Hypothermia induced by inhibition of fatty acid metabolism in anesthetized rats: contributions of the forebrain and vagal afferents.

2-Mercaptoacetate (MA) is an antimetabolic drug that inhibits the utilization of fatty acids as an energy source. The intravenous injection of MA (1.2 mmol·kg-1) elicited an increase in tail skin temperature and a decrease in body core temperature in urethane-chloralose-anesthetized, neuromuscularly blocked, artificially ventilated rats, although administration of the same amount of NaCl did not. The respiratory exchange ratio was significantly higher after administration of MA than that after the saline treatment. On the other hand, heat production was increased by either the MA- or NaCl-injection, suggesting a nonspecific effect caused by the hyperosmolality of the solutions. These results indicate that the MA-induced hypothermia was caused by an increase in heat loss but not by a decrease in heat production. The amplitudes of heat loss responses to MA in rats fasted overnight were significantly smaller than those in fed ones, suggesting a mechanism for suppression of heat loss in the fasted state. Rats pretreated with vagotomy, capsaicin-induced desensitization of sensory nerve fibers or decerebration did not exhibit the MA-induced hypothermic responses. It is possible that the MA-induced heat loss and hypothermia were mediated by the vagal afferents and required the forebrain for the full expression of the responses.

The EP3 and EP4 Receptor Subtypes both Mediate the Fever-producing Effects of Prostaglandin E2 in the Rostral Ventromedial Preoptic Area of the Hypothalamus in Rats.

This study aimed to re-examine the receptor subtype that mediates the fever-producing effects of prostaglandin E2 (PGE2) in the rostral ventromedial preoptic area (rvmPOA) of the hypothalamus. Among the four subtypes of PGE2 receptors (EP1, EP2, EP3, and EP4), EP3 receptor is crucially involved in the febrile effects of PGE2. However, it is possible for other subtypes of PGE2 receptor to contribute in the central mechanism of fever generation. Accordingly, effects of microinjection of PGE2 receptor subtype-specific agonists or antagonists were examined at the locus where a microinjection of a small amount (420 fmol) of PGE2 elicited prompt increases in the O2 consumption rate (VO2), heart rate, and colonic temperature (Tc) in the rvmPOA of urethane-chloralose-anesthetized rats. The EP3 agonist sulprostone mimicked, whereas its antagonist L-798,106 reduced, the febrile effects of PGE2 microinjected into the same site. Similarly, the EP4 agonist rivenprost mimicked, whereas its antagonist ONO-AE3-208 reduced, the effects of PGE2 microinjected into the same site. In contrast, microinjection of the EP1 agonist iloprost induced a very small increase in VO2 but did not have significant influences on the heart rate and Tc, whereas its antagonist, AH6809, did not affect the PGE2-induced responses. Microinjection of the EP2 agonist butaprost had no effects on the VO2, heart rate, and Tc. The results suggest that the EP3 and EP4 receptor subtypes are both involved in the fever generated by PGE2 in the rvmPOA.

Cell proliferation in visceral organs induced by ventromedial hypothalamic (VMH) lesions: Development of electrical VMH lesions in mice and resulting pathophysiological profiles.

We have found that ventromedial hypothalamic (VMH) lesions produced by electrocoagulation induce cell proliferation in visceral organs through vagal hyperactivity, and also stimulate regeneration of partially resected liver in rats. To facilitate identification of proliferative and/or regenerative factors at the gene level, we developed electrical production of VMH lesions in mice, for which more genetic information is available compared to rats, and examined the pathophysiological profiles in these mice. Using ddy mice, we produced VMH lesions with reference to the previously reported method in rats. We then examined the pathophysiological profiles of the VMH-lesioned mice. Electrical VMH lesions in mice were produced using the following coordinates: 1.6 mm posterior to the bregma, anteriorly; 0.5 mm lateral to the midsagittal line, transversely; and 0.2 mm above the base of the skull, vertically, with 1 mA of current intensity and 10 s duration. The VMH-lesioned mice showed similar metabolic characteristics to those of VMH-lesioned rats, including body weight gain, increased food intake, increased percentage body fat, and elevated serum insulin and leptin. However, there were some differences in short period of hyperphagia, and in normal serum lipids compared to those of VMH-lesioned rats. The mice showed a similar cell proliferation in visceral organs, including stomach, small intestine, liver, and, exocrine and endocrine pancreas. In conclusion, procedures for development of VMH lesions in mice by electrocoagulation were developed and the VMH-lesioned mice showed pathophysiological profiles similar to those of VMH-lesioned rats, particularly in cell proliferation in visceral organs. These findings have not been observed previously in gold thioglucose-induced VMH-lesioned mice. This model may be a new tool for identifying factors involved in cell proliferation or regeneration in visceral organs.

