We previously reported that glucagon-like peptide-1 decreased corticotropin-releasing factor (CRF)-induced behaviors in neonatal chicks, and such an effect is hypothesized to act through norepinephrine (NE). Experiments were designed to explore the effect of the NE on CRF-induced behaviors. In experiment 1, the chicks were intracerebroventricularly (i.c.v.) administered saline, 0.1 microg of CRF, 50.0 microg of NE, or 0.1 microg of CRF with 50.0 microg of NE. Behavior was monitored for the 10 min immediately after i.c.v. injection, and plasma corticosterone was analyzed at the end of behavior tests. Compared with the control, chicks were excited by CRF as evidenced by increased spontaneous activity and distress vocalizations (DVs). NE decreased the spontaneous activity of chicks, and the differences diverged with time. DVs completely disappeared in the presence of NE, and sleep-like (sitting with eyes closed) behavior was observed in the same birds. NE-treated birds spent most of the time in a sleep-like posture irrespective of CRF treatment. CRF-treated chicks had increased plasma corticosterone, whereas NE injection caused a decrease in corticosterone. In experiment 2, the effect of NE was further studied using i.c.v. administration with either 0.1 microg of CRF alone or 0.1 microg of CRF plus 12.5, 25.0, or 50.0 microg of NE. NE dose dependently modified the CRF-induced locomotor activity in the open field, and DVs disappeared when chicks were given any dose of NE with CRF. With these findings taken together, it is suggested that central NE interacts the CRF-induced behaviors in neonatal chicks.
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