An autonomic hypothesis for hypothalamic obesity

Subdiaphragmatic Vagotomy With Pyloroplasty Ameliorates the Obesity Caused by Genetic Deletion of the Melanocortin 4 Receptor in the Mouse

Background/Objectives: We tested the hypothesis that abolishing vagal nerve activity will reverse the obesity phenotype of melanocortin 4 receptor knockout mice (Mc4r^−/−).

Subjects/Methods: In two separate studies, we examined the efficacy of bilateral subdiaphragmatic vagotomy (SDV) with pyloroplasty in the prevention and treatment of obesity in Mc4r^−/− mice.

Results: In the first study, SDV prevented >20% increase in body weight (BW) associated with this genotype. This was correlated with a transient reduction in overall food intake (FI) in the preventative arm of the study. Initially, SDV mice had reduced weekly FI; however, FI normalized to that of controls and baseline FI within the 8-week study period. In the second study, the severe obesity that is characteristic of the adult Mc4r^−/− genotype was significantly improved by SDV with a magnitude of 30% loss in excess BW over a 4-week period. Consistent with the first preventative study, within the treatment arm, SDV mice also demonstrated a transient reduction in FI relative to control and baseline levels that normalized over subsequent weeks. In addition to the accompanying loss in weight, mice subjected to SDV showed a decrease in respiratory exchange ratio (RER), and an increase in locomotor activity (LA). Analysis of the white fat-pad deposits of these mice showed that they were significantly less than the control groups.

Conclusions: Altogether, our data demonstrates that SDV both prevents gain in BW and causes weight loss in severely obese Mc4r^−/− mice. Moreover, it suggests that an important aspect of weight reduction for this type of monogenic obesity involves loss of signaling in vagal motor neurons.

Neonatal treatment with scopolamine butylbromide prevents metabolic dysfunction in male rats

We tested whether treatment with a cholinergic antagonist could reduce insulin levels in early postnatal life and attenuate metabolic dysfunctions induced by early overfeeding in adult male rats. Wistar rats raised in small litters (SLs, 3 pups/dam) and normal litters (NLs, 9 pups/dam) were used in models of early overfeeding and normal feeding, respectively. During the first 12 days of lactation, animals in the SL and NL groups received scopolamine butylbromide (B), while the controls received saline (S) injections. The drug treatment decreased insulin levels in pups from both groups, and as adults, these animals showed improvements in glucose tolerance, insulin sensitivity, vagus nerve activity, fat tissue accretion, insulinemia, leptinemia, body weight gain and food intake. Low glucose and cholinergic insulinotropic effects were observed in pancreatic islets from both groups. Low protein expression was observed for the muscarinic M₃ acetylcholine receptor subtype (M₃mAChR), although M₂mAChR subtype expression was increased in SL-B islets. In addition, beta-cell density was reduced in drug-treated rats. These results indicate that early postnatal scopolamine butylbromide treatment inhibits early overfeeding-induced metabolic dysfunctions in adult rats, which might be caused by insulin decreases during lactation, associated with reduced parasympathetic activity and expression of M₃mAChR in pancreatic islets.

Ventromedial hypothalamic lesions enhance small intestinal cell proliferation in mice

SUMMARY

BACKGROUND

We have found previously that ventromedial hypothalamic lesions (VMH) enhance cell proliferation in the visceral organs through vagal hyperactivity in rats. The goal of the current study was to determine the characteristics and nature of cell proliferation in the small intestine in VMH-lesioned mice.

METHODS

The weight and length of the small intestine, thickness of the mucosal and muscle layers, number of proliferating cell nuclear antigen (PCNA)-positive cells, and mitotic cell count in the mucosal layer in VMH-lesioned and Sham VMH-lesioned mice were determined at 7 days after the operation.

RESULTS

The weight and length of the small intestine in VMH-lesioned mice were significantly greater than those in Sham VMH-lesioned mice, by 11.6% and 15.0%, respectively. The thicknesses of the mucosal and muscle layers of the small intestine in VMH-lesioned mice were also significantly greater than those in Sham VMH-lesioned mice, by 12.7% and 12.5%, respectively. PCNA-positive cells and mitotic cells in the mucosal layer were densely present in crypts in VMH-lesioned mice, and were significantly increased by 31.9% and 71.7%, respectively, compared to Sham VMH-lesioned mice.

CONCLUSIONS

These results demonstrate that VMH lesions in mice enhance cell proliferation in the mucosal layers and cause cell hypertrophy or cell proliferation in the muscle layers of the small intestine, which increases the weight and length of the small intestine. VMH lesions in mice may be a new tool for identifying growth factors and related genes involved in enlarging the small intestine mainly through cell proliferation.

Early postnatal low-protein nutrition, metabolic programming and the autonomic nervous system in adult life

Protein restriction during lactation has been used as a rat model of metabolic programming to study the impact of perinatal malnutrition on adult metabolism. In contrast to protein restriction during fetal life, protein restriction during lactation did not appear to cause either obesity or the hallmarks of metabolic syndrome, such as hyperinsulinemia, when individuals reached adulthood. However, protein restriction provokes body underweight and hypoinsulinemia. This review is focused on the regulation of insulin secretion and the influence of the autonomic nervous system (ANS) in adult rats that were protein-malnourished during lactation. The data available on the topic suggest that the perinatal phase of lactation, when insulted by protein deficit, imprints the adult metabolism and thereby alters the glycemic control. Although hypoinsulinemia programs adult rats to maintain normoglycemia, pancreatic β-cells are less sensitive to secretion stimuli, such as glucose and cholinergic agents. These pancreatic dysfunctions may be attributed to an imbalance of ANS activity recorded in adult rats that experienced maternal protein restriction.

Hypothalamic obesity in patients with craniopharyngioma: treatment approaches and the emerging role of gastric bypass surgery

Hypothalamic obesity is a potential sequela of craniopharyngioma, arising from hypothalamic damage inflicted by either the tumor and/or its treatment. The marked weight gain that characterizes this disorder appears to result from impaired sympathoadrenal activation, parasympathetic dysregulation, and other hormonal and hypothalamic disturbances that upset the balance between energy intake and expenditure. Given hypopituitarism is commonly present, careful management of hormonal deficits is important for weight control in these patients. In addition, diet, exercise, and pharmacotherapy aimed at augmenting sympathetic output, controlling hyperinsulinism, and promoting weight loss have been used to treat this disease, but these measures rarely lead to sustained weight loss. While surgical interventions have not routinely been pursued, emerging data suggests that surgical weight loss interventions including Roux-en-Y gastric bypass can be safely and effectively used for the management of hypothalamic obesity in patients with craniopharyngioma.

