Obese female Zucker rats (fa/fa) exhibit dendritic retraction in neurons in the ventromedial hypothalamic nucleus

The ventromedial hypothalamic nucleus (VMH) is located in the tuberal region of the hypothalamus and is traditionally considered the satiety center. In obese Zucker rats, which express a mutation in the leptin receptor gene and exhibit obesity from the first weeks of life, the morphology of VMH neurons is unknown. In the present study, we found that the dendritic length of VMH neurons in obese Zucker rats was significantly shorter than that in Long Evans rats. This finding allows us to suggest that obese Zucker rats exhibit both neuronal metabolic alterations related to leptin and a reduction in the flow of information within the neuronal circuits in which the VMH nucleus participates to regulate foraging.

Acute Blockade of PACAP-Dependent Activity in the Ventromedial Nucleus of the Hypothalamus Disrupts Leptin-Induced Behavioral and Molecular Changes in Rats

Leptin signaling pathways, stemming primarily from the hypothalamus, are necessary for maintaining normal energy homeostasis and body weight. In both rodents and humans, dysregulation of leptin signaling leads to morbid obesity and diabetes. Since leptin resistance is considered a primary factor underlying obesity, understanding the regulation of leptin signaling could lead to therapeutic tools and provide insights into the causality of obesity. While leptin actions in some hypothalamic regions such as the arcuate nuclei have been characterized, less is known about leptin activity in the hypothalamic ventromedial nuclei (VMN). Recently, pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to reduce feeding behavior and alter metabolism when administered into the VMN in a pattern similar to that of leptin. In the current study, we examined whether leptin and PACAP actions in the VMN share overlapping pathways in the regulation of energy balance. Interestingly, PACAP administration into the VMN increased STAT3 phosphorylation and SOCS3 mRNA expression, both of which are hallmarks of leptin receptor activation. In addition, BDNF mRNA expression in the VMN was increased by both leptin and PACAP administration. Moreover, antagonizing PACAP receptors fully reversed the behavioral and cellular effects of leptin injections into the VMN. Electrophysiological studies further illustrated that leptin-induced effects on VMN neurons were blocked by antagonizing PACAP receptors. We conclude that leptin dependency on PACAP signaling in the VMN suggests a potential common signaling cascade, allowing a tonically and systemically secreted neuropeptide to be more precisely regulated by central neuropeptides.

Ventromedial hypothalamic nucleus in regulation of stress-induced gastric mucosal injury in rats

Previous studies showed that restraint water-immersion stress (RWIS) increases the expression of Fos protein in the ventromedial hypothalamic nucleus (VMH), indicating the VMH involving in the stress-induced gastric mucosal injury (SGMI). The present study was designed to investigate its possible neuro-regulatory mechanisms in rats receiving either VMH lesions or sham surgery. The model for SGMI was developed by restraint and water (21 ± 1 °C) immersion for 2 h. Gastric mucosal injury index, gastric motility, gastric acid secretion and Fos expression in the hypothalamus and brainstem were examined on the 15th postoperative day in RWIS rats. Gastric mucosal injury in VMH-lesioned rats was obviously aggravated compared to the control. Gastric acidity under RWIS was obviously higher in VMH-lesioned rats than that in sham rats. Meantime, the VMH-lesioned rats exhibited marked increases in the amplitude of gastric motility in the VMH lesions group after RWIS. In VMH-lesioned rats, Fos expression significantly increased in the dorsal motor nucleus of the vagus (DMV), the nucleus of the solitary tract (NTS), the area postrema (AP), the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) in response to RWIS. These results indicate that VMH lesions can aggravate the stress-induced gastric mucosal injury through the VMH-dorsal vagal complex (DVC)-vagal nerve pathway.

Central adiponectin acutely improves glucose tolerance in male mice

Adiponectin, an adipocyte-derived hormone, regulates glucose and lipid metabolism. It is also antiinflammatory. During obesity, adiponectin levels and sensitivity are reduced. Whereas the action of adiponectin in the periphery is well established the neuroendocrine role of adiponectin is largely unknown. To address this we analyzed the expression of adiponectin and the 2 adiponectin receptors (AdipoR1 and AdipoR2) in response to fasting and to diet-induced and genetic obesity. We also investigated the acute impact of adiponectin on central regulation of glucose homeostasis. Adiponectin (1 μg) was injected intracerebroventricularly (ICV), and glucose tolerance tests were performed in dietary and genetic obese mice. Finally, the influence of ICV adiponectin administration on central signaling cascades regulating glucose homeostasis and on markers of hypothalamic inflammation was assessed. Gene expression of adiponectin was down-regulated whereas AdipoR1 was up-regulated in the arcuate nucleus of fasted mice. High-fat (HF) feeding increased AdipoR1 and AdipoR2 gene expression in this region. In mice on a HF diet and in leptin-deficient mice acute ICV adiponectin improved glucose tolerance 60 minutes after injection, whereas normoglycemia in control mice was unaffected. ICV adiponectin increased pAKT, decreased phospho-AMP-activated protein kinase, and did not change phospho-signal transducer and activator of transcription 3 immunoreactivity. In HF-fed mice, ICV adiponectin reversed parameters of hypothalamic inflammation and insulin resistance as determined by the number of phospho-glycogen synthase kinase 3 β(Ser9) and phospho-c-Jun N-terminal kinase (Thr183/Tyr185) immunoreactive cells in the arcuate nucleus and ventromedial hypothalamus. This study demonstrates that the insulin-sensitizing properties of adiponectin are at least partially based on a neuroendocrine mechanism that involves centrally synthesized adiponectin.

Unilateral lesion increases oestrogen receptor α expression in the intact side of the ventromedial hypothalamic nucleus in ovariectomised rats

To determine the relationship between the right and left sides of the ventrolateral ventromedial hypothalamic nucleus (vlVMN) in regulating the expression of oestrogen receptor (ER)α, the unilateral vlVMN was lesioned and the number of ERα-immunoreactive cells and the ERα mRNA level in the intact side of the vlVMN and arcuate nucleus (ARC) were measured in ovariectomised rats. Twenty-four hours after lesioning, brain samples were collected for analysis of ERα expression by immunohistochemistry and the real-time reverse transcriptase-polymerase chain reaction. The number of ERα-immunoreactive cells in the intact side of the vlVMN but not the ARC in the unilateral lesioned group was significantly higher than that in the control or sham-lesioned group. Expression levels of ERα mRNA in the intact side of the vlVMN but not the ARC in unilateral lesioned rats were significantly higher than those in the sham-lesioned group. Of transcript variants with alternative 5'-untranslated regions (0S, 0N, 0, 0T and E1), the ERα 0 transcript level was significantly increased. These results indicate that unilateral damage of vlVMN induces an increase in ERα in the intact side by increasing ERα transcription in a promoter-specific manner. The findings also suggest the existence of new neuroendocrine control system between the right and left sides for the expression of ERα in the vlVMN.

How do we know if the brain is wired for type 2 diabetes?

It is now widely accepted that the brain makes important contributions to the dysregulated glucose metabolism, altered feeding behaviors, and the obesity often seen in type 2 diabetes (T2D). Although studies focusing on genetic, cellular, and molecular regulatory elements in pancreas, liver, adipose tissue etc provide a good understanding of how these processes relate to T2D, our knowledge of how brain wiring patterns are organized is much less developed. This article discusses animal studies that illustrate the importance of understanding the network organization of those brain regions most closely implicated in T2D. It will describe the brain networks, as well as the methodologies used to explore them. To illustrate some of the gaps in our knowledge, we will discuss the connectional network of the ventromedial nucleus and its adjacent cell groups in the hypothalamus; structures that are widely recognized as key elements in the brain's ability to control glycemia, feeding, and body weight.

