Cocaine Exposure Increases Excitatory Synaptic Transmission and Intrinsic Excitability in the Basolateral Amygdala in Male and Female Rats and Across the Estrous Cycle

Introduction: Sex and ovarian hormones influence cocaine seeking and relapse vulnerability, but less is known regarding the cellular and synaptic mechanisms contributing to these behavioral sex differences. One factor thought to influence cue-induced seeking behavior following withdrawal is cocaine-induced changes in the spontaneous activity of pyramidal neurons in the basolateral amygdala (BLA). However, the mechanisms underlying these changes, including potential sex or estrous cycle effects, are unknown. Methods: Ex vivo whole cell patch clamp electrophysiology was conducted to investigate the effects of cocaine exposure, sex and estrous cycle fluctuations on two properties that can influence spontaneous activity of BLA pyramidal neurons: 1). Frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) and 2). Intrinsic excitability. Recordings of BLA pyramidal neurons were conducted in adult male and female rats and across the estrous cycle following 2-4 weeks of withdrawal from extended-access cocaine self-administration (6h/day for 10 days) or drug-naive conditions. Results: In both sexes, cocaine exposure increased the frequency, but not amplitude, of sEPSCs and neuronal intrinsic excitability. Across the estrous cycle, sEPSC frequency and intrinsic excitability were significantly elevated only in cocaine-exposed females in the estrus stage of the cycle, a stage when cocaine seeking behavior is known to be enhanced. Conclusions: Here we identify potential mechanisms underlying cocaine-induced alterations in the spontaneous activity of BLA pyramidal neurons in both sexes along with changes in these properties across the estrous cycle.