Effects of gastric vagotomy on visceral cell proliferation induced by ventromedial hypothalamic lesions: role of vagal hyperactivity.

In rats, ventromedial hypothalamic (VMH) lesions induce cell proliferation in the visceral organs (stomach, small intestine, liver, and pancreas) due to hyperactivity of the vagus nerve. To investigate the effects of selective gastric vagotomy on VMH lesion-induced cell proliferation and secretion of gastric acid, we assessed the mitotic index (the number of proliferating cell nuclear antigen (PCNA)-immunopositive cells per 1,000 cells in the gastric mucosal cell layer) and measured the volume of secreted basal gastric acid. Furthermore, to explore whether or not ethanol-induced acute gastric mucosal lesions (AGML) lead to ulcer formation in VMH-lesioned rats, we assessed the ulcer index of both sham-operated and VMH-lesioned rats after administration of ethanol. VMH lesions resulted in an increased mitotic index and thickness of the gastric mucosal cell layer and gave rise to the hypersecretion of gastric acid. Selective gastric vagotomy restored these parameters to normal without affecting cell proliferation in other visceral organs. Ethanol-induced AGML caused ulcers in sham VMH-lesioned rats, whereas VMH-lesioned rats were less likely to exhibit such ulcers. These results suggest that VMH lesion-induced vagally mediated cell proliferation in the visceral organs is associated with hyperfunction in these organs, and VMH lesion-induced resistance to ethanol may be due to thickening of the gastric mucosal cell layer resulting from cell proliferation in the gastric mucosa-this in turn is due to hyperactivity of the vagus nerve.

Central and peripheral administration of amylin induces energy expenditure in anesthetized rats.

Amylin is a peptide hormone that is co-released with insulin from pancreatic beta-cells following a meal. Intracerebroventricular (icv) administration of amylin (1-100 pmol), or an amylin agonist, salmon calcitonin, elicited dose-dependent thermogenic, tachycardic, and hyperthermic responses in urethane-anesthetized rats. Intravenous (iv) administration of higher doses of amylin (100 pmol-20 nmol) also induced similar responses, although the amplitudes of these responses were significantly smaller than those elicited by icv administration, suggesting the primary action of amylin to be in the brain. However, the iv administration of amylin induced the responses slightly faster than the icv injection, the former responses occurring<4 min and the latter, at 8-10 min, after the administration. The iv but not the icv injection of amylin increased the respiratory exchange ratio transiently (<20 min), though the thermogenic response lasted for a longer period after both injections, indicating a shift from mixed fuel to predominantly carbohydrate utilization in the initial phase of thermogenesis induced by the iv injection of amylin. The differences in substrate utilization and latency of the responses suggest that the actions of amylin include partly different targets when administered centrally and peripherally. Moreover, pretreatment with a beta-adrenergic blocker, propranolol (5 mg kg(-1), iv), blocked all responses elicited by either icv or iv administration of amylin, whereas ablation of the area postrema in the hindbrain did not influence the effects of icv-administered amylin. These results suggest the involvement of amylin in postprandial energy expenditure, mediated by peripheral beta-adrenoceptors.

Blockade of prostaglandin E2-induced thermogenesis by unilateral microinjection of GABAA receptor antagonist into the preoptic area.

