Hypothalamic Inhibition of Acetyl-CoA Carboxylase Stimulates Hepatic Counter-Regulatory Response Independent of AMPK Activation in Rats

Background

Hypothalamic AMPK acts as a cell energy sensor and can modulate food intake, glucose homeostasis, and fatty acid biosynthesis. Intrahypothalamic fatty acid injection is known to suppress liver glucose production, mainly by activation of hypothalamic ATP-sensitive potassium (K(ATP)) channels. Since all models employed seem to involve malonyl-CoA biosynthesis, we hypothesized that acetyl-CoA carboxylase can modulate the counter-regulatory response independent of nutrient availability.

Methodology/Principal Findings

In this study employing immunoblot, real-time PCR, ELISA, and biochemical measurements, we showed that reduction of the hypothalamic expression of acetyl-CoA carboxylase by antisense oligonucleotide after intraventricular injection increased food intake and NPY mRNA, and diminished the expression of CART, CRH, and TRH mRNA. Additionally, as in fasted rats, in antisense oligonucleotide-treated rats, serum glucagon and ketone bodies increased, while the levels of serum insulin and hepatic glycogen diminished. The reduction of hypothalamic acetyl-CoA carboxylase also increased PEPCK expression, AMPK phosphorylation, and glucose production in the liver. Interestingly, these effects were observed without modification of hypothalamic AMPK phosphorylation.

Conclusion/Significance

Hypothalamic ACC inhibition can activate hepatic counter-regulatory response independent of hypothalamic AMPK activation.     

Triiodothyronine (T3) stimulates food intake via enhanced hypothalamic AMP-activated kinase activity

Thyroid hormone regulates food intake. We previously reported that rats with triiodothyronine (T3)-induced thyrotoxicosis display hyperphagia associated with suppressed circulating leptin levels, increased hypothalamic neuropeptide Y (NPY) mRNA and decreased hypothalamic pro-opiomelanocortin (POMC) mRNA. AMP-activated kinase (AMPK) is a serine/threonine protein kinase that is activated when cellular energy is depleted. We hypothesized that T3 causes an increase in hypothalamic AMPK activity, which in turn contributes to the development of T3-induced hyperphagia. Rats that were given s.c. injections of T3 (4.5 nmol/kg) had increased food intake 2 h later without alterations in NPY and POMC mRNA levels, but with increased hypothalamic phosphorylated AMPK (169%) and phosphorylated acetyl-CoA carboxylase (194%). To determine the more chronic effects of T3, rats were given 6 daily s.c. injection of T3 or the vehicle. Food intake was significantly increased. Multiple T3 injections increased hypothalamic phosphorylated AMPK (278%) and phosphorylated acetyl-CoA carboxylase (335%) compared to the controls. Intracerebroventricular administration of compound C, an AMPK inhibitor, blocked the food intake induced by a single or multiple injections of T3. Taken together, these results suggest that enhanced hypothalamic AMPK phosphorylation contributes to T3-induced hyperphagia. Hypothalamic AMPK plays an important role in the regulation of food intake and body weight.     

Citrate diminishes hypothalamic acetyl-CoA carboxylase phosphorylation and modulates satiety signals and hepatic mechanisms involved in glucose homeostasis in rats