Hormonal regulation of vasotocin receptor mRNA in a seasonally breeding songbird

Behaviors associated with breeding are seasonally modulated in a variety of species. These changes in behavior are mediated by sex steroids, levels of which likewise vary with season. The effects of androgens on behaviors associated with breeding may in turn be partly mediated by the nonapeptides vasopressin (VP) and oxytocin (OT) in mammals, and vasotocin (VT) in birds. The effects of testosterone (T) on production of these neuropeptides have been well-studied; however, the regulation of VT receptors by T is not well understood. In this study, we investigated steroid-dependent regulation of VT receptor (VTR) mRNA in a seasonally breeding songbird, the white-throated sparrow (Zonotrichia albicollis). We focused on VTR subtypes that have been most strongly implicated in social behavior: V1a and oxytocin-like receptor (OTR). Using in situ hybridization, we show that T-treatment of non-breeding males altered V1a and OTR mRNA expression in several regions associated with seasonal reproductive behaviors. For example, T-treatment increased V1a mRNA expression in the medial preoptic area, bed nucleus of the stria terminalis, and ventromedial hypothalamus. T-treatment also affected both V1a and OTR mRNA expression in nuclei of the song system; some of these effects depended on the presence or absence of a chromosomal rearrangement that affects singing behavior, plasma T, and VT immunolabeling in this species. Overall, our results strengthen evidence that VT helps mediate the behavioral effects of T in songbirds, and suggest that the chromosomal rearrangement in this species may affect the sensitivity of the VT system to seasonal changes in T.

Leptin action in the ventromedial hypothalamic nucleus is sufficient, but not necessary, to normalize diabetic hyperglycemia

In rodent models of type 1 diabetes, leptin administration into brain ventricles normalizes blood glucose at doses that have no effect when given peripherally. The ventromedial nucleus of the hypothalamus (VMN) is a potential target for leptin's antidiabetic effects because leptin-sensitive neurons in this brain area are implicated in glucose homeostasis. To test this hypothesis, we injected leptin directly into the bilateral VMN of rats with streptozotocin-induced uncontrolled diabetes mellitus. This intervention completely normalized both hyperglycemia and the elevated rates of hepatic glucose production and plasma glucagon levels but had no effect on tissue glucose uptake in the skeletal muscle or brown adipose tissue as measured using tracer dilution techniques during a basal clamp. To determine whether VMN leptin signaling is required for leptin-mediated normalization of diabetic hyperglycemia, we studied mice in which the leptin receptor gene was deleted in VMN steroidogenic factor 1 neurons using cre-loxP technology. Our findings indicate leptin action within these neurons is not required for the correction of diabetic hyperglycemia by central leptin infusion. We conclude that leptin signaling in the VMN is sufficient to mediate leptin's antidiabetic action but may not be necessary for this effect. Leptin action within a distributed neuronal network may mediate its effects on glucose homeostasis.

Trigeminal-rostral ventromedial medulla circuitry is involved in orofacial hyperalgesia contralateral to tissue injury

BACKGROUND

Our previous studies have shown that complete Freund's adjuvant (CFA)-induced masseter inflammation and microinjection of the pro-inflammatory cytokine interleukin-1β (IL-1β) into the subnucleus interpolaris/subnucleus caudalis transition zone of the spinal trigeminal nucleus (Vi/Vc) can induce contralateral orofacial hyperalgesia in rat models. We have also shown that contralateral hyperalgesia is attenuated with a lesion of the rostral ventromedial medulla (RVM), a critical site of descending pain modulation. Here we investigated the involvement of the RVM-Vi/Vc circuitry in mediating contralateral orofacial hyperalgesia after an injection of CFA into the masseter muscle.

RESULTS

Microinjection of the IL-1 receptor antagonist (5 nmol, n=6) into the ipsilateral Vi/Vc attenuated the CFA-induced contralateral hyperalgesia but not the ipsilateral hyperalgesia. Intra-RVM post-treatment injection of the NK1 receptor antagonists, RP67580 (0.5-11.4 nmol) and L-733,060 (0.5-11.4 nmol), attenuated CFA-induced bilateral hyperalgesia and IL-1β induced bilateral hyperalgesia. Serotonin depletion in RVM neurons prior to intra-masseter CFA injection prevented the development of contralateral hyperalgesia 1-3 days after CFA injection. Inhibition of 5-HT(3) receptors in the contralateral Vi/Vc with direct microinjection of the select 5-HT(3) receptor antagonist, Y-25130 (2.6-12.9 nmol), attenuated CFA-induced contralateral hyperalgesia. Lesions to the ipsilateral Vc prevented the development of ipsilateral hyperalgesia but did not prevent the development of contralateral hyperalgesia.

CONCLUSIONS

These results suggest that the development of CFA-induced contralateral orofacial hyperalgesia is mediated through descending facilitatory mechanisms of the RVM-Vi/Vc circuitry.

Leptin potentiates the anti-obesity effects of rimonabant

We hypothesized that a combination of low doses of rimonabant and leptin would markedly reduce body weight through the modulation of neuronal activity within the hypothalamus. To this end, high fat diet-induced obese rats were randomized to receive either leptin (0.5mg/kg subcutaneously), rimonabant (3mg/kg), the combination of both, or vehicle, daily for a duration of 2 weeks. A subset of rats was pair-fed to the combination-treated animals and received either vehicle or leptin. At the end of the weight loss phase, leptin treatment was maintained for 7 days while rimonabant was discontinued to assess changes in body weight during the rebound phase. The combination of rimonabant and leptin resulted in a marked inhibition of food intake and a profound reduction in body weight that was greater than achieved with either leptin or rimonabant alone. Treatment with leptin during the rebound phase inhibited compensatory increases in body weight associated with restitution of ad libitum feeding in previously pair-fed rats. Moreover, leptin partially blunted the rebound in food intake and body weight associated with cessation of rimonabant therapy.To investigate the effect of the combination on neuronal firing in the rat hypothalamus, single unit activity was recorded from brain slices containing the ventromedial and arcuate nuclei. The combination of rimonabant and leptin synergistically increased and decreased neuronal firing in the ventromedial and arcuate nuclei, respectively. Overall, these data demonstrate profound anti-obesity effects of combining cannabinoid type 1 receptor antagonists and leptin.

A novel rodent model that mimics the metabolic sequelae of obese craniopharyngioma patients

Patients with craniopharyngioma (CP), a tumor located in the pituitary and/or hypothalamus, are susceptible to developing obesity and many metabolic complications. The study aim was to create a rodent model that mimics the complex neuroanatomical and metabolic disturbances commonly seen in obese CP patients. We compared the metabolic phenotype of animals with three distinct types of hypothalamic lesions: 1) destruction of the arcuate nucleus (ARC) induced by monosodium glutamate (MSG), 2) electrolytic lesion of the adjacent ventromedial nucleus (VMN) alone, 3) both the VMN and dorsomedial nucleus (DMN), or a 4) combined medial hypothalamic lesion (CMHL) affecting the VMN, DMN, and the ARC. Only the CMHL model exhibited all key features observed in patients with hypothalamic obesity induced by CP. These features included excessive weight gain due to increased adiposity, increased food intake, and pronounced hyperinsulinemia and hyperleptinemia. Similar to characteristics of patients with CP, CMHL animals exhibited reduced plasma levels of alpha-melanocyte stimulating hormone and reduced ambulatory activity compared with weight-matched controls. Therefore, the CMHL model best mimics the complex metabolic abnormalities observed in obese CP patients compared with lesions to other hypothalamic areas and provides a foundation for future pharmacological approaches to treat obesity in children with hypothalamic damage.

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

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

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

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

Inhibition of lesion-induced neurogenesis impaired behavioral recovery in adult ring doves

We have previously shown that electrolytic lesion-induced neurogenesis in the ventromedial nucleus of the hypothalamus (VMN) is significantly correlated with the recovery of courtship behavior in adult male ring doves. Here we revealed that reduction of lesion-induced neurogenesis in VMN impaired the behavioral recovery suggesting therefore a causal link between neurogenesis and behavioral recovery. Our results lend support that adult neurogenesis is latent in repair of injured brain.