Hypothalamic Obesity following Craniopharyngioma Surgery: Results of a Pilot Trial of Combined Diazoxide and Metformin Therapy

Objective. To assess the effect of combined diazoxide-metformin therapy in obese adolescents treated for craniopharyngioma. Design. A prospective open-label 6-month pilot treatment trial in 9 obese subjects with craniopharyngioma. Diazoxide (2 mg/kg divided b.i.d., maximum 200 mg/day) and metformin (1000 mg b.i.d.). Whole body insulin sensitivity index (WBISI) and area-under-the-curve insulin (AUC(ins)) were calculated. Results. Seven subjects completed: 4M/3F, mean ± SD age 15.4 ± 2.9 years, weight 99.7 ± 26.3 kg, BMI 35.5 ± 5.6 kg/m(2), and BMI SDS 2.3 ± 0.3. Two were withdrawn due to vomiting and peripheral edema. Of participants completing the study, the mean ± SD weight gain, BMI, and BMI SDS during the 6 months were reduced compared to the 6 months prestudy (+1.2 ± 5.9 versus +9.5 ± 2.7 kg, P = .004; -0.3 ± 2.3 versus +2.2 ± 1.5 kg/m(2), P = .04; -0.04 ± 0.15 versus +0.11 ± 0.08, P = .021, resp.). AUC(ins) correlated with weight loss (r = 0.82, P = .02) and BMI decrease (r = 0.96, P = .009). Conclusion. Combined diazoxide-metformin therapy was associated with reduced weight gain in patients with hypothalamic obesity. AUC(ins) at study commencement predicted effectiveness of the treatment.

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

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

Autonomic activity and glycemic homeostasis are maintained by precocious and low intensity training exercises in MSG-programmed obese mice

Current research employed electrical records from superior vagus and sympathetic nerve branch that supply fat retroperitoneal tissue (RS nerve) to investigate whether very moderate swim training in obese-programmed mice would change sympathetic and parasympathetic autonomic nervous system activities. Neonatal mice were treated with monosodium L: -glutamate (MSG), during their first 5 days of life, to induce obesity. Mice started training on weaning, comprising free swimming 3 days/week, 15 min/day for 10 weeks. After 12 h fasting, the nerve electrical signals of the 90-day-old mice were processed to obtain firing rates. Blood samples were collected to measure glucose and insulin levels. Adrenal catecholamine content was measured. MSG treatment caused obesity. Hyperglycemia and hyperinsulinemia in MSG-obese mice, without any change in food intake, were obtained. Vagus firing rates were higher in obese mice than those in lean ones. A decrease in RS nerve activity and lower adrenal catecholamine stores have been observed. Swimming normalized blood glucose and insulin levels and MSG-obesity onset was attenuated by exercise. Vagus activity from obese mice decreased, whereas RS nerve activity and adrenal catecholamine levels increased in trained ones. Results suggest that autonomic activity imbalance and metabolic dysfunctions observed in MSG-obese mice were inhibited by precocious and moderate exercise training.

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.

Use of somatostatin analogues in obesity

Obesity is a condition that results from dysregulation of energy balance. Insulin, a component of the efferent pathway of the energy-regulatory circuit, promotes storage of energy substrates in adipose tissue and is, therefore, a potential target for pharmacotherapy. Somatostatin and its analogues (octreotide and lanreotide) bind to somatostatin subtype 5 receptors on the beta-cell membrane, which limits insulin release and, consequently, may decrease adipogenesis. Somatostatin and its analogues have been used in trials in patients with paediatric hypothalamic obesity. These children have hypothalamic dysfunction, mainly due to brain tumours such as craniopharyngiomas, which are thought to generate increased vagal output, leading to hyperinsulinaemia and weight gain. Two small trials, each of 6 months' duration, in children with paediatric hypothalamic obesity showed either a minimal weight loss or stabilization of bodyweight. In children with Prader-Willi syndrome, the most common genetic hypothalamic disorder associated with hyperphagia, hyperghrelinaemia, massive obesity and other endocrine disturbances, somatostatin failed to control hyperphagia and weight gain in a small number of patients, although it lowered the levels of the anorexigenic hormone ghrelin. Long-acting release octreotide was recently used in hyperinsulinaemic obese adults without cranial pathology. Insulin suppression was associated with small decreases in the body mass indexes of obese subjects receiving the higher dosages of the drug, with an acceptable safety profile, similar to that in previous studies. In conclusion, somatostatin and its analogues, by suppressing beta-cell insulin secretion, can retard weight gain in children with hypothalamic obesity and induce a small amount of weight loss in some adults with hyperinsulinaemic obesity.

Weight gain in craniopharyngioma--a model for hypothalamic obesity

OBJECTIVES

To evaluate (1) the pattern of post-operative weight gain and (2) the risk factors associated with the development of post-operative weight gain and obesity in children treated for craniopharyngioma.

STUDY DESIGN

The records of 43 children who had primary craniopharyngioma resection were reviewed. Neurological, endocrine, anthropometric and radiological risk factors for the development of obesity and for post-operative increase in BMI SDS were analyzed.

RESULTS

Twenty-five patients (58%) became obese post-operatively. Obesity was significantly associated with higher BMI SDS at presentation and pre-operative hydrocephalus (p < 0.05). Increased BMI SDS from 0-12 months was significantly associated with post-operative MRI evidenced hypothalamic damage and higher BMI at presentation (p < 0.05).

CONCLUSIONS

Children who developed hypothalamic obesity had a significant, rapid BMI increase over the first 6 months, followed by stabilization, with no regression of BMI SDS.

