Thyrotropin releasing hormone (TRH): restoration of oxotremorine tremor in mice. Comparison with quipazine, a serotoninergic and dopaminergic stimulant.

Both TRH and quipazine (2.5-25 mg/kg) were found to restore and to intensify the oxotremorine-induced tremor in mice when injected i.p. 60 min after oxotremorine 0.5 mg/kg s.c. This phenomenon does not seem to be due to an increase in body temperature or muscle tone. Also other dopaminergic drugs, e.g. amphetamine, methylphenidate, nomifensine and apomorphine had a significant but lesser effect than TRH or quipazine. Haloperidol and methysergide both antagonized the effect of quipazine but not that of TRH. Neither propranolol, phenoxybenzamine, alpha-methyl-p-tyrosine, nor p-chlorophenylalanine inhibited the activity of TRH or quipazine. The restoration of oxotremorine-induced tremor could be prevented by atropine but not by methylatropine. It is concluded that quipazine exerts its effect by direct stimulation of serotoninergic and dopaminergic receptors, whereas TRH receptors may represent separate entities and TRH may function as a neurotransmitter or neuromodulator.