Effects of leptin and orexin-A on food intake and feeding related hypothalamic neurons

The lateral hypothalamic area (LHA) and the ventromedial hypothalamic nucleus (VMH) have historically been implicated in ingestive behavior, energy balance and body mass regulation. The LHA is more closely associated with the initiation of eating; whereas the VMH mediates the cessation of eating. The parvocellular part of the paraventricular nucleus (pPVN) is also included in the suppressing mechanism. Recently, two hypothalamic peptides, orexin-A and orexin-B, localized in the posterior and lateral hypothalamic perifornical region were discovered in the rat brain and they increase food intake. Leptin, a protein encoded by an obesity gene, expressed in adipose tissue and released into the blood also affects food intake. Orexin and leptin receptors have been localized in the LHA, pPVN, and VMH. The purpose of this study was to measure food intake in the rat in response to leptin and orexin-A; and to determine their electrophysiological effects on feeding related hypothalamic neurons. Results clearly show that leptin suppresses food intake whereas orexin-A increases food intake. These differences are associated with leptin and orexin-A modulatory effects on LHA, pPVN, and VMH glucose responding neurons. In the LHA, leptin inhibits a larger proportion of both glucose-sensitive neurons (GSNs) and non-GSNs. In the pPVN, leptin increases more GSNs in comparison to non-GSNs. Whereas in the VMH, leptin increases the activity of glucoreceptor neurons (GRNs) in comparison to non-GRNs. Orexin-A had opposite effects: increases activity of GSNs more than the non-GSNs in the LHA and significantly suppresses GRNs in the VMH. In the pPVN, orexin-A had no observable effects on neurons that have a low density of orexin 2 receptors. Results are discussed in terms of hypothalamic neural circuits that are sensitive to endogenous food intake inducing and reducing substances.     

厌食儿童和正常儿童食物刺激下丘脑功能区fMRI的研究

为了研究小儿厌食症患者和正常儿童在食物刺激时下丘脑食欲中枢的兴奋情况,本论文搜集了10名厌食儿童、10名正常儿童在口服葡萄糖后下丘脑的功能性核磁共振(functional magnetic resonance imaging,fMRI)共35min的信号数据,并比较两组间功能区信号强度的差异。结果显示:所有受试者的下丘脑室旁核(PVN)、腹内侧核(VMH)及外侧区(LHA)在口服葡萄糖刺激后均出现了fMRI信号的激活,在厌食儿童下丘脑PVN及LHA此激活信号强度低于正常儿童,而VMH则高于正常儿童。本实验结果提示,下丘脑PVN、VMH及LHA功能的异常可能与小儿厌食症的发病密切相关。     

Feeding after nutrient infusions: effects of hypothalamic lesions and vagotomy.

Normal rats, and rats with lesions in the lateral hypothalamic area (LHA), ventromedial hypothalamus (VMH), or with subdiaphragmatic vagotomies were duodenally infused with nutrient solutions representative of all three macronutrients, and the effect on food intake for a period up to 3 hr was assessed. Glucose reduced consumption in the control and VMH controls, but not in the LHA or vagotomized groups. Amino acids decreased intake in the control and LHA groups and showed a trend toward a decrease in the VMH group, but not in the vagotomized group. Fat suppressed intake significantly in control, VMH and LHA groups and there was a trend toward suppression in vagotomized rats. The subcutaneous injection of insulin to the same animals elicited eating in all but LHA animals. These results suggest that different nutrients reduce food consumption in the short term through different anatomical substrates involving the peripheral and central nervous system.     

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.     

Food intake control and RNA content of hypothalamic neurons in infant rats

The influence of glycerol, glucose and lysine administration on the total RNA content in individual neurons of the ventromedial hypothalamus (VMH) and lateral hypothalamus area (LHA) in infant male rats was studied. Sixty minutes after administration, the total RNA content of the VMH neurons significantly decreased--from 13th day after glycerol and from 17th day after the glucose and lysine administration. The total RNA content of LHA neurons significantly increased from 17th day after glycerol and glucose and on 25th day after lysine administration. The noted changes of the RNA content, and especially the changes of the RNA proportion in these hypothalamic regions are well corresponding with the onset of the hypophagic effect of glycerol, glucose and amino acids in infant rats. The oppositional changes of the RNA content of VMH and LHA neurons are in conformity with the different role of these hypothalamic centers in food intake control.     

