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Articles and Reports

Journal Article by M. Caroll, D. Batulis, K. Landry, A. Morgan: PCP in Rhesus Monkeys in 2004

Marilyn E. Carroll . David K. Batulis . Kerry L. Landry . Andrew D. Morgan

Sex differences in the escalation of oral phencyclidine (PCP) self-administration under FR and PR schedules in rhesus monkeys

Received: 13 July 2004 / Accepted: 6 January 2005 / Published online: 1 March 2005 # Springer-Verlag 2005

Rationale: Studies with male rats indicate that long access (LgA) vs short access (ShA) to i.v. cocaine and heroin self-administration leads to an escalation of drug intake and a subsequent upward shift of the doseresponse function.

Objective: The purpose of this experiment was to extend these results to male and female rhesus monkeys and oral phencyclidine (PCP) self-administration under fixed-ratio (FR) and progressive-ratio (PR) schedules.

Methods: Adult rhesus monkeys (seven females and nine males) orally self-administered PCP (0.25 mg/ml) and water under concurrent FR 16 FR 16 schedules during daily ShA 3-h sessions. Since females weighed less than males, each liquid delivery (0.6 ml) represented a higher unit dose mg/kg for females than males, but drug concentration mg/ml remained constant. Concurrent PR PR schedules were then used to obtain a concentration-response function (0.125, 0.25, 0.5, and 1.0 mg/ml).

Next, PCP and water were available during LgA 6-h sessions under concurrent FR 16 FR 16 schedules for 21 days. The monkeys were then retested under the concurrent FR 16 FR 16 and PR PR conditions during ShA sessions. Results: Under the initial ShA concurrent FR 16 FR 16 schedules, females and males did not differ on PCP deliveries or intake (mg/kg); however, during LgA, males and females had more PCP deliveries compared with ShA. During LgA, males exceeded females in PCP deliveries, but females were higher than males in mg/kg PCP intake. Also, PCP (but not water) deliveries and mg/kg PCP intake significantly increased from the first 3 days to the last 3 days of the 21-day LgA period in both males and females. The subsequent ShA FR 16 FR 16 performance did not differ by sex, but it was significantly elevated above the first ShA period in both sexes.

The concentration- response function for PCP break point under the PR PR schedules and PCP intake (mg/kg) were significantly shifted upward during the second (vs first) ShA period, and femalesí mg/kg intake significantly exceeded malesí. Conclusions: Male and female rhesusmonkeys both showed escalation of PCP self-administration during LgA to PCP and during ShA that occurred after (vs before) LgA. Both showed vertical upward shifts in the concentration◊intake (mg/kg) function under the PR schedule, and females exceeded males on this measure. These findings with PCP and monkeys are consistent with vertical upward shifts of cocaine dose-response functions in previous escalation studies in male rats and reports of sex differences (F>M) during several other phases of drug abuse.

Keywords Escalation . Female . Long access . Male . Oral . PCP . Phencyclidine . Rhesus monkeys . Self-administration . Short

Click here to read full article (PDF)

See University of Minnesota for additional information.

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