Lesion of area postrema attenuated hyperphagic responses to glucoprivation, but not transcriptional activation of the neuropeptide Y gene in rats

Regulation of Energy and Glucose Homeostasis by the Nucleus of the Solitary Tract and the Area Postrema

The central nervous system regulates feeding, weight and glucose homeostasis in rodents and humans, but the site-specific mechanisms remain unclear. The dorsal vagal complex in the brainstem that contains the nucleus of the solitary tract (NTS) and area postrema (AP) emerges as a regulatory center that impacts energy and glucose balance by monitoring hormonal and nutrient changes. However, the specific mechanistic metabolic roles of the NTS and AP remain elusive. This mini-review highlights methods to study their distinct roles and recent findings on their metabolic differences and similarities of growth differentiation factor 15 (GDF15) action and glucose sensing in the NTS and AP. In summary, future research aims to characterize hormonal and glucose sensing mechanisms in the AP and/or NTS carries potential to unveil novel targets that lower weight and glucose levels in obesity and diabetes.

A glucose-sensing mechanism with glucose transporter-1 and pyruvate kinase in the area postrema regulates hepatic glucose production in rats

The area postrema (AP) of the brain is exposed to circulating metabolites and hormones. However, whether AP detects glucose changes to exert biological responses remains unknown. Its neighboring nuclei, the nucleus tractus solitarius (NTS), responds to acute glucose infusion by inhibiting hepatic glucose production, but the mechanism also remains elusive. Herein, we characterized AP and NTS glucose-sensing mechanisms. Infusion of glucose into the AP, like the NTS, of chow rats suppressed glucose production during the pancreatic (basal insulin)-euglycemic clamps. Glucose transporter-1 or pyruvate kinase lentiviral-mediated knockdown in the AP negated AP glucose infusion to lower glucose production, while the glucoregulatory effect of NTS glucose infusion was also negated by knocking down glucose transporter-1 or pyruvate kinase in the NTS. Furthermore, we determined that high-fat (HF) feeding disrupts glucose infusion to lower glucose production in association with a modest reduction in expression of glucose transporter-1, but not pyruvate kinase, in the AP and NTS. However, pyruvate dehydrogenase activator dichloroacetate infusion into the AP or NTS that enhanced downstream pyruvate metabolism and recapitulated the glucoregulatory effect of glucose in chow rats still failed to lower glucose production in HF rats. We discovered that a glucose transporter-1 and pyruvate kinase-dependent glucose-sensing mechanism in the AP (as well as the NTS) lowers glucose production in chow rats, and that HF disrupts the glucose-sensing mechanism that is downstream of pyruvate metabolism in the AP and NTS. These findings highlight the role of AP and NTS in mediating glucose to regulate hepatic glucose production.

The Role of Essential Fatty Acids in Anorexia Nervosa and Obesity

The two basic questions in food intake study are what we eat, and how much do we eat. Most research is directed toward the control of how much is eaten. This is likely the result of the increased number of individuals with eating disorders in the Western world. Feeding behavior is highly complex, and is controlled by many psychological, physiological, biochemical, and immunological factors. The aim of this review is to clarify the involvement of fatty acids in eating disorders such as anorexia and binge eating disorder. The review will describe the modified fatty acid profile observed in individuals with anorexia or binge eating disorder, and discuss on what factors fatty acids can exert beneficial effects. In addition, the differences and similarities between anorexia and binge eating disorder will be discussed. We suggest that beneficial effects of essential fatty acids on both anorexia and binge eating disorder can be explained by the stabilizing effect of those fatty acids on the neuronal membrane fluidity index.

2-Deoxy-D-glucose-induced hypothermia in anesthetized rats: Lack of forebrain contribution and critical involvement of the rostral raphe/parapyramidal regions of the medulla oblongata

Systemic or central administration of 2-deoxy-d-glucose (2DG), a competitive inhibitor of glucose utilization, induces hypothermia in awake animals and humans. This response is mediated by the central nervous system, though the neural mechanism involved is largely unknown. In this study, I examined possible involvement of the forebrain, which contains the hypothalamic thermoregulatory center, and the medullary rostral raphe/parapyramidal regions (rRPa/PPy), which mediate hypoxia-induced heat-loss responses, in 2DG-induced hypothermia in urethane-chloralose-anesthetized, neuromuscularly blocked, artificially ventilated rats. The intravenous injection of 2DG (250mgkg(-1)) elicited an increase in tail skin temperature and decreases in body core temperature and the respiratory exchange ratio, though it did not induce any significant change in the metabolic rate. These results indicate that the hypothermic response was caused by an increase in heat loss, but not by a decrease in heat production and that it was accompanied by a decrease in carbohydrate utilization and/or an increase in lipid utilization as energy substrates. Complete surgical transection of the brainstem between the hypothalamus and the midbrain had no effect on the 2DG-induced hypothermic responses, suggesting that the hindbrain, but not the forebrain, was sufficient for the responses. However, pretreatment of the rRPa/PPy with the GABAA receptor blocker bicuculline methiodide, but not with vehicle saline, greatly attenuated the 2DG-induced responses, suggesting that the 2DG-induced hypothermia was mediated, at least in part, by GABAergic neurons in the hindbrain and activation of GABAA receptors on cutaneous sympathetic premotor neurons in the rRPa/PPy.