TRH-induced behavioral arousal in developing rats pretreated with 6-hydroxydopa.

The behavioral effect of thyrotropin releasing hormone (TRH) was investigated in the developing rat pretreated with 6-OHDOPA at birth. An IP injection of TRH (20 mg/kg) increased walking with sniffing, rearing, body shaking, grooming, chewing and licking in the 7-, 14-, 20- and 30-day-old as well as in the adult rat. TRH-induced locomotor stimulation began a few minutes after the injection and lasted for approximately 60 min. But on Day 7, TRH produced locomotor stimulation betwen 1.5 hr and 3.5 hr after the injection. Neonatal treatment with 6-OHDOPA markedly potentiated TRH-induced locomotor stimulation and behavioral arousal in the 7-day-old rat but not in the 14-day-old and adult rat. The marked potentiation of TRH-induced locomotor stimulation by 6-OHDOPA in the 7-day-old rat was reduced by alpha-flupenthixol (pA2=5.9) and phenoxybenzamine (pA2=4.4). These results suggest that central dopamine neurons are involved in TRH-induced behavioral arousal in the infant rat.