Dopamine in the nucleus accumbens shell controls systemic glucose metabolism via the lateral hypothalamus and hepatic vagal innervation in rodents

BACKGROUND

Growing evidence demonstrates the role of the striatal dopamine system in the regulation of glucose metabolism. Treatment with dopamine antagonists is associated with insulin resistance and hyperglycemia, while dopamine agonists are used in treatment of type 2 diabetes. The mechanism underlying striatal dopamine effects in glucose metabolism, however is not fully understood. Here, we provide mechanistic insights into the role of nucleus accumbens shell (sNAc) dopaminergic signaling in systemic glucose metabolism.

METHODS

Endogenous glucose production (EGP), blood glucose and mRNA expression in the lateral hypothalamic area (LHA) in male Wistar rats were measured following infusion of vanoxerine (VNX, dopamine reuptake inhibitor) in the sNAc. Thereafter, we analyzed projections from sNAc Drd1-expressing neurons to LHA using D1-Cre male Long-Evans rats, Cre-dependent viral tracers and fluorescence immunohistochemistry. Brain slice electrophysiology in adult mice was used to study spontaneous excitatory postsynaptic currents of sNAc Drd1-expressing neurons following VNX application. Finally, we assessed whether GABAergic LHA activity and hepatic vagal innervation were required for the effect of sNAc-VNX on glucose metabolism by combining infusion of sNAc-VNX with LHA-bicuculline, performing vagal recordings and combining infusion of sNAc-VNX with hepatic vagal denervation.

RESULTS

VNX infusion in the sNAc strongly decreased endogenous glucose production, prevented glucose increases over time, reduced Slc17A6 and Hcrt mRNA in LHA, and increased vagal activity. Furthermore, sNAc Drd1-expressing neurons increased spontaneous firing following VNX application, and viral tracing of sNAc Drd1-expressing neurons revealed direct projections to LHA with on average 67 % of orexin cells directly targeted by sNAc Drd1-expressing neurons. Importantly, the sNAc-VNX-induced effect on glucose metabolism was dependent on GABAergic signaling in the LHA and on intact hepatic vagal innervation.

CONCLUSIONS

We show that sNAc dopaminergic signaling modulates hepatic glucose metabolism through GABAergic inputs to glutamatergic LHA cells and hepatic vagal innervation. This demonstrates that striatal control of glucose metabolism involves a dopaminergic sNAc-LHA-liver axis and provides a potential explanation for the effects of dopamine agonists and antagonists on glucose metabolism.

Minor Changes in Daily Rhythms Induced by a Skeleton Photoperiod Are Associated with Increased Adiposity and Glucose Intolerance

Eating during the rest phase is associated with metabolic syndrome, proposed to result from a conflict between food consumption and the energy-saving state imposed by the circadian system. However, in nocturnal rodents, eating during the rest phase (day-feeding, DF) also implies food intake during light exposure. To investigate whether light exposure contributes to DF-induced metabolic impairments, animals receive food during the subjective day without light. A skeleton photoperiod (SP) is used to entrain rats to a 12:12 cycle with two short light pulses framing the subjective day. DF-induced adiposity is prevented by SP, suggesting that the conflict between light and feeding stimulates fat accumulation. However, all animals under SP conditions develop glucose intolerance regardless of their feeding schedule. Moreover, animals under SP with ad libitum or night-feeding have increased adiposity. SP animals show a delayed onset of the daily rise in body temperature and energy expenditure and shorter duration of nighttime activity, which may contribute to the metabolic disturbances. These data emphasize that metabolic homeostasis can only be achieved when all daily cycling variables are synchronized. Even small shifts in the alignment of different metabolic rhythms, such as those induced by SP, may predispose individuals to metabolic disease.

The Addiction-Susceptibility TaqIA/Ankk1 Controls Reward and Metabolism Through D2 Receptor-Expressing Neurons

BACKGROUND

A large body of evidence highlights the importance of genetic variants in the development of psychiatric and metabolic conditions. Among these, the TaqIA polymorphism is one of the most commonly studied in psychiatry. TaqIA is located in the gene that codes for the ankyrin repeat and kinase domain containing 1 kinase (Ankk1) near the dopamine D2 receptor (D2R) gene. Homozygous expression of the A1 allele correlates with a 30% to 40% reduction of striatal D2R, a typical feature of addiction, overeating, and other psychiatric pathologies. The mechanisms by which the variant influences dopamine signaling and behavior are unknown.

METHODS

Here, we used transgenic and viral-mediated strategies to reveal the role of Ankk1 in the regulation of activity and functions of the striatum.

RESULTS

We found that Ankk1 is preferentially enriched in striatal D2R-expressing neurons and that Ankk1 loss of function in the dorsal and ventral striatum leads to alteration in learning, impulsivity, and flexibility resembling endophenotypes described in A1 carriers. We also observed an unsuspected role of Ankk1 in striatal D2R-expressing neurons of the ventral striatum in the regulation of energy homeostasis and documented differential nutrient partitioning in humans with or without the A1 allele.

CONCLUSIONS

Overall, our data demonstrate that the Ankk1 gene is necessary for the integrity of striatal functions and reveal a new role for Ankk1 in the regulation of body metabolism.

Hypothalamic astrocytes control systemic glucose metabolism and energy balance

The hypothalamus is key in the control of energy balance. However, strategies targeting hypothalamic neurons have failed to provide viable options to treat most metabolic diseases. Conversely, the role of astrocytes in systemic metabolic control has remained largely unexplored. Here, we show that obesity promotes anatomically restricted remodeling of hypothalamic astrocyte activity. In the paraventricular nucleus (PVN) of the hypothalamus, chemogenetic manipulation of astrocytes results in bidirectional control of neighboring neuron activity, autonomic outflow, glucose metabolism, and energy balance. This process recruits a mechanism involving the astrocytic control of ambient glutamate levels, which becomes defective in obesity. Positive or negative chemogenetic manipulation of PVN astrocyte Ca2+ signals, respectively, worsens or improves metabolic status of diet-induced obese mice. Collectively, these findings highlight a yet unappreciated role for astrocytes in the direct control of systemic metabolism and suggest potential targets for anti-obesity strategy.

Exposure to dim light at night alters daily rhythms of glucose and lipid metabolism in rats

Nocturnal light pollution has been rapidly increasing during the last decades and even though dim artificial light at night (ALAN) has been associated with metabolic diseases, its mechanism is still far from clear. Therefore, the aim of our study was to thoroughly analyze the effects of ALAN on energy metabolism, metabolites, metabolic hormones, and gene expression. Male Wistar rats were kept in either the standard light:dark (12:12) cycle or exposed to ALAN (∼2 lx) during the whole 12-h dark phase for 2 weeks. Energy metabolism was measured in metabolic cages. In addition, we measured plasma and hepatic metabolites, clock and metabolic gene expression in the liver and epididymal adipose tissue, and plasma hormone levels. In ALAN rats, we observed an unexpected transitory daytime peak of locomotor activity and a suppression of the peak in locomotor activity at the beginning of the dark period. These changes were mirrored in the respiratory exchange ratio. Plasma metabolites became arrhythmic, and plasma and hepatic cholesterol levels were increased. Lost rhythmicity of metabolites was associated with disrupted behavioral rhythms and expression of metabolic genes. In the liver, the rhythms of metabolic sensors were either phase-advanced (Ppara, Pgc1a, Nampt) or arrhythmic (Sirt1, Lxra) after ALAN. The rhythmic pattern of Ppara and Sirt1 was abolished in the adipose tissue. In the liver, the amplitude of the daily rhythm in glycogen content was attenuated, the Glut2 rhythm was phase-advanced and Foxo1 lost its daily rhythmicity. Moreover, hepatic Foxo1 and Gck were up-regulated after ALAN. Interestingly, several parameters of lipid metabolism gained rhythmicity (adiponectin, Hmgcs2, Lpl, Srebf1c) in the liver, whereas Noct became arrhythmic in the adipose tissue. Peripheral clock genes maintained their robust oscillations with small shifts in their acrophases. Our data show that even a low level of ALAN can induce changes in the daily pattern of behavior and energy metabolism, and disturb daily rhythms of genes encoding key metabolic sensors and components of metabolic pathways in the liver and adipose tissue. Disturbed metabolic rhythms by ALAN could represent a serious risk factor for the development and progression of metabolic diseases.

Identification of an endocannabinoid gut-brain vagal mechanism controlling food reward and energy homeostasis

The regulation of food intake, a sine qua non requirement for survival, thoroughly shapes feeding and energy balance by integrating both homeostatic and hedonic values of food. Unfortunately, the widespread access to palatable food has led to the development of feeding habits that are independent from metabolic needs. Among these, binge eating (BE) is characterized by uncontrolled voracious eating. While reward deficit seems to be a major contributor of BE, the physiological and molecular underpinnings of BE establishment remain elusive. Here, we combined a physiologically relevant BE mouse model with multiscale in vivo approaches to explore the functional connection between the gut-brain axis and the reward and homeostatic brain structures. Our results show that BE elicits compensatory adaptations requiring the gut-to-brain axis which, through the vagus nerve, relies on the permissive actions of peripheral endocannabinoids (eCBs) signaling. Selective inhibition of peripheral CB1 receptors resulted in a vagus-dependent increased hypothalamic activity, modified metabolic efficiency, and dampened activity of mesolimbic dopamine circuit, altogether leading to the suppression of palatable eating. We provide compelling evidence for a yet unappreciated physiological integrative mechanism by which variations of peripheral eCBs control the activity of the vagus nerve, thereby in turn gating the additive responses of both homeostatic and hedonic brain circuits which govern homeostatic and reward-driven feeding. In conclusion, we reveal that vagus-mediated eCBs/CB1R functions represent an interesting and innovative target to modulate energy balance and counteract food-reward disorders.

