Background In previous studies with male and female rhesus monkeys withdrawal of access to oral phencyclidine (PCP) self administration reduced responding for food under a high fixed-ratio (FR) schedule more in males than females and with a delay discounting (DD) task with saccharin (SACC) as the reinforcer. Impulsive choice for SACC increased during PCP withdrawal more than females. Objectives The goal of the present study was to examine the effect of PCP (0.25 or 0.5 mg/ml) withdrawal on impulsive choice for SACC in females during the follicular and luteal phases of the menstrual cycle. Materials and methods In Component 1 PCP and water were available from 2 drinking spouts for 1.5 h sessions under concurrent FR 16 schedules. In Component 2 a SACC solution was available for 45 min under a DD schedule. Monkeys had a choice of one immediate SACC delivery (0.6 ml) or 6 delayed SACC deliveries, and the delay was increased by 1 sec after a response on the delayed lever and decreased by 1 sec after a response on the immediate lever. There was then a 10-day water substitution phase, or PCP-withdrawal, that occurred during the mid-folllicular phase (Days 7–11) or the late-luteal (Days 24–28) phase of the menstrual cycle. Access to PCP and concurrent water was then restored, and the PCP withdrawal procedure was repeated over several follicular and luteal menstrual phases. Results PCP deliveries were higher during the luteal vs the follicular phase. Impulsive choice was greater during the luteal (vs follicular) phase during withdrawal of the higher PCP concentration. Conclusions PCP withdrawal was associated with elevated impulsive choice for SACC, especially in the luteal (vs follicular) phase of the menstrual cycle in female monkeys.
Background In previous studies female monkeys self-administered more oral phencyclidine (PCP) than males, and PCP intake differed by phase of menstrual cycle. Objectives The purpose of this study was to examine sex and hormonal influences on oral cocaine self-administration in male and female rhesus monkeys in the follicular vs. luteal phases of the menstrual cycle, with concurrent access to an alternative nondrug reward, saccharin (SACC) vs. water. Materials and methods Concurrent access to cocaine (0.2, 0.4 and 0.8 mg/ml) and SACC or water was available from two drinking spouts under concurrent fixed-ratio (FR) 2, 4, and 8 schedules during daily 3-h sessions. Results Cocaine deliveries were similar in males and females in the females’ luteal phase, but cocaine deliveries were higher in females during the follicular phase than the luteal phase and compared to males. When SACC was available cocaine deliveries were reduced in females in the follicular phase of the cycle, and cocaine intake (mg/kg) was reduced in males and in females’ follicular and luteal phases. Conclusions Access to concurrent SACC (vs. water) reduced cocaine intake (mg/kg) in males and in females during both menstrual phases, and the magnitude of the reduction in cocaine intake was greatest during the females’ follicular phase. Thus, a nondrug alternative reward, SACC, is a viable alternative treatment for reducing cocaine’s rewarding effects on male and female monkeys, and reductions in cocaine-seeking were optimal in the females’ luteal phase.
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