Development of behavioral tolerance to cocaine

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Pigeons obtained food by making four responses on three keys in a specified sequence. Errors produced brief timeout periods, during which the keylights were off and responses had no effect. To establish a base line of repeated acquisition, the sequence of correct responses was changed from session to session. Cocaine (3 mg/kg) disrupted the behavior: total errors increased, the relative frequency of non switching errors ('perseveration') increased, the rate of within session error reduction (learning) decreased, and the total trial time (pausing) increased. During repeated drug administration (30-50 sessions), these effects disappeared, i.e., tolerance developed. Tolerance did not develop however, to cocaine induced increases or decreases in timeout responding; such effects were non disruptive in the sense that they did not reduce the rate of food reinforcement. For comparison, cocaine (3-10 mg/kg) was also studied under a 'performance' condition, in which the sequence of correct responses was the same from session to session. Cocaine increased performance errors and produced pausing, but tolerance developed more quickly than under the learning condition.

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