Fourth-ventricle leptin infusions dose-dependently activate hypothalamic signal transducer and activator of transcription 3.

Previous studies have shown that very low-dose infusions of leptin into the third or the fourth ventricle alone have little effect on energy balance, but simultaneous low-dose infusions cause rapid weight loss and increased phosphorylation of STAT3 (p-STAT3) in hypothalamic sites that express leptin receptors. Other studies show that injecting high doses of leptin into the fourth ventricle inhibits food intake and weight gain. Therefore, we tested whether fourth-ventricle leptin infusions that cause weight loss are associated with increased leptin signaling in the hypothalamus. In a dose response study 14-day infusions of increasing doses of leptin showed significant hypophagia, weight loss, and increased hypothalamic p-STAT3 in rats receiving at least 0.9 µg leptin/day. In a second study 0.6 µg leptin/day transiently inhibited food intake and reduced carcass fat, but had no significant effect on energy expenditure. In a final study, we identified the localization of STAT3 activation in the hypothalamus of rats receiving 0, 0.3, or 1.2 µg leptin/day. The high dose of leptin, which caused weight loss in the first experiment, increased p-STAT3 in the ventromedial, dorsomedial, and arcuate nuclei of the hypothalamus. The low dose that increased brown fat UCP1 but did not affect body composition in the first experiment had little effect on hypothalamic p-STAT3. We propose that hindbrain leptin increases the precision of control of energy balance by lowering the threshold for leptin signaling in the forebrain. Further studies are needed to directly test this hypothesis.

Leptin in the hindbrain facilitates phosphorylation of STAT3 in the hypothalamus.

Leptin receptors (ObRs) in the forebrain and hindbrain have been independently recognized as important mediators of leptin responses. We recently used low-dose leptin infusions to show that chronic activation of both hypothalamic and hindbrain ObRs is required to reduce body fat. The objective of the present study was to identify the brain nuclei that are selectively activated in rats that received chronic infusion of leptin in both the forebrain and hindbrain. Either saline or leptin was infused into third and fourth ventricles (0.1 µg/24 h in the third ventricle and 0.6 µg/24 h in the fourth ventricle) of male Sprague-Dawley rats for 6 days using Alzet pumps. Rats infused with leptin into both ventricles (LL rats) showed a significant increase in phosphorylated (p)STAT3 immunoreactivity in the arcuate nucleus, ventromedial hypothalamus, dorsomedial hypothalamus, and posterior hypothalamus compared with other groups. No differences in pSTAT3 immunoreactivity were observed in midbrain or hindbrain nuclei despite a sixfold higher infusion of leptin into the fourth ventricle than the third ventricle. ΔFosB immunoreactivity, a marker of chronic neuronal activation, showed that multiple brain nuclei were chronically activated due to the process of infusion, but only the arcuate nucleus, ventromedial hypothalamus, dorsomedial hypothalamus, and ventral tuberomamillary nucleus showed a significant increase in LL rats compared with other groups. These data demonstrate that low-dose leptin in the hindbrain increases pSTAT3 in areas of the hypothalamus known to respond to leptin, supporting the hypothesis that leptin-induced weight loss requires an integrated response from both the hindbrain and forebrain.

Blockade of the cerebral aqueduct in rats provides evidence of antagonistic leptin responses in the forebrain and hindbrain.

Previously, we reported that low-dose leptin infusions into the fourth ventricle produced a small but significant increase in body fat. These data contrast with reports that injections of higher doses of leptin into the fourth ventricle inhibit food intake and weight gain. In this study, we tested whether exogenous leptin in the fourth ventricle opposed or contributed to weight loss caused by third ventricle leptin infusion by blocking diffusion of CSF from the third to the fourth ventricle. Male Sprague-Dawley rats received third ventricle infusions of PBS or 0.3 µg leptin/24 h from miniosmotic pumps. After 4 days, rats received a 3-µl cerebral aqueduct injection of saline or of thermogelling nanoparticles (hydrogel) that solidified at body temperature. Third ventricle leptin infusion inhibited food intake and caused weight loss. Blocking the aqueduct exaggerated the effect of leptin on food intake and weight loss but had no effect on the weight of PBS-infused rats. Leptin reduced both body fat and lean body mass but did not change energy expenditure. Blocking the aqueduct decreased expenditure of rats infused with PBS or leptin. Infusion of leptin into the third ventricle increased phosphorylated STAT3 in the VMHDM of the hypothalamus and the medial NTS in the hindbrain. Blocking the aqueduct did not change hypothalamic p-STAT3 but decreased p-STAT3 in the medial NTS. These results support previous observations that low-level activation of hindbrain leptin receptors has the potential to blunt the catabolic effects of leptin in the third ventricle.

Aloe barbadensis Mill. formulation restores lipid profile to normal in a letrozole-induced polycystic ovarian syndrome rat model.

BACKGROUND: Polycystic ovarian syndrome (PCOS), characterized by ovulatory infertility and hyperandrogenism, is associated with metabolic complications such as dyslipidemia, insulin resistance and endothelial dysfunction. Almost 70% PCOS women have abnormal serum lipid levels (dyslipidemia) and 50% of these women are obese. Several classes of pharmacological agents have been used to manage dyslipidemia. However, studies have shown adverse effects associated with these drugs. In the light of alternate therapy, many medicinal herbs have been reported to show hypoglycemic, anti-hyperlipidemic potential. Aloe barbadensis Mill. or Aloe vera is reported as one such herb. This study was to evaluate the lipid correcting effect of Aloe vera gel (AVG) in a PCOS rat model. MATERIALS AND METHODS: PCOS was induced in Charles Foster female rats by oral administration of non-steroidal aromatase inhibitor letrozole (0.5 mg/kg body weight, 21 days). All rats were hyperglycemic and 90% rats also showed elevated plasma triglycerides, elevated LDL cholesterol levels, and lowered plasma HDL cholesterol levels indicative of a dyslipidemic profile. PCOS positive rats with an aberrant lipid profile were selected for treatment. An AVG formulation (1 ml (10 mg)/day, 30 days) was administered orally. RESULTS AND CONCLUSION: AVG treated PCOS rats exhibited significant reduction in plasma triglyceride and LDL cholesterol levels, with an increase in HDL cholesterol. The gel treatment also caused reversion of abnormal estrous cyclicity, glucose intolerance, and lipid metabolizing enzyme activities, bringing them to normal. In conclusion, AVG has phyto components with anti-hyperlipidemic effects and it has shown efficacy in management of not only PCOS but also the associated metabolic complication : dyslipidemia.