions are concomitantly involved.