Effects of methamphetamine on atropine-induced conditioned gustatory avoidance

The repeated administration of high doses of methamphetamine (MA) has been shown to cause monoaminergic damage in rhesus monkeys and rats. In view of the purported interaction between central cholinergic and monoaminergic systems, rhesus monkeys and rats previously exposed to high doses of MA were tested in conditioned gustatory avoidance studies with atropine (a muscarinic blocker) as the unconditioned stimulus. It was observed that both rhesus monkeys and rats previously exposed to high doses of MA exhibited less of an atropine-induced avoidance than control monkeys and rats. To control for the nonspecific effects of prior exposure to stimulants, an additional group of rats previously exposed to high doses of methylphenidate ( a stimulant shown to not cause catecholaminergic damage) was tested in the same paradigm. The methylphenidate treated rats showed no change in sensitivity to atropine in the conditioned gustatory avoidance paradigm as compared to control rats which indicated that prior exposure to the nonspecific effects of a stimulant without monoaminergic alterations does not alter the sensitivity of atropine's avoidance-inducing properties. The results of these experiments imply that atropine's avoidance-inducing properties may in part be mediated through the monoaminergic system.