A Probabilistic Functional Atlas of the VIM Nucleus Constructed from Pre-, Intra- and Postoperative Electrophysiological and Neuroimaging Data Acquired during the Surgical Treatment of Parkinson’s Disease Patients

We have previously introduced a concept of a probabilistic functional atlas (PFA) to overcome limitations of the current electronic stereotactic brain atlases: anatomical nature, spatial sparseness, inconsistency and lack of population information. The PFA for the STN has already been developed. This work addresses construction of the PFA for the ventrointermediate nucleus (PFA-VIM). The PFA-VIM is constructed from pre-, intra- and postoperative electrophysiological and neuroimaging data acquired during the surgical treatment of Parkinson's disease patients. The data contain the positions of the chronically implanted electrodes and their best contacts. For each patient, the intercommissural distance, height of the thalamus and width of the third ventricle were measured. An algorithm was developed to convert these data into the PFA-VIM, and to present them on axial, coronal and sagittal planes and in 3-D. The PFA-VIM gives a spatial distribution of the best contacts, and its probability is proportional to best contact concentration in a given location. The region with the highest probability corresponds to the best target. The PFA-VIM is calculated with 0.25-mm3 resolution from 107 best contacts in two situations: with and without lateral compensation against the width of the third ventricle. For the PFA-VIM compensated laterally, the anterior, lateral and dorsal coordinates of the mean value are (in mm) 6.24, 13.83, 1.68 for the left VIM and 6.54, -13.84, 2.10 for the right VIM. The coordinates of the mean value of the highest probability region along with the highest number of the best contacts (P) are: 6.25, 14.25, 1.75, P = 16, for the left VIM, and 6.0, -14.0, 1.00, P = 18, for the right VIM. The coordinate system origin is at the posterior commissure. For the PFA-VIM not compensated laterally, the coordinates of the mean value are 6.24, 13.99, 1.68 for the left VIM and 6.53, -14.13, 2.10 for the right VIM. The coordinates of the mean value of the highest probability region along with the highest number of the best contacts are 5.58, 13.67, 1.33, P = 14, for the left VIM, and 6.36, -14.03, 1.11, P = 17, for the right VIM. The PFA-VIM atlas overcomes several limitations of the current anatomical atlases and can improve targeting of thalamotomies and thalamic stimulations. It is dynamic and can easily be extended with new cases.

Loss of steroidogenic factor 1 alters cellular topography in the mouse ventromedial nucleus of the hypothalamus

Knockout (KO) mice lacking the orphan nuclear receptor steroidogenic factor 1 (SF-1) exhibit marked structural abnormalities of the ventromedial nucleus of the hypothalamus (VMH). In this study, we sought to determine the molecular mechanisms underlying the VMH abnormalities. To trace SF-1-expressing neurons, we used a SF-1/enhanced green fluorescent protein (eGFP) transgene. Although the total numbers of eGFP-positive cells in wild-type (WT) and SF-1 KO mice were indistinguishable, cells that normally localize precisely within the VMH were scattered more diffusely in adjacent regions in SF-1 KO mice. This abnormal distribution is likely due to the loss of SF-1 expression in VMH neurons rather than secondary effects of deficient steroidogenesis, as redistribution also was seen in mice with a CNS-specific KO of SF-1. Thus, the absence of SF-1 alters the distribution of cells that normally form the VMH within the mediobasal hypothalamus. Consistent with this model, the hypothalamic expression patterns of the transcription factors islet-1 and nkx2.1 also were displaced in SF-1 KO mice. Independent of gene expression, birthdate analyses further suggested that cells with earlier birthdates were affected more severely by the loss of SF-1 than were later born cells. We conclude that the absence of SF-1 causes major changes in cellular arrangement within and around the developing VMH that result from altered cell migration.

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

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

Orexin-A immunoreactivity and prepro-orexin mRNA expression in hyperphagic rats induced by hypothalamic lesions and lactation

Orexins are endogenous neuropeptides that potently facilitate appetite and food consumption. In the present study, we examined orexin immunoreactivity and prepro-orexin mRNA expression in the lateral hypothalamus by immunohistochemistry and competitive reverse transcription-polymerase chain reaction (RT-PCR) methods in different models of hyperphagia in rats. Hyperphagia was induced by lesions of either the ventromedial hypothalamus (VMHL) or the paraventricular nucleus (PVNL), and we also compared lactating rats to nonlactating controls. Both VMHL and PVNL increased food intake and body weight compared to shams. On day 7 post lesion, serum leptin and insulin concentrations exhibited 3.2- and 2.8-fold increases in VMHL rats, and nonsignificant 1.8- and 1.8-fold increases in PVNL rats; there were significant decreases (48% and 33%) in lactating rats on day 12 postpartum compared to controls, respectively. Serum glucose concentrations were not significantly changed compared to controls in these rats. Quantification by image analysis suggests that VMHL significantly decreased the number and mean staining intensity of orexin-A immunoreactive neurones compared to those in the sham-lesioned group; while PVNL did not change orexin-A immunoreactivity. Competitive RT-PCR analysis showed that VMHL significantly decreased the prepro-orexin mRNA expression compared to those in the sham-lesioned group, and PVNL did not change it. Lactating rats on days 11-12 of lactation had significantly greater number and mean staining intensity of orexin-A immunoreactive neurones, prepro-orexin mRNA expression food intake and body weight than nonlactating postpartum rats. Thus, changes in orexin-A immunoreactivity and prepro-orexin mRNA expression were not consistent between the hyperphagia models. These results suggest that the hyperphagia from VMHL or PVNL and lactating rats differ in their involvement of orexin-A, and the change in circulating leptin and insulin concentrations may be involved in the change of orexin-A immunoreactivity in these rats.

[Study of apoptosis manifestations in streptozotocin diabetes mellitus]

The aim of this work was to study manifestations of apoptosis in pancreas, brain and myocardium of rats at the type I diabetes mellitus. To reveal the apoptotic changes in cells, specific damages of DNA were identified by the TUNEL-method. Specific for apoptosis changes in chromatin and cell membranes were found after counterstaining of a specimen by methyl green. In addition, the apoptotic and non-apoptotic cells were differentiated automatically with the help of image analyzing computer system by an index of optical density of cellular nucleus. This method allowed to find out for sure that apoptotic cells were available in all the studied tissues of healthy animals. However the possibility of their revealing by the TUNEL-method depends on the way of tissue fixation. Development of the type I diabetes mellitus was accompanied with an increase in the number of such cells, which gives evidence for an important role of apoptosis in diabetes pathogenesis.

Adipose tissue selective insulin receptor knockout protects against obesity and obesity-related glucose intolerance

Insulin signaling in adipose tissue plays an important role in lipid storage and regulation of glucose homeostasis. Using the Cre-loxP system, we created mice with fat-specific disruption of the insulin receptor gene (FIRKO mice). These mice have low fat mass, loss of the normal relationship between plasma leptin and body weight, and are protected against age-related and hypothalamic lesion-induced obesity, and obesity-related glucose intolerance. FIRKO mice also exhibit polarization of adipocytes into populations of large and small cells, which differ in expression of fatty acid synthase, C/EBP alpha, and SREBP-1. Thus, insulin signaling in adipocytes is critical for development of obesity and its associated metabolic abnormalities, and abrogation of insulin signaling in fat unmasks a heterogeneity in adipocyte response in terms of gene expression and triglyceride storage.

Time course of VMN lesion effects on lordosis and proceptive behavior in female hamsters

Previous studies suggest that ultrasound production by female hamsters is better able than other reproductive behaviors to recover from an initial drop caused by damage to the ventromedial hypothalamus (VMN). At the same time, few studies have examined the time course of such lesion effects. To remedy this, female hamsters were observed before and after control operations or VMN lesions. The behaviors considered were ultrasound production, lordosis, approach, and vaginal marking. Ultrasound production, lordosis, and approach were affected by lesions, permitting the description of the time course of each of these effects. Only ultrasound rates showed evidence of recovery, which culminated in rates significantly above those observed preoperatively in the same animals. This suggests that ultrasound production is unusual in its response to VMN damage and that the underlying mechanism could be of interest in studies of the processes that determine recovery from brain damage.

