A commentary on this article appears in this issue on page 495.

No abstract

These findings suggest that stress-induced increases in corticosterone promote cocaine seeking by mobilizing 2-arachidonoylglycerol in the PL, resulting in CBR-mediated attenuation of inhibitory transmission in this brain region.

The findings demonstrate that activity of the eCB system is profoundly modulated by circadian rhythmicity and suggest that its impact on the regulation of food intake is suppressed during sleep and is maximal during early to midafternoon.

Rationale Under some conditions stress, rather than directly triggering cocaine seeking, potentiates reinstatement to other stimuli, including a sub-threshold cocaine dose. The mechanisms responsible for stress-potentiated reinstatement are not well-defined. Endocannabinoid signaling is increased by stress and regulates synaptic transmission in brain regions implicated in motivated behavior. Objectives To test the hypothesis that cannabinoid receptor 1 (CB1R) signaling is required for stress-potentiated reinstatement of cocaine seeking in rats. Methods Following i.v. cocaine self-administration (2 hr access/day) and extinction in male rats, footshock stress alone does not reinstate cocaine seeking, but reinstatement is observed when footshock is followed by an injection of an otherwise subthreshold dose of cocaine (2.5 mg/kg, i.p.). CB1R involvement was tested by systemic administration of the CB1R antagonist AM251 (0, 1, or 3 mg/kg, i.p.) prior to testing for stress-potentiated reinstatement. Results Stress-potentiated reinstatement was blocked by both 1 and 3 mg/kg AM251. By contrast, AM251 only attenuated food-reinforced lever pressing at the higher (i.e., 3 mg/kg) dose and did not affect locomotor activity at either dose tested. Neither high-dose cocaine-primed reinstatement (10 mg/kg, i.p.) nor footshock stress-triggered reinstatement following long-access cocaine self-administration (6 hr access/day) were affected by AM251 pretreatment. Footshock stress increased concentrations of both endocannabinoids, N-arachidonylethanolamine and 2-arachidonoylglycerol, in regions of the prefrontal cortex. Conclusions These findings demonstrate that footshock stress increases prefrontal cortical endocannabinoids and stress-potentiated reinstatement is CB1R-dependent, suggesting that CB1R is a potential therapeutic target for relapse prevention, particularly in individuals whose cocaine use is stress-related.

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.

Human and preclinical models of addiction demonstrate that gonadal hormones modulate acquisition of drug seeking. Little is known, however, about the effects of these hormones on extinction of drug-seeking behavior. Here, we investigated how 17b-estradiol (E 2 ) affects expression and extinction of cocaine seeking in female rats. Using a conditioned place preference (CPP) paradigm, ovariectomized rats were maintained throughout conditioning with 2 d of E 2 treatment followed by 2 d of vehicle treatment, or were injected with E 2 daily. Hormone injections were paired or explicitly unpaired with place conditioning sessions. Expression of a cocaine CPP was of equal magnitude regardless of conditioning protocol, suggesting that E 2 levels during conditioning did not affect subsequent CPP expression. During extinction, daily E 2 administration initially enhanced expression of the cocaine CPP, but resulted in significantly faster extinction compared to controls. Whereas E 2 -treated rats were extinguished within 8 d, vehicle-treated rats maintained CPP expression for more than a month, indicative of perseveration. To determine whether E 2 could rescue extinction in these rats, half were given daily E 2 treatment and half were given vehicle. E 2 -treated rats showed rapid extinction, whereas vehicle-treated rats continued to perseverate. These data demonstrate for the first time that E 2 is necessary for extinction of cocaine seeking in female rats, and that it promotes rapid extinction when administered daily. Clinically, these findings suggest that monitoring and maintaining optimal E 2 levels during exposure therapy would facilitate therapeutic interventions for female cocaine addicts.Gonadal hormones render women more susceptible than men to developing compulsive patterns of psychostimulant use. Natural fluctuations in levels of the primary ovarian hormones, estrogens and progesterone, account for this increased abuse liability. Higher levels of estrogens, and lower levels of progesterone, are associated with greater sensitivity to the euphorigenic properties of cocaine in women (Evans 2007). This increased sensitivity may contribute to why women, compared with men, start using cocaine regularly at a younger age (Chen and Kandel 2002), transition from use to abuse more quickly (McCance-Katz et al. 1999), experience greater craving in response to drug-associated cues (Robbins et al. 1999) and stress (Potenza et al. 2012;Waldrop et al. 2012), and exhibit more severe drug-seeking behavior upon relapse (Gallop et al. 2007). In contrast, more women than men remain abstinent after treatment (Weiss et al. 1997). Thus, women are both more susceptible to cocaine abuse and, paradoxically, more responsive to treatment.A substantial literature supports that estrogens mediate the enhancement of drug seeking observed in females (Febo et al. 2002;Larson et al. 2007;Segarra et al. 2010; Kerstetter and Kippin 2011), but little is known regarding the role of estrogens during treatment. Preclinically, treatment is modeled through ext...

Non-overlapping cell populations within dorsomedial prefrontal cortex (dmPFC), defined by gene expression or projection target, control dissociable aspects of reward seeking through unique activity patterns. However, even within these defined cell populations considerable cell-to-cell variability is found, suggesting that greater resolution is needed to understand information processing in dmPFC. Here we use two-photon calcium imaging in awake, behaving mice to monitor the activity of dmPFC excitatory neurons throughout Pavlovian reward conditioning. We characterize five unique neuronal ensembles that each encode specialized information related to a sucrose reward, reward-predictive cues, and behavioral responses to those cues. The ensembles differentially emerge across daily training sessions - and stabilize after learning - in a manner that improves the predictive validity of dmPFC activity dynamics for deciphering variables related to behavioral conditioning. Our results characterize the complex dmPFC neuronal ensemble dynamics that stably predict reward availability and initiation of conditioned reward seeking following cue-reward learning.