Bingeing on High-Fat Food Enhances Evoked Dopamine Release and Reduces Dopamine Uptake in the Nucleus Accumbens

Abstract

Objective: Binge-eating disorder (BED) disrupts dopamine neuron function, in part by altering dopamine transporter (DAT) activity. This study characterized the effects of high-fat bingeing on presynaptic dopamine terminals and tested the hypothesis that acute low-dose amphetamine would restore DAT function.

Methods: C57BL/6 mice were given limited access (LimA) to a high-fat diet (2 h/d, 3 d/wk) or standard chow (control). After 6 weeks, ex vivo fast-scan cyclic voltammetry was used to characterize dopamine-terminal adaptations in the nucleus accumbens. Prior to undergoing fast-scan cyclic voltammetry, some mice from each group were given amphetamine (0.5 mg/kg intraperitoneally).

Results: Escalation of high fat intake, termed bingeing, occurred in the LimA group and coincided with increased phasic dopamine release, reduced dopamine uptake rates, and increased dopamine receptor 2 (D₂ ) autoreceptor function. Acute amphetamine selectively reversed dopamine uptake changes in the LimA group and restored the potency of amphetamine to inhibit uptake.

Conclusions: High-fat bingeing enhanced dopaminergic signaling in the nucleus accumbens by promoting phasic dopamine release and reducing clearance. This study's data show that amphetamine was efficacious in restoring impaired DAT function caused by high-fat bingeing but did not reduce dopamine release to normal. These presynaptic changes should be considered if amphetamine-like dopamine releasers are used as treatments for BED.

Figure 1

Experimental design. Mice were divided into two dietary groups: (A) the control (CN) group received standard rodent chow exclusively (n = 14), and (B) the limited‐access (LimA) group (n = 14) received 24‐hour access to standard chow on Tuesday (T), Thursday (Th), Saturday (Sa), and Sunday (Su) and limited access to a high‐fat diet for 2 hours on Monday (M), Wednesday (W), and Friday (F), with standard chow the remaining 22 hours on high‐fat days. (C) After 6 weeks on each feeding paradigm, mice from each group received 0.5 mg/kg of intraperitoneal amphetamine (AMPH) or an equal volume of saline 1 hour before proceeding to ex vivo voltammetry to measure dopamine release and uptake in the nucleus accumbens. V_max, maximal rate of dopamine uptake.

Figure 2

Body weight and food intake. (A) Body weight gain over the 6‐week feeding period. (B) Daily energy intake in kilocalories averaged per mouse, including all food over 6 weeks. (C) Percentage breakdown of kilocalories consumed from chow or high‐fat food in the limited‐access (LimA) group on days with access to high‐fat food. (D) The overall kilocalorie intake was stable from week 1 to week 6, but (E) mice in the LimA group consumed significantly less standard chow in week 6 than in week 1 (P < 0.05), coinciding with a significantly higher percentage of kilocalories from high‐fat food (F) after 2 hours (P < 0.05) and (G) after 30 minutes (P < 0.05) using paired Student t tests. All data reflect the mean ± SEM (*P < 0.05).

Figure 3

Difference in dopamine release and uptake in the nucleus accumbens after intraperitoneal (i.p.) saline or amphetamine (AMPH) administered in vivo. (A) Dopamine release evoked by a single pulse in mice receiving i.p. saline or 0.5 mg/kg of AMPH 1 hour prior to brain removal. (B‐D) Dopamine release evoked by phasic five‐pulse stimulation over 5‐, 10‐, 20‐, 40‐, and 100‐Hz frequencies. (E) Maximal rate of dopamine uptake (V_max). (F) Visual comparison of averaged line traces showing dopamine release (peak height) and V_max (downward slope) representing the mean ± SEM current in the shaded area with a representative pseudocolor plot for each group. The control group included n = 9 slices from n = 5 mice, the limited‐access (LimA) group included n = 9 slices from n = 7 mice, the control group receiving 0.5 mg/kg of i.p. AMPH (CN‐AMPH) included n = 14 slices from n = 9 mice, and the LimA group receiving 0.5 mg/kg of i.p. AMPH (LimA‐AMPH) included n = 12 slices from n = 7 mice. All data reflect the mean ± SEM (*P < 0.05; ***P < 0.001).

Figure 4

Amphetamine (AMPH) potency at the dopamine transporter (DAT). (A‐D) The potency of AMPH as an uptake inhibitor at the DAT, measured as apparent K_m (app. Km) for dopamine in the presence of AMPH, applied cumulatively to the slice bath in half‐log doses. (E) Averaged dopamine traces showed impaired clearance in the presence of 10µM AMPH. (F) Finally, AMPH dose‐dependently depleted stimulated dopamine release similarly in all treatment groups. Two‐way repeated‐measures ANOVA was used to determine the effects of the drug and diet in the experimental group. The control group included n = 7 slices from n = 5 mice, the limited‐access (LimA) group included n = 6 slices from n = 6 mice, the control group receiving 0.5 mg/kg of intraperitoneal (i.p.) AMPH (CN‐AMPH) included n = 8 slices from n = 8 mice, and the LimA group receiving 0.5 mg/kg of i.p. AMPH (LimA‐AMPH) included n = 7 slices from n = 6 mice. All data reflect the mean ± SEM (*P < 0.05; **P < 0.01).

Figure 5

Dopamine transporter (DAT) protein levels. Western blot quantification of DAT protein (normalized to β‐actin) from enriched membrane and cytosolic fractions of nucleus accumbens brain tissue. Normalized DAT protein in each group was expressed as a percentage of that of the control group. (A) Histological representation of DAT band density at ~150, 78, and 68 kDa in membrane fractions and (B) cytosolic fractions showed a reduced density of only the 68‐kDa DAT band in all groups compared with the control group. Representative blots showing DAT band density at 150, 78, and 68 kDa, as well as the 46‐kDa β‐actin band containing (C) membrane and (D) cytosolic samples. All data reflect the mean ± SEM (*P < 0.05; ***P < 0.001).

Figure 6

Presynaptic dopamine receptor 2/dopamine receptor 3 (D₂/D₃) autoreceptor function. All groups showed a dose‐dependent reduction in evoked dopamine release with increasing concentrations of the D₂/D₃ agonist quinpirole. (A) Two‐way repeated‐measures ANOVA revealed a significant increase in D₂/D₃ sensitivity in the limited‐access (LimA) group compared with the control group, whereas post hoc analysis identified a significant difference between groups at 10 nM (−8.0 log M) (P < 0.05). The quinpirole dose responses were similar between (B) the control group and the control group receiving 0.5 mg/kg of intraperitoneal (i.p.) amphetamine (CN‐AMPH) and (C) the LimA group and the LimA group receiving 0.5 mg/kg of i.p. amphetamine (LimA‐AMPH). Overall, increased sensitivity is indicated by a leftward shift in the regression‐curve fit and (D) a reduction in the half‐maximal inhibitory concentration (IC₅₀) for quinpirole in the LimA group compared with the control group, and amphetamine reduced the IC₅₀ for quinpirole in the control group. The control group included n = 4 slices from n = 4 mice, the LimA group included n = 4 slices from n = 4 mice, the CN‐AMPH group included n = 5 slices from n = 4 mice, and LimA‐AMPH included n = 5 slices from n = 4 mice. All data reflect the mean ± SEM (*P < 0.05; ****P < 0.0001).