Ibotenate lesion of the ventromedial hypothalamus lowers hyperthermic effects of prostaglandin E1

This experiment tested the effects of an intracerebroventricular injection of prostaglandin E1 on the sympathetic activation and the thermogenic changes in rats with ibotenate lesions of the ventromedial hypothalamus. Under pentobarbital anesthesia, twelve Sprague-Dawley male rats were lesioned bilaterally in the ventromedial hypothalamus with an injection of ibotenic acid (30 nmol into each side). Sham lesions were carried out in other twelve control rats. After 48 h, all animals were anesthetized with ethyl-urethane. The firing rate of the sympathetic nerves innervating the interscapular brown adipose tissue and the colonic and interscapular brown adipose tissue temperatures were monitored before and after an intracerebroventricular injection of prostaglandin E1 (500 ng) or saline. Prostaglandin E1 induced an increase in the firing rate of sympathetic nerves and the colonic and interscapular brown adipose tissue temperatures. These effects were reduced by the ventromedial hypothalamic lesion. Since ibotenic acid destroys cell bodies, the findings indicate that neurons of the ventromedial hypothalamus play a considerable role in the control of sympathetic activation and the thermogenic changes during prostaglandin E1 hyperthermia.

Convergence of pre- and postsynaptic influences on glucosensing neurons in the ventromedial hypothalamic nucleus

Glucosensing neurons in the ventromedial hypothalamic nucleus (VMN) were studied using visually guided slice-patch recording techniques in brain slices from 14- to 21-day-old male Sprague-Dawley rats. Whole-cell current-clamp recordings were made as extracellular glucose levels were increased (from 2.5 to 5 or 10 mmol/l) or decreased (from 2.5 to 0.1 mmol/l). Using these physiological conditions to define glucosensing neurons, two subtypes of VMN glucosensing neurons were directly responsive to alterations in extracellular glucose levels. Another three subtypes were not directly glucose-sensing themselves, but rather were presynaptically modulated by changes in extracellular glucose. Of the VMN neurons, 14% were directly inhibited by decreases in extracellular glucose (glucose-excited [GE]), and 3% were directly excited by decreases in extracellular glucose (glucose-inhibited [GI]). An additional 14% were presynaptically excited by decreased glucose (PED neurons). The other two subtypes of glucosensing neurons were either presynaptically inhibited (PIR; 11%) or excited (PER; 8%) when extracellular glucose was raised to > 2.5 mmol/l. GE neurons sensed decreased glucose via an ATP-sensitive K(+) (K(ATP)) channel. The inhibitory effect of increased glucose on PIR neurons appears to be mediated by a presynaptic gamma-aminobutyric acid-ergic glucosensing neuron that probably originates outside the VMN. Finally, all types of glucosensing neurons were both fewer in number and showed abnormal responses to glucose in a rodent model of diet-induced obesity and type 2 diabetes.

Neurobiology of decision-making: risk and reward

Neurological patients with bilateral ventromedial (VM) lesions of the prefrontal cortex often deny, or they are not aware that they have a problem. Furthermore, they often pursue actions that bring some reward in the immediate run, despite severe long-term consequences such as the loss of job, home, and family. The somatic marker hypothesis, which provides an account of this defect in decision-making, posits that the impairment is the result of defective activation of somatic markers that normally function as covert or overt signposts for helping with the process of making choices that are advantageous to the organism. Failure to enact somatic states results from dysfunction in a neural system in which the VM cortex is one critical region. However, other neural regions, including the amygdala, and somatosensory cortices (SI, SII, and insula) are also hypothesized to be components of that same neural system. Recent evidence reveals that substance abusers suffer from decision-making deficit akin to that seen with patients with VM lesions. Thus, the strategies used to study decision-making in neurological patients have direct implications for understanding several neuropsychiatric disorders including addiction and pathological gambling.

Different responses of ventromedial hypothalamic neurons to leptin in normal and early postnatally overfed rats

Leptin is crucially involved in the central nervous regulation of body weight. Neurons of the ventromedial hypothalamic nucleus (VMH) express leptin receptors and signal satiety with increase in their firing. Normally, leptin mainly activates VMH neurons. Rats grown up in small litters (SL) develop persistent hyperphagia and obesity throughout life. We studied single unit activity in hypothalamic brain slices of juvenile SL rats overweight due to early postnatal overfeeding (Mann-Whitney U-test, P < 0.001). VMH neurons of normal rats were mainly activated by leptin (Wilcoxon test, P < 0.05, n = 39), whereas neurons of overweight SL rats were mainly inhibited (Wt, P < 0.001, n = 33). This clearly altered response to leptin in neonatally overnourished rats might contribute to their persistent overweight throughout life.

Effects of chronic administration of sibutramine on body weight, food intake and motor activity in neonatally monosodium glutamate-treated obese female rats: relationship of antiobesity effect with monoamines

When the hypothalamic ventromedial nucleus and arcuate nucleus were destroyed in rats by treatment with monosodium glutamate in the neonatal stage, increase in the Lee index (body weight 1/3/body length) and in retroperitoneal fat as well as decreases in spontaneous motor activity, food consumption and growth hormone secretion function associated with hypothalamic low body length obesity (monosodium glutamate-treated obesity; MSG-OB) were observed as these rats grew. Treatment with sibutramine at 3 and 10 mg/kg p.o. once a day continuously for 14 days improved these parameters, and the degree of improvement was dose related. The plasma lipid values in MSG-OB rats, which were the same as those in normal rats, were decreased by consecutive administration of sibutramine. Levels of hypothalamic monoamines (MAs) such as norepinephrine, 5-HT (serotonin) and dopamine and their metabolites DOPAC, HVA and 5-HIAA were decreased in MSG-OB rats, and further decrease in them, though slight, was observed with consecutive daily administration of sibutramine, probably as a result of the feedback attributable to an increase in MA in synapses caused by inhibition of MA uptake by sibutramine. These results suggest that sibutramine can activate the MA nervous system by MA uptake inhibition in regions of the brain such as the lateral hypothalamic area and the paraventricular nucleus, which control food intake and sympathetic nerve activity, and the nigrostriatal area related to the extrapyramidal motor system, and thereby exhibit anti-obesity effects in the MSG-OB rat.

Hypothalamic nuclei are malformed in weanling offspring of low protein malnourished rat dams

Maternal low protein malnutrition during gestation and lactation (LP) is an animal model frequently used for the investigation of long-term deleterious consequences of perinatal growth retardation. Both perinatal malnutrition and growth retardation at birth are risk factors for diabetic and cardiovascular disturbances in later life. The pathophysiologic mechanisms responsible are unknown. Hypothalamic nuclei are decisively involved in the central nervous regulation of food intake, body weight and metabolism. We investigated effects of a low protein diet (8% protein; control diet, 17% protein) during gestation and lactation in rat dams on the organization of hypothalamic regulators of body weight and metabolism in the offspring at weaning (d 20 of life). LP offspring had significantly lower body weight than control offspring (CO; P: < 0.001), associated with hypoglycemia and hypoinsulinemia (P: < 0. 005) on d 20 of life. This was accompanied by a greater relative volume of the ventromedial hypothalamic nucleus (P: < 0.01) and a greater numerical density of Nissl-stained neurons in this nucleus (P: < 0.01) as well as in the paraventricular hypothalamic nucleus (PVN; P: < 0.001). In contrast, no significant differences in neuronal densities were observed generally in the lateral hypothalamic area, arcuate hypothalamic nucleus (ARC), and dorsomedial hypothalamic nucleus between LP offspring and CO offspring. On the other hand, LP offspring displayed fewer neurons immunopositive for neuropeptide Y in the ARC (P: < 0.05), whereas in the PVN, lower neuronal densities of neurons immunopositive for galanin were found in LP offspring compared with CO offspring (P: < 0.001). On the contrary, in the PVN, no significant group difference in the numerical density of cholecystokinin-8S-positive neurons was present. A long-term effect of these specific hypothalamic alterations on body weight and metabolism in LP offspring during later life is suggested.

Amygdala-lesion obesity: what is the role of the various amygdaloid nuclei?

