Divergent Prelimbic Cortical Pathways Interact with BDNF to Regulate Cocaine-seeking.

A single BDNF microinfusion into prelimbic (PrL) cortex immediately after the last cocaine self-administration session decreases relapse to cocaine-seeking. The BDNF effect is blocked by NMDAR antagonists. To determine whether synaptic activity in putative excitatory projection neurons in PrL cortex is sufficient for BDNF's effect on relapse, the PrL cortex of male rats was infused with an inhibitory Designer Receptor Exclusively Activated by Designer Drugs (DREADD) viral vector driven by an αCaMKII promoter. Immediately after the last cocaine self-administration session, rats were injected with clozapine-N-oxide 30 min before an intra-PrL BDNF microinfusion. DREADD-mediated inhibition of the PrL cortex blocked the BDNF-induced decrease in cocaine-seeking after abstinence and cue-induced reinstatement after extinction. Unexpectedly, DREADD inhibition of PrL neurons in PBS-infused rats also reduced cocaine-seeking, suggesting that divergent PrL pathways affect relapse. Next, using a cre-dependent retroviral approach, we tested the ability of DREADD inhibition of PrL projections to the NAc core or the paraventricular thalamic nucleus (PVT) to alter cocaine-seeking in BDNF- and PBS-infused rats. Selective inhibition of the PrL-NAc pathway at the end of cocaine self-administration blocked the BDNF-induced decrease in cocaine-seeking but had no effect in PBS-infused rats. In contrast, selective inhibition of the PrL-PVT pathway in PBS-infused rats decreased cocaine-seeking, and this effect was prevented in BDNF-infused rats. Thus, activity in the PrL-NAc pathway is responsible for the therapeutic effect of BDNF on cocaine-seeking whereas inhibition of activity in the PrL-pPVT pathway elicits a similar therapeutic effect in the absence of BDNF. The major issue in cocaine addiction is the high rate of relapse. However, the neuronal pathways governing relapse remain unclear. Using a pathway-specific chemogenetic approach, we found that BDNF differentially regulates two key prelimbic pathways to guide long-term relapse. Infusion of BDNF in the prelimbic cortex during early withdrawal from cocaine self-administration decreases relapse that is prevented when neurons projecting from the prelimbic cortex to the nucleus accumbens core are inhibited. In contrast, BDNF restores relapse when neurons projecting from the prelimbic cortex to the posterior paraventricular thalamic nucleus are inhibited. This study demonstrates that two divergent cortical outputs mediate relapse that is regulated in opposite directions by infusing BDNF in the prelimbic cortex during early withdrawal from cocaine.