Previous studies have demonstrated that pretreatment of rats with a GABA(A) receptor antagonist microinjected bilaterally into the preoptic area (POA) blocked cold- or lipopolysaccharide-induced thermogenesis. Here, the involvement of GABA(A) receptors in prostaglandin (PG)E2-induced fever was examined. Thermogenic, tachycardic, vasoconstrictive, and hyperthermic responses were elicited by the unilateral microinjection of 0.57-1.1 pmol PGE2 into the region adjacent to the organum vasculosum of the lamina terminalis in urethane-chloralose-anesthetized rats. All these responses were blocked 10 min after pretreatment of the rats with a GABA(A) receptor antagonist, bicuculline methiodide or gabazine (50-500 pmol), microinjected unilaterally into the POA; and recovery occurred at approximately 70 min. Though the antagonist treatment alone had no effect on the O2 consumption rate or colonic temperature, it did elicit a bradycardic response. Pretreatment with the vehicle, saline, had no effect on the PGE2-induced responses. However, the blocking action of bicuculline/gabazine was efficacious when the agent was administered unilaterally, but not necessarily bilaterally, into the POA either contralateral or ipsilateral to the PGE2 injection site. These results suggest that the PGE2-induced responses are not simply mediated by the GABAergic transmission from the PGE2-sensitive site to the thermoefferent structure in the POA, although a tonic inhibitory input to POA neurons has a permissive role for the full expression of PGE2-induced fever.

Changes of neuron-specific and apoptosis gene expression levels after ventromedial hypothalamic lesions in rat intestine.

The intestinal epithelium is continuously renewed through a balance between cell proliferation and apoptosis. We identified genes of which expression profiles showed significant modulation, and we investigated the cellular mechanisms of this gene regulation in rat intestine after ventromedial hypothalamic (VMH) lesions. Total RNA was extracted, and differences in the gene expression profiles between rats at day 3 after VMH lesioning and in sham-VMH lesioned rats were investigated using DNA microarray analysis and real-time polymerase chain reaction (PCR) methods. DNA microarray analysis revealed that VMH lesions regulated the genes that were involved in functions predominantly related to neuronal development, cell proliferation and apoptosis. Real-time PCR also confirmed that gene expressions of Efnb1 were downregulated. Meanwhile, expression of Casp3 was similar. It is noted that the signaling networks of many gene families, including neuron-specific genes and apoptosis genes in the intestine were changed after VMH lesioning. VMH lesions may suppress mainly the caspase independent type II pathway for apoptosis and induce cell proliferation in the intestine.

Combined interleukin-6 and interleukin-1 deficiency causes obesity in young mice.

Proinflammatory cytokines including interleukin (IL)-1 and IL-6 exert pleiotropic effects on the neuro-immuno-endocrine system. Previously, we showed that IL-1 receptor antagonist-deficient (IL-1Ra(-/-)) mice show a lean phenotype due to an abnormal lipid metabolism. On the contrary, it was reported that IL-6(-/-) mice exhibit obesity after 6 months of age. This study sought to assess the roles of IL-1 and IL-6 in body weight homeostasis. We generated mice deficient in IL-6 and IL-1Ra (IL-6(-/-) IL-1Ra(-/-)) and IL-6, IL-1alpha, and IL-1beta (IL-6(-/-) IL-1(-/-)). IL-6(-/-) IL-1Ra(-/-) mice exhibited a lean phenotype, similar to IL-1Ra(-/-) mice. On the other hand, IL-6(-/-) IL-1(-/-) mice became obese as early as 10 weeks of age, while IL-1(-/-) mice and IL-6(-/-) mice were normal at this age. The daily food intake was significantly higher in IL-6(-/-) IL-1(-/-) mice than in IL-6(-/-) IL-1(+/-) mice, while energy expenditure was comparable in these two strains. Acute anorexia induced by peripheral administration of IL-1 was significantly suppressed in IL-6(-/-) IL-1(-/-) mice, but not in IL-1(-/-) mice or IL-6(-/-) mice compared with wild-type mice. These results indicate that IL-1 and IL-6 are both involved in the regulation of body fat in a redundant manner in young mice.