Anatomic descriptions of amygdaloid lesions resulting in hyperphagia and obesity in rats, cats, and dogs have been inconsistent and often contradictory, frequently resulting in failures to replicate. The present study attempted to reconcile these differences by examining common areas of overlap among differently placed lesions in female rats. Small bilateral lesions of the most posterodorsal aspects of the amygdala resulted in substantial weight gains (mean = 45.4 g/10 days). The smallest lesions caused damage limited to the posterodorsal medial amygdaloid nucleus and the bed nucleus of the stria terminalis and were directly in the area where axons are collecting to form the stria terminalis. Larger lesions that extensively damaged the central and/or anterodorsal medial amygdaloid nuclei sometimes resulted in excess weight gains, as did very large lesions of the basolateral nuclei, but substantial weight gains occurred only when the lesions extended (unilaterally or bilaterally) into the posterodorsal amygdala. Examination of previously published brain sections indicated that the hyperphagia and obesity that have been observed after widely differing lesion placements in cats and dogs were also the result of damage to a common area of overlap (i.e., the bed nucleus and/or stria terminalis). In rats, the critical area producing weight gain has extensive reciprocal relations with the medial hypothalamus.

Differential expression of nicotinamide adenine dinucleotide phosphate-diaphorase in hypothalamic areas of obese Zucker rats

Several studies have suggested that the activity of nitric oxide synthase (NOS) may be involved in the regulation of food intake in the genetically obese Zucker rats. In the present study, we investigated the expression of NOS in various hypothalamic regions of obese and lean Zucker rats using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. Obese Zucker rats showed significantly lower staining intensities of NADPH-diaphorase-positive neurons in the paraventricular nucleus (PVN), lateral hypothalamic area (LHA) and ventromedial hypothalamic nucleus (VMH) than lean Zucker rats did. The differences in staining intensities between obese and lean Zucker rats were large in both the PVN and LHA, but such differences were relatively small in the VMH.

Morphological evidence for neural interactions between leptin and orexin in the hypothalamus

Both leptin and orexin have been recently discovered as peptides involved in feeding regulation. The morphological evidence of neural interaction between leptin and orexin, one considered to inhibit food intake and the other to stimulate it in the central nervous system (CNS), was studied by use of double immunostaining method. The leptin receptor-like immunoreactive (LR-LI) neurons in the hypothalamic arcuate nucleus and ventromedial nucleus were innervated by orexin-like immunoreactive (OX-LI) neurons. The distribution of LR-LI neurons in the hypothalamus was very similar to that of OX-LI neurons. These results may suggest that leptin and orexin are intimately correlated with each other and that they reciprocally regulate feeding at the hypothalamic level.

Effect of VMH lesion on sucrose-Fed nociceptive responses

An initial analgesia followed by hyperalgesia to phasic noxious stimuli occurs after ingestion of sucrose ad libitum. However, the mechanism underlying hyperalgesia is not known. The present study was designed to explore the role of VMH in the mediation of the hyperalgesic effect of sucrose ingestion. Adult male albino rats received sucrose solution (20% p.o.) in addition to laboratory food pellets and tap water ad libitum. Their behavioural responses to various phasic and tonic noxious stimuli were recorded after 6, 12 and 48 h during pre and post-sucrose fed states in both the control and VMH lesion groups of rats. Sucrose feeding to control rats significantly reduced the tail flick latency (TFL) and threshold of vocalization during stimulus (SV) and after discharge (VA) indicating hyperalgesia, while the threshold of tail flick remained unaffected. The average pain rating during the formalin test (tonic pain) decreased significantly indicating analgesia. VMH lesion decreased the latency (mean +/- SD) for tail flick (11.26 +/- 4.65 from 15.61 +/- 5.12 s), threshold (median) for tail flick (0.04 from 0.08 mA), vocalization during stimulus (0.05 from 0.1 mA) and vocalization after discharge (0.15 from 0.2 mA), while the tonic pain rating increased, thereby suggesting a hyperalgesic state. However, sucrose feeding to lesioned rats neither potentiated nor attenuated their hyperalgesia. The results suggest that sucrose feeding for 6-48 h ad libitum produces hyperalgesia to phasic noxious and analgesia to tonic noxious stimuli, while VMH lesion produces hyperalgesia to both phasic and tonic noxious stimuli. Secondly, sucrose ingestion by VMH lesion rats does not affect their responses to pain, suggesting the possible role of VMH in the mediation of sucrose-fed nociceptive responses.

Extracellular hypothalamic serotonin levels after dorsal raphe nuclei stimulation of lean (Fa/Fa) and obese (fa/fa) Zucker rats

Serotonin (5-HT), acting in the medial hypothalamus (MH), is involved in appetite/satiety and sympathetic stimulation of thermogenesis. This study tested the hypothesis that the enhanced energetic efficiency of obese Zucker rats is associated with a reduced capacity of activated dorsal raphe (DR) neurons to release 5-HT in the MH. We used microdialysis and HPLC-EC to measure dynamic changes in extracellular 5-HT levels in the MH of urethane-anesthetized, 10-14 week old male lean and obese Zucker rats. These concentrations did not differ significantly between the two genotypes prior to stimulation (mean+/-S.E.M.=3.8+/-0.5 fmol/microl, lean; 3.6+/-1.0 fmol/microl, obese) or following DR stimulation at 25 Hz (200 microA). The latter elicited initial net increases of 0.54+/-0.15 fmol/microl in lean and 0.58+/-0.20 fmol/microl in obese rats; and 20 min post-stimulus, 5-HT values were still elevated and comparable in the two genotypes. Although a 50-Hz (200 microA) stimulus evoked initial increases that were similar in lean (1.37+/-0.23 fmol/microl) and obese (0.95+/-0.24 fmol/microl,) rats, the net increase in 5-HT concentration during the next 20-40 min period was higher in the lean (2.03+/-0.55 fmol/microl vs. 1.18+/-0.24 fmol/microl in the obese animals). Also, in the lean, but not obese rats, extracellular 5-HT levels were significantly greater at 50 vs. 25 Hz. These results support the hypothesis that the capacity of midbrain serotonergic neurons to release 5-HT at the MH is reduced in obese Zucker rats, consistent with their blunted responsiveness to dietary stimuli and greater energetic efficiency.

Weanling ventromedial hypothalamic syndrome. bone geometry and biomechanics

The effect of growth-retarding, obesifying lesions in the ventromedial hypothalamic nucleus (VMN) on bone geometry and biomechanics was investigated in male weanling rats. The animals received bilateral, symmetrical, electrolytic lesions (VMNL rats) shortly after weanling (age 27 days); sham-operated rats served as controls (SCON). The rats were maintained for 42 postoperative days and then terminated. Body weight, nose-tail length, food intake, carcass water, and lean body mass were all significantly (p < 0.001) reduced in the VMNL group compared to SCON rats. Carcass fat, lipogenic efficiency (carcass fat % laid down/mean food intake) (both p < 0.001) and epididymal fat pad weight (p < 0.01) were significantly increased in VMNL versus SCON. Femur length, anteroposterior diameter (both p < 0.001), and mediolateral femur diameter (p < 0.01) were significantly reduced in VMNL versus SCON rats, but torque and angle of torque were comparable among the groups. VMNL rats femora also showed a significant greater maximum shear stress compared to the control animals. The reduced parameters in the VMNL rats are in good agreement with the previously demonstrated reduced plasma and pituitary growth hormone levels found in this hypothalamus preparation.

