Cocaine potentiates the disruptive effects of phencyclidine on repeated acquisition in monkeys

Differential interaction of cholecystokinin with morphine and phencyclidine: effects on operant behavior in pigeons

To extend previous operant research in rats with morphine and cholecystokinin (CCK), these two substances were given alone and in combination to pigeons. In one component of a multiple schedule, responding of pigeons (key pecking) was reinforced under a fixed-ratio (FR 50) schedule of food presentation. In the other component, responding had no programmed consequence (timeout). Each session consisted of four 10-min timeout components alternating with four 5-min FR components. In Experiment 1, cumulative dose-effect curves for morphine were obtained by giving an IM injection before each of four FR components; successive injections increased the cumulative dose by 1/4 log-unit steps. In general, as the cumulative dose of morphine increased, the overall response rate in each FR component decreased. Dose-dependent decreases in response rate also occurred when single noncumulative doses of CCK were administered alone 20 min prior to the start of the session. This effect of CCK alone diminished as the session progressed. When CCK was given as a pretreatment before cumulative doses of morphine, the morphine dose-effect curve for response rate shifted to the left. At intermediate doses of CCK, the "potentiation" was so complete that two of three subjects failed to respond during any of the four FR components (i.e., the dose-effect curve for morphine had shifted approximately 1 log-unit to the left). In order to evaluate the pharmacological specificity of this effect, cumulative doses of phencyclidine were administered in combination with CCK (Experiment 2). Unlike the interaction between morphine and CCK, the interaction between phencyclidine and CCK was reciprocal.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin potentiates the rate-decreasing effects of morphine on schedule-controlled behavior in rats

In one component of a multiple schedule, responding (licking in rats) was reinforced under a fixed-ratio (FR 50) schedule of water presentation. In the other component, responding had no programmed consequences (timeout). Each session consisted of four 10-min timeout components alternating with four FR components. In general, increasing cumulative doses of morphine (3.2-18 mg/kg) produced a dose-dependent decrease in the overall rate of responding. In one subject, cholecystokinin (CCK) alone (10-32 micrograms/kg) produced dose-dependent decreases in rate in the first component, while in the other two subjects relatively little decrease in rate occurred. When these doses of CCK were given as a pretreatment before morphine, the decrease in overall response rate was greater than that found with morphine alone. This interaction was most noticeable at the lowest dose of morphine where CCK produced a dose-dependent "potentiation" of the rate-decreasing effects. Although the potentiation of CCK was not as evident at the intermediate doses of morphine, there were instances in which the rate-decreasing effects produced by the combination were greater than those expected from addition of the effects of CCK and morphine alone. In contrast, when naltrexone (1 mg/kg) was given as a pretreatment, little or no rate-decreasing effects were produced by the cumulative doses of morphine. Furthermore, pretreatment with naltrexone and the administration of a higher dose range of morphine indicated the dose-effect curve for morphine had shifted approximately 3/4 log-units to the right.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated acquisition and delayed performance as a baseline to assess drug effects on retention in monkeys

As an extension of previous research on repeated acquisition, a new baseline was developed to assess the effects of phencyclidine on retention in patas monkeys. Each session was divided into three phases: acquisition, delay, and performance. During acquisition, the subject acquired a four-response chain (which was different each session) by responding sequentially on three keys in the presence of four geometric forms. When the acquisition criterion (20 consecutive correct responses) was met, the keylights turned off and the delay (retention interval) began. After the delay, the keylights and a white light above the keys were turned on for 10 min (performance). The white light indicated that the response chain was the same as the chain acquired before the delay. Retention of the acquired response chain, as measured by percent "savings" in errors to criterion, decreased as the delay was increased from 5 to 180 min, and this "forgetting curve" tended to shift to the left with increasing doses of phencyclidine (administered IM 5 min before the performance phase). "Overlearning" the response chain before the 180-min delay increased retention and attenuated the disruptive effects of the lower dose of phencyclidine.