Continuous carbachol infusion promotes peripheral cell proliferation and mimics vagus hyperactivity in a rat model of hypothalamic obesity.

Lesions of the ventromedial hypothalamus (VMH) result in obesity and enhanced cellular proliferation in various organs, including the pancreas, gastrointestinal tract, and liver. Previous studies have suggested that vagal hyperactivity, rather than overeating, induces the peripheral cell proliferation in VMH-lesioned rats. The goal of the present study was to investigate the mechanism of peripheral cell proliferation in VMH-lesion-induced obesity by infusing rats with the acetylcholine agonist, carbachol, and then measuring cellular proliferation in the pancreas and duodenum using immunohistochemistry. The ventromedial hypothalamus was bilaterally lesioned in five rats. In other rats, the bilateral vagus nerves were ligated (vagotomized), and saline or carbachol was continuously administered by an osmotic minipump (n = 5 in each group). Three days later, rats were killed, and cell proliferation was assessed in the pancreas and the duodenum using immunohistochemistry for proliferating cell nuclear antigen (PCNA). Additionally, cellular proliferation in the duodenum was more precisely examined by assessing incorporation of 5-bromo-2'-deoxyuridine (BrdU). Cellular proliferation was higher in rats that received carbachol infusions and in rats with VMH-lesions when compared with control rats (P < 0.05, respectively). The pancreatic PCNA-expressing cells were predominantly identified as the B-cells of the islets of Langerhans. These data demonstrate that carbachol infusion can induce pancreatic and duodenal cell proliferation to a degree that was comparable to that in vagal hyperactivity induced by VMH lesions.

Energy expenditure by intravenous administration of glucagon-like peptide-1 mediated by the lower brainstem and sympathoadrenal system.

Glucagon-like peptide-1 (GLP-1) is released from the gut in response to nutrient ingestion. Intravenous (iv) administration of GLP-1 (50 pmol-20 nmol) elicited dose-dependent increases in the rate of whole-body O2 consumption (VO2), an index of energy expenditure, and heart rate of urethane-anesthetized rats. The body core (colonic) temperature increased up to 0.3 degrees C without accompanying alteration of tail skin temperature. Intracerebroventricular (icv) administration of GLP-1 induced a slower and smaller increase in VO2 than the intravenous administration. The injection of glucagon-like peptide-2 (iv or icv) had no effect on VO2, body temperatures, or heart rate. Decerebration had no effect on the thermogenic responses induced by the iv administration of GLP-1, suggesting that the forebrain is not essential for these responses. However, cervical spinal transection greatly attenuated the responses, suggesting the critical involvement of the lower brainstem. Adrenalectomy or pretreatment with an autonomic ganglion blocker, hexamethonium, or a beta-adrenergic blocker, propranolol, also significantly attenuated the thermogenic response. However, subdiaphragmatic vagotomy or celiac-superior mesenteric ganglionectomy had no effect. Rats made insulin-deficient by pretreatment with streptozotocin also exhibited the normal thermogenic response to GLP-1. These results suggest the involvement of the GLP-1 in postprandial energy expenditure, mediated by the lower brainstem and sympathoadrenal system.

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.

Impaired ascorbic acid metabolism in streptozotocin-induced diabetic rats.

Ascorbic acid (AA) metabolism in streptozotocin (STZ)-induced diabetic rats was determined by examining urinary excretion, renal reabsorption, reductive regeneration, and biosynthesis of AA at 3 and 14 days after STZ administration. AA concentrations in the plasma, liver, and kidney of the diabetic rats were significantly lower than those of controls on d 3, and decreased further as the diabetic state continued. Hepatic AA regeneration significantly decreased in the diabetic rats on d 3 in spite of increased gene expressions of AA regenerating enzymes and was further reduced on d 14. Hepatic activity of L-gulono-gamma-lactone oxidase, a terminal enzyme of hepatic AA biosynthesis, also decreased significantly on d 3 and decreased further on d 14. Urinary excretion of AA was significantly increased on d 3, with an increase in urine volume but no change in gene expressions of renal AA transporters (SVCT1 and SVCT2). Urinary excretion of AA was normalized on d 14. The results suggest that impaired hepatic and renal regeneration, as well as increased urinary excretion and impaired hepatic biosynthesis of AA, contributed to the decrease in AA in plasma and tissues of STZ-induced diabetic rats.

