Fundamental Sex Differences in Cocaine-Induced Plasticity of Dopamine D1 Receptor- and D2 Receptor-Expressing Medium Spiny Neurons in the Mouse Nucleus Accumbens Shell.

Background: Cocaine-induced plasticity in the nucleus accumbens shell of males occurs primarily in dopamine D receptor-expressing medium spiny neurons (D1R-MSNs), with little if any impact on dopamine D receptor-expressing medium spiny neurons (D2R-MSNs). In females, the effect of cocaine on accumbens shell D1R- and D2R-MSN neurophysiology has yet to be reported, nor have estrous cycle effects been accounted for.

Methods: We used a 5-day locomotor sensitization paradigm followed by a 10- to 14-day drug-free abstinence period. We then obtained ex vivo whole-cell recordings from fluorescently labeled D1R-MSNs and D2R-MSNs in the nucleus accumbens shell of male and female mice during estrus and diestrus. We examined accumbens shell neuronal excitability as well as miniature excitatory postsynaptic currents (mEPSCs).

Results: In females, we observed alterations in D1R-MSN excitability across the estrous cycle similar in magnitude to the effects of cocaine in males. Furthermore, cocaine shifted estrous cycle-dependent plasticity from intrinsic excitability changes in D1R-MSNs to D2R-MSNs. In males, cocaine treatment produced the anticipated drop in D1R-MSN excitability with no effect on D2R-MSN excitability. Cocaine increased mEPSC frequencies and amplitudes in D2R-MSNs from females in estrus and mEPSC amplitudes of D2R-MSNs from females in diestrus. In males, cocaine increased both D1R- and D2R-MSN mEPSC amplitudes with no effect on mEPSC frequencies.

Conclusions: Overall, while there are similar cocaine-induced disparities regarding the relative excitability of D1R-MSNs versus D2R-MSNs between the sexes, this is mediated through reduced D1R-MSN excitability in males, whereas it is due to heightened D2R-MSN excitability in females.