The behavioral effects of chronic administration of d-amphetamine in rats at a dosage of 1 mg/kg were studied with baselines involving either food or shock reinforcement. Food reinforcement was assigned according to a fixed interval or on the basis of differential reinforcement of low rate in a multiple schedule of reinforcement. Behavioral tolerance was observed in response to chronic administration of d-amphetamine when the action of drug led to a decrease in frequency of food reinforcement regardless of the schedule of reinforcement. In the second experiment, a shock avoidance situation was employed in which each avoidance response postponed the onset of grid shock. An escape contingency was provided for occasions on which an avoidance response did not occur. The chronic administration of d-amphetamine led to a uniform increase in response rate throughout the drug regimen with the consequence of decreasing rate of shock reinforcement. An hypothesis was put forward on the basis of these results which considers the development of behavioral tolerance to amphetamine administration to be a function of the drug's action in relation to its effects on the organism's behaviour in meeting reinforcement requirements.
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