The rise, fall, and resurrection of the ventromedial hypothalamus in the regulation of feeding behavior and body weight

Early researchers found that lesions of the ventromedial hypothalamus (VMH) resulted in hyperphagia and obesity in a variety of species including humans, which led them to designate the VMH as the brain's "satiety center." Many researchers later dismissed a role for the VMH in feeding behavior when Gold claimed that lesions restricted to the VMH did not result in overeating and that obesity was observed only with lesions or knife cuts that extended beyond the borders of the VMH and damaged or severed the ventral noradrenergic bundle (VNAB) or paraventricular nucleus (PVN). However, anatomical studies done both before and after Gold's study did not replicate his results with lesions, and in nearly every published direct comparison of VMH lesions vs. PVN or VNAB lesions, the group with VMH lesions ate substantially more food and gained twice as much weight. Several other important differences have also been found between VMH and both PVN and VNAB lesion-induced obesity. Concerns regarding (a) motivation to work for food and (b) the effects of nonirritative lesions have also been addressed and answered in many studies. Lesion studies with weanling rats and adult pair-tube-fed rats, as well as recent studies of knockout mice deficient in the orphan nuclear receptor steroidogenic factor 1, indicate that VMH lesion-induced obesity is in large part a metabolic obesity (due to autonomic nervous system disorders) independent of hyperphagia. However, there is ample evidence that the VMH also plays a primary role in feeding behavior. Neuroimaging studies in humans have shown a marked increase in activity in the area of the VMH during feeding. The VMH has a large population of glucoresponsive neurons that dynamically respond to blood glucose levels and numerous histamine, dopamine, serotonin, and GABA neurons that respond to feeding-related stimuli. Recent studies have implicated melanocortins in the VMH regulation of feeding behavior: food intake decreases when arcuate nucleus pro-opiomelanocortin (POMC) neurons activate VMH brain-derived neurotrophic factor (BDNF) neurons. Moderate hyperphagia and obesity have also been observed in female rats with damage to the efferent projections from the posterodorsal amygdala to the VMH. Hypothalamic obesity can result from damage to either the POMC or BDNF neurons. The concept of hypothalamic feeding and satiety centers is outdated and unnecessary, and progress in understanding hypothalamic mechanisms of feeding behavior will be achieved only by appreciating the different types of neural and blood-borne information received by the various nuclei, and then attempting to determine how this information is integrated to obtain a balance between energy intake and energy output.

Social and psycho-intellectual outcome following radical removal of craniopharyngiomas in childhood. A prospective series

BACKGROUND

A prospective study on childhood craniopharyngiomas (CPs) was conducted from 1994 to 1998 to appreciate the pre- and postoperative clinical, endocrine, mental, and intellectual status of the patients and to determine the incidence and severity of the postoperative hypothalamic syndrome.

METHODS

The series included 14 consecutive CPs. Twelve were retrochiasmatic and intraventricular, and two were partly prechiasmatic and extraventricular. All were treated with the aim of "total" removal. The removal was "total" in nine cases but incomplete in the other five. Immediate postoperative follow-up was uncomplicated in all cases.

CONCLUSION

At 2-year follow-up, the two children with an extraventricular CP and a "total" tumor removal were intellectually normal, had no hypothalamic syndrome, and attended normal school with good results. The 12 others, although still intellectually normal, were more or less severely affected by a hypothalamic syndrome which altered their social insertion and caused academic failure. The authors conclude from this study that radical surgery should be reserved to extraventricular CPs only.

Endocrine and neuroanatomic features associated with weight gain and obesity in adult patients with hypothalamic damage

PURPOSE

Obesity is a common consequence in patients with tumors of the hypothalamic region and of related treatment in children. Much less information is available on adult patients and long-term survivors. The aims of this study were to estimate the prevalence of obesity in adult patients with acquired structural hypothalamic damage and to define the characteristics of patients at greatest risk of obesity.

METHODS

A retrospective study was conducted of 52 patients (25 women; median age at diagnosis, 44 years; range, 17 to 78 years) with tumors involving the hypothalamic region. These included 22 craniopharyngiomas, 24 pituitary adenomas, and six other hypothalamic tumors. Changes in body mass index were determined, magnetic resonance imaging scans were scored by a radiologist for tumor size and the extent of involvement of the hypothalamus, and current hormone replacement therapy was recorded, to identify possible features associated with new or worsened obesity (defined as a body mass index > or =30 kg/m(2) at the latest follow-up, which had increased by at least 2 kg/m(2) since diagnosis of the tumor).

RESULTS

Serial body mass index data from diagnosis to the latest follow-up were available for 42 patients. After a median of 5 years (range, 1 to 19 years) of follow-up, most patients with hypothalamic damage were obese (52% [n = 22] vs. 24% [n = 10] at the time of diagnosis, P < 0.0001). In a multivariate model, use of desmopressin (odds ratio [OR] = 13; 95% confidence interval [CI]: 2.0 to 86; P = 0.007) and growth hormone replacement (OR = 7.6; 95% CI: 1.1 to 51; P = 0.04) were associated with new or worsened obesity during follow-up. No correlation was found between the initial size or location of the tumor and subsequent weight gain.

CONCLUSION

Obesity is highly prevalent in adult survivors of hypothalamic tumors. Use of desmopressin and growth hormone therapy, but not size or location of the tumor, were associated with weight gain and obesity following diagnosis. These findings may be helpful in identifying patients at increased risk of obesity, to whom earlier intervention could be offered.

Adrenal medullary function and expression of catecholamine-synthesizing enzymes in mice with hypothalamic obesity

The mechanisms underlying the onset of obesity are complex and not completely understood. An imbalance of autonomic nervous system has been proposed to be a major cause of great fat deposits accumulation in hypothalamic obesity models. In this work we therefore investigated the adrenal chromaffin cells in monosodium glutamate (MSG)-treated obese female mice. Newborn mice were injected daily with MSG (4 mg/g body weight) or saline (controls) during the first five days of life and studied at 90 days of age. The adrenal catecholamine content was 56.0% lower in the obese group when compared to lean controls (P < 0.0001). Using isolated adrenal medulla we observed no difference in basal catecholamine secretion percentile between obese and lean animals. However, the percentile of catecholamine secretion stimulated by high K+ concentration was lower in the obese group. There was a decrease in the tyrosine hydroxylase enzyme expression (57.3%, P < 0.004) in adrenal glands of obese mice. Interestingly, the expression of dopamine beta-hydroxylase was also reduced (47.0%, P < 0.005). Phenylethanolamine N-methyltransferase expression was not affected. Our results show that in the MSG model, obesity status is associated with a defective adrenal chromaffin cell function. We conclude that in MSG obesity the low total catecholamine content is directly related to a decrease of key catecholamine-synthesizing enzymes, which by its turn may lead to a defective catecholamine secretion.