RNA content of neurons in the ventromedial nuclei and lateral hypothalamic area relative to feeding status

The total RNA content of hypothalamic and cortex neurons in relation to the feeding status of adult male Wistar rats was studied. Experimental conditions including food deprivation (12 and 24 hours) and relative satiation (short-term refeeding, glucose or glycerol administration) changed in different ways the total RNA content of the neurons in the ventromedial hypothalamic nuclei (VMH) and in the lateral hypothalamic area (LHA) with respect to fasting or satiety. Only the long-term absence of food (24 hours) significantly increased the total RNA content of the VMH cells, while the RNA content of the LHA neurons significantly decreased in both the 12 and 24 hr fasted rats compared with those fed ad lib. The sixty minute free access to food after 12 or 24 hours of fasting fully reversed these changes. The short-term food intake significantly increased the RNA content of the LHA cells of the 12 and 24 hr fasted animals while the total RNA content of the VMH neurons significantly decreased only in the 24 hr fasted rats. The effect of glucose and glycerol administration on the RNA content of the LHA neurons (in 12 hr fasted rats) was similar to the effect of refeeding. One hour after giving glucose (1 g/kg b.wt.) or glycerol (300 mg/kg b.wt.) the total RNA content in the LHA neurons significantly increased. No changes in RNA content were observed in the neurons of the cortex when comparing the experimental and control rats. The results demonstrated the close relationship between the RNA content of the hypothalamic neurons and the feeding status.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of food restriction and adrenalectomy in rats with VMH or PVH lesions

The effects of adrenalectomy in rats with ventromedial or paraventricular hypothalamic lesions have been studied in two experiments. Rats with ventromedial hypothalamic lesions or lesions in the paraventricular nucleus were allowed to gain weight for fourteen days at which time they were adrenalectomized. Before adrenalectomy, animals with VMH lesions ate more, gained significantly more weight than animals with lesions in the paraventricular nucleus, and both were significantly heavier and consumed more food than sham-operated controls. Following adrenalectomy, food intake decreased and both groups of lesioned animals lost weight. The animals with VMH lesions stabilized at weights above the control animals. Implantation of corticosterone enhanced weight gain and food intake in animals with lesions in either the paraventricular nucleus or the ventromedial hypothalamus. In the second experiment, one subgroup of rats with VMH lesions was adrenalectomized, and allowed to eat ad lib. Two other groups of sham-operated rats with VMH lesions served as controls. One group ate ad lib and one group was pair fed to the food intake of the adrenalectomized VMH-lesioned rats. Weight gain in the adrenalectomized VMH-lesioned rats and the pair-fed VMH-lesioned controls was similar and less than the VMH-lesioned rats eating ad lib. GDP binding to interscapular brown adipose tissue was related to the degree of weight gain, not to the presence of the VMH lesion. These data show that corticosterone is essential for the expression of obesity in both PVH- and VMH-lesioned rats. They also argue that the reduction in the activity of the sympathetic nervous system of VMH-lesioned rats as estimated by the GDP binding to mitochondria from brown adipose tissue is associated with hyperphagia.     

Effects of chronic intrahypothalamic infusion of insulin on food intake and diurnal meal patterning in the rat

In Experiment 1, rats were chronically infused with insulin (2.7, 27, or 270 ng/hr) or 0.9% saline into the ventromedial (VMH), medial perifornical (PF), or lateral (LH) hypothalamus. VMH infusions of insulin caused a significant, dose-dependent decrease in food intake and body weight; PF infusion of insulin was less effective, but significant; whereas LH infusions of insulin were ineffective. In Experiment 2, rats were chronically infused with insulin (0.54 ng/hr) or 0.9% saline into the VMH, paraventricular (PVN), or posterior (PN) hypothalamic nucleus. Subjects that received VMH or PN infusions of insulin failed to regain weight lost as a result of surgery even 2 weeks after infusion; subjects that received PVN infusions of insulin regained their preoperative weights faster than did controls. All of the groups that received insulin significantly increased their daytime food intake during the infusion period and decreased their night food intake slightly; 24-hr food intake remained unchanged.     