Effects of a high-sucrose diet on body weight, plasma triglycerides, and stress tolerance.

We examine the effects of feeding a high-sucrose diet on body weight gain, plasma triglycerides, and stress tolerance in rats. Feeding a high-sucrose (60%) diet for 2 weeks did not induce a greater body weight gain compared with that of standard diet when caloric intake was similar in ventromedial hypothalamic-lesioned obese and sham-operated lean animals. The high-sucrose diet elevated plasma triglycerides by increasing the triglyceride secretion rate and decreasing the fractional catabolic rate in both groups. In response to stress, feeding a high-sucrose diet for one week induced enhanced gene expressions of heat shock proteins (HSP 70 and 27) and suppressed NOx production in the brain, whereas the standard diet did not. Results suggest that feeding a high-sucrose diet does not induce obesity in lean rats or enhance weight gain in obese rats, if caloric intake is appropriate. The diet does elevate plasma triglyerides in lean and obese rats, but it may have the potential to improve stress tolerance.

Distinct role of adiposity and insulin resistance in glucose intolerance: studies in ventromedial hypothalamic-lesioned obese rats.

It remains unclear whether adiposity plays an important role in glucose intolerance independently of insulin resistance. We investigated whether adiposity and insulin resistance had distinct roles in glucose intolerance in rats. We examined glucose tolerance and insulin resistance using ventromedial hypothalamic (VMH)-lesioned rats in the dynamic and the static phases of obesity (2 and 14 weeks after lesioning, respectively). Rats were fed either normal chow or a fructose-enriched diet (60% of total calories). The intravenous glucose tolerance test (IVGTT) was performed by bolus injection of glucose solution (1 g/kg) and blood sampling after 0, 5 10, 30, and 60 minutes. Insulin resistance was evaluated from the steady-state plasma glucose (SSPG) value during continuous infusion of glucose, insulin, and somatostatin. SSPG was not increased in VMH-lesioned rats in the dynamic phase of obesity, but increased markedly in the static phase. The area under the glucose curve (glucose AUC) during IVGTT was increased in VMH-lesioned rats in the static phase, but not in the dynamic phase, when compared with their sham-operated counterparts. A fructose-enriched diet for 2 or 14 weeks increased SSPG values to a similar extent in both sham-operated and VMH-lesioned rats without inducing excess adiposity, but glucose intolerance was only developed in the obese rats. The plasma leptin level, an excellent indicator of adiposity, was significantly related to the glucose AUC independently of the insulin level. Insulin resistance or increased adiposity alone is not sufficient to impair glucose tolerance, but increased adiposity plays an important role in the development of glucose intolerance in an insulin-resistant state.

Orexin-A-sensitive site for energy expenditure localized in the arcuate nucleus of the hypothalamus.

Orexin-A is a unique hypothalamic neuropeptide that stimulates both food intake and energy expenditure, although orexigenic peptides usually have coordinated effects on fat storage by increasing food intake and decreasing energy expenditure. Here we investigated the site of action of orexin-A-induced thermogenesis in urethane-anesthetized rats. Microinjection of 1-10 pmol orexin-A into the arcuate nucleus (Arc) specifically increased whole-body O(2) consumption (VO(2)), an index of energy expenditure; whereas it had no effect on VO(2) when injected into the paraventricular nucleus (PVN), dorsomedial nucleus (DMH), lateral hypothalamus (LH), ventromedial nucleus (VMH) or medial preoptic nucleus (MPO) of the hypothalamus or into in the paraventricular thalamic nucleus (PVT) or pontine locus coeruleus (LC). VO(2) increased immediately after an orexin-A injection into the Arc, and this increase was accompanied by a simultaneous tachycardiac response and a gradual increase in colonic temperature (T(co)), whereas an injection of the saline vehicle into the Arc had no effect. The effective dose of orexin-A into the Arc was 10 times less than that into the cerebral ventricle to induce a similar level of response. In addition, intracerebroventricular administration of orexin-A (100 pmol) elicited a significantly smaller VO(2) response in Arc-lesioned rats than that in sham-operated control rats. These results suggest that the orexin-induced energy expenditure is mediated, at least in part, by the Arc.