The hypothalamic AMP-activated protein kinase (AMPK)/acetyl-CoA carboxylase (ACC) pathway is known to play an important role in the control of food intake and energy expenditure. Here, we hypothesize that citrate, an intermediate metabolite, activates hypothalamic ACC and is involved in the control of energy mobilization. Initially, we showed that ICV citrate injection decreased food intake and diminished weight gain significantly when compared to control and pair-fed group results. In addition, we showed that intracerebroventricular (ICV) injection of citrate diminished (80% of control) the phosphorylation of ACC, an important AMPK substrate. Furthermore, citrate treatment inhibited (75% of control) hypothalamic AMPK phosphorylation during fasting. In addition to its central effect, ICV citrate injection led to low blood glucose levels during glucose tolerance test (GTT) and high glucose uptake during hyperglycemic-euglycemic clamp. Accordingly, liver glycogen content was higher in animals given citrate (ICV) than in the control group (23.3+/-2.5 vs. 2.7+/-0.5 microg mL(-1) mg(-1), respectively). Interestingly, liver AMPK phosphorylation was reduced (80%) by the citrate treatment. The pharmacological blockade of beta3-adrenergic receptor (SR 59230A) blocked the effect of ICV citrate and citrate plus insulin on liver AMPK phosphorylation. Consistently with these results, rats treated with citrate (ICV) presented improved insulin signal transduction in liver, skeletal muscle, and epididymal fat pad. Similar results were obtained by hypothalamic administration of ARA-A, a competitive inhibitor of AMPK. Our results suggest that the citrate produced by mitochondria may modulate ACC phosphorylation in the hypothalamus, controlling food intake and coordinating a multiorgan network that controls glucose homeostasis and energy uptake through the adrenergic system.     

Central Exercise Action Increases the AMPK and mTOR Response to Leptin

AMP-activated protein kinase (AMPK) and mammalian Target of Rapamycin (mTOR) are key regulators of cellular energy balance and of the effects of leptin on food intake. Acute exercise is associated with increased sensitivity to the effects of leptin on food intake in an IL-6-dependent manner. To determine whether exercise ameliorates the AMPK and mTOR response to leptin in the hypothalamus in an IL-6-dependent manner, rats performed two 3-h exercise bouts, separated by one 45-min rest period. Intracerebroventricular IL-6 infusion reduced food intake and pretreatment with AMPK activators and mTOR inhibitor prevented IL-6-induced anorexia. Activators of AMPK and fasting increased food intake in control rats to a greater extent than that observed in exercised ones, whereas inhibitor of AMPK had the opposite effect. Furthermore, the reduction of AMPK and ACC phosphorylation and increase in phosphorylation of proteins involved in mTOR signal transduction, observed in the hypothalamus after leptin infusion, were more pronounced in both lean and diet-induced obesity rats after acute exercise. Treatment with leptin reduced food intake in exercised rats that were pretreated with vehicle, although no increase in responsiveness to leptin-induced anorexia after pretreatment with anti-IL6 antibody, AICAR or Rapamycin was detected. Thus, the effects of leptin on the AMPK/mTOR pathway, potentiated by acute exercise, may contribute to appetite suppressive actions in the hypothalamus.     

Olanzapine-induced hyperphagia and weight gain associate with orexigenic hypothalamic neuropeptide signaling without concomitant AMPK phosphorylation

The success of antipsychotic drug treatment in patients with schizophrenia is limited by the propensity of these drugs to induce hyperphagia, weight gain and other metabolic disturbances, particularly evident for olanzapine and clozapine. However, the molecular mechanisms involved in antipsychotic-induced hyperphagia remain unclear. Here, we investigate the effect of olanzapine administration on the regulation of hypothalamic mechanisms controlling food intake, namely neuropeptide expression and AMP-activated protein kinase (AMPK) phosphorylation in rats. Our results show that subchronic exposure to olanzapine upregulates neuropeptide Y (NPY) and agouti related protein (AgRP) and downregulates proopiomelanocortin (POMC) in the arcuate nucleus of the hypothalamus (ARC). This effect was evident both in rats fed ad libitum and in pair-fed rats. Of note, despite weight gain and increased expression of orexigenic neuropeptides, subchronic administration of olanzapine decreased AMPK phosphorylation levels. This reduction in AMPK was not observed after acute administration of either olanzapine or clozapine. Overall, our data suggest that olanzapine-induced hyperphagia is mediated through appropriate changes in hypothalamic neuropeptides, and that this effect does not require concomitant AMPK activation. Our data shed new light on the hypothalamic mechanism underlying antipsychotic-induced hyperphagia and weight gain, and provide the basis for alternative targets to control energy balance.     