Ventromedial hypothalamus lesions induce jejunal epithelial cell hyperplasia through an increase in gene expression of cyclooxygenase

BACKGROUND

We demonstrated that ventromedial hypothalamus (VMH) lesions facilitate DNA synthesis, which reflects cell proliferation in abdominal organs, including the liver, pancreas, stomach, small intestine and large intestine, all of which are amply innervated by the vagal nerve.

OBJECTIVE

To investigate which area DNA synthesis facilitates and what factors contribute to cell proliferation in the small intestine in VMH-lesioned rats.

DESIGN

At 7 days after VMH lesions or sham operations, a segment of rat jejunum was taken for histological examination. A part of the jejunum was also removed from VMH-lesioned and sham-operated rats after 3 days and examined for 5-bromo-2'-deoxyuridine (BrdU) incorporation. At 6, 12 and 24 h after VMH lesions, the proximal intestine was removed from individual rats, from the pylorus to the mid-jejunum. Total RNA was extracted from these tissues of each rat, and the levels of epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha mRNA were determined using reverse-transcription polymerase chain reaction. Cyclooxygenase (COX)-1 and -2 mRNA levels were determined using Northern blotting.

RESULTS

: Jejunal villi in VMH-lesioned rats were markedly enlarged compared to those of sham-operated rats and jejunal crypts in VMH-lesioned rats more markedly incorporated BrdU. Northern blot analysis revealed an increase in COX-1 mRNA after 6, 12 and 24 h in the jejunum of VMH-lesioned rats. COX-2 mRNA was decreased 6 and 12 h after VMH lesioning; however, it was significantly increased 24 h after VMH lesions in comparison to sham-operated rats. The levels of EGF and TGF-alpha mRNA were unchanged in VMH lesioned rats.

CONCLUSION

VMH lesions induced enlargement of jejunal villi and increased the gene expression of COX-1 in the small intestine. Prostaglandins, probably E(2), induced by COX-1 may be one candidate factor responsible for the cell proliferation of the small intestinal epithelium in these rats.

Blood glucose dynamics and control of meal initiation: a pattern detection and recognition theory

A new framework for understanding the control of feeding behavior, with special emphasis on the evolution of hunger, the initiation of feeding, and its dependence on patterns of blood glucose, is the subject of this review. A perspective on the current status and future directions of this search for a more complete understanding of the regulation of feeding behavior in laboratory rats and humans is presented including theoretical and experimental components. First, a historical perspective on the role of blood glucose in the control of feeding is presented. Next, the theoretical approaches that have been applied to the control of feeding and had a strong influence on experimental feeding research are summarized. This is followed by a statement and overview of a current theory that has emerged from studies of the role of transient declines in blood glucose in the control of meal initiation. The current working hypothesis that transient declines in blood glucose are endogenous metabolic patterns that are detected and recognized by the central nervous system and are mapped into meal initiation in rats and are correlated with meal requests in humans are then presented. Then, the experimental studies on meal initiation and its dependence on patterns of blood glucose, first in rats and then in humans, are reviewed in detail. Finally, the future directions of the work, limitations, and the implications for the understanding of the control of feeding behavior and the regulation of energy balance are discussed.

Hypothalamic obesity in humans: what do we know and what can be done?

Obesity is a common sequel to tumours of the hypothalamic region and their treatment with surgery and radiotherapy. The prevalence of hypothalamic obesity has been underestimated because it may take some years to develop, and the problem has been under-recognized by physicians. Weight gain results from damage to the ventromedial hypothalamus which leads, variously, to hyperphagia, a low metabolic rate, autonomic imbalance, growth hormone (GH) deficiency and various other problems that contribute to weight gain. However, with the exception of GH replacement, few clinical trials have evaluated significant numbers of patients and so the roles of various behavioural, dietary, pharmacological and obesity surgery approaches are controversial. Sufficient knowledge exists to identify those at high risk of hypothalamic obesity so that weight gain prevention approaches can be offered. In those who are already obese, we propose that the principal causal mechanisms in individual patients should be considered as a basis for guiding clinical management.

Central precocious puberty: clinical and laboratory features

OBJECTIVE

To determine whether the initial presentation of patients with central precocious puberty (CPP) varies according to the aetiology, whether this permits the differentiation between idiopathic and organic forms, and whether the body mass index (BMI) and plasma leptin concentrations are linked to gonadotrophin secretion.

DESIGN

The clinical and laboratory features of 256 patients (26 boys and 230 girls) with CPP were studied separately in boys and girls. We compared patients with idiopathic CPP (seven boys and 186 girls) to those with organic CPP, whose pubertal development revealed a central nervous system (CNS) lesion (five boys and 11 girls), and to patients with organic CPP associated with a previously treated CNS lesion (14 boys and 33 girls).

RESULTS

Boys with organic CPP, having revealed or treated CNS lesions, started their puberty earlier (3.0 +/- 1.0 years and 6.7 +/- 0.5 years) than boys with idiopathic CPP (8.5 +/- 0.2 years, P < 0.01 and < 0.05). Boys with organic CPP associated with a treated CNS lesion had lower luteinizing hormone (LH)/follicle stimulating hormone (FSH) peaks ratio after stimulation with gonadotrophin releasing hormone (GnRH) (1.6 +/- 0.5) than did boys with idiopathic CPP (2.2 +/- 0.3, P < 0.05). Girls with organic CPP revealing a CNS lesion started their puberty earlier (3.6 +/- 0.9 years) than girls with idiopathic CPP (6.6 +/- 0.1 years, P < 0.0 l) and had higher LH (P < 0.01) and FSH peaks (< 0.05). Girls with organic CPP associated with a treated CNS lesion had higher BMI (1.8 +/- 0.2 z-score) than did girls with idiopathic CPP (1.3 +/- 0.1 zs, P < 0.05), higher leptin concentrations (11.7 +/- 1.8 microg/l vs. 7.7 +/- 0.5 microg/l, P < 0.0 l), LH peak (P < 0.01), FSH peak (P < 0.05) and LH/FSH peaks ratio (1 +/- 0.1 vs. 0.8 +/- 0.1, P < 0.05). Only 12.4% of the girls with idiopathic CPP had BMI-zs < 0, and their plasma leptins were positively correlated with BMI (P < 0.0001).

