Arcuate Nucleus Neuropeptide Y Research Articles

Knockdown of NPY Expression in the Dorsomedial Hypothalamus Promotes Development of Brown Adipocytes and Prevents Diet-Induced Obesity

Hypothalamic neuropeptide Y (NPY) has been implicated in control of energy balance, but the physiological importance of NPY in the dorsomedial hypothalamus (DMH) remains unclear. Here we report that knockdown of NPY expression in the DMH by adeno-associated virus-mediated RNAi reduced fat depots in rats fed regular chow and ameliorated high-fat diet-induced hyperphagia and obesity. DMH NPY knockdown resulted in development of brown adipocytes in inguinal white adipose tissue through the sympathetic nervous system. This knockdown increased uncoupling protein 1 expression in both inguinal fat and interscapular brown adipose tissue (BAT). Consistent with the activation of BAT, DMH NPY knockdown increased energy expenditure and enhanced the thermogenic response to a cold environment. This knockdown also increased locomotor activity, improved glucose homeostasis, and enhanced insulin sensitivity. Together, these results demonstrate critical roles of DMH NPY in body weight regulation through affecting food intake, body adiposity, thermogenesis, energy expenditure, and physical activity.

High Protein Diet Selectively Reduces Fat Mass and Improves Glucose Tolerance in Diet-Induced Obese (DIO) Rats

Background: Acute tail pinch is known to stimulate food intake (FI) in rats through opiate signaling pathways. However, the chronic effects remain to be characterized. Aim: To establish a model for acute and chronic stress-induced alterations of FI and investigate brain nuclei and neuropeptide Y (NPY)-activated pathways and changes in circulating ghrelin, adrenocorticotropic hormone (ACTH) and glucose levels. Methods: Ad libitum fed male Sprague-Dawley rats were subjected to acute (5 min) or chronic (5 min daily for 14 days) tail pinch using a clip fastened to the tail and FI was monitored. Results: Acute tail pinch strongly increased the 5-min FI compared to undisturbed rats (1.01±0.29 vs. 0.03±0.01 g/ 300g, P 0.05), whereas blood glucose was significantly elevated (131.6±5.3 vs. 108.6±3.1 mg/dl, P<0.01). Fos expression monitored 90 min after tail pinch was increased in the parvicellular paraventricular nucleus (pPVN), arcuate nucleus, locus coeruleus and the nucleus of the solitary tract. In the pPVN, 39% of the tail pinch-activated Fos-positive cells were also CRF-immunoreactive. When rats were pinched daily for 14 days, 5-min orexigenic response was the strongest during the first five days (1.6±0.0 g/300g) and reduced during the last five days (-50%, P<0.001). At the same time, 5-min fecal pellet output was increased during the last five days compared to the first five days of the experiment (+58%, P<0.05) resulting in a negative correlation of 5-min food intake and fecal pellet output (r=-0.55, P<0.05). Repeatedly pinched rats had a reduced 14-day cumulative food intake (-4%, P<0.05) and body weight gain (-22%, P<0.05) associated with lower gain of fat mass (-99%) and lean mass (-25%) compared to undisturbed controls (P<0.05). Conclusions: Acute tail pinch increases FI via neural mechanisms likely involving arcuate nucleus NPY Y1 → opioid pathways established to regulate feeding, whereas humoral signals such as ghrelin do not seem to be involved in the acute effect. The central CRF signaling system activated by acute tail pinch may predominate after chronic tail pinch which could explain the reduced FI and increased defecation responses and decreased body weight gain. Tail pinch is a suited model to study acute stress-induced eating while repeated exposure leads to decreased fat mass gain similar to other stressors.

Tail Pinch is a Model for Acute Stress-Induced Eating in Rats Through Activation of NPY Y 1 Receptors

