Plasma catecholamine and corticosterone levels during active and passive shock-prod avoidance behavior in rats: Effects of chlordiazepoxide

Abstract

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations were determined in rats before, during and after 15-min exposure to a constantly electrified (2 mA) or nonelectrified prod which was mounted on the wall of the home cage either with or without bedding material on the floor. Concomitantly, exploration of the prod, freezing and prod-burying behavior were recorded. Both in the presence and absence of bedding material, rats explored the nonelectrified prod and showed a small increase in plasma NA and CS contents. Exploration of the prod was strongly reduced when the prod was electrified. In the presence of bedding material, shocked rats typically displayed burying behavior (active avoidance), whereas in the absence of bedding (i.e., burying option eliminated) shocked rats engaged in freezing behavior (passive avoidance). The passive avoidance situation was accompanied by larger A and CS increases but a lower NA rise as compared to the hormonal responses associated with the active avoidance situation. Administration of the anxiolytic chlordiazepoxide (CDP; 9 mg/kg intragastrically) attenuated the shock-induced suppression of prod exploration, decreased prod-burying behavior but, paradoxically, increased freezing behavior. Irrespective of bedding condition, the prod shock-induced elevations in plasma CS and A contents were completely abolished in CDP-treated rats. The rise in plasma NA was attenuated only in CDP-treated rats tested on a bedding-floor. The resuts indicate that passive (e.g., freezing) and active (e.g., burying) behavioral coping are each accompanied by specific and dissociated patterns of neurosympathetic, adrenomedullary and adrenocortical outflow. CDP-treatment shifts an animal's behavioral coping style from an active to a passive form of avoidance responding, but abolishes the accompanying adrenocortical and adrenomedullary activation.