Maternal cannabis use alters excitatory inputs to corticostriatal efferent neurons in rat offspring
With the recent surge in cannabis legalization across North America, there is legitimate concern that rates of cannabis use during pregnancy will dramatically increase in the coming years. However, the long-term impacts of prenatal cannabis exposure (PCE) on the brain and behavior remain poorly understood. Using a model of passive cannabis vapor exposure, we have previously shown that PCE impairs behavioral flexibility in an attentional set-shifting task in adult offspring, which is orchestrated in part by excitatory inputs from the medial prefrontal cortex (mPFC) to the nucleus accumbens (NAc). Given the fundamental role of these corticostriatal inputs in coordinating flexible reward-seeking strategies, we used a combination of retrograde tracing and ex vivo electrophysiology to test the hypothesis that maternal cannabis use alters the synaptic and intrinsic membrane properties of corticostriatal efferent neurons in exposed male and female rat offspring. Specifically, pregnant rat dams were trained to self-administer vaporized cannabis (69.7% THC; 150 mg/ml) twice daily throughout mating and gestation and offspring were subsequently injected with fluorescent retrobeads into the NAc core prior to conducting whole-cell ex vivo recordings of spontaneous excitatory and inhibitory post-synaptic currents (EPSC and IPSC, respectively) in retrolabeled mPFC neurons in adulthood. Our results indicate that PCE increases the frequency of spontaneous glutamatergic events (EPSCs) in NAc-projecting mPFC neurons in a sex-specific manner, which drives changes in excitatory to inhibitory (EPSC/IPSC) ratio, particularly in females. Furthermore, the amplitude of phasic glutamatergic events was reduced in cannabis-exposed offspring of both sexes, suggesting changes in postsynaptic receptor function. Altogether, these data demonstrate that PCE shifts the balance of excitatory/inhibitory inputs onto NAc-projecting mPFC neurons with limited effects on membrane conductance in females, resulting in reduced sex differences following maternal cannabis self-administration. These results provide putative neurophysiological mechanisms mediating previously observed behavioral changes, and future studies will need to test if these cannabis-induced changes are causal to long-term deficits in behavioral flexibility that have been previously documented in exposed offspring.