Background: Acute tail pinch is known to stimulate food intake (FI) in rats through opiate signaling pathways. However, the chronic effects remain to be characterized. Aim: To establish a model for acute and chronic stress-induced alterations of FI and investigate brain nuclei and neuropeptide Y (NPY)-activated pathways and changes in circulating ghrelin, adrenocorticotropic hormone (ACTH) and glucose levels. Methods: Ad libitum fed male Sprague-Dawley rats were subjected to acute (5 min) or chronic (5 min daily for 14 days) tail pinch using a clip fastened to the tail and FI was monitored. Results: Acute tail pinch strongly increased the 5-min FI compared to undisturbed rats (1.01±0.29 vs. 0.03±0.01 g/ 300g, P 0.05), whereas blood glucose was significantly elevated (131.6±5.3 vs. 108.6±3.1 mg/dl, P<0.01). Fos expression monitored 90 min after tail pinch was increased in the parvicellular paraventricular nucleus (pPVN), arcuate nucleus, locus coeruleus and the nucleus of the solitary tract. In the pPVN, 39% of the tail pinch-activated Fos-positive cells were also CRF-immunoreactive. When rats were pinched daily for 14 days, 5-min orexigenic response was the strongest during the first five days (1.6±0.0 g/300g) and reduced during the last five days (-50%, P<0.001). At the same time, 5-min fecal pellet output was increased during the last five days compared to the first five days of the experiment (+58%, P<0.05) resulting in a negative correlation of 5-min food intake and fecal pellet output (r=-0.55, P<0.05). Repeatedly pinched rats had a reduced 14-day cumulative food intake (-4%, P<0.05) and body weight gain (-22%, P<0.05) associated with lower gain of fat mass (-99%) and lean mass (-25%) compared to undisturbed controls (P<0.05). Conclusions: Acute tail pinch increases FI via neural mechanisms likely involving arcuate nucleus NPY Y1 → opioid pathways established to regulate feeding, whereas humoral signals such as ghrelin do not seem to be involved in the acute effect. The central CRF signaling system activated by acute tail pinch may predominate after chronic tail pinch which could explain the reduced FI and increased defecation responses and decreased body weight gain. Tail pinch is a suited model to study acute stress-induced eating while repeated exposure leads to decreased fat mass gain similar to other stressors.

Moderate caloric restriction during gestation results in lower arcuate nucleus NPY‐ and αMSH‐neurons and impairs hypothalamic response to fed/fasting conditions in weaned rats

We aimed to characterize the developmental programming effects of moderate caloric restriction during early pregnancy on factors involved in hypothalamic control of energy balance. Twenty-five-days-old offspring Wistar rats from 20% caloric restricted dams (from 1 to 12 days of pregnancy) (CR) and from control dams were studied under fed and 12 h fasting conditions. Morphometric studies on arcuate nucleus (ARC) and determinations of circulating parameters and hypothalamic levels of neuropeptide Y (NPY), proopiomelanocortin (POMC), long-form leptin receptor (ObRb), insulin receptor (InsR) and suppressor of cytokine signalling-3 (SOCS-3) mRNA were performed. CR animals did not show different body weight with respect to their controls, but presented higher food intake. They exhibited lower neuropeptide Y- and alpha-melanocyte-stimulating hormone-neurons (decreases of 18 and 13% in males, and 10 and 18% in females respectively) and lower total cells (decrease of 3% in males and 18% in females) in ARC. Under fed conditions, CR animals presented lower circulating leptin and ghrelin levels (decreases of 37 and 43% in males, and 15 and 34% in females respectively); furthermore, hypothalamic POMC, NPY (only in females), ObRb and InsR mRNA levels were reduced (39, 16 and 26% in males, and 112, 33, 61 and 56% in females), and those of SOCS-3 were increased (86% in males and 74% in females). Unlike control animals, under fasting conditions, ObRb, InsR and POMC mRNA levels did not decrease in CR females, and NPY mRNA decreased instead of increase in CR males. Moderate caloric restriction during gestation affects offspring hypothalamic structure and function, impairing its response to fed/fasting conditions, which suggests a predisposition to insulin and leptin resistance.

PI3K integrates the effects of insulin and leptin on large-conductance Ca2+-activated K+ channels in neuropeptide Y neurons of the hypothalamic arcuate nucleus

The adipocyte-derived hormone leptin and the pancreatic beta-cell-derived hormone insulin function as afferent signals to the hypothalamus in an endocrine feedback loop that regulates body adiposity. They act in hypothalamic centers to modulate the function of specific neuronal subtypes, such as neuropeptide Y (NPY) neurons, by modifying neuronal electrical activity. To investigate the intrinsic activity of these neurons and their responses to insulin and leptin, we used a combination of morphological features and immunocytochemical technique to identify the NPY neurons of hypothalamic arcuate nucleus (ARC) and record whole cell large-conductance Ca(2+)-activated potassium (BK) currents on them. We found that both of the hormones increase the peak amplitude of BK currents, shifting the steady-state activation curve to the left. The effect of both insulin and leptin can be prevented by pretreatment with inhibitors of tyrosine kinase and phosphatidylinositol 3-kinase (PI3K) but not MAPK. These data indicate that PI3K-mediated signals are the common regulators of BK channels by insulin and leptin and mediated the two hormones' identical activatory effects on ARC NPY neurons. The effect of insulin and leptin together was similar to that of insulin or leptin alone, and leptin or insulin pretreatment did not lead to insulin- or leptin-sensitizing effects, respectively. These intracellular signaling mechanisms may play key roles in regulating ARC NPY neuron activity and physiological processes such as the control of food intake and body weight, which are under the combined control of insulin and leptin.

