Behaviorally equivalent stressors differentially modify the monoamine altering property of d-amphetamine.

We previously demonstrated that behaviorally equivalent heat and cold stressors interacted with d-amphetamine (AMPH) treatment to produce different effects in rats responding for food on a fixed ratio 15 (FR15) schedule of reinforcement [25]. The present study was carried out to determine if these stressors differentially affect the disposition of AMPH to brain and/or if the stressors alone or in combination with AMPH affect CNS monoamines in a dissimilar manner. Exposure to either heat or cold stressor produced equivalent elevations of [3H]-AMPH in brain following 3 mg AMPH/kg but not 1 mg AMPH/kg. Neither stressor alone significantly altered any of the neurochemical parameters measured in any of the brain regions studied. In forebrain, heat and cold stressors interacted with AMPH treatment in different manners. Thus, although [3H]-AMPH was equally elevated in stressed groups following the high dose, cold-induced stress was not associated with an increase in dopamine (DA) levels, which was observed in Nonstressed and Heat-Stressed subjects. Although serotonin (5-HT) levels were not changed by any manipulation, 5-hydroxyindoleacetic acid (5-HIAA) levels were lowered in Nonstressed and Cold-Stressed subjects following both doses of AMPH. This effect was not associated with heat-induced stress. The apparent attenuation of AMPH behavioral toxicity observed in Cold-Stressed and/or exacerbation in Heat-Stressed rats observed in the earlier study may involve a pharmacodynamic interaction of AMPH and stress with transmitter substances, including DA and/or 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)