Role of the AMP-activated protein kinase (AMPK) signaling pathway in the orexigenic effects of endogenous ghrelin

Ghrelin, released from the stomach, stimulates food intake through activation of the ghrelin receptor (GHS-R) located on neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons in the hypothalamus. A role for the energy sensor AMP-activated protein kinase (AMPK) and its downstream effector uncoupling protein 2 (UCP2) in the stimulatory effect of exogenous ghrelin on NPY/AgRP expression and food intake has been suggested. This study aimed to investigate whether a rise in endogenous ghrelin levels is able to influence hypothalamic AMPK activity, pACC, UCP2 and NPY/AgRP expression through activation of GHS-R. An increase in endogenous ghrelin levels was established by fasting (24h) or by induction of streptozotocin(STZ)-diabetes (15 days) in GHS-R(+/+) and GHS-R(-/-) mice. GHS-R(+/+) mice showed a significant increase in AgRP and NPY mRNA expression after fasting, which was not observed in GHS-R(-/-) mice. Fasting did not affect AMPK activity nor ACC phosphorylation in both genotypes and increased UCP2 mRNA expression. The hyperghrelinemia associated with STZ-induced diabetes was accompanied by an increased NPY and AgRP expression in GHS-R(+/+) but not in GHS-R(-/-) mice. AMPK activity and UCP2 expression in GHS-R(+/+) mice after induction of diabetes were decreased to a similar extent in both genotypes. Exogenous ghrelin administration tended to decrease hypothalamic AMPK activity. In conclusion, an increase in endogenous ghrelin levels triggered by fasting or STZ-induced diabetes stimulates the expression of AgRP and NPY via interaction with the GHS-R. The changes in AMPK activity, pACC and UCP2 occur independently from GHS-R suggesting that they do not play a major role in the orexigenic effect of endogenous ghrelin.     

Peripheral ghrelin stimulates feeding behavior and positive energy balance in a sciurid hibernator

Hibernators exhibit a robust circannual cycle of body mass gain and loss primarily mediated by food intake, but the pathways controlling food intake in these animals have not been fully elucidated. Ghrelin is an orexigenic hormone that increases feeding in all mammals studied so far, but has not until recently been studied in hibernators. In other mammals, ghrelin stimulates feeding through phosphorylation and activation of AMP-activated protein kinase (AMPK). Activation of AMPK phosphorylates and deactivates acetyl Co-A carboxylase (ACC), a committed step in fatty acid synthesis. In order to determine the effects of exogenous ghrelin on food intake and metabolic factors (i.e. non-esterified fatty acids (NEFAs), and hypothalamic AMPK and ACC) in hibernators, ghrelin was peripherally injected into ground squirrels in all four seasons. Changes in food intake and body mass were recorded over a 2-6 hour period post injections, and squirrels were euthanized. Brains and blood were removed, and Western blots were performed to determine changes in phosphorylation of hypothalamic AMPK and ACC. A colorimetric assay was used to determine changes in concentration of serum NEFAs. We found that food intake, body mass, and locomotor activity significantly increased with ghrelin injections versus saline-injected controls, even in animals injected during their aphagic winter season. Injected ghrelin was correlated with increased phosphorylation of AMPK, but didn't have an effect on ACC in winter. Ghrelin-injected animals also had increased levels of serum NEFAs compared with saline controls. This study is the first to show an effect of injected ghrelin on a hibernator.     

