The effect of second-order schedule history on fixed-ratio performance maintained by orally-delivered phencyclidine in rhesus monkeys.

Thirteen monkeys were trained to self-administer orally-delivered phencyclidine (0.25 mg/ml) and water under a concurrent fixed ratio (FR) 16 schedule. Phencyclidine was available from one lip-operated drinking device and water was available from another drinking device during daily 3-hr sessions. Seven monkeys were trained to respond under a second-order FR 240 (FR 20: brief stimulus) schedule. Upon completion of 4800 responses, the monkeys were allowed to self-administer 300 phencyclidine deliveries under an FR 1 schedule. After a mean of 33.3 sessions of second order schedule training, including 10 sessions at the terminal parameter, the monkeys were returned to the concurrent FR 16 schedule. Phencyclidine-maintained responding persisted at rates that were 42 percent higher than before second-order schedule training; however, concurrent water-maintained behavior increased only slightly. A second group of three monkeys were treated in an identical manner except that during second-order schedule training they received a saccharin solution (0.05%, wt/vol) instead of phencyclidine. After a mean of 30 sessions of second-order schedule training, including 10 sessions at the terminal parameter, the monkeys were returned to the concurrent FR 16 schedule, and there was no consistent change in phencyclidine or water deliveries. A third group of three monkeys received 300 phencyclidine deliveries at the same time after session onset and for the same total number of sessions as the monkeys that received second-order schedule training with phencyclidine; however, this group was not required to respond under the second-order schedule to gain access to the phencyclidine deliveries.(ABSTRACT TRUNCATED AT 250 WORDS)