Weight gain model in prepubertal rats: prediction and phenotyping of obesity-prone animals at normal body weight

Male Sprague-Dawley rats maintained from birth on a high-fat diet were examined to determine whether a specific measure before puberty can identify and allow one to characterize prepubertal rats at normal weight with high vs low risk for adult obesity. Measures from weaning (day 21) to around puberty (day 45) were taken of weight gain, absolute body weight and daily energy intake on a high-fat diet and related to the amount of body fat accumulated at maturity (80-100 days of age). Rats identified by a specific prepubertal measure as obesity-prone (OP) vs obesity-resistant (OR) were then characterized before and after puberty. Prepubertal weight gain from days 30 to 35 of age was the strongest and earliest positive correlate of ultimate body fat accrual in adult rats. The highest (8-10 g/day) compared to lowest (5-7 g/day) weight-gain scores identified accurately and reproducibly distinct OP and OR subgroups at day 35 that became obese or remained lean, respectively, as adults. The OP rats with rapid prepubertal weight gain and 50% greater adiposity at maturity (day 100) exhibited the expected phenotype of already-obese rats. These included elevated levels of leptin, insulin, triglycerides and glucose, increased galanin (GAL) peptide levels in the paraventricular nucleus (PVN) and reduced neuropeptide Y (NPY) levels in the arcuate nucleus (ARC). Before puberty (day 35), the OP rats with normal fat pad weights, energy intake and endocrine profile similar to OR rats exhibited these disturbances characteristic of obese rats. They had decreased capacity for fat oxidation in muscle, increased GAL expression in PVN and reduced expression of NPY and agouti-related protein in ARC. Prepubertal weight gain can identify OP rats on day 35 when they have minimal body fat but exhibit specific metabolic and neurochemical disturbances expected to promote obesity and characteristics of already-obese adult rats.

Leptin Suppresses Ghrelin-Induced Activation of Neuropeptide Y Neurons in the Arcuate Nucleus via Phosphatidylinositol 3-Kinase- and Phosphodiesterase 3-Mediated Pathway

Neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC) play a central role in stimulation of feeding. They sense and integrate peripheral and central signals, including ghrelin and leptin. However, the mechanisms of interaction of these hormones in NPY neurons are largely unknown. This study explored the interaction and underlying signaling cross talk between ghrelin and leptin in NPY neurons. Cytosolic Ca(2+) concentration ([Ca(2+)](i)) in single neurons isolated from ARC of adult rats was measured by fura-2 microfluorometry. Ghrelin increased [Ca(2+)](i) in 31% of ARC neurons. The [Ca(2+)](i) increases were inhibited by blockers of phospholipase C, adenylate cyclase, and protein kinase A. Ghrelin-induced [Ca(2+)](i) increases were suppressed by subsequent administration of leptin. Fifteen of 18 ghrelin-activated, leptin-suppressed neurons (83%) contained NPY. Leptin suppression of ghrelin responses was prevented by pretreatment with inhibitors of phosphatidylinositol 3-kinase and phosphodiesterase 3 (PDE3) but not MAPK. ATP-sensitive potassium channel inhibitors and activators did not prevent and mimic leptin suppression, respectively. Although leptin phosphorylated signal-transducer and activator of transcription 3 (STAT3) in NPY neurons, neither STAT3 inhibitor nor genetic STAT3 deletion altered leptin suppression of ghrelin responses. Furthermore, orexigenic effect of intracerebroventricular ghrelin in rats was counteracted by leptin in a PDE3-dependent manner. These findings indicate that ghrelin increases [Ca(2+)](i) via mechanisms depending on phospholipase C and adenylate cyclase-PKA pathways in ARC NPY neurons and that leptin counteracts ghrelin responses via a phosphatidylinositol 3-kinase-PDE3 pathway. This interaction may play an important role in regulating ARC NPY neuron activity and, thereby, feeding.

