The development of compulsive cue-controlled-incentive-drug-seeking habits, a hallmark of substance use disorder, is predicated on an intrastriatal shift in the locus of control over behaviour from a nucleus accumbens (Nac) core - dorsomedial striatum network to a Nac core - anterior dorsolateral striatum (aDLS) network. Such shift parallels striatal adaptations to chronic drug, including cocaine self-administration, marked by dopamine transporter (DAT) alterations originating in the ventral striatum that spread eventually to encompass the aDLS. Having recently shown that heroin self-administration results in a pan-striatal reduction in astrocytic DAT that precedes the development of aDLS dopamine-dependent incentive heroin-seeking habits we tested the hypothesis that similar adaptations occur following cocaine exposure. We compared DAT protein levels in whole tissue homogenates and astrocytes cultured from ventral and dorsal striatal territories of drug naïve male Sprague Dawley rats to those of rats with a history of cocaine-taking or an aDLS dopamine-dependent incentive cocaine-seeking habit. Cocaine exposure resulted in a decrease in whole tissue and astrocytic DAT across all territories of the striatum. We further demonstrated that compulsive (i.e., punishment-resistant) incentive cocaine-seeking habits were associated with a reduction in DAT mRNA levels in the Nac shell, but not the Nac core-aDLS incentive habit system. Together with the recent evidence of heroin-induced downregulation of striatal astrocytic DAT, these findings suggest that alterations in astrocytic DAT may represent a common mechanism underlying the development of compulsive incentive drug-seeking habits across drug classes.

The emergence of compulsive drug seeking habits, a hallmark feature of substance use disorder, has been shown to be predicated on the engagement of dorsolateral striatum (DLS) control over behaviour, which is underpinned by a dopamine-dependent functional coupling of the nucleus accumbens and the DLS. However, the mechanisms by which this coupling occurs have not been fully elucidated. The striatum is tiled by a syncytium of astrocytes that express the dopamine transporter (DAT), whose expression is altered in individuals with a heroin use disorder. Thus, astrocytes are uniquely placed functionally to bridge dopamine-dependent mechanisms across the striatum. Thus, here we tested the hypothesis that exposure to heroin, which does not interact with DAT, influences its expression in astrocytes across the striatum before the development of DLS-dependent incentive heroin seeking habits. Using Western-blot, qPCR and RNAscope we measured DAT protein and mRNA levels in whole tissue, cultured or in situ astrocytes from striatal territories of rats with a well-established cue-controlled heroin seeking habit and rats trained to respond for heroin or food under continuous reinforcement. Incentive heroin seeking habits were associated with a reduction in DAT protein levels in the anterior DLS (aDLS) that was preceded by a heroin-induced reduction in DAT mRNA and protein content in astrocytes across the striatum. aDLS astrocytes were also shown to be uniquely susceptible to direct dopamine- and opioid-induced downregulation of DAT expression. These results suggest that astrocytes may critically regulate the striatal dopaminergic adaptations that lead to the development of incentive habits for heroin.