Chronic treatment with prazosin or duloxetine lessens concurrent anxiety-like behavior and alcohol intake: evidence of disrupted noradrenergic signaling in anxiety-related alcohol use

Abstract

Background: Alcohol use disorders have been linked to increased anxiety, and enhanced central noradrenergic signaling may partly explain this relationship. Pharmacological interventions believed to reduce the excitatory effects of norepinephrine have proven effective in attenuating ethanol intake in alcoholics as well as in rodent models of ethanol dependence. However, most preclinical investigations into the effectiveness of these drugs in decreasing ethanol intake have been limited to acute observations, and none have concurrently assessed their anxiolytic effects. The purpose of these studies was to examine the long-term effectiveness of pharmacological interventions presumed to decrease norepinephrine signaling on concomitant ethanol self-administration and anxiety-like behavior in adult rats with relatively high levels of antecedent anxiety-like behavior.

Methods: Adult male Long-Evans rats self-administered ethanol on an intermittent access schedule for eight to ten weeks prior to being implanted with osmotic minipumps containing either an a1-adrenoreceptor antagonist (prazosin, 1.5 mg/kg/day), a β1/2-adrenoreceptor antagonist (propranolol, 2.5 mg/kg/day), a serotonin/norepinephrine reuptake inhibitor (duloxetine, 1.5 mg/kg/day) or vehicle (10% dimethyl sulfoxide). These drugs were continuously delivered across four weeks, during which animals continued to have intermittent access to ethanol. Anxiety-like behavior was assessed on the elevated plus maze before treatment and again near the end of the drug delivery period.

Results: Our results indicate that chronic treatment with a low dose of prazosin or duloxetine significantly decreases ethanol self-administration (P < 0.05). Furthermore, this decrease in drinking is accompanied by significant reductions in the expression of anxiety-like behavior (P < 0.05).

Conclusions: These findings suggest that chronic treatment with putative inhibitors of central noradrenergic signaling may attenuate ethanol intake via a reduction in anxiety-like behavior.

Keywords: Duloxetine; osmotic minipump; plus maze; prazosin; propranolol; stress.

Figures

Figure 1

Experimental timeline. Adult male Long-Evans rats were singly housed upon arrival and allowed to acclimate to the environment for 2 weeks. Following this, baseline anxiety-like behavior was assessed using the elevated plus maze and open field tests. Animals were then given intermittent access to ethanol (20% v/v) and water 3 days a week (MWF) for 24 h; this homecage drinking continued for 8–10 weeks. Animals were weighed prior to ethanol access on drinking days. Following this intermittent access period, all animals underwent a surgical procedure during which osmotic minipumps were implanted containing either vehicle (10% DMSO in sterile saline), propranolol (2.5 mg/kg/day), prazosin (1.5 mg/kg/day), or duloxetine (1.5 mg/kg/day). Animals were then allowed to continue intermittent access homecage drinking for four additional weeks. During the last week, animals were again exposed to the elevated plus maze and open field on nondrinking days. Animals underwent a second surgery to remove the osmotic minipumps, and were again exposed to the drinking procedure for 4 weeks prior to being sacrificed.

Figure 2

Chronic treatment with prazosin or duloxetine decreases anxiety-like behavior on the elevated plus maze. Top bar graphs illustrate that neither anxiety-like behavior, measured as time spent on the open arms of the maze (A) and total number of open arm entries (B), nor general locomotor activity (C) (assessed as number of closed arm entries) differed significantly between groups of adult male Long-Evans rats at baseline (one-way ANOVAs, P > 0.05). Bottom bar graphs illustrate that 4 week treatment with prazosin (n = 6, 1.5 mg/kg/day) or duloxetine (n = 6, 1.5 mg/kg/day) via osmotic minipump selectively increased time spent on the open arms of the maze (D) and total number of open arm entries (E), reflecting a decrease in anxiety-like behavior while having no effect on general locomotor activity (F) (*, significant difference relative to propranolol-treated animals (n = 7, 2.5 mg/kg/day), one-way ANOVAs and Newman–Keuls post hoc tests, P < 0.05; †, significant difference relative to vehicle-treated animals (n = 7, 10% DMSO), one-way ANOVAs and Newman–Keuls post hoc tests, P < 0.05).