Fasting increases gene expressions of uncoupling proteins and peroxisome proliferator-activated receptor-gamma in brown adipose tissue of ventromedial hypothalamus-lesioned rats.

Uncoupling proteins (UCPs) are supposed to be involved in diet-induced thermogenesis. Their activities are usually elevated by feeding and reduced by fasting in normal animals. To investigate whether fasting affects the expression of UCPs mRNA in brown adipose tissue (BAT) of bilateral ventromedial hypothalamus (VMH)-lesioned rats, we determined the gene expression of UCP1, UCP2 or UCP3 in BAT of VMH-lesioned rats and examined oxygen consumption in these rats under fed or 48-h fasted conditions. Northern blotting revealed no difference in the expression of UCPs mRNA in BAT between VMH-lesioned and sham-operated rats under the fed condition, however, expressions were increased markedly in BAT of VMH-lesioned rats under the fasted condition. Under the fed condition, no difference in oxygen consumption was observed between VMH-lesioned and sham-operated rats. Under the fasted condition, oxygen consumption decreased in both rats, however, it decreased in VMH-lesioned less than in sham operated rats. To explore the mechanism that fasting elevated BAT UCPs mRNA in VMH-lesioned rats, we measured peroxisome proliferator-activated receptor (PPAR)-gamma mRNA and protein in BAT, because PPAR-gamma agonist can elevate UCPs mRNA levels in BAT. Under the fed condition, no differences in the expression of PPAR-gamma mRNA and protein content were observed between in BAT of VMH-lesioned and sham-operated rats. Under the fasted condition, however, both increased in BAT of VMH-lesioned rats. These results suggest that VMH-lesions enhance the gene expression of UCPs in BAT under long-term fasting as a defensive reaction to inhibit the reduction of body temperature through an increase in PPAR-gamma activity.

Vagal hyperactivity due to ventromedial hypothalamic lesions increases adiponectin production and release.

In obese humans and animals, adiponectin production and release in adipose tissue are downregulated by feedback inhibition, resulting in decreased serum adiponectin. We investigated adiponectin production and release in ventromedial hypothalamic (VMH)-lesioned animals. VMH-lesioned mice showed significant increases in food intake and body weight gain, with hyperinsulinemia and hyperleptinemia at 1 and 4 weeks after VMH-lesioning. Serum adiponectin was elevated in VMH-lesioned mice at 1 and 4 weeks, despite adipocyte hypertrophy in subcutaneous and visceral adipose tissues and increased body fat. Adiponectin production and mRNA were also increased in both adipose tissues in VMH-lesioned mice at 1 week. These results were replicated in VMH-lesioned rats at 1 week. Daily atropine administration for 5 days or subdiaphragmatic vagotomy completely reversed the body weight gain and eliminated the increased adiponectin production and release in these rats, with reversal to a normal serum adiponectin level. Parasympathetic nerve activation by carbachol infusion for 5 days in rats increased serum adiponectin, with increased adiponectin production in visceral and subcutaneous adipose tissues without changes of body weight. These results demonstrate that activation of the parasympathetic nerve by VMH lesions stimulates production of adiponectin in visceral and subcutaneous adipose tissues and adiponectin release, resulting in elevated serum adiponectin.

Galanin-like peptide (GALP) facilitates thermogenesis via synthesis of prostaglandin E2 by astrocytes in the periventricular zone of the third ventricle.