Striatal opioid peptide gene expression differentially tracks short-term satiety but does not vary with negative energy balance in a manner opposite to hypothalamic NPY

It has long been known that central opioid systems play an important role in certain aspects of appetite and food intake, particularly with regard to the hedonic or rewarding impact of calorically dense food, such as fat and sugar. Ventral striatal enkephalin may be a key component of this system, as infusions of mu-opiate agonists into this region strongly increase feeding, whereas infusions of opiate antagonists decrease food intake. While pharmacological analysis has consistently supported such a role, direct measurement of enkephalin gene expression in relation to differing food motivational conditions has not been examined. In this study, the effects of a restricted laboratory chow diet (resulting in negative energy balance) as well has recent consumption of chow (short-term satiety) on striatal preproenkephalin (PPE) and prodynorphin (PD) mRNA expression were measured in rats, using both Northern blot analysis and in situ hybridization methods. As a comparison, hypothalamic (arcuate nucleus) neuropeptide Y (NPY) was also measured in these conditions. PPE expression was broadly downregulated throughout the striatum in animals that had recently consumed a meal, whereas it was unaffected by negative energy balance. Expression of an additional striatal peptide gene, PD, did not follow this pattern, although diet restriction caused a decrease in accumbens core dynorphin mRNA. Conversely, as expected, arcuate nucleus NPY mRNA expression was markedly upregulated by negative energy balance, but was unchanged by recent food consumption. This double dissociation between striatal and hypothalamic peptide systems suggests a specific role for striatal PPE in relatively short-term food motivational states, but not in long-term metabolic responses to diet restriction.

Hindbrain catecholamine neurons control multiple glucoregulatory responses

Reduced brain glucose availability evokes an integrated constellation of responses that protect and restore the brain's glucose supply. These include increased food intake, adrenal medullary secretion, corticosterone secretion and suppression of estrous cycles. Our research has focused on mechanisms and neural circuitry underlying these systemic glucoregulatory responses. Using microinjection techniques, we found that localized glucoprivation of hindbrain but not hypothalamic sites, elicited key glucoregulatory responses, indicating that glucoreceptor cells controlling these responses are located in the hindbrain. Selective destruction of hindbrain catecholamine neurons using the retrogradely transported immunotoxin, anti-dopamine beta-hydroxylase conjugated to saporin (DSAP), revealed that spinally-projecting epinephrine (E) or norepinephrine (NE) neurons are required for the adrenal medullary response to glucoprivation, while E/NE neurons with hypothalamic projections are required for feeding, corticosterone and reproductive responses. We also found that E/NE neurons are required for both consummatory and appetitive phases of glucoprivic feeding, suggesting that multilevel collateral projections of these neurons coordinate various components of the behavioral response. Epinephrine or NE neurons co-expressing neuropeptide Y (NPY) may be the neuronal phenotype required for glucoprivic feeding: they increase NPY mRNA expression in response to glucoprivation and are nearly eliminated by DSAP injections that abolish glucoprivic feeding. In contrast, lesion of arcuate nucleus NPY neurons, using the toxin, NPY–saporin, does not impair glucoprivic feeding or hyperglycemic responses. Thus, hindbrain E/NE neurons orchestrate multiple concurrent glucoregulatory responses. Specific catecholamine phenotypes may mediate the individual components of the overall response. Glucoreceptive control of these neurons resides within the hindbrain.

Omega-3 fatty acids improve appetite in cancer anorexia, but tumor resecting restores it

Tumor growth leads to cancer anorexia that is ameliorated using omega-3 fatty acids (omega-3FA). We hypothesize that omega-3FA modulates up-regulation of hypothalamic orexigenic neuropeptide Y (NPY) and down-regulation of anorexigenic alpha melanocyte-stimulating hormone (alpha-MSH) and serotonin 1B receptors (5-HT(1B)-receptors) in tumor-bearing rats. Twenty-eight tumor-bearing rats were fed either chow (TB-Control) or omega-3FA (TB-omega-3FA). When anorexia developed in TB-Control rats, they and a cohort of TB-omega-pi-3 rats were killed. The rest had their tumor resected (R-Control and R-omega-3FA), and when anorexic TB-Controls normalized their food intake, brains were removed for hypothalamic immunocytochemical study of NPY, alpha-MSH, and 5-HT(1B)-receptor antibodies concentrations. Comparison among slides were assessed by image analysis and analyzed by ANOVA and t test. At anorexia, hypothalamic NPY in arcuate nucleus (ARC) increased by 38% in TB-omega3FA versus TB-Control, whereas alpha-MSH decreased 64% in ARC and 29% in paraventricular nucleus (PVN). Omega-3FA diet in anorexia (TB-omega-3FA vs R-omega-3FA) produced similar qualitative changes of NPY (22% increase) and alpha-MSH (31% decrease) in ARC, with concomitant decrease of 37% in 5-HT(1B)-receptors in PVN, confirming the influence of omega-3FA on the hypothalamic food intake modulators. However, after tumor resection (TB-Control vs R-Control) a 97% increase in NPY and a 62% decrease in alpha-MSH occurred that was significantly greater than in rats fed omega-3FA diet. Tumor resection and omega-3FA modifies hypothalamic food intake activity, up-regulating NPY and down-regulating alpha-MSH and 5-HT(1B)-receptors. Tumor resection in anorexic rats on chow diet restored hypothalamic NPY, alpha-MSH, and food intake quantitatively more than in rats fed omega3FA diet.