Ghrelin raises [Ca2+]i via AMPK in hypothalamic arcuate nucleus NPY neurons

Ghrelin, an orexigenic hormone, directly activates neuropeptide (NPY) neurons in the hypothalamic arcuate nucleus (ARC), and thereby stimulates food intake. The hypothalamic level of AMP-activated protein kinase (AMPK), an intracellular energy sensor, is activated by peripheral and central administration of ghrelin. We examined whether ghrelin regulates AMPK activity in NPY neurons of the ARC. Single neurons were isolated from the ARC and cytosolic Ca²⁺ concentration ([Ca²⁺]_i) was measured by fura-2 microfluorometry, followed by immunocytochemical identification of NPY, phospho-AMPK, and phospho-acetyl-CoA carboxylase (ACC). Ghrelin and AICAR, an AMPK activator, increased [Ca²⁺]_i in neurons isolated from the ARC. The ghrelin-responsive neurons highly overlapped with AICAR-responsive neurons. The neurons that responded to both ghrelin and AICAR were primarily NPY-immunoreactive neurons. Treatment with ghrelin increased phosphorylation of AMPK and ACC. An AMPK inhibitor, compound C, suppressed ghrelin-induced [Ca²⁺]_i increases. These results demonstrate that ghrelin increases [Ca²⁺]_i via AMPK-mediated signaling in the ARC NPY neurons.     

Leptin receptor-deficient obese Zucker rats reduce their food intake in response to hypobaric hypoxia

Exposure to hypoxia induces anorexia in humans and rodents, but the role of leptin remains under discussion and that of orexigenic and anorexigenic hypothalamic neuropeptides remains unknown. The present study was designed to address this issue by using obese (Lepr(fa)/Lepr(fa)) Zucker rats, a rat model of genetic leptin receptor deficiency. Homozygous lean (Lepr(FA)/Lepr(FA)) and obese (Lepr(fa)/Lepr(fa)) rats were randomly assigned to two groups, either kept at ambient pressure or exposed to hypobaric hypoxia for 1, 2, or 4 days (barometric pressure, 505 hPa). Food intake and body weight were recorded throughout the experiment. The expression of leptin and vascular endothelial growth factor (VEGF) genes was studied in adipose tissue with real-time quantitative PCR and that of selected orexigenic and anorexigenic neuropeptides was measured in the hypothalamus. Lean and obese rats exhibited a similar hypophagia (38 and 67% of initial values at day 1, respectively, P < 0.01) and initial decrease in body weight during hypoxia exposure. Hypoxia led to increased plasma leptin levels only in obese rats. This resulted from increased leptin gene expression in adipose tissue in response to hypoxia, in association with enhanced VEGF gene expression. Increased hypothalamic neuropeptide Y levels in lean rats 2 days after hypoxia exposure contributed to accounting for the enhanced food consumption. No significant changes occurred in the expression of other hypothalamic neuropeptides involved in the control of food intake. This study demonstrates unequivocally that altitude-induced anorexia cannot be ascribed to anorectic signals triggered by enhanced leptin production or alterations of hypothalamic neuropeptides involved in anabolic or catabolic pathways.     

C75, a fatty acid synthase inhibitor, reduces food intake via hypothalamic AMP-activated protein kinase

Energy homeostasis and feeding are regulated by the central nervous system. C75, a fatty acid synthase (FAS) inhibitor, causes weight loss and anorexia, implying a novel central nervous system pathway(s) for sensing energy balance. AMP-activated protein kinase (AMPK), a sensor of peripheral energy balance, is phosphorylated and activated when energy sources are low. Here, we identify a role for hypothalamic AMPK in the regulation of feeding behavior and in mediating the anorexic effects of C75. 5-Aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), an activator of AMPK, increased food intake, whereas compound C, an inhibitor of AMPK, decreased food intake. C75 rapidly reduced the level of the phosphorylated AMPK alpha subunit (pAMPKalpha) in the hypothalamus, even in fasted mice that had elevated hypothalamic pAMPKalpha levels. Furthermore, AICAR reversed both the C75-induced anorexia and the decrease in hypothalamic pAMPKalpha levels. C75 elevated hypothalamic neuronal ATP levels, which may contribute to the mechanism by which C75 decreased AMPK activity. C75 reduced the levels of pAMPKalpha and phosphorylated cAMP response element-binding protein (pCREB) in the arcuate nucleus neurons of the hypothalamus, suggesting a mechanism for the reduction in NPY expression seen with C75 treatment. These data indicate that modulation of FAS activity in the hypothalamus can alter energy perception via AMPK, which functions as a physiological energy sensor in the hypothalamus.     