Chemical and neuronal control of feeding motivation

The sugar acids, 3,4-dihydroxybutanoic acid gamma-lactone, 2-buten-4-olide and 2,4,5-trihydroxy pentanoic acid gamma-lactone which were found in blood modulate feeding behavior of rats by modifying neuronal activity in the lateral hypothalamic area [LHA] and the ventromedial hypothalamic nucleus [VMH]. The former two act as satiety substances and the latter as a hunger substance. Detection of changes in the concentration of these sugar acids in the blood by glucoreceptor neurons in the VMH and glucose-sensitive neurons in the LHA is important in the regulation of feeding. A phasic increase in fibroblast growth factor [FGF] was found in the cerebrospinal fluid after feeding. Cerebroventricular application of acidic FGF suppresses food intake. Interleukin-1 beta and tumor necrosis factor which have a quite similar amino acid sequence as FGF also suppress feeding. The neuronal mechanism of satiety action of these polypeptides is the same as the sugar acids. The results indicate that these endogenous substances participate in the central regulation of feeding. Hierarchial organization of the endogenous chemical information processing system which is composed of the viscera, medulla, hypothalamus and the cortex is discussed.     

Stress-induced changes in cellular responses in hypothalamic structures to administration of an antigen (lipopolysaccharide) (in terms of c-Fos protein expression)

Stress is known to affect the intensity of the immune response. The involvement of central regulatory structures in mediating these changes was addressed by analyzing the extent of activation of neurons in the hypothalamus (in terms of the number of c-Fos-positive cells) in rats 2 h after i.v. administration of lipopolysaccharide alone and on the background of electrical pain stimulation. Studies were performed using 52 male Wistar rats weighing 200–250 g. c-Fos protein expression was studied by immunohistochemical analysis. Increases in the quantity of c-Fos-positive cells 2 h after administration of lipopolysaccharide were seen in the following hypothalamic structures: AHN, PVH, LHA, VMH, DMH, and PH. After electrical pain stimulation, the number of c-Fos-positive cells increased in these same hypothalamic structures (AHN, PVH, LHA, VMH, DMH, and PH). The combination of electrical pain stimulation and lipopolysaccharide administration led to a decrease in the extent of activation in hypothalamic structures AHN, PVH, LHA, and VMH as compared with the characteristic reaction to lipopolysaccharide without electrical pain stimulation. Electrical pain stimulation suppressed the intensity of the immune response induced by lipopolysaccharide (as assessed by local hemolysis and counts of the numbers of spleen antibody-forming cells). Thus, changes in the extent of activation of hypothalamic structures (AHN, PVH, LHA, VMH) correlated with the development of stress-induced immunosuppression, i.e., morphofunctional mapping of the extent of activation of hypothalamic structures allowed identification of which changes in hypothalamic cell activity occurred with stress-induced changes in immune system responses to antigen administration. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 11, pp. 1296–1304. November, 2006.     

Influence of litter size on the RNA content of VMH and LHA in preweaning rats

The nutritional status in the early postnatal period may significantly influence the development and functional activity of food intake regulating mechanisms. Therefore we investigated the weight gains and total RNA content of the ventromedial (VMH) and lateral (LHA) hypothalamic cells of rat pups in normal litters (8 pups/nest) and in reduced litters (2 pups/nest) reared permanently (from birth to weaning) or temporarily (from 1st to 5th day) in reduced nests. A significant decrease of weight gains was found in pups reared in reduced litters during the first 5 days which resulted in significant differences of body weight between the pups from normal and reduced litters on 5th day of life. On the 15th and 30th days, there were no significant differences in body weight between these animals, but the RNA content in VMH cells of pups reared in reduced litters was significantly increased on the 15th and 30th days. The RNA content in the LHA cells was unchanged. The results show that reducing a rat litter to 2 pups caused short-term undernutrition leading to permanent changes of the RNA content in the VMH neurons. The possible consequences of the permanently changed RNA content of this hypothalamic structure are discussed.     

Modulation of neuronal histamine in control of food intake

Neuronal histamine affects physiological functions of the hypothalamus. To investigate involvement of histamine receptors in feeding, histamine antagonists were infused into the rat third cerebroventricle. All H1- but no H2-antagonists tested, induced transient feeding during the early light when concentration of hypothalamic histamine was highest. No periprandial drinking was observed. Ambulation concomitantly increased during feeding. The effect on feeding was attenuated when brain histamine was normally low during the early dark or was decreased by alpha-fluoromethylhistidine (alpha-FMH). Bilateral microinjection indicated that the ventromedial hypothalamus, but not the lateral hypothalamus or the paraventricular nucleus, was a main locus for the induction of feeding by an H1-antagonist. The effect was completely abolished when brain histamine was decreased by pretreatment with alpha-FMH. Hypothalamic neuronal histamine suppresses food intake, at least in part, through H1-receptors in the VMH, and diurnal fluctuations of food intake may mirror neuronal histamine level.     