CONCLUSIONS

The features of central precocious puberty vary according to the aetiology, but it is impossible to exclude a central nervous system lesion in a given patient with central precocious puberty without performing central nervous system imaging. This imaging remains necessary in all cases of central precocious puberty. Most of the girls with idiopathic central precocious puberty had increased BMI, but we found no correlation between plasma leptin concentrations and gonadotrophin secretion.

Hormonal factors influencing weight and growth pattern in craniopharyngioma

Patients operated on for craniopharyngioma frequently suffer from hyperphagia and are obese, but their statural growth is normal despite growth hormone (GH) deficiency. We have evaluated the hormonal factors influencing changes in weight and growth in 17 children before and 1, 3-6, 12, and/or 24 months after surgical resection of a craniopharyngioma performed at 7.7 +/- (SE) 1 years of age. Of these, 15 patients had a GH deficiency before surgery, and all had complete pituitary deficiency after it. The plasma fasting insulin concentrations before surgery were positively correlated with body mass index (BMI, kg/m(2); p < 0.05), plasma insulin-like growth factors (IGFI, p = 0.03, and IGFII, p = 0.04), and leptin (p = 0.03). They increased significantly 1 month after surgery and continued to increase thereafter, whereas leptin increased significantly only 3-6 months after surgery, paralleling changes in BMI. The plasma fasting insulin concentrations before surgery were also positively correlated with the weight changes (12.3 +/- 2.3 kg, p < 0.01) during the 12 months after surgery, but not with changes in BMI SDS (3.1 +/- 0.5, p = 0.07). Both expressions of weight change were correlated with the concomitant growth rates (4.8 +/- 0.7 cm, p < 0.01). IGFI was above the 10th percentile for children with idiopathic short stature in 10 of 15 patients with craniopharyngioma-induced GH deficiency and IGF-binding protein 3 in 14 of 15 patients. Craniopharyngioma itself modified the control of insulin secretion, and surgery increased the insulin secretion which continued in the same way in a given patient after surgery. The increased insulin secretion in turn increases weight and keeps IGFI nearly normal. This may explain the normal growth rate despite the complete lack of GH.

Neural sites and pathways regulating food intake in birds: a comparative analysis to mammalian systems

The paper reviews hypotheses explaining the regulation of food intake in mammals that have addressed specific anatomical structures in the brain. An hypothesis, poikilostasis, is introduced to describe multiple, homeostatic states whereby the regulation of metabolism and feeding occur in birds. Examples are given for both wild and domestic avian species, illustrating dynamic shifts in homeostasis responsible for the changes in body weights that are seen during the course of an annual cycle or by a particular strain of bird. The following neural structures are reviewed as each has been shown to affect food intake in birds or in mammals: ventromedial hypothalamic nucleus (n.), lateral hypothalamic area, paraventricular hypothalamic n., n. tractus solitarius and area postrema, amygdala, parabrachial n., arcuate n. and bed n. of the stria terminalis. Two neural pathways are described which have been proposed to regulate feeding. The trigeminal sensorimotor pathway is the most complete neural pathway characterized for this behavior and encompasses the mechanics of pecking, grasping and mandibulating food particles from the tip of the bill to the back of the buccal cavity. A second pathway, the visceral forebrain system (VFS), affects feeding by regulating metabolism and the balance of the autonomic nervous system. Wild, migratory birds are shown to exhibit marked changes in body weight which are hypothesized to occur due to shifts in balance between the sympathetic and parasympathetic nervous systems. Domestic avian species, selected for a rapid growth rate, are shown to display a dominance of the parasympathetic nervous system. The VFS is the neural system proposed to effect poikilostasis by altering the steady state of the autonomic nervous system in aves and perhaps is applicable to other classes of vertebrates as well.

Serotonin-depleting midbrain lesions do not prevent ovariectomy-induced weight gain

Past research has shown that subdiaphragmatic vagotomy and midbrain raphe lesions are each effective in impeding the development of hypothalamic obesity while neither affects the development of genetic obesity in Zucker rats. To further test the parallels that may exist between these two manipulations on another putative obesity model, we studied the effects of midbrain raphe lesions on the development of ovariectomy-induced weight gain, previously shown to be unaffected by vagotomy. Ten adult female rats received thermal lesions of the dorsal and median raphe nuclei (RAPHE) while 7 served as sham controls (SHAM). Following a 26-day recovery period during which body weight, food intake and water intake were periodically monitored, bilateral ovariectomy (OVX) was performed on 7 RAPHEs and 4 SHAMs, with laparotomy (LAP) being performed on 3 RAPHEs and 3 SHAMs. Body weights and intake variables were monitored for an additional 58 days, then animals were sacrificed for brain histological and biochemical assessments. RAPHEs weighed less despite eating and drinking more than SHAMs throughout this study. Nevertheless, OVX rats gained more weight regardless of lesion (mean +/- SEM weight gain = 73.9 +/- 5.5 g for RAPHE + OVX and 67.0 +/- 6.6 g for SHAM + OVX vs. 30.7 +/- 3.0 g for RAPHE + LAP and 39.7 +/- 5.5 g for SHAM + LAP). This occurred without reliable changes in the food or water intakes of either OVX subgroup. Histology confirmed that RAPHE lesions were largely localized to the dorsal and median raphe nuclei, as planned.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the efferent and afferent vagus nerve in the development of ventromedial hypothalamic (VMH) obesity

Hyperactivity of the vagus nerve and hypoactivity of the sympathetic nerves after VMH lesions both cooperatively contribute to the development of VMH obesity, mainly through hyperinsulinemia. Recently it has turned out that we should discriminate the role of the efferent vagus from that of the afferent vagus in the pancreatic hormone secretion. The hepatic branch is the main pathway of afferent fibers in the vagus, while the celiac (pancreatic) branch is the main pathway of efferent fibers. We investigated the role of the afferent and efferent vagus on the development of VMH obesity using the sectioning of the hepatic and celiac branch. Celiac vagotomy decreased insulin secretion and food intake, while hepatic vagotomy did not change them. The results suggested that the efferent vagus plays the main role in the development of VMH obesity, while the role of afferent vagus seems less apparent.