Progesterone-Receptive Dopaminergic and Neuropeptide Y Neurons Project from the Arcuate Nucleus to Gonadotropin-Releasing Hormone-Rich Regions of the Ovine Preoptic Area

Progesterone inhibits gonadotropin-releasing hormone (GnRH) secretion in sheep through an interneuronal system located in the mediobasal hypothalamus. This study focused on known inhibitors of GnRH secretion in sheep, dopamine and neuropeptide Y (NPY). As the distributions of tyrosine hydroxylase (TH)- and NPY-immunoreactive neurons overlap with progesterone receptors (PR) in the arcuate nucleus, we hypothesized that, if these neurons mediate, at least partially, the inhibitory feedback signal of progesterone, then they should co-express PRs. Fluorogold (FG), a retrograde tracer, was injected into the preoptic area of ovariectomized ewes pretreated with estrogen and progesterone. When the FG injection site encompassed at least 80 GnRH neurons, sections from the arcuate nucleus were processed using dual immunocytochemistry for PR and either TH or NPY. We found that 30% of PR-immunoreactive, 12% of TH-containing and 21% of NPY-synthesizing neurons project toward this GnRH-rich region. Of the PR/TH dual-labeled cells, which represent 21% of PR and 31% of TH cells, respectively, 22% displayed FG labeling. Of the PR/NPY neurons, which account for 19% of PR and 67% of NPY neurons, respectively, 26% were FG fluorescent. This study suggests that subsets of arcuate nucleus dopaminergic and NPY neurons may transduce, at least in part, the progesterone-mediated inhibition of GnRH secretion.

Gamma aminobutyric acid regulates glucosensitive neuropeptide Y neurons in arcuate nucleus via A/B receptors

Gamma aminobutyric acid (GABA) is localized in neuropeptide Y (NPY) neurons of the hypothalamic arcuate nucleus (ARC). We examined regulation of ARC NPY neurons by GABA. Light and electron microscopic immunohistochemistry confirmed that GABA-containing nerve terminals contacted NPY-containing neurons in the ARC. Lowering glucose (1 mM) increased cytosolic Ca2+ concentration ([Ca2+]i) in isolated ARC neurons that were immunoreactive to NPY. The [Ca2+]i increases were inhibited by GABA, the gamma-aminobutyric acid type A receptor (GABAA) agonist muscimol and the gamma-aminobutyric acid type B receptor (GABAB) agonist baclofen. Neither the GABAA antagonist bicuculline nor the GABAB antagonist CGP35348 counteracted the GABA inhibition when applied alone, but did so when applied together. These results indicate that GABA regulates ARC glucose-sensitive NPY neurons via GABAA and GABAB receptors, which could function to attenuate the orexigenic NPY pathway when it is not beneficial.

Differential effects of methamphetamine on expression of neuropeptide Y mRNA in hypothalamus and on serum leptin and ghrelin concentrations in ad libitum-fed and schedule-fed rats

