Patterns of ethanol intake in male rats with partial dopamine transporter deficiency

Abstract

Mesolimbic dopamine signaling plays a major role in alcohol and substance use disorders as well as comorbidities such as anxiety and depression. Growing evidence suggests that alcohol drinking is modulated by the function of the dopamine transporter (DAT), which tightly regulates extracellular dopamine concentrations. Adult male rats on a Wistar Han background (DAT+/+) and rats with a partial DAT deletion (DAT+/-) were used in this study. First, using fast-scan cyclic voltammetry in brain slices containing the nucleus accumbens core from ethanol-naïve subjects, we measured greater evoked dopamine concentrations and slower dopamine reuptake in DAT+/- rats, consistent with increased dopamine signaling. Next, we measured ethanol drinking using the intermittent access two-bottle choice paradigm (20% v/v ethanol vs. water) across 5 weeks. DAT+/- rats voluntarily consumed less ethanol during its initial availability (the first 30 min), especially after longer periods of deprivation. In addition, DAT+/- males consumed less ethanol that was adulterated with the bitter tastant quinine. These findings suggest that partial DAT blockade and concomitant increase in brain dopamine levels has potential to reduce drinking and ameliorate alcohol use disorder (AUD).

Keywords: Wistar; alcohol use disorder; binge; dopamine; dopamine transporter; drinking; ethanol; fast-scan cyclic voltammetry; hypodopaminergia; intermittent access; locomotor activity; novelty; nucleus accumbens; quinine; reuptake.

FIGURE 1

Single pulse evoked [DA]_e and reuptake in the nucleus accumbens core of DAT+/+ and DAT+/− males measured by FSCV. (A) Averaged mean (dark shading) ± SEM (light shading) evoked DA (measured every 0.1 s) across time during final stable collection under baseline conditions; representative color plots are shown below, depicting the voltammetric current (shown on scale to right) as color along the z‐axis, plotted against the applied potential on the y‐axis and time on the x‐axis. (B) Mean ± SEM peak evoked DA concentration and (C, D) reuptake, expressed as (C) V _max (maximum rate of DA reuptake) and (D) half‐life (time required for half of DA clearance); n = 3 animals, 13 slices DAT+/+, and 5 animals, 19 slices DAT+/− ****p < 0.0001, unpaired t‐test.

FIGURE 2

Horizontal activity (distance traveled) and anxiety‐like behavior in a novel open field. (A) Mean ± SEM distance traveled (m) per minute (A) and total (B) during 30‐min session. (C) Mean ± SEM percent of time spent on perimeter of novel open field. *p < 0.05 (unpaired t‐test) **p < 0.01 (2‐way RM ANOVA panel A, unpaired t‐test panels B and C). (D, E) Traces of beam breaks (horizontal activity) of one representative animal from each group.

FIGURE 3

Experimental timeline for voluntary drinking study. Created with BioRender.com.

FIGURE 4

Altered pattern of ethanol consumption in DAT+/− males during first 30 min of intermittent access two‐bottle choice sessions. (A) Mean ± SEM voluntary consumption of 20% ethanol during the first 30 min of each session. (B) Ethanol (EtOH) intake during the first 30 min, cumulative across all sessions. (C) Deprivation effect: On Mondays, after extended period of EtOH deprivation over the weekend, the amount of EtOH consumed in the first 30 min. divided by total; averaged over Mondays 3–5. (D) Mean ± SEM voluntary consumption of 20% ethanol during each session. (E) Ethanol (EtOH) intake (g/kg), cumulative across all sessions. (F) Average EtOH consumption across weeks 3–5. (G) EtOH preference (EtOH consumed divided by total fluid consumed) during first 30 min of each session. (H) EtOH preference (EtOH consumed divided by total fluid consumed) over entire session. **p < 0.01 (RM two‐way ANOVA and unpaired t‐test).

FIGURE 5

Locomotor response to novelty predicts future binge‐like drinking (see Figure 3A for full analysis of locomotor activity; see Figure 4 for full analysis of EtOH drinking and Figure 4C description of the “deprivation effect”).

FIGURE 6

Differences in consumption of alcohol adulterated with quinine between DAT+/+ and DAT+/− males. (A) Mean ± SEM voluntary consumption (during first 30 min) of 20% ethanol adulterated with 0–300 mg/L quinine. (B) Mean ± SEM percent ethanol preference (during first 30 minutes). (C) Mean ± SEM voluntary consumption (during full 24 h). (D) Mean ± SEM percent ethanol preference (during full 24 h). *p < 0.05 (RM two‐way ANOVA and unpaired t‐test).