Specific Silencing of Microglial Gene Expression in the Rat Brain by Nanoparticle-Based Small Interfering RNA Delivery

Microglia are the major innate immune cells in the brain and are essential for maintaining homeostasis in a neuronal microenvironment. Currently, a genetic tool to modify microglial gene expression in specific brain regions is not available. In this report, we introduce a tailor-designed method that uses lipid and polymer hybridized nanoparticles (LPNPs) for the local delivery of small interfering RNAs (siRNAs), allowing the silencing of specific microglial genes in the hypothalamus. Our physical characterization proved that this LPNP-siRNA was uniform and stable. We demonstrated that, due to their natural phagocytic behavior, microglial cells are the dominant cell type taking up these LPNPs in the hypothalamus of rats. We then tested the silencing efficiency of LPNPs carrying a cluster of differentiation molecule 11b (CD11b) or Toll-like receptor 4 (TLR4) siRNA using different in vivo and in vitro approaches. In cultured microglial cells treated with LPNP-CD11b siRNA or LPNP-TLR4 siRNA, we found a silencing efficiency at protein expression levels of 65 or 77%, respectively. In line with this finding, immunohistochemistry and western blotting results from in vivo experiments showed that LPNP-CD11b siRNA significantly inhibited microglial CD11b protein expression in the hypothalamus. Furthermore, following lipopolysaccharide (LPS) stimulation of cultured microglial cells, gene expression of the TLR4 downstream signaling component myeloid differentiation factor 88 and its associated cytokines was significantly inhibited in LPNP-TLR4 siRNA-treated microglial cells compared with cells treated with LPNP-scrambled siRNA. Finally, after LPNP-TLR4 siRNA injection into the rat hypothalamus, we observed a significant reduction in microglial activation in response to LPS compared with the control rats injected with LPNP-scrambled siRNA. Our results indicate that LPNP-siRNA is a promising tool to manipulate microglial activity locally in the brain and may serve as a prophylactic approach to prevent microglial dysfunction-associated diseases.

Disrupted Circadian Control of Hormonal Rhythms and Anticipatory Thirst by Dim Light at Night

AIMS

Our study addresses underlying mechanisms of disruption of the circadian timing system by low-intensity artificial light at night (ALAN), which is a growing global problem, associated with serious health consequences.

METHODS

Rats were exposed to low-intensity (∼2 lx) ALAN for 2 weeks. Using in situ hybridization, we assessed 24-h profiles of clock and clock-controlled genes in the suprachiasmatic nuclei (SCN) and other hypothalamic regions, which receive input from the master clock. Moreover, we measured the daily rhythms of hormones within the main neuroendocrine axes as well as the detailed daily pattern of feeding and drinking behavior in metabolic cages.

RESULTS

ALAN strongly suppressed the molecular clockwork in the SCN, as indicated by the suppressed rhythmicity in the clock (Per1, Per2, and Nr1d1) and clock output (arginine vasopressin) genes. ALAN disturbed rhythmic Per1 expression in the paraventricular and dorsomedial hypothalamic nuclei, which convey the circadian signals from the master clock to endocrine and behavioral rhythms. Disruption of hormonal output pathways was manifested by the suppressed and phase-advanced corticosterone rhythm and lost daily variations in plasma melatonin, testosterone, and vasopressin. Importantly, ALAN altered the daily profile in food and water intake and eliminated the clock-controlled surge of drinking 2 h prior to the onset of the rest period, indicating disturbed circadian control of anticipatory thirst and fluid balance during sleep.

CONCLUSION

Our findings highlight compromised time-keeping function of the central clock and multiple circadian outputs, through which ALAN disturbs the temporal organization of physiology and behavior.

Thermal lesions of the SCN do not abolish all gene expression rhythms in rat white adipose tissue, NAMPT remains rhythmic

Obesity and type 2 diabetes mellitus are major health concerns worldwide. In obese-type 2 diabetic patients, the function of the central brain clock in the hypothalamus, as well as rhythmicity in white adipose tissue (WAT), are reduced. To better understand how peripheral clocks in white adipose tissue (WAT) are synchronized, we assessed the importance of the central brain clock for daily WAT rhythms. We compared gene expression rhythms of core clock genes (Bmal1, Per2, Cry1, Cry2, RevErbα, and DBP) and metabolic genes (SREBP1c, PPARα, PPARγ, FAS, LPL, HSL, CPT1b, Glut4, leptin, adiponectin, visfatin/NAMPT, and resistin) in epididymal and subcutaneous white adipose tissue (eWAT and sWAT) of SCN-lesioned and sham-lesioned rats housed in regular L/D conditions. Despite complete behavioral and hormonal arrhythmicity, SCN lesioning only abolished Cry2 and DBP rhythmicity in WAT, whereas the other clock gene rhythms were significantly reduced, but not completely abolished. We observed no major differences in the effect of SCN lesions between the two WAT depots. In contrast to clock genes, all metabolic genes lost their daily rhythmicity in WAT, with the exception of NAMPT. Interestingly, NAMPT rhythmicity was even less affected by SCN lesioning than the core clock genes, suggesting that it is either strongly coupled to the remaining rhythmicity in clock gene expression, or very sensitive to other external rhythmic factors. The L/D cycle could be such a rhythmic external factor that generates modulating signals by photic masking via the intrinsic photosensitive retinal ganglion cells in combination with the autonomic nervous system. Our findings indicate that in normal weight rats, gene expression rhythms in WAT can be maintained independent of the central brain clock.

Role of central kisspeptin and RFRP-3 in energy metabolism in the male Wistar rat

Kisspeptin (Kp) and (Arg)(Phe) related peptide 3 (RFRP-3) are two RF-amides acting in the hypothalamus to control reproduction. In the past 10 years, it has become clear that, apart from their role in reproductive physiology, both neuropeptides are also involved in the control of food intake, as well as glucose and energy metabolism. To investigate further the neural mechanisms responsible for these metabolic actions, we assessed the effect of acute i.c.v. administration of Kp or RFRP-3 in ad lib. fed male Wistar rats on feeding behaviour, glucose and energy metabolism, circulating hormones (luteinising hormone, testosterone, insulin and corticosterone) and hypothalamic neuronal activity. Kp increased plasma testosterone levels, had an anorexigenic effect and increased lipid catabolism, as attested by a decreased respiratory exchange ratio (RER). RFRP-3 also increased plasma testosterone levels but did not modify food intake or energy metabolism. Both RF-amides increased endogenous glucose production, yet with no change in plasma glucose levels, suggesting that these peptides provoke not only a release of hepatic glucose, but also a change in glucose utilisation. Finally, plasma insulin and corticosterone levels did not change after the RF-amide treatment. The Kp effects were associated with an increased c-Fos expression in the median preoptic area and a reduction in pro-opiomelanocortin immunostaining in the arcuate nucleus. No effects on neuronal activation were found for RFRP-3. Our results provide further evidence that Kp is not only a very potent hypothalamic activator of reproduction, but also part of the hypothalamic circuit controlling energy metabolism.

Postprandial Hyperglycemia Stimulates Neuroglial Plasticity in Hypothalamic POMC Neurons after a Balanced Meal

Mechanistic studies in rodents evidenced synaptic remodeling in neuronal circuits that control food intake. However, the physiological relevance of this process is not well defined. Here, we show that the firing activity of anorexigenic POMC neurons located in the hypothalamus is increased after a standard meal. Postprandial hyperactivity of POMC neurons relies on synaptic plasticity that engages pre-synaptic mechanisms, which does not involve structural remodeling of synapses but retraction of glial coverage. These functional and morphological neuroglial changes are triggered by postprandial hyperglycemia. Chemogenetically induced glial retraction on POMC neurons is sufficient to increase POMC activity and modify meal patterns. These findings indicate that synaptic plasticity within the melanocortin system happens at the timescale of meals and likely contributes to short-term control of food intake. Interestingly, these effects are lost with a high-fat meal, suggesting that neuroglial plasticity of POMC neurons is involved in the satietogenic properties of foods.

Synergistic Effect of Feeding Time and Diet on Hepatic Steatosis and Gene Expression in Male Wistar Rats

OBJECTIVE

Eating out of phase with the endogenous biological clock alters clock and metabolic gene expression in rodents and can induce obesity and type 2 diabetes mellitus. Diet composition can also affect clock gene expression. This study assessed the combined effect of diet composition and feeding time on (1) body composition, (2) energy balance, and (3) circadian expression of hepatic clock and metabolic genes.

METHODS

Male Wistar rats were fed a chow or a free-choice high-fat, high-sugar (fcHFHS) diet, either ad libitum or with food access restricted to either the light or dark period. Body weight, adiposity, and hepatic fat accumulation as well as hepatic clock and metabolic mRNA expression were measured after 5 weeks of the diet. Energy expenditure was measured using calorimetric cages.

RESULTS

Animals with access to the fcHFHS diet only during the light period showed more hepatic fat accumulation than fcHFHS dark-fed animals despite less calories consumed. In contrast, within the chow-fed groups, light-fed animals showed the lowest hepatic fat content, but they also showed the lowest caloric intake. Locomotor activity and heat production followed feeding times, except in the fcHFHS light-fed group. Hepatic clock and metabolic gene expression rhythms also followed timing of food intake. Yet, in the fcHFHS light-fed animals, clock gene expression appeared 3 hours advanced compared with chow light-fed animals, an effect not observed in the fcHFHS dark-fed animals.

