Compulsion derived from incentive cocaine-seeking habits is associated
with a downregulation of the dopamine transporter in striatal astrocytes
Abstract
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.