Preclinical data have indicated that extended access to cocaine self-administration (e.g., 6-12 h/day) facilitates an escalation in daily cocaine intake that is not seen when rats are given shorter (e.g., 1-2 h/day) access to cocaine for self-administration. Data from studies with rats have shown that females self-administer more cocaine than males during all phases of drug abuse (e.g., acquisition, maintenance, and reinstatement). The purpose of this study was to examine potential differences between males and females in the escalation of intravenous cocaine intake following a differential access (e.g., 1 vs. 6 h) period of cocaine self-administration. Four groups of rats were compared: (1) long-access (LgA; 6 h) females; (2) LgA males; (3) short-access (ShA; 1 h) females; and (4) ShA males. Animals were given LgA or ShA to intravenous cocaine (0.5 mg/kg/infusion) self-administration under an Fr 1 schedule for 21 days. Subsequently, access conditions were made equal (3 h) across groups, and dose-response curves for cocaine were compared. Results revealed that the LgA groups' dose-response curves were significantly elevated above those of ShA groups. Additionally, the dose-response curve of LgA female rats was significantly elevated above that of LgA male rats. These results suggest that female rats are more sensitive than male rats to factors that contribute to the escalation of cocaine intake (e.g., extended access conditions).
Bibliographical noteFunding Information:
The authors are grateful to Dr. Kelly P. Cosgrove, Erin B. Larson, Andrew D. Morgan, and Jennifer Perry for critically reviewing the manuscript. We are also grateful to Annemarie Loth for her technical assistance in collecting data for this study. This study was supported by NIDA grants K05 DA15267 and R01 DA03240 (M.E.C.) and F31 DA14161 and T32 DA07097 (M.E.R.).
- Differential access
- Sex differences