Ventral pallidal GABAergic neurons drive consumption in male, but not female rats

Abstract

Food intake is controlled by multiple converging signals: hormonal signals that provide information about energy homeostasis, but also hedonic and motivational aspects of food and food cues that can drive non-homeostatic or "hedonic "feeding. The ventral pallidum (VP) is a brain region implicated in the hedonic and motivational impact of food and foods cues, as well as consumption of rewards. Disinhibition of VP neurons has been shown to generate intense hyperphagia, or overconsumption. While VP gamma-Aminobutyric acidergic (GABA) neurons have been implicated in cue-elicited reward seeking and motivation, the role of these neurons in the hyperphagia resulting from VP activation remains unclear. Here, we used Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) to activate or inhibit VP GABA neurons in sated male and female rats during chow and sucrose consumption. We found that activation of VP GABA neurons increases consumption of chow and sucrose in male rats, but not female rats. We also found that, while inhibition of VP GABA neurons tended to decrease sucrose consumption, this effect was not statistically significant. Together, these findings suggest that activation of VP GABA neurons can stimulate consumption of routine or highly palatable rewards selectively in male rats.

Figure 1.. Characterization of DREADD localization and functional impact.

(A) Representative section from striatum (top), ventral pallidum (middle), and septum (bottom), used for analysis in QUINT workflow. (B) Output results of QUINT workflow (n=8), showing all brain regions where mCherry (DREADD virus reporter) was detected in rats that received 600 nl (n=4, circles) and 800 nl (n=4, triangles) injections. The VP atlas region was where 81.2 +/− 4.86% of objects (proxy for cell count) were detected by analysis software. LME showed a significant effect of brain region (F(3,28)=113.34, p < 0.001), on spread of virus, with follow-up comparisons indicating that significantly more expression was found in VP was significantly greater in expression compared to other brain regions that were found to have expression in multiple animals (corticofugal tract and corona radiata 8.72 +/− 4.41%, caudate putamen 8.60 +/− 2.52%, bed nucleus of the stria terminalis 1.51 +/− 0.67%). (C) Percent of DREADD-positive cells expressing c-Fos after 0, 0.05 or 0.5 mg/kg J60 in male (circles) and female (triangles) rats expressing Gq or Gi DREADD. Ligand injections increased the % of DREADD-expressing cells that expressed cFos in the Gq group but not the Gi group. * p < 0.05 (left). D) Representative VP images from a Gq male (left) and a Gi male (right) injected with 0.5 mg/kg J60.

Figure 2:. VP GABA activation increases consumption of chow and sucrose in male rats.

(A) A mixture of GAD1-cre and DIO-hM2Dq-mCherry was injected bilaterally into the VP. (B) Colormaps show viral placement (brightest point of expression) a horizontal cross section of the VP and behavioral changes from baseline following a high dose (0.5 mg/kg) of J60, for all Gq rats (left), female Gq rats (middle), and male Gq rats (right). Chow consumption (C), sucrose consumption (D), and sucrose preference (E) following injections of saline (light green), low dose J60 (medium green) and high dose J60 (dark green) for all Gq rats (left), female Gq rats (middle), and male Gq rats (right). Bar plots and error bars indicate mean +/− SEM. Dots and lines represent individual rats. Asterix indicate p-values less than 0.05 for Sidak corrected pairwise comparisons.

Figure 3.. VP GABA inhibition does not significantly affect consumption of chow and sucrose in male or female rats.

(A) A mixture of GAD1-cre and DIO-hM4Di-mCherry viruses was injected bilaterally into the VP. (B) Colormaps show viral placement (brightest point of expression) a horizontal cross section of the VP and behavioral changes from baseline following a high dose (0.5 mg/kg) of J60, for all Gi rats (left), female Gi rats (middle), and male Gi rats (right). Chow consumption (C), sucrose consumption (D), and sucrose preference (E) following injections of saline (light green), low dose J60 (medium green) and high dose J60 (dark green) for all Gi rats (left), female Gi rats (middle), and male Gi rats (right). Bar plots and error bars indicate mean +/− SEM. Dots and lines represent individual rats.

Figure 4.. Effect of DREADD ligand in control rats expressing mCherry.

(A) A mixture of GAD1-cre and DIO- mCherry was injected bilaterally into the VP. (B) Colormaps show viral placement (brightest point of expression) in a horizontal cross section of the VP and behavioral changes from baseline following a high dose (0.5 mg/kg) of J60 on, for all mCherry rats (left), female mCherry rats (middle), and male mCherry rats (right). Chow consumption (C), sucrose consumption (D), and sucrose preference (E) following injections of saline (light green), low dose J60 (medium green) and high dose J60 (dark green) for all control rats (left), female controls (middle), and male controls (right). Bar plots and error bars indicate mean +/− SEM. Dots and lines represent individual rats. Asterix indicate p-values less than 0.05 for Sidak corrected pairwise comparisons.