Disulfiram attenuates drug-primed reinstatement of cocaine seeking via inhibition of dopamine β-hydroxylase

Abstract

The antialcoholism medication disulfiram (Antabuse) inhibits aldehyde dehydrogenase (ALDH), which results in the accumulation of acetaldehyde upon ethanol ingestion and produces the aversive 'Antabuse reaction' that deters alcohol consumption. Disulfiram has also been shown to deter cocaine use, even in the absence of an interaction with alcohol, indicating the existence of an ALDH-independent therapeutic mechanism. We hypothesized that disulfiram's inhibition of dopamine β-hydroxylase (DBH), the catecholamine biosynthetic enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons, underlies the drug's ability to treat cocaine dependence. We tested the effects of disulfiram on cocaine and food self-administration behavior and drug-primed reinstatement of cocaine seeking in rats. We then compared the effects of disulfiram with those of the selective DBH inhibitor, nepicastat. Disulfiram, at a dose (100 mg/kg, i.p.) that reduced brain NE by ∼40%, did not alter the response for food or cocaine on a fixed ratio 1 schedule, whereas it completely blocked cocaine-primed (10 mg/kg, i.p.) reinstatement of drug seeking following extinction. A lower dose of disulfiram (10 mg/kg) that did not reduce NE had no effect on cocaine-primed reinstatement. Nepicastat recapitulated the behavioral effects of disulfiram (100 mg/kg) at a dose (50 mg/kg, i.p.) that produced a similar reduction in brain NE. Food-primed reinstatement of food seeking was not impaired by DBH inhibition. Our results suggest that disulfiram's efficacy in the treatment of cocaine addiction is associated with the inhibition of DBH and interference with the ability of environmental stimuli to trigger relapse.

Figure 1

Catecholamine biosynthetic pathway. Because DBH converts DA to NE in noradrenergic neurons, inhibition of DBH is unique in its ability to decrease NE while increasing DA.

Figure 2

Effect of disulfiram on catecholamine levels in the rat frontal cortex. Shown is the mean±SEM for (a) NE levels, (b) DA levels, and (c) the NE/DA ratio in the frontal cortex of rats after treatment with saline or disulfiram (single injection of 100 mg/kg, i.p., catecholamines measured 2 h after disulfiram administration by HPLC followed by electrochemical detection; N=6 per group). ^*p<0.05, ^**p<0.01, ^***p<0.001 compared with saline.

Figure 3

Disulfiram does not affect maintenance of cocaine self-administration. After reaching maintenance levels for operant cocaine self-administration (Maint), rats were pretreated with saline (Sal Pre) or disulfiram (100 mg/kg, i.p.; Dis Pre) 2 h before cocaine self-administration sessions. Shown are mean±SEM active lever responses and number of reinforcers obtained over a 2-h session. Maintenance values reflect an average number of responses and reinforcers obtained over the last 3 days of maintenance. Occasional active lever pressing during the 20-s timeout periods result in more active lever presses than reinforcers received. N=8 per group.

Figure 4

Disulfiram blocks cocaine-primed reinstatement. Once maintenance (Maint) and extinction (Ext) criteria for operant cocaine self-administration were met, rats were pretreated with saline (Rein-Sal, N=13) or disulfiram (10 or 100 mg/kg, i.p.) (Rein-Dis10, N=6 and Rein-Dis100, N=7) 2 h before cocaine prime (10 mg/kg, i.p.) and placement into the self-administration chambers. Shown are active and inactive lever responses. Maintenance values reflect an average of the last 3 days of maintenance sessions, and extinction values reflect an average of the last 3 days of extinction. ^*p<0.05 compared with active lever responses during extinction, ^#p<0.05 compared with active lever responses during cocaine-induced reinstatement tests with saline pretreatment (N=7 per group).

Figure 5

Effect of nepicastat on catecholamine levels in the rat frontal cortex. Shown is the mean±SEM for (a) NE levels, (b) DA levels, and (c) the NE/DA ratio in the frontal cortex of rats after treatment with vehicle or nepicastat (single injection of 50 mg/kg, i.p., catecholamines measured 2 h after nepicastat administration by HPLC followed by electrochemical detection; N=8 per group). ^**p<0.01, ^***p<0.001 compared with vehicle.

Figure 6

Nepicastat does not affect maintenance of cocaine self-administration. After reaching maintenance levels of operant cocaine self-administration (Maint), rats were pretreated with vehicle (Veh Pre) or nepicastat (50 mg/kg, i.p.; Nep Pre) 2 h before cocaine self-administration sessions. Shown are mean ± SEM active lever responses and number of reinforcers obtained over a 2-h session. Maintenance values reflect an average number of responses and reinforcers obtained over the last 3 days of maintenance. Occasional active lever pressing during the 20-s timeout periods result in more active lever presses than reinforcers received. (N=6 per group).

Figure 7

Nepicastat blocks cocaine-primed reinstatement. Once maintenance (Maint) and extinction (Ext) criteria for operant cocaine self-administration were met, rats were pretreated with vehicle (Rein-Veh) or nepicastat (50 mg/kg, i.p.; Rein-Nep50) 2 h before cocaine prime (10 mg/kg, i.p.) and placement into the self-administration chambers. Shown are mean±SEM active and inactive lever responses. Maintenance values reflect an average of the last 3 days of maintenance sessions, and extinction values reflect an average of the last 3 days of extinction. ^**p<0.01 compared with active lever responses during extinction, ^##p<0.01 compared with active lever responses during cocaine-induced reinstatement tests with vehicle pretreatment (N=6 per group).

Figure 8

Nepicastat does not affect food-primed reinstatement of food seeking. Once maintenance (Maint) and extinction (Ext) criteria for operant food self-administration were met, rats were pretreated with vehicle (Rein-Veh) or nepicastat (50 mg/kg, i.p.; Rein-Nep50) 2 h before food prime (three pellets at beginning of the session, then one pellet every 3 min over the 60 min session) and placement into the self-administration chambers. Shown are mean±SEM active and inactive lever responses. Maintenance values reflect an average of the last 3 days of maintenance sessions, and extinction values reflect an average of the last 3 days of extinction. ^*p<0.05 compared with active lever responses during extinction (N=7 per group).