CHRONIC IMMOBILIZATION STRESS APPEARS TO INCREASE THE ROLE OF DOPAMINE IN THE CONTROL OF ACTIVE BEHAVIOR IN THE FORCED SWIMMING TEST

Previously, we have demonstrated that chronic exposure to immobilizati on (IMO) did not modify the influence of catecholamines on active beha viour of rats in the holeboard, but clearly increased the role of thes e amines in the forced swimming test (FST). In the present experiment, it was studied whether or not chronic IMO altered the role of dopamin e in the two tests. Adult male Sprague-Dawley rats were left either un disturbed or subjected daily to 2 h of IMO stress for 12 days. On the following day, half of the rats were administered saline and the other s the dopamine antagonist haloperidol (0.5 mg/kg). Then the rats remai ned undisturbed in the animal room (controls) or were subjected to acu te IMO for 2 h. Finally, all animals were exposed consecutively to the holeboard (4 min) and the FST (5 min). In non-chronically stressed ra ts, acute IMO depressed behaviour in the holeboard but not in the FST. In chronic IMO rats the inhibitory effect of acute IMO on holeboard a ctivity was slightly reduced as compared to controls. Acute IMO increa sed struggling in rats previously exposed to chronic IMO but did not a lter struggling in non-chronically stressed rats. Whereas the inhibiti on caused by haloperidol treatment in the active behaviour of rats in the holeboard was not altered by chronic IMO, the inhibitory effect of haloperidol in the active behaviour of rats in the FST was greater af ter chronic IMO, particularly in rats also subjected to acute IMO. The se data suggest that chronic IMO stress potentiates the role of dopami ne in a specific behavioural task such as the FST and adds support to the previously published data demonstrating enhanced behavioural and n eurochemical responses to dopamine-related drugs after chronic stress. (C) 1998 Elsevier Science B.V. All rights reserved.