Stress-induced alterations in plasma catecholamines and behavior of rats: Effects of chlorisondamine and bretylium

Abstract

The response of the sympathetic nervous system and the adrenal medulla was examined in rats subjected to the stress of handling and transfer to a shock chamber and to the stress of 5 min of intermittent footshock. Ganglionic blockade with chlorisondamine chloride (3 mg/kg) resulted in a significant decrease below basal levels in plasma norepinephrine (NE) and epinephrine (EPI) that persisted following transfer and footshock whereas in saline-injected controls there were significant elevations in NE and EPI. In addition, chlorisondamine-treated rats were less active and deposited fewer fecal boli than did controls. In a second experiment, sham-operated and adrenal demedullated (A-D) rats received injections of saline or bretylium tosylate (a drug which blocks release of NE from sympathetic nerve endings). Administration of bretylium attenuated the increase in circulating levels of NE in rats following transfer to the shock chamber. In A-D rats, there was a reduction (> 90%) in plasma EPI throughout testing. Both bretylium and A-D significantly reduced increments in plasma levels of NE following 5 min of footshock. In addition, rats injected with bretylium were less active during footshock than were saline-injected rats. These results indicate that the adrenal medulla of rats is a significant source of circulating NE during mildly and intensely stressful stimulation (approximately 33 and 45%, respectively). Further, activity during footshock stress was greater in rats with an intact sympathetic nervous system. The presence of EPI in the circulation did not appear to have a significant effect on the activity of rats during stress. The possible mechanisms of alterations in behavior induced by peripheral catecholamines and the usefulness of bretylium in blocking sympathetic responses are discussed.