CONCLUSIONS

An fcHFHS diet consumed in the light period promotes hepatic fat accumulation and advances clock gene expression in male Wistar rats, likely because of a mismatch between energy intake and expenditure.

The Iminosugar AMP-DNM Improves Satiety and Activates Brown Adipose Tissue Through GLP1

Obesity is taking on worldwide epidemic proportions, yet effective pharmacological agents with long-term efficacy remain unavailable. Previously, we designed the iminosugar N-adamantine-methyloxypentyl-deoxynojirimycin (AMP-DNM), which potently improves glucose homeostasis by lowering excessive glycosphingolipids. Here we show that AMP-DNM promotes satiety and activates brown adipose tissue (BAT) in obese rodents. Moreover, we demonstrate that the mechanism mediating these favorable actions depends on oral, but not central, administration of AMP-DNM, which ultimately stimulates systemic glucagon-like peptide 1 (GLP1) secretion. We evidence an essential role of brain GLP1 receptors (GLP1r), as AMP-DNM fails to promote satiety and activate BAT in mice lacking the brain GLP1r as well as in mice treated intracerebroventricularly with GLP1r antagonist exendin-9. In conclusion, AMP-DNM markedly ameliorates metabolic abnormalities in obese rodents by restoring satiety and activating BAT through central GLP1r, while improving glucose homeostasis by mechanisms independent of central GLP1r.

New roles for prokineticin 2 in feeding behavior, insulin resistance and type 2 diabetes: Studies in mice and humans

Objective

Prokineticin 2 (PROK2) is a hypothalamic neuropeptide that plays a critical role in the rhythmicity of physiological functions and inhibits food intake. PROK2 is also expressed in the main olfactory bulb (MOB) as an essential factor for neuro-and morphogenesis. Since the MOB was shown to be strongly involved in eating behavior, we hypothesized that PROK2 could be a new target in the regulation of food intake and energy homeostasis, through its effects in the MOB. We also asked whether PROK2 could be associated with the pathophysiology of obesity, the metabolic syndrome (MetS), and type 2 diabetes (T2D) in humans.

Methods

We assessed in wild type mice whether the expression of Prok2 in the MOB is dependent on the nutritional status. We measured the effect of human recombinant PROK2 (rPROK2) acute injection in the MOB on food intake and olfactory behavior. Then, using a lentivirus expressing Prok2-shRNA, we studied the effects of Prok2 underexpression in the MOB on feeding behavior and glucose metabolism. Metabolic parameters and meal pattern were determined using calorimetric cages. In vivo 2-deoxyglucose uptake measurements were performed in mice after intraperitoneally insulin injection. Plasmatic PROK2 dosages and genetic associations studies were carried out respectively on 148 and more than 4000 participants from the D.E.S.I.R. (Data from an Epidemiologic Study on the Insulin Resistance Syndrome) cohort.

Results

Our findings showed that fasting in mice reduced Prok2 expression in the MOB. Acute injection of rPROK2 in the MOB significantly decreased food intake whereas Prok2-shRNA injection resulted in a higher dietary consumption characterized by increased feeding frequency and decreased meal size. Additionally, Prok2 underexpression in the MOB induced insulin resistance compared to scrambled shRNA-injected mice. In the human D.E.S.I.R. cohort, we found a significantly lower mean concentration of plasma PROK2 in people with T2D than in those with normoglycemia. Interestingly, this decrease was no longer significant when adjusted for Body Mass Index (BMI) or calorie intake, suggesting that the association between plasma PROK2 and diabetes is mediated, at least partly, by BMI and feeding behavior in humans. Moreover, common Single Nucleotide Polymorphisms (SNPs) in PROK2 gene were genotyped and associated with incident T2D or impaired fasting glycemia (IFG), MetS, and obesity.

Conclusions

Our data highlight PROK2 as a new target in the MOB that links olfaction with eating behavior and energy homeostasis. In humans, plasma PROK2 is negatively correlated with T2D, BMI, and energy intake, and PROK2 genetic variants are associated with incident hyperglycemia (T2D/IFG), the MetS and obesity.

•

Fasting alters prokineticin 2 (Prok2) expression in the main olfactory bulb (MOB).

•

Acute injection of PROK2 into the MOB diminishes food intake.

•

Partial deletion of MOB-Prok2 affects meal pattern and induces insulin resistance.

•

Type 2 diabetes (T2D) in humans is correlated with lower plasma PROK2 level.

•

Polymorphisms of PROK2 gene associate with incident T2D and the metabolic syndrome.

Effects of Light-at-Night on the Rat Liver - A Role for the Autonomic Nervous System

Exposure to light at night (LAN) has been associated with serious pathologies, including obesity, diabetes and cancer. Recently we showed that 2 h of LAN impaired glucose tolerance in rats. Several studies have suggested that the autonomic nervous system (ANS) plays an important role in communicating these acute effects of LAN to the periphery. Here, we investigated the acute effects of LAN on the liver transcriptome of male Wistar rats. Expression levels of individual genes were not markedly affected by LAN, nevertheless pathway analysis revealed clustered changes in a number of endocrine pathways. Subsequently, we used selective hepatic denervations [sympathetic (Sx), parasympathetic (Px), total (Tx, i.e., Sx plus Px), sham] to investigate the involvement of the ANS in the effects observed. Surgical removal of the sympathetic or parasympathetic hepatic branches of the ANS resulted in many, but small changes in the liver transcriptome, including a pathway involved with circadian clock regulation, but it clearly separated the four denervation groups. On the other hand, analysis of the liver metabolome was not able to separate the denervation groups, and only 6 out of 78 metabolites were significantly up- or downregulated after denervations. Finally, removal of the sympathetic and parasympathetic hepatic nerves combined with LAN exposure clearly modulated the effects of LAN on the liver transcriptome, but left most endocrine pathways unaffected.

Conclusion: One-hour light-at-night acutely affects the liver transcriptome. Part of this effect is mediated via the nervous innervation, as a hepatectomy modulated and reduced the effect of LAN on liver transcripts.

Time-Restricted Feeding Improves Glucose Tolerance in Rats, but Only When in Line With the Circadian Timing System

Epidemiological studies indicate that shift-workers have an increased risk of type 2 diabetes mellitus (T2DM). Glucose tolerance and insulin sensitivity both are dependent on the circadian timing system (i.e., the time-of-day) and fasting duration, in rodents as well as humans. Therefore, question is whether manipulation of the circadian timing system, for example by changing the timing of feeding and fasting, is a potential preventive treatment for T2DM. Time-restricted feeding (TRF) is well-known to have profound effects on various metabolic measures, including glucose metabolism. However, experiments that directly measure the effects of TRF on glucose tolerance and/or insulin sensitivity at different time points throughout the 24 h cycle are lacking. Here we show, in rats, that TRF in line with the circadian timing system (i.e., feeding during the active phase) improves glucose tolerance during intravenous glucose tolerance tests (ivGTT) in the active phase, as lower insulin levels were observed with similar levels of glucose clearance. However, this was not the case during the inactive phase in which more insulin was released but only a slightly faster glucose clearance was observed. Contrasting, TRF out of sync with the circadian timing system (i.e., feeding during the inactive phase) worsened glucose tolerance, although only marginally, likely because of adaptation to the 4 week TRF regimen. Our results show that TRF can improve glucose metabolism, but strict adherence to the time-restricted feeding period is necessary, as outside the regular eating hours glucose tolerance is worsened.

An Ultradian Feeding Schedule in Rats Affects Metabolic Gene Expression in Liver, Brown Adipose Tissue and Skeletal Muscle with Only Mild Effects on Circadian Clocks

Restricted feeding is well known to affect expression profiles of both clock and metabolic genes. However, it is unknown whether these changes in metabolic gene expression result from changes in the molecular clock or in feeding behavior. Here we eliminated the daily rhythm in feeding behavior by providing 6 meals evenly distributed over the light/dark-cycle. Animals on this 6-meals-a-day feeding schedule retained the normal day/night difference in physiological parameters including body temperature and locomotor activity. The daily rhythm in respiratory exchange ratio (RER), however, was significantly phase-shifted through increased utilization of carbohydrates during the light phase and increased lipid oxidation during the dark phase. This 6-meals-a-day feeding schedule did not have a major impact on the clock gene expression rhythms in the master clock, but did have mild effects on peripheral clocks. In contrast, genes involved in glucose and lipid metabolism showed differential expression. In conclusion, eliminating the daily rhythm in feeding behavior in rats does not affect the master clock and only mildly affects peripheral clocks, but disturbs metabolic rhythms in liver, skeletal muscle and brown adipose tissue in a tissue-dependent manner. Thereby, a clear daily rhythm in feeding behavior strongly regulates timing of peripheral metabolism, separately from circadian clocks.