Alteration of NPY and Y1 receptor in dorsomedial and ventromedial areas of hypothalamus in anorectic tumor-bearing rats

Although previous studies have implicated NPY in the etiology of experimental cancer anorexia, the results have been difficult to interpret. Studies have suggested that although NPY level and message were decreased in the dorsomedial hypothalamic area (DMA), they were elevated in the ventromedial hypothalamic area (VMA). To better assess specific intra-area alterations of NPY, Y(1) receptor (Y(1) R), and agouti-related peptide (AgRP) in TB rats, we used radioimmunoassay, quantitative real-time RT-PCR, and immunohistochemistry. We found that NPY and AgRP mRNA were elevated significantly in whole hypothalamus of anorectic TB rats, while Y(1) R mRNA was decreased. Based on two replicates of four pooled samples each, both NPY and AgRP mRNA appeared to be elevated in the VMA of anorectic TB rats, while only AgRP exhibited a similar increase in the DMA. Levels of NPY were elevated in the VMA of both TB and pair-fed (PF) rats, but in the DMA only PF rats exhibited a significant NPY increase. NPY and Y(1) R immunohistochemistry revealed reduced NPY staining in PVN and ARC nucleus of TB and PF rats. Y(1) R immunostaining was also reduced in the ARC and PVN of TB rats, while PF rats exhibited elevated immunostaining in the PVN. These results continue to implicate dysfunction of NPY feeding systems in experimental cancer anorexia and suggest down-regulation of Y(1) R receptors as well as possible problems in NPY translation.     

Decreased orexigenic response to neuropeptide Y in rats with obstructive cholestasis

Neuropeptide Y (NPY) is a key factor in the neurochemical control of food intake, and obstructive cholestasis can be associated with disturbances in food intake. Our aim in this study was to determine whether obstructive cholestasis in the rat is associated with defective central responsiveness to NPY. Cholestasis was induced in rats by surgical bile duct resection. Rats with obstructive cholestasis exhibited a 20% reduction in food intake 2 days after laparotomy (compared with sham-resected controls) that had resolved by 4 days after surgery. Responsiveness to the orexigenic action of NPY was tested by measuring food intake after intracerebroventricular injection of NPY. In sham-resected rats, NPY infusion strikingly increased food intake, whereas bile duct-resected (BDR) rats showed a consistent significantly impaired feeding response to NPY at postlaparotomy days 2, 4, and 7. Separate experiments measured specific binding of [(3)H]NPY to hypothalamic receptors. Fos protein expression was measured in the hypothalamic paraventricular nucleus (PVN) as a marker of NPY-induced neuronal activation. The decreased orexigenic responsiveness to NPY was not caused by altered NPY binding at hypothalamic receptors or its ability to activate neurons in the PVN. Therefore, cholestatic rats demonstrate an attenuated NPY-induced orexigenic drive that occurs early after biliary obstruction, when cholestatic rats exhibit reduced food intake, and persists despite the return of food intake to normal levels and the presence of intact central NPY-related neuronal pathways.     

Involvement of hypothalamic neuropeptide Y in regulating the amphetamine-induced appetite suppression in streptozotocin diabetic rats

BACKGROUND AND AIM: Amphetamine (AMPH) is a well-known anorectic agent. In normal rats, AMPH-induced anorexia has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. In diabetic rats, however, if this anorectic response of AMPH might still be observed was uncertain. METHODS: Rats (including normal, diabetic and insulin-treated diabetic rats) were given daily with saline or AMPH for 6 days. Changes in food intake, plasma glucose level (PGL) and NPY content of these rats were measured and compared. RESULTS: The AMPH-induced anorectic response was altered in diabetic rats. Although the anorectic effects of AMPH on the first day of dosing were similar between diabetic and control rats, diabetic rats developed tolerance to this anorexia more rapidly than control rats. This alteration was independent of PGL since PGL levels were not changed following AMPH treatment and PGL normalization induced by phlorizin could not restore the level of AMPH anorexia. On the other hand, this alteration was dependent on the action of NPY because NPY contents were decreased following AMPH treatment and the replacement of insulin in diabetic rats could restore both NPY content and AMPH anorexia. CONCLUSION: These results suggested that the elevated hypothalamic NPY content in diabetic rats was involved in modifying the anorectic response of AMPH.     

