Incubation of oxycodone craving is associated with CP-AMPAR upregulation in D1 and A2a receptor-expressing medium spiny neurons in nucleus accumbens core and shell.

A major problem in treating opioid use disorder is persistence of craving after protracted abstinence. This has been modeled in rodents using the incubation of craving model, in which cue-induced drug seeking increases over the first weeks of abstinence from drug self-administration and then remains high for an extended period. Incubation has been reported for several opioids, including oxycodone, but little is known about underlying synaptic plasticity. In contrast, it is well established that incubation of cocaine and methamphetamine craving depends on strengthening of glutamate synapses in the nucleus accumbens (NAc) through incorporation of calcium-permeable AMPARs (CP-AMPARs). CP-AMPARs have higher conductance than the calcium-impermeable AMPARs that mediate NAc excitatory transmission in drug-naïve animals, as well as other distinct properties. Here we examined AMPAR transmission in medium spiny neurons (MSN) of NAc core and shell subregions after forced abstinence from extended-access oxycodone or saline self-administration, using male and female wild-type and transgenic rats. Before incubation (abstinence days 1-2), CP-AMPAR upregulation was not detected in either D1 or A2a (D2) receptor-expressing MSN. After incubation had stably plateaued (abstinence days 17-33), CP-AMPARs were elevated in both MSN subtypes in both subregions. These results explain the prior demonstration that infusion of a selective CP-AMPAR antagonist into NAc core or shell prevents expression of oxycodone incubation. However, CP-AMPAR upregulation on both MSN subtypes contrasts with selective upregulation on D1 MSN after cocaine and methamphetamine incubation. Our results demonstrate a common role for CP-AMPAR upregulation in psychostimulant and oxycodone incubation, albeit with differences in MSN subtype-specificity.