Inhibition of the casein-kinase-1-ε/δ/ prevents relapse-like alcohol drinking

Abstract

During the past decade, it has been shown that circadian clock genes have more than a simple circadian time-keeping role. Clock genes also modulate motivational processes and have been implicated in the development of psychiatric disorders such as drug addiction. Recent studies indicate that casein-kinase 1ε/δ (CK1ε/δ)--one of the components of the circadian molecular clockwork-might be involved in the etiology of addictive behavior. The present study was initiated to study the specific role of CK1ε/δ in alcohol relapse-like drinking using the 'Alcohol Deprivation Effect' model. The effect of CK1ε/δ inhibition was tested on alcohol consumption in long-term alcohol-drinking rats upon re-exposure to alcohol after deprivation using a four-bottle free-choice paradigm with water, 5%, 10%, and 20% ethanol solutions, as well as on saccharin preference in alcohol-naive rats. The inhibition of CK1ε/δ with systemic PF-670462 (0, 10, and 30 mg/kg) injections dose-dependently decreased, and at a higher dosage prevented the alcohol deprivation effect, as compared with vehicle-treated rats. The impact of the treatment was further characterized using nonlinear regression analyses on the daily profiles of drinking and locomotor activity. We reveal that CK1ε/δ inhibition blunted the high daytime alcohol intake typically observed upon alcohol re-exposure, and induced a phase shift of locomotor activity toward daytime. Only the highest dose of PF-670462 shifted the saccharin intake daily rhythm toward daytime during treatment, and decreased saccharin preference after treatment. Our data suggest that CK1 inhibitors may be candidates for drug treatment development for alcoholism.

Figure 1

Total daily alcohol (a) and water (b) intake in vehicle- (n=8), 10 mg/kg PF-670462- (n=8), and 30 mg/kg PF-670462-treated (n=8) animal groups. (a) Total daily intake is presented as the sum of all alcohol solution taken for a period of 24 h. Baseline drinking (b) is calculated as the daily average intake across the last 6 measuring days. Alcohol intake was significantly affected by the re-introduction of alcohol solutions following the period of deprivation as compared with the baseline drinking intake (F_Day(6, 126)=27.4, p<0.0001). However, although the vehicle-treated group showed a characteristic increase in alcohol consumption, the pharmacological treatments with 10 or 30 mg/kg PF-670462 caused a significant and dose-dependent (F_Group(2, 21)=13.2, p<0.001) reduction in alcohol intake during the postabstinence drinking phase (F_{Day × Group}(12, 126)=11.7, p<0.0001). (b) After the deprivation phase, daily water intake was affected in all groups as compared with baseline drinking (F_Day(6, 126)=32.4, p<0.0001). However, the treatment differentially affected water intake (F_{Day × Group}(12, 126)=3.6, p<0.001): vehicle- and 10 mg/kg PF-670462-treated rats decreased their consumption, whereas 30 mg/kg PF-670462-treated rats showed no change on the first day. From the fifth postabstinent day on, all animals had similar water consumption as in baseline conditions. Arrows indicate the administration of either vehicle or PF-670462. Data are presented as means+SEM;+ and ^* indicate post-hoc significant difference (p<0.05) from baseline drinking and control vehicle group, respectively.

Figure 2

Curve fittings of daily rhythm alcohol drinking patterns under baseline conditions (a), during (b), and after (c) administration of vehicle and 10 and 30 mg/kg of PF-670462. Group-averaged total alcohol intake is presented as the sum of alcohol intake from all alcohol solutions taken every 30 min over a light/dark cycle for the last 6 baseline days (a), the 2 first days of alcohol re-exposure (b), and the 4 following days (c). During treatment and following reintroduction of the alcohol, alcohol intake significantly increased in vehicle-treated rats, especially during the light phase. During treatment with 10 and 30 mg/kg PF-670462, the shift in daytime drinking intake observed in vehicle-treated rats was less obvious and absent, respectively. Curve fits represent the best equation fit of our data. Data are presented as means+SEM.

Figure 3

Curve fittings of daily rhythm locomotor activity patterns under baseline conditions (a), during (b), and after (c) treatment administration in vehicle- and 10 and 30 mg/kg PF-670462-treated animal groups. Group-averaged locomotor activity taken every 30 min over a light/dark cycle for the last 6 baseline days (a), the 2 first days of alcohol re-exposure (b), and the 4 following days (c). Curve fits represent the best equation fit of our data. Data are presented as means+SEM.

Figure 4

Daily saccharin preference in vehicle (n=8), 10 mg/kg PF-670462 (n=7), and 30 mg/kg PF-670462 (n=5) groups. Group-averaged daily preference taken for a period of 24 h averaged for the last 6 baseline days, the 2 last days of the treatment, and 4 last following days. The treatment differentially affected preference for the saccharin solution (F_{Day × Group}(12, 102)=4.7, p<0.0001). During the posttreatment phase, 30 mg/kg PF-670462-treated rats showed decreased preference for saccharin as compared with vehicle-treated rats, as revealed by the significant post-hoc tests (p<0.05) for the days after treatment. Arrows indicate the administration of either vehicle or PF-670462. Data are presented as means+SEM. ^*Significant differences from the control vehicle group, p<0.05.

Figure 5

Curve fittings of daily rhythm saccharin intake patterns under baseline conditions (a), during (b), and after (c) treatment administration in vehicle, 10 mg/kg PF-670462, and 30 mg/kg PF-670462 groups. Group-averaged total saccharin intake taken every 30 min over a light/dark cycle for the last 6 baseline days (a), the 2 last days of the treatment (b), and the 4 following days (c). A clear daily rhythm in saccharin intake was measured during baseline conditions, with most intakes occurring during the night. Upon 30 mg/kg PF-670462 treatment, the rhythmic pattern of saccharin intake shifted toward daytime as compared with vehicle-treated rats. Curve fits represent the best equation fit of our data. Data are presented as means+SEM.