The role of the daily feeding rhythm in the regulation of the day/night rhythm in triglyceride secretion in rats

Plasma triglyceride (TG) levels show a clear daily rhythm, however, thus far it is still unknown whether this rhythm results from a daily rhythm in TG production, TG uptake or both. Previous studies have shown that feeding activity affects plasma TG concentrations, but it is not clear how the daily rhythm in feeding activity affects plasma TG concentrations. In the present study, we measured plasma TG concentrations and TG secretion rates in rats at 6 Zeitgeber times to investigate whether plasma TG concentrations and TG secretion show a daily rhythm. We found that plasma TG concentrations and TG secretion show a significant day/night rhythm. Next, we removed the daily rhythm in feeding behavior by introducing a 6-meals-a-day (6M) feeding schedule to investigate whether the daily rhythm in feeding behavior is necessary to maintain the daily rhythm in TG secretion. We found that the day/night rhythm in TG secretion was abolished under 6M feeding conditions. Hepatic apolipoprotein B (ApoB) and microsomal TG transfer protein (Mttp), which are both involved in TG secretion, also lost their daily rhythmicity under 6M feeding conditions. Together, these results indicate that: (1) the daily rhythm in TG secretion contributes to the formation of a day/night rhythm in plasma TG levels and (2) a daily feeding rhythm is essential for maintaining the daily rhythm in TG secretion.

Administration of Thyrotropin-Releasing Hormone in the Hypothalamic Paraventricular Nucleus of Male Rats Mimics the Metabolic Cold Defense Response

BACKGROUND

Cold exposure increases thyrotropin-releasing hormone (TRH) expression primarily in the hypothalamic paraventricular nucleus (PVN). The PVN is a well-known hypothalamic hub in the control of energy metabolism. TRH terminals and receptors are found on PVN neurons. We hypothesized that TRH release in the PVN plays an important role in the control of thermogenesis and energy mobilization during cold exposure.

METHODS

Male Wistar rats were exposed to a cold environment (4°C) or TRH retrodialysis in the PVN for 2 h. We compared the effects of cold exposure and TRH administration in the PVN on plasma glucose, corticosterone, and thyroid hormone concentrations, body temperature, locomotor activity, as well as metabolic gene expression in the liver and brown adipose tissue.

RESULTS

Cold exposure increased body temperature, locomotor activity, and plasma corticosterone concentrations, but blood glucose concentrations were similar to that of room temperature control animals. TRH administration in the PVN also promptly increased body temperature, locomotor activity and plasma corticosterone concentrations. However, TRH administration in the PVN markedly increased blood glucose concentrations and endogenous glucose production (EGP) compared to saline controls. Selective hepatic sympathetic or parasympathetic denervation reduced the TRH-induced increase in glucose concentrations and EGP. Gene expression data indicated increased gluconeogenesis in liver and lipolysis in brown adipose tissue, both after cold exposure and TRH administration.

CONCLUSIONS

We conclude that TRH administration in the rat PVN largely mimics the metabolic and behavioral changes induced by cold exposure indicating a potential link between TRH release in the PVN and cold defense.

Time-of-Day Effects on Metabolic and Clock-Related Adjustments to Cold

BACKGROUND

Daily cyclic changes in environmental conditions are key signals for anticipatory and adaptive adjustments of most living species, including mammals. Lower ambient temperature stimulates the thermogenic activity of brown adipose tissue (BAT) and skeletal muscle. Given that the molecular components of the endogenous biological clock interact with thermal and metabolic mechanisms directly involved in the defense of body temperature, the present study evaluated the differential homeostatic responses to a cold stimulus at distinct time-windows of the light/dark-cycle.

METHODS

Male Wistar rats were subjected to a single episode of 3 h cold ambient temperature (4°C) at one of 6 time-points starting at Zeitgeber Times 3, 7, 11, 15, 19, and 23. Metabolic rate, core body temperature, locomotor activity (LA), feeding, and drinking behaviors were recorded during control and cold conditions at each time-point. Immediately after the stimulus, rats were euthanized and both the soleus and BAT were collected for real-time PCR.

RESULTS

During the light phase (i.e., inactive phase), cold exposure resulted in a slight hyperthermia (p < 0.001). Light phase cold exposure also increased metabolic rate and LA (p < 0.001). In addition, the prevalence of fat oxidative metabolism was attenuated during the inactive phase (p < 0.001). These metabolic changes were accompanied by time-of-day and tissue-specific changes in core clock gene expression, such as DBP (p < 0.0001) and REV-ERBα (p < 0.01) in the BAT and CLOCK (p < 0.05), PER2 (p < 0.05), CRY1 (p < 0.05), CRY2 (p < 0.01), and REV-ERBα (p < 0.05) in the soleus skeletal muscle. Moreover, genes involved in substrate oxidation and thermogenesis were affected in a time-of-day and tissue-specific manner by cold exposure.

CONCLUSION

The time-of-day modulation of substrate mobilization and oxidation during cold exposure provides a clear example of the circadian modulation of physiological and metabolic responses. Interestingly, after cold exposure, time-of-day mostly affected circadian clock gene expression in the soleus muscle, despite comparable changes in LA over the light-dark-cycle. The current findings add further evidence for tissue-specific actions of the internal clock in different peripheral organs such as skeletal muscle and BAT.

Complex interaction between circadian rhythm and diet on bile acid homeostasis in male rats

Desynchronization between the master clock in the brain, which is entrained by (day) light, and peripheral organ clocks, which are mainly entrained by food intake, may have negative effects on energy metabolism. Bile acid metabolism follows a clear day/night rhythm. We investigated whether in rats on a normal chow diet the daily rhythm of plasma bile acids and hepatic expression of bile acid metabolic genes is controlled by the light/dark cycle or the feeding/fasting rhythm. In addition, we investigated the effects of high caloric diets and time-restricted feeding on daily rhythms of plasma bile acids and hepatic genes involved in bile acid synthesis. In experiment 1 male Wistar rats were fed according to three different feeding paradigms: food was available ad libitum for 24 h (ad lib) or time-restricted for 10 h during the dark period (dark fed) or 10 h during the light period (light fed). To allow further metabolic phenotyping, we manipulated dietary macronutrient intake by providing rats with a chow diet, a free choice high-fat-high-sugar diet or a free choice high-fat (HF) diet. In experiment 2 rats were fed a normal chow diet, but food was either available in a 6-meals-a-day (6M) scheme or ad lib. During both experiments, we measured plasma bile acid levels and hepatic mRNA expression of genes involved in bile acid metabolism at eight different time points during 24 h. Time-restricted feeding enhanced the daily rhythm in plasma bile acid concentrations. Plasma bile acid concentrations are highest during fasting and dropped during the period of food intake with all diets. An HF-containing diet changed bile acid pool composition, but not the daily rhythmicity of plasma bile acid levels. Daily rhythms of hepatic Cyp7a1 and Cyp8b1 mRNA expression followed the hepatic molecular clock, whereas for Shp expression food intake was leading. Combining an HF diet with feeding in the light/inactive period annulled CYp7a1 and Cyp8b1 gene expression rhythms, whilst keeping that of Shp intact. In conclusion, plasma bile acids and key genes in bile acid biosynthesis are entrained by food intake as well as the hepatic molecular clock. Eating during the inactivity period induced changes in the plasma bile acid pool composition similar to those induced by HF feeding.

Differential effects of diet composition and timing of feeding behavior on rat brown adipose tissue and skeletal muscle peripheral clocks

The effects of feeding behavior and diet composition, as well as their possible interactions, on daily (clock) gene expression rhythms have mainly been studied in the liver, and to a lesser degree in white adipose tissue (WAT), but hardly in other metabolic tissues such as skeletal muscle (SM) and brown adipose tissues (BAT). We therefore subjected male Wistar rats to a regular chow or free choice high-fat-high sugar (fcHFHS) diet in combination with time restricted feeding (TRF) to either the light or dark phase. In SM, all tested clock genes lost their rhythmic expression in the chow light fed group. In the fcHFHS light fed group rhythmic expression for some, but not all, clock genes was maintained, but shifted by several hours. In BAT the daily rhythmicity of clock genes was maintained for the light fed groups, but expression patterns were shifted as compared with ad libitum and dark fed groups, whilst the fcHFHS diet made the rhythmicity of clock genes become more pronounced. Most of the metabolic genes in BAT tissue tested did not show any rhythmic expression in either the chow or fcHFHS groups. In SM Pdk4 and Ucp3 were phase-shifted, but remained rhythmically expressed in the chow light fed groups. Rhythmic expression was lost for Ucp3 whilst on the fcHFHS diet during the light phase. In summary, both feeding at the wrong time of day and diet composition disturb the peripheral clocks in SM and BAT, but to different degrees and thereby result in a further desynchronization between metabolically active tissues such as SM, BAT, WAT and liver.

•

Both timing of feeding and diet composition affect clock genes in BAT and SM.

•

Light phase time-restricted feeding abolishes SM clock gene rhythms.

•

A fcHSHS diet strengthens rhythmic expression of several clock genes in BAT and SM.

•

Metabolic genes PDK4 and UCP1/3 are affected by both timing of feeding and diet.

•

Light phase time-restricted feeding causes desynchronization of BAT and SM clocks.

Light at night acutely impairs glucose tolerance in a time-, intensity- and wavelength-dependent manner in rats

AIMS/HYPOTHESIS

Exposure to light at night (LAN) has increased dramatically in recent decades. Animal studies have shown that chronic dim LAN induced obesity and glucose intolerance. Furthermore, several studies in humans have demonstrated that chronic exposure to artificial LAN may have adverse health effects with an increased risk of metabolic disorders, including type 2 diabetes. It is well-known that acute exposure to LAN affects biological clock function, hormone secretion and the activity of the autonomic nervous system, but data on the effects of LAN on glucose homeostasis are lacking. This study aimed to investigate the acute effects of LAN on glucose metabolism.

METHODS

Male Wistar rats were subjected to i.v. glucose or insulin tolerance tests while exposed to 2 h of LAN in the early or late dark phase. In subsequent experiments, different light intensities and wavelengths were used.

