Effects of intraventricular infusion of corticotropin-releasing factor on VMH-lesioned obese rats

A Microelectrode Array Modified by PtNPs/PB Nanocomposites Used for the Detection and Analysis of Glucose-Sensitive Neurons under Different Blood Glucose States

Hypoglycemia state damages the organism, and glucose-excited and glucose-inhibited neurons from the ventral medial hypothalamus can regulate this state. Therefore, it is crucial to understand the functional mechanism between blood glucose and electrophysiology of glucose-excited and glucose-inhibited neurons. To better detect and analyze this mechanism, a PtNPs/PB nanomaterials modified 32-channel microelectrode array with low impedance (21.91 ± 6.80 kΩ), slight phase delay (-12.7° ± 2.7°), high double layer capacitance (0.606 μF), and biocompatibility was developed to realize in vivo real-time detection of the electrophysiology activities of glucose-excited and glucose-inhibited neurons. The phase-locking level of some glucose-inhibited neurons elevated during fasting (low blood glucose state) and showed theta rhythms after glucose injection (high blood glucose state). With an independent oscillating ability, glucose-inhibited neurons can provide an essential indicator to prevent severe hypoglycemia. The results reveal a mechanism for glucose-sensitive neurons to respond to blood glucose. Some glucose-inhibited neurons can integrate glucose information input and convert it into theta oscillating or phase lock output. It helps in enhancing the interaction between neurons and glucose. Therefore, the research can provide a basis for further controlling blood glucose by modulating the characteristics of neuronal electrophysiology. This helps reduce the damage of organisms under energy-limiting conditions, such as prolonged manned spaceflight or metabolic disorders.

Corticotrophin-releasing factor mediates hypophagia after adrenalectomy, increasing meal-related satiety responses

Adrenalectomy-induced hypophagia is associated with increased satiety-related responses, which involve neuronal activation of the nucleus of the solitary tract (NTS). Besides its effects on the pituitary-adrenal axis, corticotrophin-releasing factor (CRF) has been shown to play an important role in feeding behaviour, as it possesses anorexigenic effects. We evaluated feeding-induced CRF mRNA expression in the paraventricular nucleus (PVN) and the effects of pretreatment with CRF(2) receptor antagonist (Antisauvagine-30, AS30) on food intake and activation of NTS neurons in response to feeding in adrenalectomised (ADX) rats. Compared to the sham group, ADX increased CRF mRNA levels in the PVN of fasted animals, which was further augmented by refeeding. AS30 treatment did not affect food intake in the sham and ADX+corticosterone (B) groups; however, it reversed hypophagia in the ADX group. In vehicle-pretreated animals, refeeding increased the number of Fos and Fos/TH-immunoreactive neurons in the NTS in the sham, ADX and ADX+B groups, with the highest number of neurons in the ADX animals. Similarly to its effect on food intake, pretreatment with AS30 in the ADX group also reversed the increased activation of NTS neurons induced by refeeding while having no effect in the sham and ADX+B animals. The present results show that adrenalectomy induces an increase in CRF mRNA expression in the PVN potentiated by feeding and that CRF(2) receptor antagonist abolishes the anorexigenic effect and the increased activation of NTS induced by feeding in the ADX animals. These data indicate that increased activity of PVN CRF neurons modulates brainstem satiety-related responses, contributing to hypophagia after adrenalectomy.

Feeding microstructure in diet-induced obesity susceptible versus resistant rats: central effects of urocortin 2

With one billion people overweight worldwide, the need to identify risk factors and treatments for obesity is urgent. The present study determined whether rats genetically prone to diet-induced obesity (DIO) show preexisting differences in meal microstructure and are sensitive to central anorectic effects of corticotropin-releasing factor type 2 (CRF(2)) receptor stimulation. Male, selectively bred DIO rats and their diet resistant (DR) counterparts (n = 9/genotype) were weaned onto low-fat chow and compared as young adults for spontaneous or intracerebroventricular urocortin 2 administration-induced (0, 0.3, 1, 3 microg) differences in ingestion. DIO rats were hyperphagic selectively at the dark cycle onset, showing shorter latencies to initiate feeding, faster returns to eating following meal completion, and a lower satiety ratio than DR rats. At other times, DIO rats had briefer postmeal intervals, but ate smaller and briefer meals, resulting in normal intake. DIO rats also ate faster than DR rats. Urocortin 2 was less potent in DIO rats, ineffective at the 0.3 microg dose, but produced CRF(2) antagonist-reversible anorexia at higher doses. Though heavier, chow-maintained DIO rats were proportionately as or more lean than DR rats. Thus, DIO rats showed signs of a preexisting, heritable deficit in the maintenance of postmeal satiety and a reduced sensitivity to anorectic CRF(2) agonist stimulation. The meal patterns of DIO rats temporally resemble human 'snacking' behaviour, which predicts adult obesity. Because central CRF(2) stimulation retains full anorectic efficacy at higher doses in the DIO model, manipulating this neuropeptidergic system might yield new therapeutic approaches for diet-induced obesity.

