Background: Withdrawal of phencyclidine (PCP), ethanol (ETOH), and other drugs reduces operant responding maintained by food. Objectives: Experiment 1 examined the effects of withdrawing daily short access (2 h) to drug on impulsivity for saccharin (SACC) using a delay discounting task and comparing male and female rhesus monkeys. Experiment 2 examined the effects of withdrawing a nondrug substance (e.g., food or SACC) on impulsivity for PCP. Materials and methods: In experiment 1, either PCP or ETOH was available daily with water for 2 h under a fixed ratio 16 (FR 16) or FR 8 schedule, respectively. In a second component, SACC was available for 45 min under a delay discounting schedule. Next, water was substituted, and drug access was then restored. In experiment 2, PCP was available under a delay discounting schedule during food satiation or restriction or during concurrent SACC vs water access. Results: In experiment 1, withdrawal of 0.5 mg/ml PCP increased impulsivity for SACC, but not SACC intake, in males and females. During 16% ETOH access, impulsivity for SACC was elevated compared to baseline water access, and it returned to baseline levels during ETOH withdrawal. In experiment 2, food restriction resulted in increased PCP intake in males and females and increases in impulsivity for PCP that were greater in males than in females. SACC withdrawal had no effect on impulsivity for PCP or PCP intake. Conclusions: Withdrawal of PCP and reduced food access increased impulsivity for SACC or PCP, respectively. Impulsivity is a sensitive indicator of drug dependence.
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Acknowledgements The authors are grateful to Dr. Jennifer L. Perry for initial development of the delay discounting procedures with monkeys and to Sarah Fahnhorst, Jenny Falor, Alison Grace, Alayna Fogal, Tim Franke, Krista Johnson, and Lisa Tsackert for technical assistance. We would like to thank Justin Anker for reviewing an earlier version of this manuscript and for assistance with the graphics. This research was supported by the National Institute on Drug Abuse grants R01 DA02486-29, K05 DA15267-07 (MEC), and T32 DA 07097-29 (JLN).
- Delay discounting
- Food restriction
- Food satiation
- Phencyclidine (PCP)
- Rhesus monkeys