17β-Estradiol Potentiates the Reinstatement of Cocaine Seeking in Female Rats: Role of the Prelimbic Prefrontal Cortex and Cannabinoid Type-1 Receptors

Clinical observations imply that female cocaine addicts experience enhanced relapse vulnerability compared with males, an effect tied to elevated estrogen phases of the ovarian hormone cycle. Although estrogens can enhance drug-seeking behavior, they do not directly induce reinstatement on their own. To model this phenomenon, we tested whether an estrogen could augment drug-seeking behavior in response to an ordinarily subthreshold reinstatement trigger. Following cocaine self-administration and extinction, female rats were ovariectomized to isolate estrogen effects on reinstatement. Although neither peak proestrus levels of the primary estrogen 17β-estradiol (E2; 10 μg/kg, i.p., 1-h pretreatment) nor a subthreshold cocaine dose (1.25 mg/kg, i.p.) alone were sufficient to reinstate drug-seeking behavior, pretreatment with E2 potentiated reinstatement to the ordinarily subthreshold cocaine dose. Furthermore, E2 microinfusions revealed that E2 (5 μg/0.3 μl, 15-min pretreatment) acts directly within the prelimbic prefrontal cortex (PrL-PFC) to potentiate reinstatement. As E2 has been implicated in endocannabinoid mobilization, which can disinhibit PrL-PFC projection neurons, we investigated whether cannabinoid type-1 receptor (CB1R) activation is necessary for E2 to potentiate reinstatement. The CB1R antagonist AM251 (1 or 3 mg/kg, i.p., 30-min pretreatment) administered prior to E2 and cocaine suppressed reinstatement in a dose-dependent manner. Finally, PrL-PFC AM251 microinfusions (300 ng/side, 15-min pretreatment) also suppressed E2-potentiated reinstatement. Together, these results suggest that E2 can augment reactivity to an ordinarily subthreshold relapse trigger in a PrL-PFC CB1R activation-dependent manner

Sex, Stress, and Prefrontal Cortex: Influence of Biological Sex on Stress-Promoted Cocaine Seeking

Clinical reports suggest that females diagnosed with substance use disorder experience enhanced relapse vulnerability compared with males, particularly during stress. We previously demonstrated that a stressor (footshock) can potentiate cocaine seeking in male rats via glucocorticoid-dependent cannabinoid type-1 receptor (CB1R)-mediated actions in the prelimbic prefrontal cortex (PrL-PFC). Here, we investigated the influence of biological sex on stress-potentiated cocaine seeking. Despite comparable self-administration and extinction, females displayed a lower threshold for cocaine-primed reinstatement than males. Unlike males, footshock, tested across a range of intensities, failed to potentiate cocaine-primed reinstatement in females. However, restraint potentiated reinstatement in both sexes. While sex differences in stressor-induced plasma corticosterone (CORT) elevations and defensive behaviors were not observed, differences were evident in footshock-elicited ultrasonic vocalizations. CORT administration, at a dose which recapitulates stressor-induced plasma levels, reproduced stress-potentiated cocaine-primed reinstatement in both sexes. In females, CORT effects varied across the estrous cycle; CORT-potentiated reinstatement was only observed during diestrus and proestrus. As in males, CORT-potentiated cocaine seeking in females was localized to the PrL-PFC and both CORT- and restraint-potentiated cocaine seeking required PrL-PFC CB1R activation. In addition, ex vivo whole-cell electrophysiological recordings from female layer V PrL-PFC pyramidal neurons revealed CB1R-dependent CORT-induced suppression of inhibitory synaptic activity, as previously observed in males. These findings demonstrate that, while stress potentiates cocaine seeking via PrL-PFC CB1R in both sexes, sensitivity to cocaine priming injections is greater in females, CORT-potentiating effects vary with the estrous cycle, and whether reactivity to specific stressors may manifest as drug seeking depends on biological sex