∆9-Tetrahydrocannabinol Self-Administration Induces Cell-Type Specific Adaptations and cFOS Expression in the Nucleus Accumbens Core

Given that 30% of chronic cannabis users develop cannabis use disorder (CUD), it is critical to identify neuroadaptations that contribute to this disease. The nucleus accumbens core (NAcore) is important for drug seeking and ~ 90% of all NAcore neurons are divided into D1- and D2-medium spiny neurons (MSNs) that serve opposing roles in drug seeking. Drugs of abuse induce D1- and D2-MSN specific adaptations but whether ∆9-tetrahydrocannabinol (THC) use initiates similar neuroadaptations is unknown. D1- and D2-Cre transgenic rats were transfected with Cre-dependent reporters and trained to self-administer THC + cannabidiol (THC + CBD). After extinction training dendritic spine morphology, glutamate transmission, CB1R function and cFOS expression were quantified. We found that extinction from THC + CBD induced a loss of large spine heads in D1- but not D2-MSNs and a commensurate reduction in glutamate synaptic transmission. Also, CB1R function was impaired on glutamatergic synapses onto D1-MSNs and this was paralleled by an augmented capacity to potentiate glutamate transmission in D1-MSNs. CB1R function and glutamate synaptic transmission on D2-MSN synapses were unaffected by THC + CBD use. Using cFOS expression as an activity marker, we found that D1-MSNs activity remained unchanged after extinction from THC + CBD but significantly increased after 60 minutes cue-induced drug seeking. Surprisingly, the percentage of D2-MSNs expressing cFOS decreased after extinction from THC + CBD and this decrease was restored by drug cues. Thus, glutamatergic adaptations in D1-MSNs partially predict activity changes and pose modulating CB1R function that is down-regulated selectively at D1-MSN synapses as a potential treatment strategy for CUD.