RESULTS

LAN exposure early in the dark phase at ZT15 caused increased glucose responses during the first 20 min after glucose infusion (p < 0.001), whereas LAN exposure at the end of the dark phase, at ZT21, caused increased insulin responses during the first 10 min (p < 0.01), indicating that LAN immediately induces glucose intolerance in rats. Subsequent experiments demonstrated that the effect of LAN was both intensity- and wavelength-dependent. White light of 50 and 150 lx induced greater glucose responses than 5 and 20 lx, whereas all intensities other than 5 lx reduced locomotor activity. Green light induced glucose intolerance, but red and blue light did not, suggesting the involvement of a specific retina-brain pathway.

CONCLUSIONS/INTERPRETATION

Together, these data show that exposure to LAN has acute adverse effects on glucose metabolism in a time-, intensity- and wavelength-dependent manner.

Dietary sugars, not lipids, drive hypothalamic inflammation

Objective

The hypothalamus of hypercaloric diet-induced obese animals is featured by a significant increase of microglial reactivity and its associated cytokine production. However, the role of dietary components, in particular fat and carbohydrate, with respect to the hypothalamic inflammatory response and the consequent impact on hypothalamic control of energy homeostasis is yet not clear.

Methods

We dissected the different effects of high-carbohydrate high-fat (HCHF) diets and low-carbohydrate high-fat (LCHF) diets on hypothalamic inflammatory responses in neurons and non-neuronal cells and tested the hypothesis that HCHF diets induce hypothalamic inflammation via advanced glycation end-products (AGEs) using mice lacking advanced glycation end-products (AGEs) receptor (RAGE) and/or the activated leukocyte cell-adhesion molecule (ALCAM).

Results

We found that consumption of HCHF diets, but not of LCHF diets, increases microgliosis as well as the presence of N(ε)-(Carboxymethyl)-Lysine (CML), a major AGE, in POMC and NPY neurons of the arcuate nucleus. Neuron-secreted CML binds to both RAGE and ALCAM, which are expressed on endothelial cells, microglia, and pericytes. On a HCHF diet, mice lacking the RAGE and ALCAM genes displayed less microglial reactivity and less neovasculature formation in the hypothalamic ARC, and this was associated with significant improvements of metabolic disorders induced by the HCHF diet.

Conclusions

Combined overconsumption of fat and sugar, but not the overconsumption of fat per se, leads to excessive CML production in hypothalamic neurons, which, in turn, stimulates hypothalamic inflammatory responses such as microgliosis and eventually leads to neuronal dysfunction in the control of energy metabolism.

•

HCHF, but not LCHF diets, induce obesity and increase the hypothalamic inflammatory response.

•

A HCHF diet increases N-epsilon-(carboxymethyl)lysine content in hypothalamic neurons in the ARC.

•

Obesity and metabolic symptoms induced by a HCHF diet are improved in mice lacking functional RAGE and ALCAM genes.

•

Lacking RAGE and ALCAM prevents the hypothalamic inflammatory response and angiogenesis that occur on a HCHF diet.

Effects of Chronic Estrogen Administration in the Ventromedial Nucleus of the Hypothalamus (VMH) on Fat and Bone Metabolism in Ovariectomized Rats

Estrogen deficiency after ovariectomy (OVX) results in increased adiposity and bone loss, which can be prevented by systemic 17-β estradiol (E2) replacement. Studies in transgenic mice suggested that in addition to direct actions of estrogen in peripheral tissues, also estrogen signaling in the hypothalamus regulates fat distribution and bone metabolism. We hypothesized that the protective effect of systemic E2 on fat and bone metabolism in the OVX model is partly mediated through the ventromedial nucleus of the hypothalamus (VMH). To test this hypothesis, we determined the effect of systemic, central, and targeted VMH administration of E2 on fat and bone metabolism in OVX rats. Subcutaneous administration of E2 for 4 weeks decreased body weight, gonadal and perirenal fat, and bone formation rate in OVX rats. This effect was completely mimicked by intracerebroventricular injections of E2, once every 4 days for 4 weeks. Administration of E2 locally in the VMH by retromicrodialysis (3 h) acutely increased expression of the lipolytic gene hormone-sensitive lipase in gonadal and perirenal fat. Finally, chronic administration of E2 in the VMH for 8 weeks decreased perirenal fat but did not affect body weight, trabecular bone volume, or cortical thickness. In conclusion, we demonstrated that intracerebroventricular E2 replacement reduces body weight gain, ameliorates intraabdominal fat accumulation, and reduces bone formation in the OVX rats. E2 administration selectively in the VMH also reduced intraabdominal fat but did not affect bone metabolism.

Dim light at night disturbs the daily sleep-wake cycle in the rat

Exposure to light at night (LAN) is associated with insomnia in humans. Light provides the main input to the master clock in the hypothalamic suprachiasmatic nucleus (SCN) that coordinates the sleep-wake cycle. We aimed to develop a rodent model for the effects of LAN on sleep. Therefore, we exposed male Wistar rats to either a 12 h light (150–200lux):12 h dark (LD) schedule or a 12 h light (150–200 lux):12 h dim white light (5 lux) (LDim) schedule. LDim acutely decreased the amplitude of daily rhythms of REM and NREM sleep, with a further decrease over the following days. LDim diminished the rhythms of 1) the circadian 16–19 Hz frequency domain within the NREM sleep EEG, and 2) SCN clock gene expression. LDim also induced internal desynchronization in locomotor activity by introducing a free running rhythm with a period of ~25 h next to the entrained 24 h rhythm. LDim did not affect body weight or glucose tolerance. In conclusion, we introduce the first rodent model for disturbed circadian control of sleep due to LAN. We show that internal desynchronization is possible in a 24 h L:D cycle which suggests that a similar desynchronization may explain the association between LAN and human insomnia.

Sleep restriction acutely impairs glucose tolerance in rats

Chronic sleep curtailment in humans has been related to impairment of glucose metabolism. To better understand the underlying mechanisms, the purpose of the present study was to investigate the effect of acute sleep deprivation on glucose tolerance in rats. A group of rats was challenged by 4‐h sleep deprivation in the early rest period, leading to prolonged (16 h) wakefulness. Another group of rats was allowed to sleep during the first 4 h of the light period and sleep deprived in the next 4 h. During treatment, food was withdrawn to avoid a postmeal rise in plasma glucose. An intravenous glucose tolerance test (IVGTT) was performed immediately after the sleep deprivation period. Sleep deprivation at both times of the day similarly impaired glucose tolerance and reduced the early‐phase insulin responses to a glucose challenge. Basal concentrations of plasma glucose, insulin, and corticosterone remained unchanged after sleep deprivation. Throughout IVGTTs, plasma corticosterone concentrations were not different between the control and sleep‐deprived group. Together, these results demonstrate that independent of time of day and sleep pressure, short sleep deprivation during the resting phase favors glucose intolerance in rats by attenuating the first‐phase insulin response to a glucose load. In conclusion, this study highlights the acute adverse effects of only a short sleep restriction on glucose homeostasis.

Metabolic Effects of Chronic T3 Administration in the Hypothalamic Paraventricular and Ventromedial Nucleus in Male Rats

Thyroid hormone is a key regulator of energy metabolism. Apart from its direct effects on peripheral metabolism, thyroid hormone exerts acute metabolic effects via distinct nuclei within the hypothalamus. Recently we developed a method for chronic and local intrahypothalamic T₃ administration in rats. The present study evaluated the metabolic effects of T₃ delivered during either 7 or 28 days to the paraventricular or ventromedial nucleus of the hypothalamus (PVN or VMH). T₃ administration for 7 days in the PVN decreased only plasma T₃. There were no effects on body weight, food intake, plasma glucose concentrations, energy expenditure, locomotor activity, and respiratory exchange rate. In the liver and brown adipose tissue (BAT), there were no changes in mRNA expression of genes involved in glucose metabolism and thermogenesis. T₃ administration for 7 days in the VMH did not change any of these parameters. T₃ administration for 28 days in the PVN decreased food intake without affecting body weight, glucose concentrations, and body temperature. Liver and BAT gene expression was unaltered, except for decreased liver Dio1 mRNA. T₃ administration for 28 days in the VMH did not affect liver and BAT mRNA expression, body weight, food intake, and body temperature, whereas blood glucose concentrations were slightly lower. In conclusion, we showed that chronic T₃ administration to the PVN or VMH does not affect energy metabolism in a major way. Our results imply that the effects of intrahypothalamic T₃ administration on metabolism largely depend on the duration of treatment.

Feeding during the resting phase causes profound changes in physiology and desynchronization between liver and muscle rhythms of rats

Shiftworkers run an increased risk of developing metabolic disorders, presumably as a result of disturbed circadian physiology. Eating at a time-of-day that is normally dedicated to resting and fasting, may contribute to this association. The hypothalamus is the key brain area that integrates different inputs, including environmental time information from the central biological clock in the suprachiasmatic nuclei, with peripheral information on energy status to maintain energy homeostasis. The orexin system within the lateral hypothalamus is an important output of the suprachiasmatic nuclei involved in the control of sleep/wake behavior and glucose homeostasis, among other functions. In this study, we tested the hypothesis that feeding during the rest period disturbs the orexin system as a possible underlying contributor to metabolic health problems. Male Wistar rats were exposed to an 8-week protocol in which food was available ad libitum for 24-h, for 12-h during the light phase (i.e., unnatural feeding time) or for 12-h during the dark phase (i.e., restricted feeding, but at the natural time-of-day). Animals forced to eat at an unnatural time, i.e., during the light period, showed no changes in orexin and orexin-receptor gene expression in the hypothalamus, but the rhythmic expression of clock genes in the lateral hypothalamus was absent in these animals. Light fed animals did show adverse changes in whole-body physiology and internal desynchronization of muscle and liver clock and metabolic gene expression. Eating at the 'wrong' time-of-day thus causes internal desynchronization at different levels, which in the long run may disrupt body physiology.