Administration of galanin-like peptide (GALP) leads to a decrease in both total food intake and body weight 24 h after injection, compared to controls. Moreover, GALP induces an increase in core body temperature. To elucidate the mechanism by which GALP exerts its effect on energy homeostasis, urethane-anesthetized rats were intracerebroventricularly injected with GALP or saline, after which oxygen consumption, heart rate, and body temperature were monitored for 4 h. In some cases, animals were also pretreated with the cyclooxygenase (COX) inhibitor, diclofenac, via intracerebroventricular (i.c.v.) or intravenous (i.v.) injection. c-Fos expression in the brain was also examined after injection of GALP, and the levels of COX and prostaglandin E(2) synthetase (PGES) mRNA in primary cultured astrocytes treated with GALP were analyzed by using qPCR. The i.c.v. injection of GALP caused biphasic thermogenesis, an effect which could be blocked by pretreatment with centrally (i.c.v.), but not peripherally (i.v.) administered diclofenac. c-Fos immunoreactivity was observed in astrocytes in the periventricular zone of the third ventricle. GALP treatment also increased COX-2 and cytosolic PGES, but not COX-1, microsomal PGES-1, or microsomal PGES-2 mRNA levels in cultured astrocytes. We, therefore, suggest that GALP elicits thermogenesis via a prostaglandin E(2)-mediated pathway in astrocytes of the central nervous system.

Masked function of amino acid sensors on pancreatic hormone secretion in ventromedial hypothalamic (VMH) lesioned rats with marked hyperinsulinemia.

SUMMARY: In neural regulation of the endocrine pancreas, there is much evidence to suggest that vagal efferents alter insulin and glucagon secretion, but less information on the effects of vagal afferents. In this study, we investigated the role and function of afferent fibers of the vagus nerve in normal and ventromedial hypothalamic (VMH) lesioned rats with marked hyperinsulinemia. In normal rats, hepatic vagotomy was associated with intraperitoneal (ip) arginine-induced enhancement of insulin and glucagon secretion without an accompanying change in blood glucose levels, ip leucine induced enhancement of insulin secretion accompanied by a decrease in blood glucose levels, and ip alanine-induced enhancement of glucagon secretion accompanied by an increase in blood glucose levels. In VMH lesioned rats with marked hyperinsulinemia, none of these amino acids caused significant changes in insulin and glucagon secretion. We conclude that amino acid sensors in normal rats inhibit excess release of pancreatic hormones induced directly by intake of amino acids, such as that in excess protein ingestion, and maintain blood glucose levels within the normal range. In contrast, in VMH lesioned rats with marked hyperinsulinemia, the function of the amino acid sensors is masked due to the marked hyperinsulinemia in these rats.:

Ventromedial hypothalamic lesions enhance small intestinal cell proliferation in mice.

BACKGROUND: We have found previously that ventromedial hypothalamic lesions (VMH) enhance cell proliferation in the visceral organs through vagal hyperactivity in rats. The goal of the current study was to determine the characteristics and nature of cell proliferation in the small intestine in VMH-lesioned mice. METHODS: The weight and length of the small intestine, thickness of the mucosal and muscle layers, number of proliferating cell nuclear antigen (PCNA)-positive cells, and mitotic cell count in the mucosal layer in VMH-lesioned and Sham VMH-lesioned mice were determined at 7 days after the operation. RESULTS: The weight and length of the small intestine in VMH-lesioned mice were significantly greater than those in Sham VMH-lesioned mice, by 11.6% and 15.0%, respectively. The thicknesses of the mucosal and muscle layers of the small intestine in VMH-lesioned mice were also significantly greater than those in Sham VMH-lesioned mice, by 12.7% and 12.5%, respectively. PCNA-positive cells and mitotic cells in the mucosal layer were densely present in crypts in VMH-lesioned mice, and were significantly increased by 31.9% and 71.7%, respectively, compared to Sham VMH-lesioned mice. CONCLUSIONS: These results demonstrate that VMH lesions in mice enhance cell proliferation in the mucosal layers and cause cell hypertrophy or cell proliferation in the muscle layers of the small intestine, which increases the weight and length of the small intestine. VMH lesions in mice may be a new tool for identifying growth factors and related genes involved in enlarging the small intestine mainly through cell proliferation.