CB1 receptor antagonism blocks stress-potentiated reinstatement of cocaine seeking in rats

Abstract

Rationale: Under some conditions, stress, rather than directly triggering cocaine seeking, potentiates reinstatement to other stimuli, including a subthreshold 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: The objective of this study was to test the hypothesis that cannabinoid type 1 receptor (CB1R) signaling is required for stress-potentiated reinstatement of cocaine seeking in rats.

Methods: Following i.v. cocaine self-administration (2 h 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 dose (i.e., 3 mg/kg) 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 h access/day) was 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.

Keywords: Addiction; Cocaine; Endocannabinoid; Reinstatement; Relapse; Self-administration; Stress.

Figure 1

Stress-potentiated reinstatement is CB1R-dependent. Data represent mean active lever responses (± SEM) during 2-h extinction and reinstatement tests. Stress-potentiated reinstatement is observed when rats are exposed to a stressor, 15 min intermittent electric footshock stress (EFS) followed immediately by a subthreshold dose of cocaine (COC, 2.5 mg/kg, i.p.; **p<.01, compared to reinstatement). Stress-potentiated reinstatement is blocked by pre-treatment with the CB1R antagonist AM251 (1 (n=6), 3 (n=6) mg/kg, i.p.) 30 min prior to the reinstatement test (#p<.05 compared to Veh/EFS/COC).

Figure 2

Cocaine-primed or stress-induced reinstatement is not CB1R-dependent. Data represent mean active lever responses (± SEM) during 2-h extinction and reinstatement tests. A. Cocaine-primed reinstatement is observed when rats are given a systemic injection of a high dose of cocaine (COC, 10 mg/kg, i.p.; **p<.01 compared to extinction). Cocaine-primed reinstatement is not significantly attenuated by pre-treatment with the CB1R antagonist, AM251 (1 (n=8), 3 (n=8) mg/kg, i.p.) 30 min prior to the cocaine injection. B. Stress-induced reinstatement is observed when rats are given electric footshock stress (EFS) for 15 min immediately followed by the reinstatement session in rats with a history of long-access self-administration (**p<.01 compared to extinction). Stress-induced reinstatement is not significantly attenuated by pretreatment with AM251 (1 mg/kg, i.p.; n=5) 30 min prior to EFS.

Figure 3

Food-reinforced lever pressing is attenuated by pre-treatment with the CB1R antagonist AM251. Data are presented as mean food lever responses during the 30-min session ± SEM. Pre-treatment with AM251 30 min prior to the beginning of the session significantly attenuated food-reinforced lever pressing at the higher dose (3 mg/kg, i.p), but not the low dose (1 mg/kg, i.p.; n=7; *p<.05 compared to Veh). Each rat received each drug treatment and the order of drug treatment was counterbalanced.