Figure 3

Chronic treatment with prazosin (A) or duloxetine (B) decreases intermittent ethanol (EtOH) self-administration relative to vehicle-treated conspecifics. Graphs represent 24 h (daily) EtOH intake each week for eight consecutive baseline weeks, followed by 4 week treatment with prazosin (n = 6, 1.5 mg/kg/day), duloxetine (n = 6, 1.5 mg/kg/day), propranolol (n = 7, 2.5 mg/kg/day), or vehicle (n = 7, 10% DMSO), and four additional posttreatment weeks. Animals had access to EtOH (20% v/v) 3 days a week for 24 h; weekly intake was averaged for each rat. Both prazosin (A) and duloxetine-treated (B) rats self-administered significantly less EtOH than vehicle-treated animals by the third week of drug delivery; this effect persisted through the final treatment week and was abolished following cessation of treatment (*, significant difference relative to vehicle-treated animals, two-way ANOVAs comparing treatment across time and Newman–Keuls post hoc tests, P < 0.05). Daily ethanol intake among propranolol-treated animals did not differ significantly from controls at any point (C) (two-way ANOVA comparing propranolol-treated animals to vehicle-treated conspecifics, P > 0.05).

Figure 4

Chronic treatment with prazosin, duloxetine, or propranolol does not decrease preference for ethanol (EtOH) relative to vehicle-treated conspecifics. Graphs represent 24 h (daily) EtOH preference relative to water each week for eight consecutive baseline weeks, followed by 4 week treatment with prazosin (n = 6, 1.5 mg/kg/day), duloxetine (n = 6, 1.5 mg/kg/day), propranolol (n = 7, 2.5 mg/kg/day), or vehicle (n = 7, 10% DMSO), and four additional posttreatment weeks. Animals had access to EtOH (20% v/v) 3 days a week for 24 h; weekly EtOH preference was averaged for each rat. Treatment with prazosin (A), duloxetine (B), or propranolol (C) did not significantly decrease ethanol preference, relative to vehicle-treated conspecifics two-way ANOVAs comparing treatment across time, P > 0.05).

Figure 5

Chronic treatment with prazosin, duloxetine, or propranolol does not decrease binge-like ethanol (EtOH) self-administration relative to vehicle-treated conspecifics. Graphs represent EtOH intake in the first 30 min of daily access (binge-like intake) each week for eight consecutive baseline weeks, followed by 4 week treatment with prazosin (n = 6, 1.5 mg/kg/day), duloxetine (n = 6, 1.5 mg/kg/day), propranolol (n = 7, 2.5 mg/kg/day), or vehicle (n = 7, 10% DMSO), and four additional posttreatment weeks. Animals had access to EtOH (20% v/v) 3 days a week for 24 h; weekly binge-like intake was averaged for each rat. Treatment with prazosin (A), duloxetine (B), or propranolol (C) had no signiricant effect on binge-like ethanol intake relative to vehicle-treated animals, two-way ANOVAs comparing treatment across time, P > 0.05).

Figure 6

Chronic treatment with prazosin or duloxetine decreases intermittent ethanol (EtOH) self-administration relative to pretreatment baseline. Graphs represent 24 h (daily) EtOH intake during the last of eight consecutive baseline weeks, followed by 4 week treatment with prazosin (C) (n = 6, 1.5 mg/kg/day), duloxetine (D) (n = 6, 1.5 mg/kg/day), propranolol (B) (n = 7, 2.5 mg/kg/day), or vehicle (A) (n = 7, 10% DMSO), and four additional posttreatment weeks. Animals had access to EtOH (20% v/v) 3 days a week for 24 h; weekly intake was averaged for each rat. Treatment with prazosin resulted in reduced EtOH self-administration by the second week of drug delivery, and this difference persisted through the fourth treatment week (B). Duloxetine-treated animals consumed significantly less EtOH during the fourth week of drug delivery, while propranolol and vehicle had no significant effect on EtOH intake, relative to baseline (D). Following cessation of treatment, animals who had received prazosin (C) or duloxetine (D) returned to pretreatment levels of EtOH self-administration (*, significant difference relative to the last baseline week, one-way repeated measures ANOVAs and Newman–Keuls post hoc tests, P < 0.05; †, significant difference relative to the last treatment week, one-way repeated measures ANOVAs and Newman–Keuls post hoc tests, P < 0.05).