Ventromedial hypothalamic obesity: a reexamination of the irritative hypothesis

The basic assumption of brain research utilizing lesions is that any observed changes in behavior or physiological responses must be the result of tissue destruction. Reynolds suggested 25 years ago that in the case of electrolytic ventromedial hypothalamic lesions, the observed hyperphagia and obesity were due instead to metallic ion deposits from the electrode tip irritating adjacent tissue. His "irritative hypothesis" was largely ignored after others reported obesity in rats given nonirritative (i.e., no deposits) VMH lesions. However, recent studies have shown that the experimental observations by both Reynolds and his critics were correct and that the early discrepancies were largely due to the sex of the animals used in the experiments. Obesity can be produced with nonirritative VMH lesions, but the weight gain is only about 60% of that observed with irritative VMH lesions and the animals do not display the characteristic lesion-induced elevations in basal insulin levels. A new combination ablation-irritative hypothesis is proposed in which electrolytic VMH lesion obesity is attributed in part to tissue ablation and in part to metallic ion deposits stimulating (rather than disinhibiting) vagally mediated insulin responses.

Glucocorticoids and hypothalamic obesity

Recent studies have demonstrated a role for adrenal glucocorticoid hormones in the hyperphagia and obesity which follow lesions of the ventromedial hypothalamus (VMH). Although VMH lesions elevate morning plasma corticosterone levels, it is concluded that this contributes little to the development of obesity. More importantly, animals with VMH lesions appear to be hyperresponsive to very low levels of circulating glucocorticoids. The overeating and obesity are both prevented and reversed by either complete adrenalectomy or complete hypophysectomy (i.e., resulting in plasma corticosterone levels of less than 1.0 microgram/dl) and restored by dosages of glucocorticoids that have no effect on feeding behavior and weight gain in nonlesioned adrenalectomized animals. Mineralocorticoid hormones have no effect on hypothalamic obesity. Judging by the time course of effects on feeding behavior in VMH-damaged mice of a single intracerebroventricular injection of a low dose of glucocorticoid, which has no effect when administered intraperitoneally, it is concluded that glucocorticoids exert their effect centrally in a permissive, rather than a regulatory, manner. Stimulation of the neighboring paraventricular nuclei (PVN) with norepinephrine or neuropeptide Y produces a rapid feeding response which is also abolished by adrenalectomy and restored with administration of glucocorticoids. However, it is unlikely that the PVN is the site at which glucocorticoids exert their effect in animals with VMH lesions, for PVN lesions or knife-cuts, or combination VMH-PVN lesions, also result in hyperphagia and obesity. It is concluded that adrenal glucocorticoid hormones exert their permissive effects on feeding behavior at brain sites other than the medial hypothalamus. The septo-hippocampal complex is suggested as a possible site.

Controversies in plastic surgery: suction-assisted lipectomy (SAL) and the hCG (human chorionic gonadotropin) protocol for obesity treatment

The advent of SAL (suction-assisted lipectomy) has dramatically increased the number of obese patients coming to our consultation offices. Despite several articles suggesting a conservative approach to fat suction, some reports insinuate that SAL might be a useful tool for obesity treatment. This hypothesis is refuted by a vast body of evidence that concludes that the adipose tissue may regenerate in adult humans. Therefore, surgical procedures are not advised as the method of choice to manage the disease. On the other hand, the terms obesity and being overweight may not be interchangeable. Obesity may be a disease whereas being overweight is a sign of the disease. Consequently, proper preoperative selection of candidates for SAL becomes mandatory. The hCG (human chorionic gonadotropin) method for obesity treatment appears to be a complete program for the management of obesity. It contains pharmacologic, dietetic, and behavior modification aspects in a 40-day course of treatment. Some data suggest hCG to be lipolytic, thus explaining former clinical observations regarding body fat redistribution in treated patients. hCG commercial preparations contain beta-endorphin, an opioid peptide linked to mood behavior. This article speculates on the possible actions of the complex hCG beta-endorphin in the neuromodulation of mood and energy metabolism. The method comprises a behavior modification that helps in handling the patient better. There are some correlations between a current behavior modification program and the basic guidelines contained in the hCG protocol. Thus, the hCG method appears to be a reasonable alternative in the management of a long-standing, unsolved problem of human metabolism.

Autonomic and endocrine factors in the regulation of food intake

Destruction of the ventromedial hypothalamus produces hyperphagia, hyperinsulinemia and hypertriglyceridemia. These changes appear to be partly the result of increased firing rate of the vagus nerve and reduced firing rate of the sympathetic nerves. These reciprocal changes in the function of the autonomic nervous system appear to provide an adequate explanation for the hyperinsulinemia in this syndrome, and for the reduced heat expenditure. Destruction of the lateral hypothalamus, has effects opposite to those of the ventromedial hypothalamus with a reduction in food intake, a decrease in body fat, and an increase in the activity of the sympathetic nervous system. These reciprocal functions of the hypothalamus are associated with different adrenergic receptors. A medial hypothalamic alpha-adrenergic system mediates the epinephrine stimulation of feeding, and a beta-adrenergic system mediates the lateral hypothalamic inhibition of eating. Peptides from the endorphin family can stimulate food intake, but most other peptides are inhibitory. Growth hormone and thyroid hormone stimulate food intake under appropriate conditions. Insulin and adrenal steroids appear to play the most important role of all the hormones in regulating food intake. Deficiency of adrenal glucocorticoids is associated with decreased food intake and a wasting of body flesh. Increased levels of glucocorticoids, on the other hand, produce a variety of truncal obesity. In animals with ventromedial hypothalamic lesions and obesity, adrenalectomy will reverse the obesity. In genetically obese rats and mice, adrenalectomy will attenuate the progression of the syndrome. These effects appear to be through a reduction of food intake, and an increase in energy expenditure. Injections of insulin will stimulate food intake and may lead to obesity.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced norepinephrine turnover in mice with monosodium glutamate-induced obesity

The disappearance of norepinephrine from the heart, interscapular brown adipose tissue (BAT), and pancreas has been examined in mice with monosodium glutamate (MSG)-induced obesity and in untreated controls. MSG-treated mice became obese in the absence of increased food intake and their core temperature was significantly lower compared to control mice. The rate of norepinephrine turnover following blockade of norepinephrine synthesis with alpha-methyl-para-tyrosine was significantly slower in heart and interscapular BAT of these mice than in untreated controls, but MSG had no effect on the pancreas. It is suggested that reduced norepinephrine turnover may be a major factor in the development of obesity after neonatal administration of MSG.

