Escalation of intravenous cocaine self-administration, progressive-ratio performance, and reinstatement in rats selectively bred for high (HiS) and low (LoS) saccharin intake

Rationale: Rats selectively bred for high saccharin (HiS) intake consume more alcohol and acquire intravenous (IV) cocaine self-administration more rapidly than their low saccharin (LoS) consuming counterparts. Objectives: The purpose of the present study was to determine whether HiS and LoS rats also differ in the escalation, maintenance, and reinstatement of IV cocaine self-administration. Methods: LoS and HiS female rats were allowed to self-administer cocaine [0.4 mg/kg; fixed ratio (FR) 1] under short (ShA, 2 h per day) or long (LgA, 12 h per day) access conditions for 21 days. Session lengths were subsequently equated (2 h) and (1) FR1-maintained cocaine (0.4 mg/kg) self-administration, (2) progressive ratio (PR)-maintained cocaine (0.2-1.6 mg/ kg) self-administration, and (3) saline-induced and cocaine (10 mg/kg, IP)-induced reinstatement of drug-seeking behavior were examined. Results: HiS LgA rats escalated their cocaine intake more rapidly and self-administered more cocaine (mg/kg) than LoS LgA rats; however, there was no LoS versus HiS phenotype difference in the number of infusions self-administered by Day 21. Post-escalation cocaine self-administration under an FR1 schedule did not differ as a function of phenotype (LoS versus HiS) or access condition (ShA versus LgA); however, LoS rats responded more for cocaine under the PR schedule than HiS rats, and they showed a greater reinstatement of cocaine-seeking behavior than HiS rats. In contrast, ShA versus LgA did not affect PR or reinstatement performance in the LoS and HiS groups. Conclusions: These results suggest that LoS and HiS rats have distinct drug-seeking and drug-taking profiles that differ as a function of the experimental phase and access condition. The LoS and HiS rats differ along a wide range of behavioral dimensions and represent an important model to study the interactions of feeding, emotionality, and other factors related to vulnerability to drug abuse.