Central administration of corticotropin-releasing hormone stimulates locomotor activity in juvenile chinook salmon (Oncorhynchus tshawytscha)

Abstract

This study evaluated the effect of corticotropin-releasing hormone (CRH) on locomotor activity, habitat choice, and social behavior in juvenile spring chinook salmon (Oncorhynchus tshawytscha). An intracerebroventricular (ICV) injection of CRH caused a dose-dependent increase in locomotor activity. The stimulatory effect of exogenous CRH on locomotor activity lasted for at least 24 h. Injection (ICV) of a peptide antagonist of CRH, alpha-helical CRH(9-41) (ahCRH), prevented the increase in locomotor activity when administered concurrently with CRH. Furthermore, fish administered the antagonist alone had significantly lower locomotor activity levels compared to saline-injected control fish. The effects of CRH are often dependent on the social context. However, no evidence was found that the presence of conspecifics during the testing procedure affected locomotor activity following ICV injections of CRH. Similarly, ICV injections of CRH or ahCRH did not have a significant effect on the mean time spent in contact with a conspecific. However, the position of fish in the tank was affected by the treatments. ICV injections of CRH significantly increased the amount of time that fish spent near the center of the tank. Furthermore, ICV injections of ahCRH significantly increased the mean time taken for fish to find cover in the tank. The effect of CRH and ahCRH on locomotor activity was not related to changes in plasma cortisol or thyroxine. These results support the hypothesis that endogenous CRH within the central nervous system is involved in the stimulation of locomotor activity in fish. Furthermore, CRH may also alter habitat choice in a novel environment.