Intraventricular insulin potentiates the anorexic effect of corticotropin releasing hormone in rats

Intraventricular corticotropin releasing hormone (CRH) suppresses food intake and body weight as a stress response. Insulin, acting within the brain, also suppresses food intake and body weight, and this suppression is related to caloric homeostasis. We determined if increased insulin within the brain potentiates the anorexic effects of intraventricular CRH. Rats were food deprived for 17 h each day and then given 30-min access to Ensure. One-half received continuous third ventricular infusion of synthetic cerebrospinal fluid via osmotic minipumps, and one-half received insulin (0.6 mU/day). During the infusion, rats also received 0, 0.1, 1.0, or 5.0 microg of CRH into the lateral ventricle just before access to Ensure. Insulin alone had no effect on Ensure intake or body weight. CRH dose dependently reduced Ensure intake in both groups, and the reduction was greater in the insulin group. Hence, central insulin potentiated the ability of centrally administered CRH to suppress food intake. These findings suggest that stress-related influences over food intake, particularly those mediated via CRH, interact with relative adiposity as signaled to the brain by central insulin.

Adrenalectomy reduces neuropeptide Y-induced insulin release and NPY receptor expression in the rat ventromedial hypothalamus

Chronic central administration of neuropeptide Y (NPY) causes hyperphagia, hyperinsulinemia, and obesity, a response that is prevented by prior adrenalectomy (ADX) in rats. The basis of NPY's effect and how the acute responses to this peptide are affected by ADX remain unknown. This study investigates the role of glucocorticoids in acute NPY-stimulated food intake, acute NPY-induced insulin release, and hypothalamic NPY-receptor mRNA expression levels. NPY-induced food intake was similar in ADX and control rats after acute intracerebroventricular injection of NPY. Injection of NPY caused a significant increase in plasma insulin in control rats, but this effect was completely absent in ADX rats in which basal plasma insulin levels were also lower than controls. In addition, ADX significantly reduced the number of neurons expressing NPY receptor Y(1) and Y(5) mRNAs in the ventromedial hypothalamus (VMH), without affecting Y(1)- or Y(5)-mRNA expression in the paraventricular hypothalamus or the arcuate nucleus. These data indicate that glucocorticoids are necessary for acute NPY-mediated insulin release and suggest that the mechanisms involve glucocorticoid regulation of Y(1) and Y(5) receptors specifically within the VMH nucleus.

Corticotropin-releasing factor-binding protein ligand inhibitor blunts excessive weight gain in genetically obese Zucker rats and rats during nicotine withdrawal

Elevation of the neuropeptide corticotropin-releasing factor (CRF) in the brain is associated with a reduction of food intake and body weight gain in normal and obese animals. A protein that binds CRF and the related peptide, urocortin, with high affinity, CRF-binding protein (CRF-BP), may play a role in energy homeostasis by inactivating members of this peptide family in ingestive and metabolic regulatory brain regions. Intracerebroventricular administration in rats of the high-affinity CRF-BP ligand inhibitor, rat/human CRF (6-33), which dissociates CRF or urocortin from CRF-BP and increases endogenous brain levels of "free" CRF or urocortin significantly blunted exaggerated weight gain in Zucker obese subjects and in animals withdrawn from chronic nicotine. Chronic administration of CRF suppressed weight gain nonselectively by 60% in both Zucker obese and lean control rats, whereas CRF-BP ligand inhibitor treatment significantly reduced weight gain in obese subjects, without altering weight gain in lean control subjects. Nicotine abstinent subjects, but not nicotine-naive controls, experienced a 35% appetite suppression and a 25% weight gain reduction following acute and chronic administration, respectively, of CRF-BP ligand inhibitor. In marked contrast to the effects of a CRF-receptor agonist, the CRF-BP ligand inhibitor did not stimulate adrenocorticotropic hormone secretion or elevate heart rate and blood pressure. These results provide support for the hypothesis that the CRF-BP may function within the brain to limit selected actions of CRF and/or urocortin. Furthermore, CRF-BP may represent a novel and functionally selective target for the symptomatic treatment of excessive weight gain associated with obesity of multiple etiology.

Modulation by corticotropin-releasing factor of monoamine metabolism in the lateral hypothalamus

Corticotropin-releasing factor (CRF) was injected into the lateral hypothalamus of conscious unrestrained rats and the local concentration of monoamines in the vicinity of the microinjection monitored by microdialysis. The concentration of norepinephrine and MHPG in the dialysis fluid from the lateral hypothalamic areas of rats fasted for 24 h was nearly 4 times higher than in fed rats. Following the injection of 2 micrograms of CRF into the lateral hypothalamus of fasted rats there was a rapid decline in levels of both norepinephrine and 3-methoxy-4-hydroxyphenylglycol (MHPG) to the level in fed rats after 60-90 min. The changes in MHPG and norepinephrine in the fed rats were not significant There was no difference in serotonin concentration between fasted and fed animals, although the mean value for 5-hydroxyindoleacetic acid (5-HIAA) was slightly increased. Following the injection of CRF, there was a fall in serotonin in the fed rats but not in the fasted animals. There was a fall in the concentration of 5-HIAA in both the fasted and fed rats so that at 30, 60 and 90 min their concentrations were not significantly different. The concentration of DOPAC in the lateral hypothalamus was twice as high in the fasted as in the fed rats. Following injection of CRF there was a rapid decline in DOPAC concentrations in the fasted rats and a small decline in the fed rats. By the end of 30 min after the injection of CRF, concentrations of DOPAC were similar in fed and fasted rats.(ABSTRACT TRUNCATED AT 250 WORDS)