The Suprachiasmatic Nucleus Modulates the Sensitivity of Arcuate Nucleus to Hypoglycemia in the Male Rat

The suprachiasmatic nucleus (SCN) and arcuate nucleus (ARC) have reciprocal connections; catabolic metabolic information activates the ARC and inhibits SCN neuronal activity. Little is known about the influence of the SCN on the ARC. Here, we investigated whether the SCN modulated the sensitivity of the ARC to catabolic metabolic conditions. ARC neuronal activity, as determined by c-Fos immunoreactivity, was increased after a hypoglycemic stimulus by 2-deoxyglucose (2DG). The highest ARC neuronal activity after 2DG was found at the end of the light period (zeitgeber 11, ZT11) with a lower activity in the beginning of the light period (zeitgeber 2, ZT2), suggesting the involvement of the SCN. The higher activation of ARC neurons after 2DG at ZT11 was associated with higher 2DG induced blood glucose levels as compared with ZT2. Unilateral SCN-lesioned animals, gave a mainly ipsilateral activation of ARC neurons at the lesioned side, suggesting an inhibitory role of the SCN on ARC neurons. The 2DG-induced counterregulatory glucose response correlated with increased ARC neuronal activity and was significantly higher in unilateral SCN-lesioned animals. Finally, the ARC as site where 2DG may, at least partly, induce a counterregulatory response was confirmed by local microdialysis of 2DG. 2DG administration in the ARC produced a higher increase in circulating glucose compared with 2DG administration in surrounding areas such as the ventromedial nucleus of the hypothalamus (VMH). We conclude that the SCN uses neuronal pathways to the ARC to gate sensory metabolic information to the brain, regulating ARC glucose sensitivity and counterregulatory responses to hypoglycemic conditions.

Effects of Intracerebroventricular Administration of Neuropeptide Y on Metabolic Gene Expression and Energy Metabolism in Male Rats

Neuropeptide Y (NPY) is an important neurotransmitter in the control of energy metabolism. Several studies have shown that obesity is associated with increased levels of NPY in the hypothalamus. We hypothesized that the central release of NPY has coordinated and integrated effects on energy metabolism in different tissues, resulting in increased energy storage and decreased energy expenditure (EE). We first investigated the acute effects of an intracerebroventricular (ICV) infusion of NPY on gene expression in liver, brown adipose tissue, soleus muscle, and sc and epididymal white adipose tissue (WAT). We found increased expression of genes involved in gluconeogenesis and triglyceride secretion in the liver already 2-hour after the start of the NPY administration. In brown adipose tissue, the expression of thermogenic genes was decreased. In sc WAT, the expression of genes involved in lipogenesis was increased, whereas in soleus muscle, the expression of lipolytic genes was decreased after ICV NPY. These findings indicate that the ICV infusion of NPY acutely and simultaneously increases lipogenesis and decreases lipolysis in different tissues. Subsequently, we investigated the acute effects of ICV NPY on locomotor activity, respiratory exchange ratio, EE, and body temperature. The ICV infusion of NPY increased locomotor activity, body temperature, and EE as well as respiratory exchange ratio. Together, these results show that an acutely increased central availability of NPY results in a shift of metabolism towards lipid storage and an increased use of carbohydrates, while at the same time increasing activity, EE, and body temperature.

Suprachiasmatic Nucleus Neuropeptides and Their Control of Endogenous Glucose Production

Defective control of endogenous glucose production is an important factor responsible for hyperglycaemia in the diabetic individual. During the past decade, progressively more evidence has appeared indicating a strong and potentially causal relationship between disturbances of the circadian system and defects of metabolic regulation, including glucose metabolism. The detrimental effects of disturbed circadian rhythms may have their origin in disturbances of the molecular clock mechanisms in peripheral organs, such as the pancreas and liver, or in the central brain clock in the hypothalamic suprachiasmatic nuclei (SCN). To assess the role of SCN output per se on glucose metabolism, we investigated (i) the effect of several SCN neurotransmitters on endogenous glucose production and (ii) the effect of SCN neuronal activity on hepatic and systemic insulin sensitivity. We show that silencing of SCN neuronal activity results in decreased hepatic insulin sensitivity and increased peripheral insulin sensitivity. Furthermore, both oxytocin neurones in the paraventricular nucleus of the hypothalamus (PVN) and orexin neurones in the lateral hypothalamus may be important targets for the SCN control of glucose metabolism. These data further highlight the role of the central clock in the pathophysiology of insulin resistance.

A model for chronic, intrahypothalamic thyroid hormone administration in rats

In addition to the direct effects of thyroid hormone (TH) on peripheral organs, recent work showed metabolic effects of TH on the liver and brown adipose tissue via neural pathways originating in the hypothalamic paraventricular and ventromedial nucleus (PVN and VMH). So far, these experiments focused on short-term administration of TH. The aim of this study is to develop a technique for chronic and nucleus-specific intrahypothalamic administration of the biologically active TH tri-iodothyronine (T3). We used beeswax pellets loaded with an amount of T3 based on in vitro experiments showing stable T3 release (∼5 nmol l(-1)) for 32 days. Upon stereotactic bilateral implantation, T3 concentrations were increased 90-fold in the PVN region and 50-fold in the VMH region after placing T3-containing pellets in the rat PVN or VMH for 28 days respectively. Increased local T3 concentrations were reflected by selectively increased mRNA expression of the T3-responsive genes Dio3 and Hr in the PVN or in the VMH. After placement of T3-containing pellets in the PVN, Tshb mRNA was significantly decreased in the pituitary, without altered Trh mRNA in the PVN region. Plasma T3 and T4 concentrations decreased without altered plasma TSH. We observed no changes in pituitary Tshb mRNA, plasma TSH, or plasma TH in rats after placement of T3-containing pellets in the VMH. We developed a method to selectively and chronically deliver T3 to specific hypothalamic nuclei. This will enable future studies on the chronic effects of intrahypothalamic T3 on energy metabolism via the PVN or VMH.

The role of feeding rhythm, adrenal hormones and neuronal inputs in synchronizing daily clock gene rhythms in the liver

The master clock in the hypothalamic suprachiasmatic nucleus (SCN) is assumed to distribute rhythmic information to the periphery via neural, humoral and/or behavioral connections. Until now, feeding, corticosterone and neural inputs are considered important signals for synchronizing daily rhythms in the liver. In this study, we investigated the necessity of neural inputs as well as of the feeding and adrenal hormone rhythms for maintaining daily hepatic clock gene rhythms. Clock genes kept their daily rhythm when only one of these three signals was disrupted, or when we disrupted hepatic neuronal inputs together with the adrenal hormone rhythm or with the daily feeding rhythm. However, all clock genes studied lost their daily expression rhythm after simultaneous disruption of the feeding and adrenal hormone rhythm. These data indicate that either a daily rhythm of feeding or adrenal hormones should be present to synchronize clock gene rhythms in the liver with the SCN.

Visualization of Active Glucocerebrosidase in Rodent Brain with High Spatial Resolution following In Situ Labeling with Fluorescent Activity Based Probes

Gaucher disease is characterized by lysosomal accumulation of glucosylceramide due to deficient activity of lysosomal glucocerebrosidase (GBA). In cells, glucosylceramide is also degraded outside lysosomes by the enzyme glucosylceramidase 2 (GBA2) of which inherited deficiency is associated with ataxias. The interest in GBA and glucosylceramide metabolism in the brain has grown following the notion that mutations in the GBA gene impose a risk factor for motor disorders such as α-synucleinopathies. We earlier developed a β-glucopyranosyl-configured cyclophellitol-epoxide type activity based probe (ABP) allowing in vivo and in vitro visualization of active molecules of GBA with high spatial resolution. Labeling occurs through covalent linkage of the ABP to the catalytic nucleophile residue in the enzyme pocket. Here, we describe a method to visualize active GBA molecules in rat brain slices using in vivo labeling. Brain areas related to motor control, like the basal ganglia and motor related structures in the brainstem, show a high content of active GBA. We also developed a β-glucopyranosyl cyclophellitol-aziridine ABP allowing in situ labeling of GBA2. Labeled GBA2 in brain areas can be identified and quantified upon gel electrophoresis. The distribution of active GBA2 markedly differs from that of GBA, being highest in the cerebellar cortex. The histological findings with ABP labeling were confirmed by biochemical analysis of isolated brain areas. In conclusion, ABPs offer sensitive tools to visualize active GBA and to study the distribution of GBA2 in the brain and thus may find application to establish the role of these enzymes in neurodegenerative disease conditions such as α-synucleinopathies and cerebellar ataxia.

Effects of central gastrin-releasing peptide on glucose metabolism

Gastrin-releasing peptide (GRP) mediated signals in the central nervous system (CNS) influence many functions associated with energy metabolism. The purpose of the present study was to investigate the central effect of GRP on glucose metabolism in the male rat. Intracerebroventricular (icv) administration of GRP caused an immediate hyperglycaemia which was sustained till the end of the infusion. The rise in plasma glucose levels was accompanied by an increase in endogenous glucose production (EGP), as well as increases in plasma glucagon and insulin concentrations. Furthermore, no differences in plasma corticosterone levels were noted between control and GRP treated rats. These results demonstrate that central GRP increases plasma glucose levels, probably by stimulating pancreatic glucagon release and concomitantly or subsequently endogenous glucose production.

