Cocaine-induced reward enhancement measured with intracranial self-stimulation in rats bred for low versus high saccharin intake.

Rats selectively bred for high (HiS) or low (LoS) saccharin intake are a well-established model of drug-abuse vulnerability, with HiS rats being more likely to consume sweets and cocaine than LoS rats. Still, the nature of these differences is poorly understood. This study examined whether the motivational consequences of cocaine exposure are differentially expressed in HiS and LoS rats by measuring intracranial self-stimulation (ICSS) thresholds following acute injections of cocaine (10 mg/kg). Reductions in ICSS thresholds following cocaine injection were greater in HiS rats than in LoS rats, suggesting that the reward-enhancing effects of cocaine are greater in the drug-vulnerable HiS than LoS rats. Higher cocaine-induced reward, indicated by lower ICSS thresholds, may explain the higher rates of drug consumption in sweet-preferring animal models, providing a clue to the etiology of cocaine addiction in vulnerable populations.