Activation of Dorsomedial Hypothalamic Neurons Promotes Physical Activity and Decreases Food Intake and Body Weight in Zucker Fatty Rats

Abstract

Previous reports have shown that running wheel activity or voluntary exercise prevents hyperphagia and obesity in various animal models of obesity, but such effects seem only minimal in obese animals lacking leptin or leptin receptors. The mechanisms underlying this ineffectiveness remain unclear. Here, we identified the action of neuronal activation in the dorsomedial hypothalamus (DMH) in modulating physical activity, food intake and body weight using leptin receptor mutant obese Zucker (Lepr(fa), ZF) and Koletsky (Lepr(fak), SHROB) rats. Ad lib-fed SHROB rats with locked running wheels became hyperphagic and gained body weight rapidly. These alterations were not ameliorated in ad lib-fed SHROB rats with voluntary access to running wheels, but the body weight of SHROB rats with running wheel access was significantly decreased when they were pair-fed to the amounts consumed by lean controls. Determinations of hypothalamic gene expression revealed that sedentary ad lib-fed SHROB rats had increased expression of neuropeptide Y (Npy) and decreased expression of pro-opiomelanocortin (Pomc) in the arcuate nucleus (ARC). Both ARC Npy and Pomc expression were further altered under running and pair-fed conditions, indicating that both genes are appropriately regulated in response to increased energy demands or alterations caused by running activity and food restriction. Strikingly, c-Fos immunohistochemistry revealed that while voluntary running activity elevated the number of c-Fos positive cells in the DMH (particularly in the ventral and caudal subregions) of intact rats, such activation was not observed in ZF rats. Using adeno-associated virus (AAV)-mediated expression of the designer receptors hM3D(Gq) in the ventral and caudal DMH of ZF rats, we found that chemogenetic stimulation of neurons in these DMH subregions via injection of the designer drug clozapine N-oxide (CNO) significantly increased their running activity and reduced their food intake and body weight. Together, these results demonstrate that activation of ventral and caudal DMH neurons promotes physical activity and decreases food intake and body weight and suggest that intact DMH neural signaling is likely crucial for exercise-induced reductions of food intake and body weight in obese rats lacking leptin receptors.

Keywords: body weight; dorsomedial hypothalamus; food intake; leptin; leptin receptor; obesity; physical activity; running wheel.

Figure 1

Effects of running wheel activity on food intake and body weight in SHROB rats. (A) Running wheel activity in SHROB rats with access to running wheels (SHROB-RW). (B) Food intake in lean sedentary control rats with locked running wheels (CTL-SED), sedentary SHROB rats with locked running wheels (SHROB-SED) and SHROB-RW rats. (C) Body weight in the three groups of rats. Values are means ± SEM. n = 4 rats per group. *P < 0.05 vs. CTL-SED and ^#P < 0.05 vs. SHROB-SED.

Figure 2

Hypothalamic mRNA expression in SHROB rats. (A) Proopiomelanocortin (Pomc) and neuropeptide Y (Npy) mRNA expression in the arcuate nucleus (ARC). (B) Npy and corticotrophin-releasing factor (Crf) mRNA expression in the dorsomedial hypothalamus (DMH). (C) Crf mRNA expression in the paraventricular nucleus (PVN). Values are means ± SEM. n = 4 rats per group. *P < 0.05 vs. CTL-SED and ^#P < 0.05 vs. SHROB-SED.

Figure 3

Characterization of running activity-induced brain c-Fos activation in Zucker fatty (ZF) rats. (A) Brain c-Fos activation in lean intact rats with running wheel access (LEAN-RW, n = 5) compared to lean sedentary control rats with locked running wheels (LEAN-SED, n = 5). (B) Brain c-Fos activation in ZF rats with running wheel access (ZF-RW, n = 7) compared to sedentary ZF rats with locked running wheels (ZF-SED, n = 5). VMH: the ventromedial hypothalamus (VMH); LH: the lateral hypothalamus; CeA: the central nucleus of amygdala; AP: area postrema; NTS: the nucleus of the solitary tract. Values are means ± SEM. n = 5–7 rats per group. *P < 0.05 vs. sedentary controls (LEAN-SED or ZF-SED).

Figure 4

Running activity-induced c-Fos activation in the DMH. (A–C) Representative micrograph shows running activity-induced c-Fos activation in the DMH (A) particularly in the ventral subregion (vDMH, B) and the caudal DMH (C) in LEAN-RW rats. (D–F) c-Fos activation was decreased in the DMH (D) particularly in the ventral subregion (E) and the caudal DMH (F) in ZF-RW rats. Scale bar, 150 μm.

Figure 5

Chemogenetic stimulation of DMH neurons in ZF rats via designer receptors exclusively activated by designer drugs (DREADD). (A,B) Representative micrograph shows mCherry expression in the DMH post-viral DMH injection as examined under fluorescence microscopy; (A) the ventral subregion of the DMH (vDMH) and (B) the caudal DMH. (C) Food intake in ZF rats receiving DMH injection of the vector AAVhM3D (hM3D, n = 6) or the control vector (CTL, n = 4) at 2, 4, 24 h following intraperitoneal clozapine N-oxide (CNO; 1 mg/kg body weight, ip) or saline. (D) Body weight change in hM3D and CTL rats at 24 h after ip CNO or saline. Values are means ± SEM. n = 4–6 rats per group. *P < 0.05 vs. CTL rats. Scale bar, 250 μm.

Figure 6

Effects of chemogenetic stimulation of DMH neurons on running activity, food intake and body weight in ZF rats. (A) Running wheel activity in the two groups of hM3D (n = 6) and CTL rats (n = 4) following ip CNO (1 mg/kg body weight, daily) for 3 days. (B) Food intake in the two groups of hM3D and CTL rats receiving ip CNO. (C) Body weight gain in the two groups of hM3D and CTL rats receiving ip CNO. Values are means ± SEM. n = 4–6 rats per group. *P < 0.05 vs. CTL rats.