VMN hypothalamic dopamine and serotonin in anorectic septic rats

During sepsis, catabolism of proteins and associated changes in plasma amino acids occur. Tryptophan and tyrosine, and their derivatives serotonin (5-HT) and dopamine (DA), influence hypothalamic feeding-related areas and are associated with the onset of anorexia. We hypothesized that anorexia of sepsis is associated with changes in serotonin and dopamine in the ventromedial nucleus (VMN) of the hypothalamus. The aim of this study was to test our hypothesis by measuring intra-VMN changes of these two neurotransmitters at the onset of anorexia during sepsis. Fischer 344 male rats had an intracerebral guide cannula stereotaxically implanted into the VMN. Ten days later, in awake, overnight-food-deprived rats, a microdialysis probe was inserted through the in situ VMN cannula. Two hours thereafter, serial baseline serotonin and dopamine concentrations were measured. Then cecal ligation and puncture to induce sepsis or a control laparotomy was performed under isoflurane anesthesia. VMN microdialysis samples were serially collected every 30 min for 8 h after the surgical procedure to determine 5-HT and DA changes in response to sepsis. During the hypermetabolic response to sepsis, a strong association occurred between anorexia and a significant reduction of VMN dopamine concentration (P < 0.05; constant rate of dopamine decrease in the Study group of 0.99 pg per 2 h); no changes occurred in 5-HT in association with anorexia of sepsis. Six hours after operation, a single meal was offered for 20 min to assess the response of neurotransmitters to food ingestion. Food intake was minimal in anorectic septic rats (mean size of the after food-deprived meal in the Septic group was 0.03+/-0.01 g, that of the Control group was 1.27+/-0.14 g; P = 0.0001), while Control rats demonstrated anticipated changes in neurotransmitters in response to eating. We conclude that the onset of anorexia in septic rats is associated with a reduction in VMN dopamine.

Morphological alterations of hypothalamic nuclei due to intrahypothalamic hyperinsulinism in newborn rats

In former studies, a temporary, intrahypothalamically localized hyperinsulinism during brain development was shown to result in overweight and metabolic disturbances during later life in rats. Therefore, we tested the hypothesis whether intrahypothalamic insulin treatment during early postnatal life may lead to hypothalamic morphological alterations, i.e., of numerical density of neurons and area of neuronal nuclei or area of neuronal cytoplasm, in this animal model. For this purpose, on the 8th day of age in Wistar rats a long-acting insulin was bilaterally applicated stereotactically into the hypothalamus (12 mIU on each side), while in controls the insulin-free agar-vehicle was given only. By computer-assisted morphometric analysis on the 15th day of life a decrease of the mean area of neuronal nuclei and the mean nucleus-cytoplasm-ratio within the VMN of the insulin-treated animals was observed, as compared to control rats (P < 0.05), while no significant alterations were found in the lateral hypothalamic area (LHA). Analysis of topographically distinct parts of the VMN revealed significant reductions of the mean area of neuronal nuclei (P < 0.001) and nucleus-cytoplasm-ratio (P < 0.05) in the anterior part of the VMN (VMNpa). Furthermore, in the ventrolateral part (VMNpv) a decreased mean neuronal density was observed in the insulin group (P < 0.01). In contrast, the dorsomedial part of the VMN (VMNpd) displayed an increased mean neuronal density in the insulin-treated animals (P < 0.05). In the dorsomedial hypothalamic nucleus (DMN) a significant increase of the mean area of neuronal nuclei (P < 0.01) and the area of neuronal cytoplasm were observed (P < 0.001). These alterations were accompanied by a significantly elevated mean numerical density of astrocytes (positive for glial fibriallary acidic protein; GFAP+) within the periventricular hypothalamic area (PER) of the insulin-treated rats (P < 0.05). These observations speak for a varying vulnerability of LHA, DMN and distinct parts of the VMN to hyperinsulinism during early development, possibly leading to a disturbed organization and, consecutively, permanent dysfunction of these morphologically connected and functionally interacting hypothalamic nuclei.

Lesions of glucose-responsive neurons impair synchronizing effects of calorie restriction in mice

Calorie restriction can induce phase-advances of daily rhythms in rodents exposed to light-dark cycles. To test whether glucose-responsive neurons are involved in the synchronizing effects of calorie restriction, C57BL/6J mice were injected with gold-thioglucose (GTG; 0.6 g/kg) which damages glucose-responsive neurons, primarily located in the ventromedial hypothalamus. From the day of injection, GTG-treated and control mice received a hypocaloric diet (66% of ad libitum food intake) 2 h after lights on. When mice were transferred to constant darkness after 4 weeks and fed ad libitum, the onset of circadian rhythm of locomotor activity was phase-advanced by 1 h in control but not in GTG-treated mice. Therefore, glucose-responsive neurons in the ventromedial hypothalamus may play a role in the synchronizing effects of calorie restriction on circadian rhythmicity.

Early morphologic changes of atherosclerosis induced by ventromedial hypothalamic lesion in the spontaneously diabetic Goto-Kakizaki rat

It is generally thought that typical atherosclerotic lesions do not develop in the rodent. The Goto-Kakizaki (GK) rat is a nonobese strain in which a spontaneous type of non-insulin-dependent diabetes mellitus develops without apparent macroangiopathy. In our previous study, making ventromedial hypothalamic (VMH) lesions in GK rats induced hyperphagia and a further deterioration in glucose metabolism. In the current study, male GK rats in which VMH lesions were made were examined for vascular changes, with special reference to atherosclerotic lesions. Marked hyperglycemia in GK rats with VMH lesions (hereafter referred to as VMH lesion rats) was revealed over an observation period (plasma glucose levels 16 weeks after the operation: VMH lesion GK rats, 19.3 +/- 2.0 mmol/L, vs sham-operated GK rats, 10.1 +/- 1.3 mmol/L; p < 0.0001). Light microscopic observation of the descending aorta in VMH lesion GK rats 16 weeks after the surgery revealed that the intimal thickening and the number of infiltrating cells into the intima were significantly increased as compared with sham-operated GK rats (17531 +/- 3747 microm2 vs 3072 +/- 1192 microm2, p < 0.0001; 15.6 +/- 3.1 per one transverse section vs 6.8 +/- 2.5 per one transverse section, p < 0.0005). Electron microscopic observations demonstrated an increased number of microvilli and lysosomes in endothelial cells, infiltration of macrophages and lymphocytes into the intima, and migration of medial smooth muscle cells into the intima that are considered to be early events in atherosclerosis. These morphologic changes could be induced by a deterioration in glucose metabolism. This rat may thus be useful for studying the process of the initiation of atherosclerosis in diabetes mellitus.

Injection with gold thioglucose impairs sensitivity to glucose: evidence that glucose-responsive neurons are important for long-term regulation of body weight

It has been proposed, but never demonstrated, that glucose-responsive neurons are essential for the long-term regulation of body weight, and that mice injected with gold-thio-glucose (GTG) become obese due to destruction of glucose-responsive neurons. To assess these hypotheses, mice were injected with either saline (control) or a dose of GTG that produces obesity, and the effects on feeding of peripheral injection of saline, glucose, 2-deoxyglucose (2-DG), or cholecystokinin (CCK) were measured. In control mice, 2-DG increased, whereas glucose and CCK decreased, food intake significantly. In contrast, in GTG-treated mice, 2-DG and glucose did not have a significant effect on food intake. The GTG-treated mice remained sensitive to the inhibitory effect of CCK on food intake. These data indicate that i.p. injection of GTG, which produces obesity, also destroys glucose-responsive neurons, consistent with the hypothesis that glucose-responsive neurons contribute to the long-term regulation of body weight.

Effects of gold thioglucose on neuropeptide Y messenger RNA levels in the mouse hypothalamus

Elevated hypothalamic neuropeptide Y (NPY) expression is found in several rodent genetic models of obesity, but any association in nongenetic models of obesity is unclear. Consequently, we have measured NPY mRNA levels in the ventromedial hypothalamus of a well-characterized model of obesity, the gold thioglucose (GTG)-injected mouse. Fourteen days after injection (early stage), animals were hyperphagic but not obese, hyperglycemic, or overtly hyperinsulinemic. Ten weeks after treatment (late stage), animals were obese, markedly hyperinsulinemic, and hyperglycemic. In both the early and late stages, NPY mRNA levels were reduced in the arcuate nucleus of GTG-injected animals. Although overnight fasting doubled NPY mRNA levels in control animals, there was no change at either stage in GTG-injected animals. NPY mRNA levels in the deep layers of the cerebral cortex and in the dentate gyrus were not affected by GTG treatment or overnight fasting. We conclude that GTG treatment reduces the expression of NPY mRNA in the arcuate nucleus and that, therefore, increased hypothalamic NPY expression is unlikely to be an important factor causing the obesity and other metabolic changes found in this model.

