The effect of non-contingent amphetamine injections on the extinction of food- and drug-reinforced lever pressing in rats.

Abstract

In a series of experiments rats were trained in either drug- or food-reinforced lever pressing. After this training period non-contingent injections of d-amphetamine (0.25 mg/kg), phenmetrazine (1.0 or 2.0 mg/kg), diethylpropion (1.0 mg/kg) or saline were given prior to self-administration of saline or responding without programmed consequences. Single doses of amphetamine, phenmetrazine, diethylpropion or saline were given before saline was offered for self-administration for 2 or 3 hr in rats previously made “dependent” on amphetamine. High rate of responding was observed when amphetamine was given before the session. Rats trained in food-reinforced lever pressing were given single doses of amphetamine, phenmetrazine or saline before the number of responses without programmed consequences were recorded for 3 hr. Low rate of responding was observed for all pre-treatment conditions. A rat trained in food-reinforced lever pressing was given a single dose of amphetamine (10 mg/kg) each day. Single doses of amphetamine, phenmetrazine or saline were given prior to sessions where the number of responses (without programmed consequences) were recorded for 3 hr. Low rate of responding was observed for all pre-treatment conditions. Rats pre-treated with single doses of amphetamine and trained in food-reinforced lever pressing were also given saline pre-treatment where lever pressing was followed by no programmed consequences, when single doses of amphethamine or saline were given before the sessions where the number of responses were recorded for 2 hr. High rate of responding was observed when amphetamine was given before the session. It is concluded that the increased rate of lever pressing for no programmed consequences after single doses of amphetamine is due to the experience of amphetamine during food-reinforced behavior, i.e. the drug acts as a discriminative stimulus for subsequent responding. Also the increased rate of saline self-injections after single doses of an amphetamine analogue can be explained in terms of the drug acting as a discriminative stimulus. It is therefore concluded that the increased rate of responding cannot be explained in terms of a general activity effect of amphetamine or amphetamine analogues.