Central nervous system neuropeptide Y regulates mediators of hepatic phospholipid remodeling and very low-density lipoprotein triglyceride secretion via sympathetic innervation

OBJECTIVE

Elevated very low-density lipoprotein (VLDL)-triglyceride (TG) secretion from the liver contributes to an atherogenic dyslipidemia that is associated with obesity, diabetes and the metabolic syndrome. Numerous models of obesity and diabetes are characterized by increased central nervous system (CNS) neuropeptide Y (NPY); in fact, a single intracerebroventricular (icv) administration of NPY in lean fasted rats elevates hepatic VLDL-TG secretion and does so, in large part, via signaling through the CNS NPY Y1 receptor. Thus, our overarching hypothesis is that elevated CNS NPY action contributes to dyslipidemia by activating central circuits that modulate liver lipid metabolism.

METHODS

Chow-fed Zucker fatty (ZF) rats were pair-fed by matching their caloric intake to that of lean controls and effects on body weight, plasma TG, and liver content of TG and phospholipid (PL) were compared to ad-libitum (ad-lib) fed ZF rats. Additionally, lean 4-h fasted rats with intact or disrupted hepatic sympathetic innervation were treated with icv NPY or NPY Y1 receptor agonist to identify novel hepatic mechanisms by which NPY promotes VLDL particle maturation and secretion.

RESULTS

Manipulation of plasma TG levels in obese ZF rats, through pair-feeding had no effect on liver TG content; however, hepatic PL content was substantially reduced and was tightly correlated with plasma TG levels. Treatment with icv NPY or a selective NPY Y1 receptor agonist in lean fasted rats robustly activated key hepatic regulatory proteins, stearoyl-CoA desaturase-1 (SCD-1), ADP-ribosylation factor-1 (ARF-1), and lipin-1, known to be involved in remodeling liver PL into TG for VLDL maturation and secretion. Lastly, we show that the effects of CNS NPY on key liporegulatory proteins are attenuated by hepatic sympathetic denervation.

CONCLUSIONS

These data support a model in which CNS NPY modulates mediators of hepatic PL remodeling and VLDL maturation to stimulate VLDL-TG secretion that is dependent on the Y1 receptor and sympathetic signaling to the liver.

Timing of fat and liquid sugar intake alters substrate oxidation and food efficiency in male Wistar rats

In addition to the amount of ingested calories, both timing of food intake and meal composition are determinants of body weight gain. However, at present, it is unknown if the inappropriate timing of diet components is responsible for body weight gain. In the present study, we therefore studied a time-dependent effect of the diet composition on energy homeostasis. Male Wistar rats were subjected to chow ad libitum (chow group) or a choice diet with saturated fat, a 30% sugar solution, chow and tap water. The choice diet was provided either with all components ad libitum (AL), with ad libitum access to chow, tap water and a 30% sugar solution, but with access to saturated fat only during the light period (LF), or with ad libitum access to chow, tap water and saturated fat, but access to a 30% sugar solution only during the light period (LS). Caloric intake and body weight gain were monitored during 31 days. Energy expenditure was measured in the third week in calorimetric cages. All rats on a choice diet showed hyperphagia and gained more body weight compared to the chow group. Within the choice diet groups, rats on the LS diet were most food efficient (i.e. gained most body weight per ingested calorie) and showed a lower respiratory exchange ratio (RER) with an anti-phasic pattern, whereas no differences in locomotor activity or heat production were found. Collectively these data indicate that the timing of the diet composition affects food efficiency, most likely due to a shifted oxidation pattern, which can predispose for obesity. Further studies are underway to assess putative mechanisms involved in this dysregulation.

Olanzapine-induced changes in glucose metabolism are independent of the melanin-concentrating hormone system

Atypical antipsychotic drugs such as Olanzapine (Ola) induce weight gain and metabolic changes associated with the development of type 2 diabetes. The mechanisms underlying these undesired side-effects are currently unknown. Chagnon et al. showed that the common allele rs7973796 of the prepro-melanin-concentrating hormone (PMCH) gene is associated with a greater body mass index in Ola-treated schizophrenic patients. As PMCH encodes for the orexigenic neuropeptide melanin-concentrating hormone (MCH), it was hypothesized that MCH is involved in Ola-induced metabolic changes. We have recently reported that the intragastric infusion of Ola results in hyperglycaemia and insulin resistance in male rats. In order to test in vivo the possible involvement of the PMCH gene in the pathogenesis of Ola side-effects, we administered Ola intragastrically in wild-type (WT) and PMCH knock-out (KO) rats. Our results show that glucose and corticosterone levels, as well as endogenous glucose production, are elevated by the infusion of Ola in both WT and KO animals. Thus, the lack of MCH does not seem to affect the acute effects of Ola on glucose metabolism. On the other hand, these effects might be obliterated by compensatory changes in other hypothalamic systems. In addition, possible modulatory effects of the MCH KO on the long term effects of Ola, i.e. increased adiposity, body weight gain, have not been investigated yet.

The autonomic nervous system regulates postprandial hepatic lipid metabolism

The liver is a key organ in controlling glucose and lipid metabolism during feeding and fasting. In addition to hormones and nutrients, inputs from the autonomic nervous system are also involved in fine-tuning hepatic metabolic regulation. Previously, we have shown in rats that during fasting an intact sympathetic innervation of the liver is essential to maintain the secretion of triglycerides by the liver. In the current study, we hypothesized that in the postprandial condition the parasympathetic input to the liver inhibits hepatic VLDL-TG secretion. To test our hypothesis, we determined the effect of selective surgical hepatic denervations on triglyceride metabolism after a meal in male Wistar rats. We report that postprandial plasma triglyceride concentrations were significantly elevated in parasympathetically denervated rats compared with control rats (P = 0.008), and VLDL-TG production tended to be increased (P = 0.066). Sympathetically denervated rats also showed a small rise in postprandial triglyceride concentrations (P = 0.045). On the other hand, in rats fed on a six-meals-a-day schedule for several weeks, a parasympathetic denervation resulted in >70% higher plasma triglycerides during the day (P = 0.001), whereas a sympathetic denervation had no effect. Our results show that abolishing the parasympathetic input to the liver results in increased plasma triglyceride levels during postprandial conditions.

Intrahypothalamic estradiol regulates glucose metabolism via the sympathetic nervous system in female rats

Long-term reduced hypothalamic estrogen signaling leads to increased food intake and decreased locomotor activity and energy expenditure, and ultimately results in obesity and insulin resistance. In the current study, we aimed to determine the acute obesity-independent effects of hypothalamic estrogen signaling on glucose metabolism. We studied endogenous glucose production (EGP) and insulin sensitivity during selective modulation of systemic or intrahypothalamic estradiol (E2) signaling in rats 1 week after ovariectomy (OVX). OVX caused a 17% decrease in plasma glucose, which was completely restored by systemic E2. Likewise, the administration of E2 by microdialysis, either in the hypothalamic paraventricular nucleus (PVN) or in the ventromedial nucleus (VMH), restored plasma glucose. The infusion of an E2 antagonist via reverse microdialysis into the PVN or VMH attenuated the effect of systemic E2 on plasma glucose. Furthermore, E2 administration in the VMH, but not in the PVN, increased EGP and induced hepatic insulin resistance. E2 administration in both the PVN and the VMH resulted in peripheral insulin resistance. Finally, sympathetic, but not parasympathetic, hepatic denervation blunted the effect of E2 in the VMH on both EGP and hepatic insulin sensitivity. In conclusion, intrahypothalamic estrogen regulates peripheral and hepatic insulin sensitivity via sympathetic signaling to the liver.

Differential involvement of the suprachiasmatic nucleus in lipopolysaccharide-induced plasma glucose and corticosterone responses

The hypothalamic suprachiasmatic nucleus (SCN) is an essential component of the circadian timing system, and an important determinant of neuroendocrine and metabolic regulation. Recent data indicate a modulatory role for the immune system on the circadian timing system. The authors investigated how the circadian timing system affects the hypothalamo-pituitary-adrenal (HPA) axis and glucose regulatory responses evoked by an immune challenge induced by lipopolysaccharide (LPS). LPS-induced increases in corticosterone were minimal during the trough of the daily corticosterone rhythm; in contrast, LPS effects on glucose, glucagon, and insulin did not vary across time-of-day. Complete ablation of the SCN resulted in increased corticosterone responses but did not affect LPS-induced hyperglycemia. The paraventricular nucleus (PVN) of the hypothalamus is an important neuroendocrine and autonomic output pathway for hypothalamic information, as well as one of the main target areas of the SCN. Silencing the neuronal activity in the PVN did not affect the LPS-induced corticosterone surge and only slightly delayed the LPS-induced plasma glucose and glucagon responses. Finally, surgical interruption of the neuronal connection between hypothalamus and liver did not affect the corticosterone response but slightly delayed the LPS-induced glucose response. Together, these data support the previously proposed circadian modulation of LPS-induced neuroendocrine responses, but they are at variance with the suggested major role for the hypothalamic pacemaker on the autonomic output of the hypothalamus, as reflected by the effects of LPS on glucose homeostasis. The latter effects are more likely due to direct interactions of LPS with peripheral tissues, such as the liver.

