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

Effects of acute and long-term treatments with thyrotropin-releasing hormone on locomotor activity and jumping behavior in mice

The acute and chronic effects of thyrotropin-releasing hormone (TRH) on ambulation and, in combination with apomorphine, on jumping behavior were investigated in mice. A single administration of TRH (1-10 mg/kg SC) produced an initial hyperactivity in a dose-dependent manner. Following administration of TRH (1-10 mg/kg SC) for 21 successive days, the stimulatory effect on locomotion progressively increased. Haloperidol exerted a biphasic action on hyperlocomotion induced by acute and repeated TRH, i.e., stimulation at lower doses (0.01-0.02 mg/kg SC) and inhibition at higher doses (0.05-1 mg/kg SC). When TRH was administered in combination with low doses of apomorphine, locomotor activity was inhibited but jumping behavior occurred. The inhibitory effect of low doses of apomorphine on locomotion was shifted from doses of 0.1-0.25 mg/kg SC of apomorphine for acute TRH (10 mg/kg) to 0.25-0.35 mg/kg for repeated TRH (10 mg/kg), whereas the stimulatory effect of higher doses of apomorphine (0.5-1 mg/kg SC) on locomotion tended to decrease with repeated TRH. Jumping behavior induced by the combined treatment of TRH and apomorphine was proportional to the dose of TRH but exhibited an inverted-U response to the dose of apomorphine. Chronic TRH (10 mg/kg) in combination with apomorphine (0.1-1 mg/kg SC) also produced jumping behavior, but the dose-response curve for apomorphine was shifted to the right. The present results suggest that repeated treatment with TRH in mice produces hyperlocomotion, despite attenuation of both pre- and postsynaptic receptor activity, and that the inhibitory effect of repeated TRH on presynaptic receptors may be more potent than that on postsynaptic receptors.

Neuronal mechanisms involved in drug-induced jumping behavior in mice

Previously we have found that lithium chloride (250 mg/kg i.p.) plus haloperidol (4 mg/kg i.p.), or apomorphine (0.25 mg/kg i.p.) plus thyrotropin releasing hormone (TRH, 20 mg/kg i.p.), elicited a jumping behavior which involves dopaminergic and cholinergic inhibition, and noradrenergic activation. Pretreatment with antiserotonergic agents such as methysergide (5 and 10 mg/kg i.p.) and cyproheptadine (5 mg/kg i.p.) enhanced the jumping behavior induced by these drugs. 5-Methoxy-N,N-dimethyltryptamine (5-MDMT, 5 mg/kg i.p.), a serotonergic receptor agonist, inhibited the jumping behavior. Muscimol, a GABA receptor agonist, at 2 mg/kg, potentiated jumping. GABA receptor antagonists such as bicuculline (4 mg/kg i.p.) and picrotoxin (0.2 and 1 mg/kg i.p.) depressed jumping. An antihistamine agent, diphenhydramine (5 mg/kg i.p.), also potentiated the jumping behavior. Furthermore methysergide (10 mg/kg i.p.), but not muscimol (2 mg/kg i.p.) elicited jumping behavior when combined with clonidine (0.5 mg/kg i.p.), TRH (20 mg/kg i.p.), haloperidol (4 mg/kg i.p.) or atropine (5 mg/kg i.p.). These results suggest that in addition to dopaminergic, cholinergic and noradrenergic mechanisms, serotonergic inhibition may be directly contributing to the initiation of jumping behavior, whereas GABAergic activation appears to be a modulating factor in this behavior.

Lithium in combination with haloperidol or thyrotropin-releasing hormone induces jumping in mice

Lithium (250 mg/kg IP) administered in combination with haloperidol (2-5 mg/kg IP) or thyrotropin-releasing hormone (TRH) (10 or 20 mg/kg, IP) evoked jumping in mice. Jumping elicited by lithium (250 mg/kg) plus haloperidol (4 mg/kg) or TRH (20 mg/kg) was decreased by physostigmine (0.2 mg/kg IP) and phentolamine (10 mg/kg IP), but was increased by atropine (5 mg/kg IP) and clonidine (0.5 mg/kg IP). While the jumping was not affected by either methylatropine (5 mg/kg IP) or propranolol (10 mg/kg IP). Jumping was also induced by haloperidol (4 mg/kg IP), but not by lithium (250 mg/kg IP), administered after atropine (5 mg/kg IP) or clonidine (0.5 mg/kg IP). The results indicate that lithium plus haloperidol or TRH produces jumping in which dopaminergic and cholinergic inhibition as well as noradrenergic activation may be involved.