Intermittent access cocaine self-administration produces context-specific escalation and increased motivation

The intermittent-access (IntA) self-administration procedure has been reported to produce intensified addiction-like behavior compared to continuous-access (ContA) procedures. In a common variation of the IntA procedure, cocaine is available for 5 min at the beginning of each half hour of a 6-h session. In contrast, during ContA procedures, cocaine is available continuously throughout a session, typically lasting one or more hours. Previous studies comparing procedures have used between-subjects designs, where separate groups of rats self-administer cocaine on either IntA or ContA procedures. The present study used a within-subjects design where subjects self-administered cocaine on the IntA procedure in one context and self-administered cocaine on the continuous short-access (ShA) procedure in another context during separate sessions. Across sessions, rats escalated cocaine intake in the IntA, but not ShA, context. Following sessions eight and 11, rats were administered a progressive ratio test in each context to monitor the change in cocaine motivation. Rats obtained more cocaine infusions on the progressive ratio test in the IntA context than in the ShA context following 11 sessions. These results suggest that addiction-like behaviors following IntA self-administration may be influenced by context-specific learning factors.

Effects of access condition on substance use disorder-like phenotypes in male and female rats self-administering MDPV or cocaine

Substance use disorder (SUD) is a heterogeneous disorder, where severity, symptoms, and patterns of use vary across individuals. Yet, when rats self-administer cocaine under short-access conditions, their behavior tends to be well-regulated, though individual differences can emerge with long- or intermittent-access. In contrast, significant individual differences emerge when rats self-administer 3,4-methylenedioxypyrovalerone (MDPV), even under short-access conditions, wherein ~30 % of rats exhibit high levels of drug-taking. This study assessed SUD-like phenotypes of male and female rats self-administering MDPV or cocaine by comparing level of drug intake, responding during periods of signaled drug unavailability, and sensitivity to footshock punishment to determine whether: (1) under short-access conditions, rats that self-administer MDPV will exhibit a more robust SUD-like phenotype than rats that self-administer cocaine; (2) female rats will have a more severe phenotype than male rats; and (3) compared to short-access, long- and intermittent-access to MDPV or cocaine self-administration will result in a more robust SUD-like phenotype. Compared to cocaine, rats that self-administered MDPV exhibited a more severe phenotype, even under short-access conditions. Long- and intermittent-access to cocaine and MDPV temporarily altered drug-taking patterns but did not systematically change SUD-like phenotypes. Behavioral and quantitative autoradiography studies suggest phenotypic differences are not due to expression of dopamine transporter, dopamine D2 or D3 receptors, or 5-HT1B, 5-HT2A, or 5-HT2C receptors. This study suggests individuals who use synthetic cathinones may be at greater risk for developing a SUD, and short-access MDPV self-administration may provide a useful method to study the transition to disordered substance use in humans.