PROJECT SUMMARY
Research into the mechanisms underlying methamphetamine craving, a key driver of relapse, is dwarfed in
comparison to other drugs of abuse (e.g., cocaine, opioids). Exacerbated drug craving can be modeled in rats
using the incubation of methamphetamine craving paradigm. The nucleus accumbens plays a key role in
mediating drug seeking which intensifies commensurate with abstinence duration. Approximately 95% of
accumbens neurons are GABAergic medium spiny neurons which can be distinguished by expression of the
D1 dopamine receptors (D1DRs) or D2 dopamine receptors (D2DRs), although a relatively small proportion of
these cells express both of these receptors. Canonically, D1DR-containing neurons were thought to project
exclusively to the ventral tegmental area, whereas D2DR-expressing accumbens efferents extended to the
ventral pallidum; however, recent evidence suggests that there is some overlap such that D1DR-containing
neurons also project to the ventral pallidum and modulate drug seeking. Generally, D1DR-containing neurons
promote drug-related behaviors, whereas D2DR-containing neurons inhibit drug-related behaviors. Importantly,
the influence of specific projections of these neuronal subtypes on methamphetamine seeking is unknown.
Specific Aim 1 will combine D1DR-Cre and D2DR-Cre transgenic rats, optogenetics, and electrophysiology to
dissociate the role of D1DR- vs. D2DR-containing striatopallidal and striatotegmental projections in the
incubation of methamphetamine craving. The time-dependent molecular adaptations within accumbens D1DR-
containing and D2DR-containing neurons that occur during abstinence from methamphetamine are also
unexplored. Very recent advances in single cell sequencing methodologies have enabled simultaneous
profiling of the transcriptome and chromatin accessibility in defined cell populations. This is particularly relevant
for the current proposal since it will allow us to differentiate in silico effects in accumbens neurons which
express either the D1DR or D2DR. Specific Aim 2 will define the landscape of accessible chromatin and gene
expression by coupling ATAC sequencing and RNA sequencing from the same single nuclei droplets in rats
following short or prolonged abstinence from methamphetamine. Functional validation of a candidate gene will
be performed by bidirectionally manipulating gene expression in selectively in D1DR-containing or D2DR-
containing neurons and assessing the incubation of methamphetamine craving. Collectively, the proposed
studies will elucidate the neurocircuitry and molecular mechanisms underlying the incubation of
methamphetamine craving.