Co-administration of dopamine D1 and D2 agonists additively decreases daily food intake, body weight and hypothalamic neuropeptide Y level in rats

This study investigated whether co-administration of dopamine D1 and D2 agonists might additively inhibit the feeding effect and whether this effect was mediated by the action on hypothalamic neuropeptide Y (NPY). The D1 agonist SKF 38393 (SKF) and D2 agonists apomorphine (APO) or quinpirole (QNP) were administered, alone or in combination, to examine this possibility. In single administration, decreases of daily food intake were observed only in rats treated twice a day with a higher dose of SKF, APO or QNP. However, combined administration of D1 and D2 agonists, with each agent at a dose that alone did not induce anorexia in one daily treatment, exerted a significant effect. These results reveal that co-activation of D1 and D2 receptors can additively reduce daily food intake and body weight. The same treatment also decreased the level of hypothalamic NPY 24 h post-treatment. These results suggest an additive effect during combined activation of D1 and D2 receptor subtypes to decrease food intake and body weight that are mediated by the action of hypothalamic NPY. Similar to the effects seen in healthy rats, combined D1/D2 administration was also effective in the reduction of food intake in diabetic rats, revealing the efficiency of D1/D2 agonist in the improvement of hyperphasia in diabetic animals.     

AICAR and Compound C regulate food intake independently of AMP-activated protein kinase in lines of chickens selected for high or low body weight

AMP-activated protein kinase (AMPK) functions to maintain cellular and body energy balance. Our aim was to investigate the effect of intracerebroventricular (ICV) administration of AMPK stimulator AICAR and AMPK inhibitor Compound C on food intake in lines of chickens that had undergone long-term selection from a common founder population for high (HWS) or low (LWS) body weight. AICAR caused a quadratic dose-dependent decrease in food intake in LWS but not HWS chicks. Compound C caused a quadratic dose-dependent increase in food intake in HWS but not in LWS chicks. Key aspects of the AMPK pathway, including upstream kinases mRNA expression, AMPK subunit α mRNA expression and phosphorylation, and a downstream target acetyl CoA carboxylase (ACC) phosphorylation were not affected by either AICAR or Compound C in either line. The exception was a significant inhibitory effect of AICAR on ACC phosphorylation ratio due to increased total ACC protein content without changing phosphorylated ACC protein levels. Thus, the anorexigenic effect of AICAR in LWS chicks and orexigenic effect of Compound C in HWS chicks resulted from activation or inhibition of other kinase pathways separate from AMPK. These results suggest genetic variation in feeding response for central AICAR and Compound C in chickens, which may contribute to the different body weights between the HWS and LWS lines.     

Myosin heavy chain composition of skeletal muscles in young rats growing under hypobaric hypoxia conditions.

This study investigated the effects of voluntary wheel running on the myosin heavy chain (MHC) composition of the soleus (Sol) and plantaris muscles (Pla) in rats developing under hypobaric choronic hypoxia (CH) conditions during 4 wk in comparison with those of control rats maintained under local barometric pressure conditions (C) or rats pair-fed an equivalent quantity of food to that consumed by CH animals (PF). Compared with C animals, sedentary rats subjected to CH conditions showed a significant decrease in type I MHC in Sol (-12%, P < 0.01). Although strongly decreased under hypoxia, spontaneous running activity increased the expression of type I MHC (P < 0.01) so that no difference in the MHC profile of Sol was shown between CH active and C active rats. The MHC distribution in Sol of PF rats was not significantly different from that found in C animals. CH resulted in a significant decrease in type I (P < 0.01) and type IIA (P < 0.005) MHC, concomitant with an increase in type IIB MHC in Pla (P < 0.001), compared with C and PF animals. In contrast to results in Sol muscle, this slow-to-fast shift in the MHC profile was unaffected by spontaneous running activity. These results suggest that running exercise suppresses the hypoxia-induced slow-to-fast transition in the MHC expression in Sol muscles only. The hypoxia-induced decrease in food intake has no major influence on MHC expression in developing rats.     