The origins and role of efferent vagal nuclei in hyperinsulinemia in hypothalamic and genetically obese rodents

The main brainstem parasympathetic efferent neurons that ultimately reach the pancreas and facilitate insulin secretion are located in the nucleus ambiguus (NA) and the dorsal motor nucleus of the vagus nerve (DMX). With regard to insulin secretion, hypothalamic (produced by ventromedial hypothalamic (VMH) lesions) and genetic obesities have features in common: (a) insulin oversecretion is an early abnormality in both syndromes; and (b) this abnormality is vagus nerve-mediated. VMH lesions and possible, spontaneously occurring (i.e. genetic) CNS-located abnormalities appear to result in an increased parasympathetic efferent tone together with decreased sympathetic efferent tone that is likely to be responsible for the occurrence of hyperinsulinemia, obesity and, eventually, insulin resistance.

Lateral hypothalamic lesions and norepinephrine turnover in rats

Animals with lateral hypothalamic lesions lost significantly more weight in the 18 h following this lesion than did sham-operated animals or rats with cerebral cortical lesions deprived of food for the same time period. In the acutely fasted sham-operated animals the turnover of norepinephrine in interscapular brown adipose tissue, heart, and pancreas was slowed but in fasted rats with lateral hypothalamic lesions norepinephrine turnover rates were three- to ninefold faster in all three organs. Exposure to the cold (4 degrees C) significantly increased norepinephrine turnover in the interscapular brown adipose tissue, heart, and pancreas of fasted sham-operated rats, but did not further increase the rate of turnover in lateral hypothalamic-lesioned rats. Rats with lesions in the cerebral cortex responded in a fashion similar to that of the sham-operated animals. Gastric erosions and microhemorrhagic gastric mucosa were observed in five of six acutely fasted rats with lateral hypothalamic lesions whereas all sham-operated rats had a normal appearance of the stomach lining. Animals with lateral hypothalamic lesions made 3 wk earlier also showed an increased rate of norepinephrine turnover in the interscapular brown adipose tissue, heart, and pancreas following an 18 h fast. Rats with bilateral lesions in the paraventricular region of the hypothalamus, however, responded similarly to sham-operated animals with a reduction in the turnover in norepinephrine with fasting and an increase in norepinephrine turnover rate after cold exposure even with fasting. These data suggest that lateral hypothalamic lesions produce an acute increase in turnover of norepinephrine, and that this increased turnover persists for up to 3 wk.

Hypothalamic hyperinsulinemia and obesity: role of adrenal glucocorticoids

The effects of adrenalectomy on the obesity and hyperinsulinemia induced by ventromedial hypothalamic (VMH) lesions were studied in female rats. Plasma insulin and glucose levels were assayed after a 4-h fast and 17 min after the initiation of a meal (6 ml sweetened milk in 7 min). The development of hypothalamic obesity was prevented by prior adrenalectomy and restored by administration of corticosterone. Adrenalectomy abolished both the basal and postabsorptive hyperinsulinemia observed in sham-adrenalectomized rats with VMH lesions. Corticosterone treatment of adrenalectomized animals enhanced both basal and postabsorptive insulin levels, but adrenalectomized rats with VMH lesions were hyperinsulinemic compared with animals with sham lesions only under the postabsorptive condition. Postabsorptive glucose levels were unaffected by either the lesion or adrenal ablation. The results support our previous conclusion that postabsorptive hyperinsulinemia is of greater importance than is basal hyperinsulinemia in the pathogenesis of hypothalamic obesity. Although the results are consistent with a stimulatory role of corticosterone on food intake mediating the postabsorptive hyperinsulinemia, a primary effect on CNS loci involved with the regulation of insulin secretion is also possible.

The effect of streptozotocin-induced diabetes on pituitary and hypothalamic endorphin equivalents

This study examines the effect of experimentally induced diabetes mellitus in rats on tissue concentrations of opioid peptides in the neurointermediate lobe (NIL), anterior pituitary (AP) and hypothalamus. Diabetic animals were found to have a marked increase in endorphin equivalents, measured by opiate receptor binding assay, in the NIL whereas no change was observed in beta endorphin-like immunoreactivity (beta ELI) or ACTH measured by RIA. These results may indicate the presence of a feedback mechanism and suggest the possibility that opioid peptides may be physiologically important in the maintenance of glucose homeostasis.

Chronic sucrose ingestion induces mild hypertension and tachycardia in rats

As a means for increasing sympathetic activity, male weanling rats were given 8% sucrose solution to drink instead of water. After 5 weeks, systolic pressures measured with a tail-cuff method became appreciably elevated, and the elevation was verified when phasic pressures were later recorded directly from femoral catheters. Successful induction of sympathetic overactivity was considered a likely explanation because sucrose-ingesting rats, compared with untreated controls, had faster heart rates and larger hypotensive responses to alpha-adrenergic blockade with phentolamine. Upon graded electrical stimulation of the ventromedial hypothalamus under urethane anesthesia, resulting pressor and sympathetic nerve responses were also larger in sucrose-treated rats. By contrast, pressor responses to injections of norepinephrine or tyramine were unaffected, thereby indicating that cardiovascular sensitivity had not been enhanced by sucrose ingestion. During intravenous glucose tolerance tests, increases in plasma insulin were consistently lower in sucrose-treated than control rats even though corresponding increases in plasma glucose were just transiently higher. These results support the interpretation that chronic sucrose ingestion inhibits pancreatic insulin secretion and elevates blood pressure by stimulating the ventromedial hypothalamus to increase sympathetic activity.