Relatively little is known concerning the interaction of psychostimulants with hypothalamic neuropeptide systems or metabolic hormones implicated in regulation of energy balance. The present studies tested whether methamphetamine alters the expression of neuropeptide Y (NPY) and agouti-related peptide (AgRP), two important orexigenic neuropeptides, or proopiomelanocortin (POMC), the precursor for the anorexigenic peptide α-melanocyte-stimulating hormone, or the secretion of leptin, insulin and ghrelin, concomitant with inhibition of food intake. Female rats were either fed ad libitum (AL) or placed on a scheduled feeding (SF) regimen, with access to food limited to 4 h/day. Administration of (±)-methamphetamine (7.5 mg/kg, i.p.) 2 h prior to food presentation significantly inhibited food intake in SF animals, but did not affect intake in AL animals. In a separate study, AL and SF animals were killed just prior to expected food presentation, and expression of NPY, AgRP and POMC mRNAs in hypothalamus was determined using in situ hybridisation; concentrations of leptin, insulin and ghrelin in serum were determined with radioimmunoassays. In saline-treated, SF controls, NPY and AgRP mRNA expression in arcuate nucleus and serum ghrelin were significantly elevated, and serum leptin and insulin were significantly reduced. Methamphetamine reversed the up-regulation of NPY mRNA expression observed in the SF condition, without affecting AgRP mRNA or the serum concentrations of metabolic hormones. However, in AL animals, NPY mRNA expression in arcuate and dorsomedial nuclei was significantly increased by methamphetamine, which also reduced serum leptin and insulin and increased serum ghrelin concentrations. These findings suggest that the inhibition of NPY expression in SF animals may be a mechanism underlying the anorexigenic effect of methamphetamine seen in this condition. The increase in NPY expression produced by methamphetamine in AL animals may be mediated by the ability of this drug to decrease secretion of leptin and insulin and increase secretion of ghrelin.

Basomedial Hypothalamic Injections of Neuropeptide Y Conjugated to Saporin Selectively Disrupt Hypothalamic Controls of Food Intake

Neuropeptide Y (NPY) conjugated to saporin (NPY-SAP), a ribosomal inactivating toxin, is a newly developed compound designed to selectively target and lesion NPY receptor-expressing cells. We injected NPY-SAP into the basomedial hypothalamus (BMH), just dorsal to the arcuate nucleus (ARC), to investigate its neurotoxicity and to determine whether ARC NPY neurons are required for glucoprivic feeding. We found that NPY-SAP profoundly reduced NPY Y1 receptor and alpha MSH immunoreactivity, as well as NPY, Agouti gene-related protein (AGRP), and cocaine and amphetamine-related transcript mRNA expression in the BMH. NPY-SAP lesions were localized to the injection site with no evidence of retrograde transport by hindbrain NPY neurons with BMH terminals. These lesions impaired responses to intracerebroventricular (icv) leptin (5 microg/5 microl x d) and ghrelin (2 microg/5 microl), which are thought to alter feeding primarily by actions on ARC NPY/AGRP and proopiomelanocortin/cocaine and amphetamine-related transcript neurons. However, the hypothesis that NPY/AGRP neurons are required downstream mediators of glucoprivic feeding was not supported. Although NPY/AGRP neurons were destroyed by NPY-SAP, the lesion did not impair either the feeding or the hyperglycemic response to 2-deoxy-D-glucose-induced blockade of glycolysis use. Similarly, responses to glucagon-like peptide-1 (GLP-1, 5 microg/3 microl icv), NPY (5 microg/3 microl icv), cholecystokinin octapeptide (4 microg/kg ip), and beta-mercaptoacetate (68 mg/kg ip) were not altered by the NPY-SAP lesion. Thus, NPY-SAP destroyed NPY receptor-expressing neurons in the ARC and selectively disrupted controls of feeding dependent on those neurons but did not disrupt peptidergic or metabolic controls dependent upon circuitry outside the BMH.

Neurobiologic changes in the hypothalamus associated with weight loss after gastric bypass

Effects of Roux-en-Y gastric bypass (RYGB) on hypothalamic food intake regulation have not been investigated. The hypothalamic arcuate nucleus (ARC) and the magnocellular (m) and parvocellular (p) parts of the paraventricular nucleus (PVN) regulate hunger and satiety, and are under control of the orexigenic neuropeptide Y (NPY), and the anorexigenic alpha-melanocyte stimulating hormone (alpha-MSH) and serotonin (5-HT). We hypothesized that after RYGB, weight loss is associated with hypothalamic down regulation of NPY and up regulation of 5-HT and alpha-MSH. Obesity was induced in 12 Sprague Dawley rats using a high-energy diet for 7 weeks, and then the rats were divided into three groups (n = 4/group): RYGB, sham-operated pair-fed (PF), and sham-operated ad libitum (obese control). Ten days after operation, immunohistochemical quantification of NPY, alpha-MSH, and 5-HT(1B)-receptors in ARC and PVN was performed. Data were analyzed using ANOVA and Tukey's test. Body weight decreased in RYGB (417 +/- 21 g; mean +/- SE) and in PF (436 +/- 14 g) rats 10 days after operation compared with obese control rats (484 +/- 15 g; p < 0.05 for each comparison). NPY in ARC, pPVN, and mPVN decreased by 43%, 43%, and 61%, respectively in RYGB and by 55%, 42%, and 71% in PF, respectively, compared with obese controls (p < 0.05 for each pairwise comparison). RYGB versus PF did not show differences. alpha-MSH in ARC, pPVN and mPVN increased by 35%, 175%, and 67%, respectively in RYGB and by 29%, 162%, and 116% in PF, respectively, compared with obese controls (each p < 0.05). In mPVN, alpha-MSH significantly decreased by 23% in RYGB versus PF (p < 0.05). 5-HT-(1B)-receptor in pPVN increased by 58% in RYGB and by 26% in PF, compared with obese controls (p < 0.05). Compared with obese controls, 5HT-(1B)-receptor in mPVN increased by 39% in RYGB (p < 0.05) and by 9% in PF (p > 0.05). An increase of 5-HT-(1B)-receptor in pPVN and mPVN occurred in RYGB versus PF (p < 0.05). Obese rats that undergo weight loss after RYGB demonstrate changes in hypothalamic down regulation of NPY and up regulation of alpha-MSH and serotonin.