Inhibitory effect of ghrelin on food intake is mediated by the corticotropin-releasing factor system in neonatal chicks

It is known that, in rats, central and peripheral ghrelin increases food intake mainly through activation of neuropeptide Y (NPY) neurons. In contrast, intracerebroventricular (ICV) injection of ghrelin inhibits food intake in neonatal chicks. We examined the mechanism governing this inhibitory effect in chicks. The ICV injection of ghrelin or corticotropin-releasing factor (CRF), which also inhibits feeding and causes hyperactivity in chicks. Thus, we examined the interaction of ghrelin with CRF and the hypothalamo-pituitary-adrenal (HPA) axis. The ICV injection of ghrelin increased plasma corticosterone levels in a dose-dependent or a time-dependent manner. Co-injection of a CRF receptor antagonist, astressin, attenuated ghrelin-induced plasma corticosterone increase and anorexia. In addition, we also investigated the effect of ghrelin on NPY-induced food intake and on expression of hypothalamic NPY mRNA. Co-injection of ghrelin with NPY inhibited NPY-induced increase in food intake, and the ICV injection of ghrelin did not change NPY mRNA expression. These results indicate that central ghrelin does not interact with NPY as seen in rodents, but instead inhibits food intake by interacting with the endogenous CRF and its receptor.     

Role of hypothalamic neuropeptide Y (NPY) in the change of feeding behavior induced by repeated treatment of amphetamine

Neuropeptide Y (NPY), an orexigenic peptide, is involved in the control of food intake. Repeated administration of amphetamine (AMPH), an anorectic agent, results in an anorectic effect on day 1 and a tolerant anorectic effect on the followings. In an attempt to know the role of hypothalamic NPY in these effects of AMPH, contents of hypothalamic NPY were determined by radioimmunoassay at first. In AMPH-treated groups, the contents of hypothalamic NPY decreased rapidly on day 1 but restored gradually to the normal level on the following days as observed in repeated AMPH. An involvement of hypothalamic NPY in the feeding change of repeated AMPH can thus be considered. Moreover, daily injection of NPY antisense oligonucleotide into brain (10 microg/10 microl/day, i.c.v.) to inhibit the gene expression of hypothalamic NPY were performed at 1 hour before daily 2 mg/kg AMPH. The reversion of food intake from the anorectic level to the normal level (tolerant anorexia) was abolished by this antisense pretreatment. It is suggested that hypothalamic NPY may play a role in the change of feeding behavior induced by repeated AMPH administration.     

Bilateral neural transections at the level of mesencephalon increase food intake and reduce latency to onset of feeding in response to neuropeptide Y

Administration of neuropeptide Y (NPY) into the IIIrd ventricle of the rat brain induces robust ingestive behavior with a latency to onset of feeding (LOF) ranging from 12 to 20 min. Since substantial amounts of NPY found in hypothalamic sites that mediate the control of feeding behavior originate from the brain stem, we studied the effects of NPY on LOF and food intake in male and female rats after bilateral severing of brain stem NPY input to the hypothalamus at the level of the mesencephalon. NPY in doses of 117 pmol significantly increased food intake and decreased LOF in both male and female transected rats. Higher doses of 470 pmol NPY decreased only the LOF in transected rats as compared to sham control rats. Additionally, 117 pmol NPY in transected rats elicited food consumption equivalent to that produced by 470 pmol NPY in control rats. These studies show that decreases in NPY levels found in the paraventricular nucleus and neighboring hypothalamic sites as a result of these neural transections may render rats hyperresponsive to NPY, presumably due to denervation-induced hypersensitivity in these sites.