Ventromedial hypothalamic lesion-induced vagal hyperactivity stimulates rat pancreatic cell proliferation

BACKGROUND & AIMS

Ventromedial hypothalamic (VMH) lesions cause an increase in DNA content in the rat pancreas. This study examined the role of cell proliferation in the mitotic response of the rat pancreas after VMH lesion formation.

METHODS

Alterations in rat pancreatic DNA content, DNA synthesis, and labeling indices using antiproliferation cell nuclear antigen molecular antibody were measured 0,1,3, and 7 days after VMH lesion formation. Additionally, the effects of vagotomy, atropine, or anti-insulin antibody on VMH lesion-induced alterations in DNA synthesis were examined. Pancreatic samples were also treated with double immunostaining: first for PCNA and then for insulin, glucagon, and somatostatin.

RESULTS

Pancreatic weight, DNA content, and DNA synthesis increased in animals receiving VMH lesions. Proliferation was primarily observed in islet B and acinar cells beginning 1 day after VMH lesion formation, reaching a maximum rate after 3 days. VMH lesion-induced stimulation of DNA synthesis was completely inhibited by vagotomy or atropine administration but not by anti-insulin antibody.

CONCLUSIONS

Vagal hyperactivity produced by VMH lesions stimulated cell proliferation of rat pancreatic islet B and acinar cells primarily through a cholinergic receptor mechanism.

Ventromedial hypothalamic lesions inhibit corticosteroid feedback regulation of basal ACTH during the trough of the circadian rhythm

We have determined the effects of bilateral electrolytic lesions of the ventromedial hypothalamus (VMH) on activity in the hypothalamo-pituitary-adrenal (HPA) system. Acutely, during the first 5 days, lesions of the anterior-medial VMH caused loss of the diurnal rhythms in food intake and plasma corticosterone (B) levels. Plasma B concentrations were elevated during the time of the normal trough of the basal diurnal rhythm in HPA axis activity and the diurnal rhythm in food intake was abolished, in agreement with the results of others. Consistent with hyperactivity in the HPA axis, lesioned rats had increased adrenal weight, decreased thymus and body weights and decreased plasma transcortin concentrations. To determine how lesions of the VMH provoke these increases in activity of the HPA system, the sensitivity of ACTH in adrenalectomized, lesioned rats to replacement with exogenous B was determined under basal conditions during the trough (morning-AM) and peak (evening-PM) of the diurnal rhythm in HPA axis activity. ACTH in lesioned rats in the AM was insensitive to feedback over the very low range of plasma B of 1-4 micrograms/dl, whereas sham-lesioned controls exhibited the normal, high sensitivity of ACTH to B at this time of day. There was no difference between the sensitivity of ACTH to this low range of B in the PM in VMH- and sham-lesioned rats. Two to 5 weeks after VMH lesions, as found by others, mean daily plasma B levels did not differ from sham-lesioned controls; however, plasma B during the AM was still mildly elevated in these rats. Inhibition of plasma B in the PM by dexamethasone was less effective in lesioned rats. Although HPA system responses to hypoglycemia, corticotropin-releasing factor and ACTH were normal, the lesioned rats exhibited obesity, hyperinsulinemia, hyperglycemia, hypertension and tachycardia, all signs consistent with mild hyperactivity of the PHA axis. Occupancy of type I, high-affinity corticosteroid receptors is known to control basal activity of the HPA system during the trough of the diurnal rhythm and to interact with glucocorticoid receptors to affect basal activity during the peak of the diurnal rhythm and during AM stress. We conclude that VMH lesions disrupt transmission of inhibitory signals, mediated by occupancy of type I corticosteroid receptors, that are initiated by a B feed-back site.

The nuclear receptor steroidogenic factor 1 is essential for the formation of the ventromedial hypothalamic nucleus

The nuclear receptor steroidogenic factor 1 (SF-1) regulates the biosynthesis of the two essential mediators of male sexual differentiation, androgens and Müllerian-inhibiting substance, and is required for adrenal and gonadal development and gonadotropin expression. SF-1 is also expressed in the embryonic ventral diencephalon, subsequently localizing to the ventromedial hypothalamic nucleus, a region important for reproductive behavior. Mice lacking SF-1 secondary to targeted disruption of the Ftz-F1 gene had normal numbers and location of GnRH neurons but exhibited grossly impaired ventromedial hypothalamic nucleus structure. Despite their apparently normal GnRH neurons, treatment of Ftz-F1-disrupted mice with GnRH restored pituitary gonadotropin expression. These studies define SF-1's essential role within a discrete hypothalamic nucleus previously linked to reproduction.

Effects of intraventricular administration of neuropeptide Y on feeding behavior in fasted female rats with ventromedial hypothalamic lesions

The role of ventromedial hypothalamic nucleus (VMN) in feeding behavior induced by central administration of porcine neuropeptide Y (NPY) in fasted female rats was investigated focusing on the effect of the intracerebroventricular (i.c.v.) injection of NPY on food intake in rats with VMN lesions after 24 h of food deprivation. Cumulative food intake was measured 1, 3 and 6 h after injection. In Exp. 1, the i.c.v. injection of NPY into intact rats stimulated food intake compared with the injection of saline 1 and 3 h after the injections in a dose dependent manner (1 h; NPY 1 microgram, 3.29 +/- 0.43, 2 micrograms, 4.64 +/- 0.88, 5 micrograms, 5.15 +/- 0.61 vs. saline 2.48 +/- 0.42 g, P < 0.05 in 2 and 5 micrograms). 5 micrograms of NPY significantly stimulated food intake 6 h later. In Exp. 2, i.c.v. injection of NPY (2 micrograms) in VMN-lesioned rats showed no significant effect on food intake compared with the injection of saline 3 weeks after VMN lesioning (1 h; NPY 2 micrograms, 2.46 +/- 0.58 vs. saline 2.39 +/- 0.12 g). These results suggest that central administration of NPY enhances food intake in fasted female rats and that the VMN is one of the crucial sites of NPY induced feeding.

[Transplacental neurotoxic effects of monosodium glutamate on structures and functions of specific brain areas of filial mice]

Monosodium glutamate (MSG) was shown to penetrate placental barrier and distribute almost evenly among embryonic tissues using 3H-Glu as a tracer. When a lower (1.0 mg/g) and a higher (2.5 mg/g) doses of MSG were alternatively injected to Kunming maternal mice in every other days from mating to deliveries, obvious injury occurred in the ability of memory retention and Y-maze discrimination learning of adult filial mice pregnantly treated with higher doses (2.5 mg/g) of MSG. Meanwhile, the neuronal damages were observed in not only arcuate nucleus but also ventromedial nucleus of hypothalamus. Characteristic cytopathological changes induced by MSG showed swollen cytoplasm, dark pyknotic nuclei and loss of neurons. The radioligand-bindings in both hippocampus and hypothalamus altered significantly after the pregnant treatment of MSG. Possible mechanisms underlying MSG excitotoxic phenomena studied in single neuron by use of Ca2+ sensitive indicator Fura-2 with Spex AR-CM-MIC Cation Measurement System, might be due to increases of intracellular free Ca2+ concentration induced by MSG exposure, which was related to both the influx of Ca2+ and the depletion of Ca2+ from the intracellular Ca2+ stores. These experimental findings indicated that MSG performed its transplacental neurotoxicity in a dose-dependent manner. The excessive activation of Glu receptors and the overloading of intracellular Ca2+ induced by MSG ultimately leading to neuronal death may result in the reduction of the capability of learning and memory in adult filial mice pregnantly treated with MSG.

[Development of complete liver cirrhosis in hyperphagia-induced fatty liver]

The progression of alimentary fatty liver to liver cirrhosis is a very rare observation. During the year after surgical extirpation of a suprasellar craniopharyngioma in a seven years old boy developed severe obesity and again six years later at autopsy a complete liver cirrhosis with fatty liver was established. Injury of the ventromedial hypothalamic nuclei and resulting hyperphagia is the reason for the obesity following suprasellar tumours. The pathogenesis of liver cirrhosis following alimentary fatty liver is not completely evident up to now, such a progression is possible--as shown in this case--also in children and within a short period.

