Narcotic tolerance and operant behavior

Narcotic tolerance was measured as a shift to the right in dose-effect relations on operant behavior following repeated administration of drug. Tolerance has been observed with operant responding in both pigeons and rhesus monkeys. The amount of tolerance observed with food-reinforced responding is related both to the amount of morphine administered and to the nature of the drug-induced change in operant responding. Pharmacological specificity of the narcotic tolerance has been confirmed by equivalent loss of sensitivity to other narcotics without concomitant changes in sensitivity to nonnarcotic stereoisomers. Tolerant birds do not show disturbed operant behavior when narcotic administration is terminated abruptly. Tolerance has been induced by narcotic self-injection and its effects measured on rates and patterns of food- and narcotic-reinforced responding. Tolerance does not necessarily confer changes in narcotic-reinforced responding. Moreover, narcotic-reinforced responding may be initiated and maintained for periods of over one month without conferring tolerance.