Prelimbic and infralimbic cortical regions differentially encode cocaine-associated stimuli and cocaine-seeking before and following abstinence

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Abstract

Cocaine stimuli often trigger relapse of drug-taking, even following periods of prolonged abstinence. Here, electrophysiological recordings were made in rats (n =29) to determine how neurons in the prelimbic (PrL) or infralimbic (IL) regions of the medial prefrontal cortex (mPFC) encode cocaine-associated stimuli and cocaine-seeking, and whether this processing is differentially altered after 1 month of cocaine abstinence. After self-administration training, neurons (n=308) in the mPFC were recorded during a single test session conducted either the next day or 1 month later. Test sessions consisted of three phases during which (i) the tone–houselight stimulus previously paired with cocaine infusion during self-administration was randomly presented by the experimenter, (ii) rats responded on the lever previously associated with cocaine during extinction and (iii) the tone–houselight was presented randomly between cocaine-reinforced responding during resumption of cocaine self-administration. PrL neurons showed enhanced encoding of the cocaine stimulus and drug-seeking behavior (under extinction and self-administration) following 30 days of abstinence. In contrast, although IL neurons encoded cocaine cues and cocaine-seeking, there were no pronounced changes in IL responsiveness following 30 days of abstinence. Importantly, cue-related changes do not represent a generalised stimulus-evoked discharge as PrL and IL neurons in control animals (n=4) exhibited negligible recruitment by the tone–houselight stimulus. The results support the view that, following abstinence, neural encoding in the PrL but not IL may play a key role in enhanced cocaine-seeking, particularly following re-exposure to cocaine-associated cues.

Neurons in both the PrL and IL are responsive to drug-associated cues and instrumental contingencies before and following abstinence. Importantly, one month of abstinence from cocaine self-administration enhances recruitment of PrL neurons that encode cocaine-associated stimuli and drug-seeking behavior, under both extinction and self-administration conditions. In contrast, while there was a general increase in IL recruitment during instrumental actions compared to cocaine associated cues, neural encoding in the IL did not significantly change in either condition after 30 days of cocaine abstinence.

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