Extended cocaine-seeking produces a shift from goal-directed to habitual responding in rats

Abstract

Cocaine addiction is often characterized by a rigid pattern of behavior in which cocaine users continue seeking and taking drug despite negative consequences associated with its use. As such, full acquisition and relapse of drug-seeking behavior may be attributed to a shift away from goal-directed responding and a shift towards the maladaptive formation of rigid and habit-like responses. This rigid nature of habitual responding can be developed with extended training and is typically characterized by insensitivity to changes in outcome value. The present study determined whether cocaine (primary reinforcer) and cocaine associated cues (secondary reinforcer) could be devalued in rats with different histories of cocaine self-administration. Specifically, rats were trained on two schedules of cocaine self-administration (long-access vs. short-access). Following training the cocaine reinforcer was devalued through three separate pairings of lithium chloride with cocaine infusions. Cocaine history did not have an impact on devaluation of cocaine-associated cues. However, the reinforcing properties of cocaine were devalued only in rats on a short-access cocaine schedule but not those trained on a long-access schedule. Taken together this pattern of findings suggests that, in short access rats, devaluation is specific to the primary reinforcer and not associative stimuli such as cues. Importantly, rats that received extended training during self-administration displayed insensitivity to outcome devaluation of the primary reinforcer as well as all associative stimuli, thus displaying rigid behavioral responding similar to behavioral patterns found in addiction. Alternatively, long access cocaine exposure may have altered the devaluation threshold.