Increased Excitability and Synaptic Plasticity of Drd1- and Drd2-Expressing Prelimbic Neurons Projecting to Nucleus Accumbens after Heroin Abstinence Are Reversed by Cue-Induced Relapse and Protein Kinase A Inhibition

Abstract

Dysregulation of the input from the prefrontal cortex (PFC) to the nucleus accumbens (NAc) contributes to cue-induced opioid seeking but the heterogeneity in, and regulation of, prelimbic (PL)-PFC to NAc (PL->NAc) neurons that are altered has not been comprehensively explored. Recently, baseline and opiate withdrawal-induced differences in intrinsic excitability of Drd1⁺ (D1⁺) versus Drd2⁺ (D2⁺) PFC neurons have been demonstrated. Thus, here we investigated physiological adaptations of PL->NAc D1⁺ versus D2⁺ neurons after heroin abstinence and cue-induced relapse. Drd1-Cre⁺ and Drd2-Cre⁺ transgenic male Long-Evans rats with virally labeled PL->NAc neurons were trained to self-administer heroin followed by 1 week of forced abstinence. Heroin abstinence significantly increased intrinsic excitability in D1⁺ and D2⁺ PL->NAc neurons and increased postsynaptic strength selectively in D1⁺ neurons. These changes were normalized by cue-induced relapse to heroin seeking. Based on protein kinase A (PKA)-dependent changes in the phosphorylation of plasticity-related proteins in the PL cortex during abstinence and cue-induced relapse to cocaine seeking, we assessed whether the electrophysiological changes in D1⁺ and D2⁺ PL->NAc neurons during heroin abstinence were regulated by PKA. In heroin-abstinent PL slices, application of the PKA antagonist (R)-adenosine, cyclic 3',5'-(hydrogenphosphorothioate) triethylammonium (RP-cAMPs) reversed intrinsic excitability in both D1⁺ and D2⁺ neurons and postsynaptic strength in only D1⁺ neurons. Additionally, in vivo bilateral intra-PL infusion of RP-cAMPs after abstinence from heroin inhibited cue-induced relapse to heroin seeking. These data reveal that PKA activity in D1⁺ and D2⁺ PL->NAc neurons is not only required for abstinence-induced physiological adaptations but is also required for cue-induced relapse to heroin seeking.SIGNIFICANCE STATEMENT Neuronal plasticity in the medial prefrontal cortex is thought to underlie relapse to drug seeking, yet the subpopulation of neurons that express this plasticity to functionally guide relapse is unclear. Here we show cell type-specific adaptations in Drd1-expressing versus Drd2-expressing prelimbic pyramidal neurons with efferent projections to nucleus accumbens. These adaptations are bidirectionally regulated during abstinence versus relapse and involve protein kinase A (PKA) activation. Furthermore, we show that disruption of the abstinence-associated adaptations via site-specific PKA inhibition abolishes relapse. These data reveal the promising therapeutic potential of PKA inhibition for preventing relapse to heroin seeking and suggest that cell type-specific pharmacologies that target subpopulations of prefrontal neurons would be ideal for future therapeutic developments.

Keywords: abstinence; dopamine receptors; excitability; heroin; prelimbic cortex; protein kinase A.