Role of leptin in the regulation of food intake in fasted mice

Abstract

Leptin is well acknowledged as an anorexigenic hormone that plays an important role in feeding control. Hypothalamic GABA system plays a significant role in leptin regulation on feeding and metabolism control. However, the pharmacological relationship of leptin and GABA receptor is still obscure. Therefore, we investigated the effect of leptin or combined with baclofen on the food intake in fasted mice. We detected the changes in hypothalamic c-Fos expression, hypothalamic TH, POMC and GAD67 expression, plasma insulin, POMC and GABA levels to demonstrate the mechanisms. We found that leptin inhibit fasting-induced increased food intake and activated hypothalamic neurons. The inhibitory effect on food intake induced by leptin in fasted mice can be reversed by pretreatment with baclofen. Baclofen reversed leptin's inhibition on c-Fos expression of PAMM in fasted mice. Therefore, these results indicate that leptin might inhibit fasting-triggered activation of PVN neurons via presynaptic GABA synaptic functions which might be partially blocked by pharmacological activating GABA-B. Our findings identify the role of leptin in the regulation of food intake.

Keywords: GABA-B; baclofen; feeding behaviour; hypothalamus; leptin.

Figure 1

Effect of leptin or combined with baclofen on cumulative food intake in fasted mice. Cont: control group; Lep: Leptin (1 mg/kg); Bac: Baclofen (8 mg/kg); Columns represent the mean ± SEM n = 8. (*P < .05, **P < .01, ***P < .001, n = 8 mice per group)

Figure 2

Effect of leptin or combined with baclofen on c‐Fos expression in hypothalamus. A, Schematic image of the DM and VM of hypothalamus from mouse brain stereotaxic coordinates. B‐F, Representative photomicrographs of c‐Fos expression in the DM and VM of different groups. G, H, Quantitative analysis of the c‐Fos expression in DM and VM; DM: dorsal medial nucleus of hypothalamus, VM: ventromedial nucleus of the hypothalamus; Data are represented as the mean ± SEM; (*P < .05, **P < .01. n = 2‐3 mice per group)

Figure 3

Effect of leptin or combined with baclofen on c‐Fos expression in PVN of hypothalamus. A, Schematic image of the PVN from mouse brain stereotaxic coordinates; B‐F, Representative photomicrographs of c‐Fos expression in the PAMM and PALM of PVN in different groups. G, H, Quantitative analysis of the c‐Fos expression in the PAMM and PALM of PVN in different groups; PVN: paraventricular thalamus of hypothalamus; PAMM: medial magnocellular part of paraventricular hypothalamic nucleus; PALM: lateral magnocellular part of paraventricular hypothalamic nucleus; Data are represented as the mean ± SEM; (*P < .05, **P < .01, ***P < .001. n = 2‐3 mice per group)

Figure 4

Effect of leptin or combined with baclofen on c‐Fos expression in hypothalamus. A‐E, Representative photomicrographs of c‐Fos expression in the LH; F, Quantitative analysis of the c‐Fos expression in the LH. LH: lateral hypothalamus; Data are represented as the mean ± SEM; (*P < .05, **P < .01, ***P < .001. n = 2‐3 mice per group)

Figure 5

Effect of leptin or combined with baclofen on c‐Fos expression in hypothalamus. A‐E, Representative photomicrographs of c‐Fos expression in the AHP; F, Quantitative analysis of the c‐Fos expression in the AHP; AHP: anterior hypothalamic nucleus; Data are represented as the mean ± SEM; (*P < .05, **P < .01, ***P < .001. n = 2‐3 mice per group)

Figure 6

Effect of leptin or combined with baclofen on GAD67, POMC and TH expression in hypothalamus. A, Representative Western blots for GAD67 and β‐actin. B, Representative Western blots for POMC and β‐actin. C, Representative Western blots for TH and β‐actin. Data are represented as the mean ± SEM; (*P < .05, **P < .01, ***P < .001. n = 5‐6 mice per group)

Figure 7

Effect of leptin or combined with baclofen on plasma insulin, GABA and POMC levels. A, Effect of leptin or combined with baclofen on plasma insulin levels. B, A, Effect of leptin or combined with baclofen on plasma GABA levels. C, Effect of leptin or combined with baclofen on plasma POMC levels. Data are represented as the mean ± SEM; (*P < .05, **P < .01, ***P < .001. n = 5‐6 mice per group)