Basal and hyperinsulinemia-induced immunoreactive hypothalamic insulin changes in lean and genetically obese Zucker rats revealed by microdialysis

Lean and genetically obese Zucker rats were implanted with permanent intravenous catheters and a guide cannula was aimed at the region of the ventromedial (VMH) and paraventricular (PVN) nuclei to measure immunoreactive insulin collected by means of microdialysis. Preliminary experiments assessed the validity of a novel assay of insulin in microdialysates by a sensitized radioimmunoassay technique. This method was then used to measure basal levels of insulin and those induced by i.v. infusion of 0.5 U of insulin over 30 min in both lean and obese rats. Basal hypothalamic immunoreactive insulin levels were lower in the obese rats than in the lean Zucker rats. When insulin was infused i.v. for 30 min, hypothalamic immunoreactive insulin showed an increase in the 30-60 min sample, which was twice as great in the obese rats. Two facts suggest that the insulin found in the microdialysates was of cerebral, not vascular origin: the short latency in the response and the finding that the response was greater in obese rats.

Functional neuroanatomy and neuropathology of the human hypothalamus

The human hypothalamus is involved in a wide range of functions in the developing, adult and aging subject and is responsible for a large number of symptoms of neuroendocrine, neurological and psychiatric diseases. In the present review some prominent hypothalamic nuclei are discussed in relation to normal development, sexual differentiation, aging and a number of neuropathological conditions. The suprachiasmatic nucleus, the clock of the brain, shows seasonal and circadian variations in its vasopressin neurons. During normal aging, but even more so in Alzheimer's disease, the number of these neurons decreases. In homosexual men this nucleus is larger than in heterosexual men. The difference between the sexually dimorphic nuclei of men and women arises between the ages of 2-4 to puberty. In adult men this nucleus is twice as large as in adult women. In the process of aging, a sex-dependent decrease in cell number occurs. The vasopressin and oxytocin cells of the supraoptic and paraventricular nucleus are present in adult numbers as early as mid-gestation. Lower oxytocin neuron numbers are found in Prader-Willi syndrome, AIDS and Parkinson's disease. Familial hypothalamic diabetes insipidus is based upon a point mutation in the vasopressin-neurophysin-glycopeptide gene. Parvicellular corticotropin-releasing hormone-containing neurons in the paraventricular nucleus increase in number and are activated during the course of aging. In post-menopausal women, the infundibular or arcuate nucleus contains hypertrophic neurons containing oestrogen receptors. These neurons may be involved in the initiation of menopausal flushes. The nucleus tuberalis lateralis may be involved in feeding behaviour and metabolism. In Huntington's disease the majority of its neurons is lost; in Alzheimer's disease it shows very strong cytoskeletal alterations. Tuberomammillary nucleus neurons contain, e.g., histamine or galanine, and project to the cortex. Strong cytoskeletal changes, as well as plaques and tangles are found in this nucleus in Alzheimer's disease. The various hypothalamic nuclei are probably involved in many functions and symptoms of which only a minority has been revealed.

Genetic influences on glucose neurotoxicity, aging, and diabetes: a possible role for glucose hysteresis

Glucose may drive some age-correlated impairments and may mediate some effects of dietary restriction on senescence. The hypothesis that cumulative deleterious effects of glucose may impair hypothalamic neurons during aging, leading to hyperinsulinemia and other age-correlated pathologies, is examined in the context of genetic influences. Susceptibility to toxic effects of gold-thio-glucose (GTG) is correlated with longevity across several mouse strains. GTG and chronic hyperglycemia induce specific impairments in the ventromedial hypothalamus similar to impairments which occur during aging. GTG and a high-calorie diet both induce chronic hyperinsulinemia, leading initially to hypoglycemia, followed by the development of insulin resistance and hyperglycemia. Aging in humans and rodents appears to entail a similar pattern of hyperinsulinemia followed by insulin resistance. In humans, genetic susceptibility to high-calorie diet-induced impairments in glucose metabolism is extremely common in many indigenous populations, possibly due to the selection of the 'thrifty genotype'. It is suggested that the 'thrifty genotype' may entail enhanced sensitivity to the neurotoxic effects of glucose, and may represent an example of antagonistic pleiotropy in human evolution. These data are consistent with the hypothesis that genetic susceptibility of hypothalamic neurons to the cumulative toxic effects of glucose (glucose neurohumoral hysteresis) may correlate with genetic influences on longevity.

Importance of imparied insulin-gene expression in occurrence of diabetes in obese rats

To investigate the role of the beta-cell in the occurrence of diabetes in obesity, longitudinal changes of insulin-gene expression and pancreatic insulin content were compared among genetically obese diabetic (Wistar fatty) rats, genetically obese nondiabetic (Zucker fatty) rats, and ventromedial hypothalamus (VMH)-lesioned obese rats. Plasma glucose levels were significantly elevated with age in Wistar fatty rats, whereas they were virtually unchanged in VMH-lesioned and Zucker fatty rats. Obesity and hyperinsulinemia were evident in VMH-lesioned rats 1 wk after the operation and in Zucker and Wistar fatty rats at 5 wk of age. In VMH-lesioned rats, the pancreatic preproinsulin I mRNA (pplmRNA) level and pancreatic insulin content markedly increased approximately two- to threefold (P less than 0.001) with the development of hyperinsulinemia, whereas sham-operated rats showed no significant change. In Zucker and Wistar lean rats, the pplmRNA level and pancreatic insulin content increased with age, corresponding to increases in body weight. In Zucker fatty rats, the pplmRNA level and pancreatic insulin content at 5 and 14 wk of age were significantly higher than those of lean littermates. The pplmRNA level in Zucker fatty rats at 14 wk of age reached 290% of that of their lean littermates (P less than 0.001). On the other hand, the pplmRNA level and pancreatic insulin content in Wistar fatty rats at 5 and 14 wk of age did not increase more than those of their lean littermates at the corresponding ages and were therefore significantly lower than in Zucker fatty rats, which had a higher grade of hyperinsulinemia at 14 wk of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric analysis of obesity (ob/ob)- and diabetes (db/db)-associated hypothalamic neuronal degeneration in C57BL/KsJ mice

The influence of the obese (ob/ob) and diabetes (db/db) genetic mutations on hypothalamic structure was investigated in C57BL/KsJ and C57BL/6J mice strains by morphometric analysis of medial basal nuclei which are recognized to possess glucoregulatory neurons. Brains were collected and prepared for histomorphometric analysis at selected times following the development of expressed obesity and diabetes (Type II, non-insulin dependent) syndromes in order to compare both the strain and genomic influences on neuronal viability in the hypothalamic ventromedial (VMH) and arcuate (ARC) nuclei of mutant and age-matched control mice. The severity of each syndrome was determined by monitoring the concomitant changes in body weight and blood glucose levels in all groups. Both (db/db) and (ob/ob) mutant C57BL/KsJ mice exhibited an increase in the number and distribution of degenerated neurons in the VMH and ARC nuclei relative to corresponding controls. The mutation-associated exacerbation of the normal age-related neuronal loss, as observed in control MBH nuclei, was temporally associated with the overt expression of the hyperglycemic component of the obese and diabetes syndromes in aging C57BL/KsJ mice. No temporal or causal relationships were noted between the enhanced rate of premature neuronal degeneration, and either body weight or blood glucose levels, in either (db/db) or (ob/ob) C57BL/6J mice relative to controls. These data suggest that the hyperglycemic condition which characterizes the (ob/ob) and (db/db) mutant C57BL/KsJ mice is causally associated with the pronounced, premature MBH neuronal degeneration in these mouse strains. Neuronal changes were not pronounced when the genetic mutations were expressed in C57BL/6J mice. The accompanying alterations in brain glucose metabolism, hormone sensitivity, bioamine content and function which are recognized to occur in these mutant C57BL/KsJ mice may be causally associated consequences of the observed changes in MBH structural integrity and neuronal competence, with the severity of the mutation-associated changes being related to genetic background of the murine strain.