Effects of TRH on acquisition and extinction of shuttlebox-avoidance behavior in Fischer344 rats.

Thyrotropin-releasing hormone (TRH) was injected intraperitoneally into male Fischer344 rats in doses ranging between 1 mg/kg and 20 mg/kg to assess the effects on the acquisition and extinction of shuttlebox-avoidance behavior. Administration of 20 mg/kg TRH resulted in a rapid acquisition of avoidance behavior in early training trials. This enhancement did not involve changes in the occurrence of anticipatory responses to an inevitable shock but was correlated with an increase of concurrent intertrial-responses. Thus, the behavioral changes observed would be a reflection of TRH-induced changes on motor activity. TRH treatment did not alter the resistance to extinction of the avoidance response. This finding is corroborated by the fact that rats given the TRH treatment withheld the well-learned response to a warning signal, when this response was selectively punished after initial acquisition stage.