Acute peripheral but not central administration of olanzapine induces hyperglycemia associated with hepatic and extra-hepatic insulin resistance

Atypical antipsychotic drugs such as Olanzapine induce weight gain and metabolic changes associated with the development of type 2 diabetes. The mechanisms underlying the metabolic side-effects of these centrally acting drugs are still unknown to a large extent. We compared the effects of peripheral (intragastric; 3 mg/kg/h) versus central (intracerebroventricular; 30 µg/kg/h) administration of Olanzapine on glucose metabolism using the stable isotope dilution technique (Experiment 1) in combination with low and high hyperinsulinemic-euglycemic clamps (Experiments 2 and 3), in order to evaluate hepatic and extra-hepatic insulin sensitivity, in adult male Wistar rats. Blood glucose, plasma corticosterone and insulin levels were measured alongside endogenous glucose production and glucose disappearance. Livers were harvested to determine glycogen content. Under basal conditions peripheral administration of Olanzapine induced pronounced hyperglycemia without a significant increase in hepatic glucose production (Experiment 1). The clamp experiments revealed a clear insulin resistance both at hepatic (Experiment 2) and extra-hepatic levels (Experiment 3). The induction of insulin resistance in Experiments 2 and 3 was supported by decreased hepatic glycogen stores in Olanzapine-treated rats. Central administration of Olanzapine, however, did not result in any significant changes in blood glucose, plasma insulin or corticosterone concentrations nor in glucose production. In conclusion, acute intragastric administration of Olanzapine leads to hyperglycemia and insulin resistance in male rats. The metabolic side-effects of Olanzapine appear to be mediated primarily via a peripheral mechanism, and not to have a central origin.

Unaltered instrumental learning and attenuated body-weight gain in rats during non-rotating simulated shiftwork

Exposure to shiftwork has been associated with multiple health disorders and cognitive impairments in humans. We tested if we could replicate metabolic and cognitive consequences of shiftwork, as reported in humans, in a rat model comparable to 5 wks of non-rotating night shifts. The following hypotheses were addressed: (i) shiftwork enhances body-weight gain, which would indicate metabolic effects; and (ii) shiftwork negatively affects learning of a simple goal-directed behavior, i.e., the association of lever pressing with food reward (instrumental learning), which would indicate cognitive effects. We used a novel method of forced locomotion to model work during the animals' normal resting period. We first show that Wistar rats, indeed, are active throughout a shiftwork protocol. In contrast with previous findings, the shiftwork protocol attenuated the normal weight gain to 76 ± 8 g in 5 wks as compared to 123 ± 15 g in the control group. The discrepancy with previous work may be explained by the concurrent observation that with our shiftwork protocol rats did not adjust their between-work circadian activity pattern. They maintained a normal level of activity during the "off-work" periods. In the control experiment, rats were kept active during the dark period, normally dominated by activity. This demonstrated that forced activity, per se, did not affect body-weight gain (mean ± SEM: 85 ± 11 g over 5 wks as compared to 84 ± 11 g in the control group). Rats were trained on an instrumental learning paradigm during the fifth week of the protocol. All groups showed equivalent increases in lever pressing from the first (3.8 ± .7) to the sixth (21.3 ± 2.4) session, and needed a similar amount of sessions (5.1 ± .3) to reach a learning criterion (≥ 27 out of 30 lever presses). These results suggest that while on prolonged non-rotating shiftwork, not fully reversing the circadian rhythm might actually be beneficial to prevent body-weight gain and cognitive impairments.

Intrahypothalamic estradiol modulates hypothalamus-pituitary-adrenal-axis activity in female rats

Estrogen plays an important role in the regulation of the hypothalamus-pituitary-adrenal (HPA)-axis, but the neuroendocrine pathways and the role of estrogen receptor (ER) subtypes involved in specific aspects of this interaction remain unknown. In a first set of experiments, we administered estradiol (E2) intravenously, intracerebroventricularly, and by intrahypothalamic microdialysis to ovariectomized rats to measure plasma corticosterone (CORT) concentrations from carotid artery blood. Systemic infusion of E2 did not increase plasma CORT, but intracerebroventricular E2 induced a 3-fold CORT increase (P = 0.012). Local E2 infusions in the hypothalamic paraventricular nucleus (PVN) significantly increased plasma CORT (P < 0.001). A similar CORT increase was seen after PVN infusion of the ERα agonist propylpyrazoletriol, whereas the ERβ agonist diarylpropiolnitrile had no effect. In a second set of experiments, we investigated whether E2 modulates the HPA-axis response to acute stress by administering E2 agonists or its antagonist ICI 182,780 into the PVN during restraint stress exposure. After 30 min of stress exposure, plasma CORT had increased 5.0-fold (P < 0.001). E2 and propylpyrazoletriol administration in the PVN enhanced the stress-induced plasma CORT increase (8-fold vs. baseline), whereas ICI 182,780 and diarylpropiolnitrile reduced it, as compared with both E2 and vehicle administration in the PVN. In conclusion, central E2 modulates HPA-axis activity both in the basal state and during restraint stress. In the basal condition, the stimulation is mediated by ERα-sensitive neurons, whereas during stress, it is mediated by both ERα and ERβ.

Hypothalamic neuropeptide Y (NPY) controls hepatic VLDL-triglyceride secretion in rats via the sympathetic nervous system

Excessive secretion of triglyceride-rich very low-density lipoproteins (VLDL-TG) contributes to diabetic dyslipidemia. Earlier studies have indicated a possible role for the hypothalamus and autonomic nervous system in the regulation of VLDL-TG. In the current study, we investigated whether the autonomic nervous system and hypothalamic neuropeptide Y (NPY) release during fasting regulates hepatic VLDL-TG secretion. We report that, in fasted rats, an intact hypothalamic arcuate nucleus and hepatic sympathetic innervation are necessary to maintain VLDL-TG secretion. Furthermore, the hepatic sympathetic innervation is necessary to mediate the stimulatory effect of intracerebroventricular administration of NPY on VLDL-TG secretion. Since the intracerebroventricular administration of NPY increases VLDL-TG secretion by the liver without affecting lipolysis, its effect on lipid metabolism appears to be selective to the liver. Together, our findings indicate that the increased release of NPY during fasting stimulates the sympathetic nervous system to maintain VLDL-TG secretion at a postprandial level.

Glucocorticoid signaling in the arcuate nucleus modulates hepatic insulin sensitivity

Glucocorticoid receptors are highly expressed in the hypothalamic paraventricular nucleus (PVN) and arcuate nucleus (ARC). As glucocorticoids have pronounced effects on neuropeptide Y (NPY) expression and as NPY neurons projecting from the ARC to the PVN are pivotal for balancing feeding behavior and glucose metabolism, we investigated the effect of glucocorticoid signaling in these areas on endogenous glucose production (EGP) and insulin sensitivity by local retrodialysis of the glucocorticoid receptor agonist dexamethasone into the ARC or the PVN, in combination with isotope dilution and hyperinsulinemic-euglycemic clamp techniques. Retrodialysis of dexamethasone for 90 min into the ARC or the PVN did not have significant effects on basal plasma glucose concentration. During the hyperinsulinemic-euglycemic clamp, retrodialysis of dexamethasone into the ARC largely prevented the suppressive effect of hyperinsulinemia on EGP. Antagonizing the NPY1 receptors by intracerebroventricular infusion of its antagonist largely blocked the hepatic insulin resistance induced by dexamethasone in the ARC. The dexamethasone-ARC-induced inhibition of hepatic insulin sensitivity was also prevented by hepatic sympathetic denervation. These data suggest that glucocorticoid signaling specifically in the ARC neurons modulates hepatic insulin responsiveness via NPY and the sympathetic system, which may add to our understanding of the metabolic impact of clinical conditions associated with hypercortisolism.

Pituitary adenylate cyclase-activating polypeptide stimulates glucose production via the hepatic sympathetic innervation in rats

OBJECTIVE

The unraveling of the elaborate brain networks that control glucose metabolism presents one of the current challenges in diabetes research. Within the central nervous system, the hypothalamus is regarded as the key brain area to regulate energy homeostasis. The aim of the present study was to investigate the hypothalamic mechanism involved in the hyperglycemic effects of the neuropeptide pituitary adenylyl cyclase-activating polypeptide (PACAP).

RESEARCH DESIGN AND METHODS

Endogenous glucose production (EGP) was determined during intracerebroventricular infusions of PACAP-38, vasoactive intestinal peptide (VIP), or their receptor agonists. The specificity of their receptors was examined by coinfusions of receptor antagonists. The possible neuronal pathway involved was investigated by 1) local injections in hypothalamic nuclei, 2) retrograde neuronal tracing from the thoracic spinal cord to hypothalamic preautonomic neurons together with Fos immunoreactivity, and 3) specific hepatic sympathetic or parasympathetic denervation to block the autonomic neuronal input to liver.

RESULTS

Intracerebroventricular infusion of PACAP-38 increased EGP to a similar extent as a VIP/PACAP-2 (VPAC2) receptor agonist, and intracerebroventricular administration of VIP had significantly less influence on EGP. The PACAP-38 induced increase of EGP was significantly suppressed by preinfusion of a VPAC2 but not a PAC1 receptor antagonist, as well as by hepatic sympathetic but not parasympathetic denervation. In the hypothalamus, Fos immunoreactivity induced by PACAP-38 was colocalized within autonomic neurons in paraventricular nuclei projecting to preganglionic sympathetic neurons in the spinal cord. Local infusion of PACAP-38 directly into the PVN induced a significant increase of EGP.

CONCLUSIONS

This study demonstrates that PACAP-38 signaling via sympathetic preautonomic neurons located in the paraventricular nucleus is an important component in the hypothalamic control of hepatic glucose production.