Energy fuel and hormonal profile in experimental obesities

Several types of experimental obesities are characterized by the occurrence of an early hypersecretion of insulin that produces an increase in both triglyceride secretion by the liver and fat deposition in adipose tissue. This hypersecretion of insulin, together with other ill-defined factors, is subsequently responsible for a state of insulin resistance. The early oversecretion of insulin in hypothalamic and genetic (e.g. fa/fa rats) obesities can be experimentally demonstrated. Thus, within 20 min of acute lesion of the ventromedial hypothalamus (VMH), glucose-induced insulin secretion is greater in lesioned than in non-lesioned control rats; this increase can be blocked by superimposed, acute vagotomy. Moreover, an infusion of glucose to 17-day-old, pre-weaned control and genetically pre-obese rats (i.e. animals genetically-determined to become obese but with a normal body weight at this age) elicits much greater insulinaemia in the pre-obese than in the controls, despite similar basal, pre-infusion values in both. This increased insulin secretion in the pre-obese rats can be restored to normal by pre-treating them acutely with the cholinergic inhibitor, atropine. Thus, in these two types of obesity, an increased vagal tone appears to be of importance for the early occurrence of insulin over-secretion. Hyperinsulinaemia produced by increased tone of the vagus nerve appears to be reinforced by the decreased activity of the sympathetic system observed in obese rodents. In many obese rodents, plasma growth hormone levels are abnormally low. The inadequate secretion of this hyperglycaemic hormone may explain why, in some types of obesity syndrome, hyperglycaemia is not necessarily present, despite insulin resistance. Insulin resistance in experimental obesities has been shown to occur at the level of the adipose tissue, the muscles and more recently, the liver. The latter has been demonstrated using the in vivo euglycaemic clamp technique; thus, glycogenolysis of genetically obese (fa/fa) rats could not be shut off, as in controls, by either basal or increased plasma insulin levels. This particular pathway is therefore insulin resistant. The precise etiology of the early over-secretion of insulin in VMH-lesioned rats is, however, unknown: with VMH lesions, the origin is clearly the central nervous system (CNS), but the pathways actually interrupted by the lesions and those responsible for the hyperactivity of the vagus, remain to be determined.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of vagally-medicated hyperinsulinemia in hypothalamic obesity

Evidence that the obesity syndrome which follows ventromedial hypothalamic (VMH) lesions is at least partially the result of a primary metabolic dysfunction is reviewed, as are proposals that the altered metabolism is due to enhanced vagally-mediated insulin release. This hypothesis was based largely on experiments demonstrating the complete reversal of hypothalamic obesity by subdiaphragmatic vagotomy, but subsequent studies have revealed that hypothalamic obesity is not always prevented by prior vagal transections. Interpretation of these discrepant results has been made difficult because of the frequent use of gastric secretion, behavioral, or other indirect tests for completeness of vagotomy. A review of more recent studies which have employed either direct assessment of vagotomy effects on insulin levels, pharmacological blockade of vagal efferent activity, or selective vagotomies indicates that vagally-mediated hyperinsulinemia can account for no more than 40% of the weight gain observed in animals with VMH lesions fed ad libitum, and may not be involved in the obesity that results from some parasagittal VMH knife cuts. It is concluded that vagally-mediated hyperinsulinemia does make a substantial, although not exclusive, contribution to the increased carcass lipid content observed in VMH animals that are food-restricted or pair-fed with control animals.

Hypothalamic regulation of lipid metabolism in the rat: effect of hypothalamic stimulation on lipolysis

In unanesthetized rats, electrical stimulation of the ventromedial hypothalamic nucleus (VMH) induced a marked increase in plasma concentration of glycerol, but did not increase the plasma free fatty acid (FFA) concentration, probably owing to a great elevation of plasma lactate which might inhibit the release of FFA from adipose tissue. In anesthetized rats, on stimulation of the VMH there was no remarkable increase in the plasma lactate, and the plasma glycerol and FFA concentrations were both elevated markedly. Electrical stimulation of the lateral hypothalamic nucleus (LH), on the other hand, had no significant effects on plasma glycerol and FFA levels. Bilateral adrenodemedullation did not prevent the lipolytic response to VMH stimulation, although it reduced slightly the increment of plasma glycerol and FFA. However, the lipolytic response was completely blocked by previous treatment of the animals with hexamethonium or propranolol, but not with phentolamine. These results suggest that sympathetic innervation of the adipose tissue is the dominant factor involved in VMH-induced lipolysis in the rat, while the role of the adrenal medulla is subdominant; the effect of VMH stimulation is mainly transmitted through the sympathetic nervous system to beta-adrenergic receptor of the adipose tissue.

Hypothalamic obesity : The autonomic hypothesis and the lateral hypothalamus

Several lines of evidence support the hypothesis that derangements in the function of the autonomic nervous system play an important role in the development of hypothalamic obesity. Vagotomy below the diaphragm reverses the syndrome. In diabetic rats cured of their diabetes with transplants of fetal pancreatic tissue beneath the renal capsule, ventromedial hypothalamic (VMH) lesions do not produce the characteristic rise in food intake nor do they significantly increase serum insulin. These observations indicate that the hyperinsulinaemia following VMH lesions is the result of neural connections rather than from a circulating humoral factor released following VMH injury. The smaller salivary glands, reduced level of glucagon and impaired mobilization of fatty acids during stress in VMH lesioned rats point to reduced activity of the sympathetic nervous system. The impaired mobilization of fat from retroperitoneal depots in VMH lesioned rats during fasting is similar to the effect of sympathetic denervation of the retroperitoneal fat pad. Similarly, unilateral sympathectomy caused an increased weight gain in rats almost as much as unilateral VMH lesions but significantly less than in bilaterally lesioned rats. These studies with fasting and feeding implicate the VMH in the control of the sympathetic nervous system. When atropine and epinephrine were given to VMH lesioned rats, there was a significant depression in basal and glucose-stimulated levels of insulin. Finally when VMH lesions were placed after lateral hypothalamic lesions, the effect of the VMH lesions did not seem to be reduced, suggesting that the two effects are independent. A model dealing with the effects of VMH lesions is presented in an attempt to integrate these findings.