Metabolic fuels, neuropeptide Y, and estrous behavior in Syrian hamsters

Of the various environmental factors influencing reproduction, food availability plays a particularly significant role, and an insufficient supply of oxidizable metabolic fuels inhibits reproduction in female mammals. When ovariectomized, steroid-primed hamsters are food deprived for 48 h, estrous behavior is suppressed. However, the specific neuroendocrine alterations that mediate the suppression of estrous behavior are unknown. Several conditions that inhibit female sexual behavior are thought to be associated with altered neuropeptide Y (NPY) activity in the brain. Intracerebroventricular (ICV) infusion of NPY inhibits estrous behavior in ovariectomized steroid-primed rats and hamsters. Furthermore, food-deprived rats have an increase in NPY mRNA in the arcuate nucleus (ARC) of the hypothalamus. Unlike rats, studies in Syrian hamsters have failed to detect any alterations in ARC NPY mRNA following food deprivation. Here we show that ARC NPY immunoreactivity and mRNA is increased in food-deprived hamsters but not in hamsters given other metabolic challenges that inhibit estrous behavior. These findings support the hypothesis that NPY contribute to, but not be critical for, the nutritional inhibition of sexual receptivity.

Chronic exercise lowers the defended body weight gain and adiposity in diet-induced obese rats.

The effects of running wheel exercise and caloric restriction on the regulation of body weight, adiposity, and hypothalamic neuropeptide expression were compared in diet-induced obese male rats over 6 wk. Compared with sedentary controls, exercising rats had reduced body weight gain (24%), visceral (4 fat pads; 36%) and carcass (leptin; 35%) adiposity but not insulin levels. Hypothalamic arcuate nucleus (ARC) proopiomelanocortin (POMC) mRNA expression was 25% lower, but ARC neuropeptide Y (NPY), agouti- related peptide, dorsomedial nucleus (DMN) NPY, and paraventricular nucleus (PVN) corticotropin- releasing hormone (CRH) expression was comparable to controls. Sedentary rats calorically restricted to 85% of control body weight reduced their visceral adiposity (24%), leptin (64%), and insulin (21%) levels. ARC NPY (23%) and DMN NPY (60%) were increased, while ARC POMC (40%) and PVN CRH (14%) were decreased. Calorically restricted exercising rats an half as much as ad libitum-fed exercising rats and had less visceral obesity than comparably restricted sedentary rats. When sedentary restricted rats were refed after 4 wk, they increased intake and regained the weight gain and adiposity of sedentary controls. While refed exercising rats and sedentary rats ate comparable amounts, refed exercising rats regained weight and adiposity only to the level of ad libitum-fed exercising rats. Thus exercise lowers the defended level of weight gain and adiposity without a compensatory increase in intake and with a very different profile of hypothalamic neuropeptide expression from calorically restricted rats. This may be due to exercise-related factors other than plasma insulin and leptin.

Reduced hypothalamic neuropeptide Y expression in growth hormone- and prolactin-deficient Ames and Snell dwarf mice.

