title: Progressive augmentation of locomotor activity in mice by long-term treatment with thyrotropin releasing hormone.
abstract: The effect of daily administration of thyrotropin releasing hormone (TRH) on exploratory behavior (ambulation) was investigated in mice. TRH administered subcutaneously (2.5 and 10 mg/kg) exerted a biphasic action on locomotion, that is, an increase followed by a subsequent decrease. This TRH-induced hyperlocomotion was inhibited by a small dose of apomorphine (0.25 mg/kg, s.c.), a dopamine receptor agonist, but was conversely increased by a small dose of haloperidol (0.02 mg/kg, s.c.). Following administration of TRH (2.5 mg/kg, s.c.) for 21 successive days, the stimulatory effect on locomotion progressively increased whereas the inhibitory effect decreased, the hyperlocomotion continuing at a later period. At this time, the stimulatory effect of apomorphine (1 mg/kg, s.c.) on locomotion tended to decrease but that of methamphetamine (0.5 mg/kg, s.c.), a catecholamine releaser, was potentiated. The present results suggest that the long-term, daily administration of TRH enhances exploratory behavior of mice, presumably by increasing the synthesis and release of dopamine.
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D004347:Drug Interactions; D006220:Haloperidol / Q000494:pharmacology; D006801:Humans; D006948:Hyperkinesis / Q000139:chemically induced; D007279:Injections, Subcutaneous; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D013973:Thyrotropin-Releasing Hormone; D006220:Haloperidol; D001058:Apomorphine