INTRACRANIAL SELF-STIMULATION IN FEMALE AND MALE-RATS - NO SEX-DIFFERENCES USING A RATE-INDEPENDENT PROCEDURE

Given gender differences in human drug use and dependence, this study examined sex differences in reinforcement processes that may underlie such behavior. A psychophysical determination of reinforcement thresho ld was made using an intracranial self-stimulation (ICSS) paradigm, el ectrically activating the medial forebrain bundle (MFB) as it passes t hrough the lateral hypothalamus (LH). Using this response rate-indepen dent procedure, basal reinforcement thresholds were not significantly different in male vs. female rats (119.4 +/- 3.3 mu A vs. 110.8 +/- 4. 0 mu A, respectively; N = 8/sex). Further, baseline reinforcement thre shold did not fluctuate systematically across stages of the estrous cy cle in female rats. The psychostimulants D-amphetamine (0.056-0.56 mg/ kg s.c.) and cocaine (1.8-18.0 mg/kg i.p.) dose-dependently lowered re inforcement threshold, with no significant sex difference. The opioid morphine (0.56-5.6 mg/kg s.c.) did not significantly lower reinforceme nt threshold in either sex. These results contrast those of some previ ous studies that have used response rate-dependent measures of reinfor cement threshold; procedures which are less rate-dependent may be more appropriate when examining subject variables such as sex and stage of estrous. (C) 1997 Elsevier Science Ireland Ltd.