Neuropeptide Y (NPY)-producing neurons in the hypothalamic arcuate nucleus (ARC) have been implicated in GH feedback in several studies in rats. Ames (df/df) and Snell (dw/dw) dwarf mice carry mutations in transcription factors Prop-1 and Pit-1, respectively, that abrogate detectable expression of GH, prolactin, and TSH. The present study was undertaken to determine whether and to what extent hypothalamic NPY neurons are affected by the lifelong absence of pituitary hormone feedback in hypopituitary Ames and Snell dwarf mice. Total ARC NPY mRNA levels were quantified using in situ hybridization, and numbers of ARC NPY-producing cells were quantified using immunocytochemistry. For in situ hybridization, dwarf and normal coronal brain sections were hybridized with 35S-labeled riboprobe complementary to rat NPY cDNA, and then analyzed for total signal intensity from the entire ARC for each animal as well as for mRNA per neuron. NPY-containing perikarya in ARC were counted in sections of colchicine-treated (intracerebroventricular) dwarf and normal mice. Total ARC NPY mRNA was reduced in df/df mice to 33.6% (P < 0.01) of that in normal littermates, and reduced in dw/dw mice to 46.3% (P < 0.05) of normals, but there was no difference in expression per neuron as determined by reduced silver-grain counting. The decrement in dwarf mice of total ARC NPY mRNA without reduction in mRNA per cell suggested a reduction in NPY-containing neuron number, which was the case as shown by immunocytochemistry. NPY neuronal number in adult Ames dwarf mice (1048 +/- 104) was significantly (P < 0.01) reduced to 68% of that in DF/df littermates (1536 +/- 73), and significantly (P < 0.05) reduced in Snell dwarf mice to 63% of normals (1138 +/- 137 vs. 1726 +/- 205). This study represents the first enumeration of NPY-producing neurons in mouse hypothalamus and the first demonstration of lower NPY neuron number in a hypopituitary model. The reduction in total NPY mRNA was greater than that reported in studies of GH-deficient rats, suggesting that NPY expression may be affected by the lifelong absence of prolactin or TSH or both, as well as GH.

Directional cues for arcuate NPY projections are present in the adult brain

Arcuate nucleus neuropeptide Y (NPY) neurons project within the hypothalamus and to several extrahypothalamic brain areas. Plasticity in the formation of arcuate NPY projections established postnatally may underlie the phenotypic characteristics of food intake and body weight. In this work we determined if directional cues for axonal outgrowth of NPY arcuate neurons exist in the adult brain. For this purpose, an embryonic (E15) arcuate nucleus of WT mice was grafted into the third ventricle of 2-week- and 2-month-old NPY knockout (KO) mice. One month after the transplantation, the distribution of NPY-positive terminals in the brains of NPY-KO mice was studied using immunohistochemistry. NPY-positive terminals were found inside of the grafted tissue as well as in the host hypothalamus, including the arcuate nucleus, the paraventricular and periventricular nuclei, the lateral hypothalamic and preoptic areas, and in extrahypothalamic areas such as the amygdala and the thalamic paraventricular nucleus. This pattern of distribution of NPY fibers was found in both groups of grafted mice. The brain areas reinnervated by NPY-positive terminals in the NPY-KO mice closely corresponded to the normal targets for the arcuate NPY neurons as revealed by the distribution of agouti gene-related protein immunoreactivity. Our data show that directional cues for NPY arcuate nucleus projections are present in the adult brain, suggesting their involvement in the formation of normal arcuate NPY connections and a possibility for their functional reconstruction.

Sibutramine alters the central mechanisms regulating the defended body weight in diet-induced obese rats.

Chronic administration of sibutramine lowers body weight, presumably by altering brain monoamine metabolism. Here the effect of sibutramine on sympathoadrenal function (24-h urine norepinephrine and epinephrine levels) and arcuate nucleus (ARC) neuropeptide Y (NPY) and proopiomelanocortin (POMC) expression was assessed in diet-induced obese rats fed a low-fat diet. Chronic (10 wk) sibutramine [5 mg. kg(-1). day(-1) ip; rats fed ad libitum and injected with sibutramine (AS)] lowered body weight by 15% but only transiently (3-4 wk) reduced intake compared with vehicle-treated controls [rats fed chow ad libitum and injected with vehicle daily (AV)]. Other rats food restricted (RS) to 90% of the weight of AS rats and then given sibutramine restored their body weights to the level of AS rats when allowed libitum food intake. After reequilibration, RS rats were again energy restricted to reduce their weight to 90% of AS rats, and additional vehicle-treated rats (RV) were restricted to keep their body weights at the level of AS rats for 3 wk more. Terminally, total adipose depot weights and leptin levels paralleled body weights (AV > AS = RV > RS), although AS rats had heavier abdominal and lighter peripheral depots than RV rats of comparable body weights. Sibutramine treatment increased sympathetic activity, attenuated the increased ARC NPY, and decreased POMC mRNA levels induced by energy restriction in RV rats. Thus sibutramine lowered the defended body weight in association with compensatory changes in those central pathways involved in energy homeostasis.