The discriminative stimulus properties of cyclazocine: generalization studies involving nalorphine, morphine and LSD

Rats learned to discriminate cyclazocine (2 mg/kg, i.p.) from saline using a two-lever operant (FR-4) procedure within 10 sessions under each drug condition. The cyclazocine discriminative stimulus (DS) was both dose- and time-related, being antagonized by naloxone at doses approximately 80 times that necessary to block the discriminative stimulus effect of morphine. Cyclazocine also generalized to nalorphine, but not to morphine, pentazocine or LSD. These data suggest that cyclazocine produced DS control of behavior by acting at CNS sites different from those affected by morphine or LSD.