Figure 7

Chronic treatment with propranolol increases preference for ethanol (EtOH) relative to pretreatment baseline. Graphs represent 24 h (daily) EtOH preference during the last of eight consecutive baseline weeks, followed by 4 week treatment with prazosin (n = 6, 1.5 mg/kg/day), duloxetine (n = 6, 1.5 mg/kg/day), propranolol (n = 7, 2.5 mg/kg/day), or vehicle (n = 7, 10% DMSO), and four additional posttreatment weeks. Animals had access to EtOH (20% v/v) 3 days a week for 24 h; weekly intake was averaged for each rat. Treatment with propranolol (B) significantly increased EtOH preference by the second week of drug delivery; this effect persisted throughout treatment and was not reversed following removal of the drug. Animals in the duloxetine (D), prazosin (C), and vehicle-treated (A) groups did not exhibit significant alterations in EtOH preference during treatment, although following cessation of prazosin delivery (C), preference for EtOH increased significantly relative to the last week of treatment and remained elevated for the duration of the study (*, significant difference relative to the last baseline week, one-way repeated measures ANOVAs and Newman–Keuls post hoc tests, P < 0.05; †, significant difference relative to the last treatment week, one-way repeated measures ANOVAs and Newman–Keuls post hoc tests, P < 0.05).

Figure 8

Chronic treatment with prazosin or duloxetine decreases binge-like ethanol (EtOH) self-administration relative to pretreatment baseline. Graphs represent EtOH intake in the first 30 min of daily access (binge-like intake) during the last of eight consecutive baseline weeks, followed by 4 week treatment with prazosin (n = 6, 1.5 mg/kg/day), duloxetine (n = 6, 1.5 mg/kg/day), propranolol (n = 7, 2.5 mg/kg/day), or vehicle (n = 7, 10% DMSO), and four additional posttreatment weeks. Animals had access to EtOH (20% v/v) 3 days a week for 24 h; weekly intake was averaged for each rat. Binge-like EtOH intake was significantly reduced by the third week of prazosin delivery (C), and by the final week of treatment with duloxetine (D). Propranolol (B) and vehicle-treated (A) animals did not change their binge-like EtOH intake in response to treatment (*, significant difference relative to the last baseline week, one-way repeated measures ANOVAs and Newman–Keuls post hoc tests, P < 0.05; †, significant difference relative to the last treatment week, one-way repeated measures ANOVAs and Newman–Keuls post hoc tests, P < 0.05).

Figure 9

Change in daily ethanol administration (baseline – treatment week 4) was not correlated with posttreatment anxiety-like behavior on the elevated plus maze (open arm time), although there was a modest trend toward a positive relationship between these variables. Animals from all treatment groups (propranolol, 2.5 mg/kg/day; prazosin 1.5 mg/kg/day; duloxetine 1.5 mg/kg/day; vehicle 10% DMSO in sterile saline) had access to EtOH (20% v/v) 3 days a week for 24 h; weekly intake was averaged for each rat. At the end of a 4 week drug delivery period, all animals were tested for anxiety-like behavior on the elevated plus maze. The change in each animal's daily intake following 4 weeks of drug delivery (24 h g/kg baseline – 24 h g/kg treatment week 4) is plotted on the y-axis, and time spent in the open arms of the elevated plus maze is plotted on the x-axis. Although the relationship between these factors was not statistically significant, a positive trend emerged (r2 = 0.13, F = 3.441, P = 0.07).