Long-lasting increase of alcohol relapse by the cannabinoid receptor agonist WIN 55,212-2 during alcohol deprivation

Abstract

Alcoholism is characterized by successive relapses. Recent data have shown a cross-talk between the cannabinoid system and ethanol. In this study, male Wistar rats with a limited (30 min sessions), intermittent, and extended background of alcohol operant self-administration were used. The relapse to alcohol after 1 week of alcohol deprivation was evaluated. Two weeks later, the animals were treated with the cannabinoid agonist WIN 55,212-2 (R-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate) (0, 0.4, 2.0, and 10.0 mg/kg, s.c.) during a similar alcohol deprivation period, and alcohol relapse during 2 weeks was assessed. A conditioned place preference (CPP) paradigm was used to study the rewarding properties of the cannabinoid agonist. Locomotor activity was also recorded. All doses of WIN 55,212-2 produced aversion in the CPP paradigm. The doses of 2.0 and 10.0 mg/kg resulted in an important suppression of spontaneous locomotor activity and a progressive weight loss during the next 2 weeks. The single alcohol deprivation was followed by a transient increase in their responding for alcohol from a range of 20-24 lever presses at baseline to a range of 38-48 responses in the first and second days (alcohol deprivation effect). However, the administration of WIN 55,212-2 during ethanol deprivation produced similar increased responses for alcohol but in a long-term way (at least over 2 weeks). These findings suggest that noncontingent chronic exposure to cannabinoids during alcohol deprivation can potentiate the relapse into alcohol use, indicating that functional changes in the cannabinoid brain receptor may play a key role in ethanol relapse.

Figure 1.

Effects in relapse to alcohol after a single alcohol deprivation period (hatched bars) and relapse to alcohol after WIN 55,212-2 treatment during alcohol deprivation (filled bars). Doses of WIN 55,212-2 are in milligrams/kilogram. These data represent the responses for alcohol by day (30 min session) averaged over a 1 week period. Asterisks indicate statistically significant differences between baseline and increases in ethanol responding in the first and second weeks postdeprivation after 7 d of ethanol deprivation. The groups treated with WIN 55,212-2 showed a significantly higher increase and persistent responding for alcohol during the second week. # symbols indicate statistically significant differences between the first and second week of alcohol relapse after a single alcohol deprivation and their corresponding first and second week of alcohol relapse after an alcohol deprivation period concomitant with WIN 55,212-2. Only the animals treated with this cannabinoid receptor agonist showed statistically significant differences. Values are expressed as mean ± SEM of responding for alcohol by weeks. ^*p < 0.05; ^**p < 0.01; ^***p < 0.001; ^#p < 0.05; ^##p < 0.01; ^###p < 0.001.

Figure 2.

Effects in relapse to alcohol after a single alcohol deprivation period (dotted lines, open circles) and relapse to alcohol after WIN 55,212-2 treatment during alcohol deprivation (black lines, filled squares). Doses of WIN 55,212-2 are in milligrams/kilogram. These data represent the responses for alcohol (30 min session) for 5 consecutive days with a 1 week interval between baseline and postdeprivation period and a 2 d interval between week 1 and week 2 of the postdeprivation period. Black asterisks show the statistically significant differences between the first and second week of alcohol relapse after a single alcohol deprivation and their corresponding first and second week of alcohol relapse after an alcohol deprivation period concomitant with WIN 55,212-2. Only the animals treated with WIN 55,212-2 showed statistically significant differences. Differences were not significant in the vehicle group. With the highest dose of WIN 55,212-2 (10.0 mg/kg) (d), the responding for alcohol seemed to be blocked on the first day of relapse after treatment but abruptly increased on the second day of relapse and was maintained during 2 weeks. White asterisks represent significant differences on day 1 for WIN and saline groups compared with their corresponding baseline values (alcohol deprivation effect). Values are expressed as mean ± SEM of responding for alcohol by days. ^*p < 0.05; ^**p < 0.01; ^***p < 0.001.

Figure 3.

Changes in the cumulative reinforcements obtained (30 min session, at 5 min intervals) by the rats during 3 representative days: the last day of baseline (dotted lines, open circles), the first day of alcohol relapse (dotted lines, filled circles), and the fifth day of alcohol relapse (black lines, filled squares) after vehicle or WIN 55,212-2 treatment (doses are in milligrams/kilogram). Asterisks show statistically significant differences compared with baseline. As can be seen, the vehicle group reached its baseline level of alcohol reinforcements at the fifth day of alcohol reinstatement. The groups pretreated with 0.4 and 2.0 mg/kg WIN 55,212-2 showed a persistent increase compared with baseline. The dose of 10.0 mg/kg WIN 55,212-2 showed an opposite pattern in relation to the vehicle group; the greatest number of alcohol reinforcements occurred on the fifth day, whereas similar reinforcing levels compared with baseline was obtained on the first day. Values are expressed as mean ± SEM of reinforcements obtained during three different sessions. ^*p < 0.05; ^**p < 0.01.

Figure 4.

Change in compartment preference after 5 d of exposure to WIN 55,212-2 or vehicle. This parameter is expressed as the difference in seconds spent in each compartment associated with WIN 55,212-2 (0.2, 2.0, and 10.0 mg/kg, s.c.), vehicle, or nonpaired compartment between the preconditioning and postconditioning day. The score was calculated by subtracting the time spent by the animal in each compartment in the preconditioning session from the time spent in the same compartment in the postconditioning session. Values are mean seconds ± SEM. Data were analyzed by repeated-measures ANOVA and followed by the corresponding post hoc analysis for repeated measures. ^**p < 0.01; ^***p < 0.001.

Figure 5.

Photocell counts of locomotor activity during the 5 consecutive days of WIN 55,212-2 or vehicle treatment (a total of 10 conditioning sessions). The rats were placed into the compartments immediately after treatment, and their activity was registered throughout the following 30 min. The effects of WIN 55,212-2 or vehicle on locomotor activity are shown in a and b, respectively. The hypolocomotor effects observed in the saline sessions with the highest dose of WIN 55,212-2 were caused by the long half-life of WIN 55,212-2. Values are expressed as mean ± SEM. Data were first analyzed by repeated-measures ANOVA, followed by Tukey's post hoc test for contrast between groups. ^*p < 0.05; ^***p < 0.001 when compared with the vehicle group.

Figure 6.

Changes in animals' weight during the 2 weeks of alcohol relapse after a single alcohol deprivation period (a), during the 5 d of the treatment with the agonist cannabinoid WIN 55,212-2 (b), and during the 2 weeks of alcohol relapse after WIN 55,212-2 treatment in alcohol deprivation period (c). The animals' weight (mean, 402 gm ± SEM) from the week of the establishment of baseline was used as 100% of weight. Data were analyzed by percentage. ^*p < 0.05; ^**p < 0.01; ^***p < 0.001, different from vehicle (Tukey's post hoc tests analysis after between-groups ANOVA).