CCK as a central satiety factor: behavioral and electrophysiological evidence

CCK and its derivatives potently inhibit feeding, even after vagotomy. This effect is thus considered to be peripheral. Recently, however, the vagal gastric branch was reported to essentially bring feeding inhibition into full play. In the present study, it was found that CCK-8, administered into the third cerebroventricle (III-cv), or into the lateral hypothalamus (LHA), significantly and dose-dependently inhibited feeding induced by electrical stimulation of the contralateral LHA (LHA-ESIF) in the chronic rat. This inhibition by CCK-8 was not affected by systemic pretreatment with proglumide (1 mg), a selective antagonist, while CCK (250 ng) simultaneously microinjected into the III-cv with 5 micrograms proglumide almost completely eliminated the CCK effect on LHA-ESIF. Neuronal activity of the ventromedial hypothalamus (VMH) was enhanced, and that of the LHA was suppressed by electrophoretic direct application of CCK on neurons in urethane-chloralose-anesthetized rats. CCK also markedly decreased the threshold of VMH glucose responding neurons. These results indicate that the satiety effect is not only peripheral, but might also be central, especially through feeding-related hypothalamic neurons, which are probably important in feeding inhibition.     

Influence of early undernutrition in rats on their body fat and RNA content in VMH neurons.

The RNA content of the ventromedial hypothalamus (VMH) and lateral hypothalamic area (LHA) neurons, and the epididymal, retroperitoneal, and liver fat content of 150-day-old male rats submitted to neonatal undernutrition, were investigated. The neonatal undernutrition was carried out by two different ways. First, by reducing the litters to two pups per nest from birth to weaning. The pups from normal litters (eight pups/nest) served as controls. Secondly, by separating half of the pups (four pups) from normal litters for 8 h daily during the first 5 postnatal days. The remaining nonseparated pups served as their controls. The data show that both groups of early undernourished pups had a significantly increased RNA content in the VMH neurons (RNA content in the LHA neurons was unchanged) and a significantly decreased epididymal, retroperitoneal, and liver fat content in comparison with their controls. The results indicate that early undernutrition leads to a permanent increase in the functional activity of VMH and alteration in fat metabolism in rats.     

Effects of hypothalamic stimulation on activity of dorsomedial medulla neurons that respond to subdiaphragmatic vagal stimulation

1. Effects of hypothalamic stimulation on activity of dorsomedial medulla neurons that responded to subdiaphragmatic vagal stimulation were investigated in urethan-anesthetized rats. 2. Extracellular recordings were made from 231 neurons in the nucleus of the tractus solitarius (NTS) that fired repetitively in response to single-pulse subdiaphragmatic vagal stimulation and from 320 neurons in the dorsal motor nucleus of the vagal nerve (DMV) that responded antidromically to subdiaphragmatic vagal stimulation. The mean latencies of responses to subdiaphragmatic vagal stimulation were 90.3 +/- 17.1 ms (mean +/- SD) for NTS neurons, and 90.8 +/- 11.2 ms for DMV neurons. This indicated that both afferent and efferent subdiaphragmatic vagal fibers were thin and unmyelinated and had a conduction velocity of approximately 1 m/s. 3. In extracellular recordings from 320 DMV neurons, marked inhibition preceded the antidromic response and subdiaphragmatic vagal stimulation evoked orthodromic spikes in only a few neurons. 4. Intracellular recordings from 66 DMV neurons revealed inhibitory postsynaptic potentials (IPSPs) before the antidromic responses. These IPSPs suppressed spontaneous firing and prevented excitatory postsynaptic potentials (EPSPs) from generating action potentials. 5. Stimulation in all hypothalamic loci studied, the ventromedial hypothalamic nucleus (VMH), the lateral hypothalamic area (LHA), and the paraventricular nucleus (PVN), induced responses with similar characteristics of excitation alone or excitation followed by inhibition in most NTS and DMV neurons. 6. No reciprocal effect of VMH and LHA stimulation was observed on NTS and DMV neurons. 7. Intracellular recordings from DMV neurons revealed monosynaptic EPSPs in response to stimulation of the VMH, the LHA, and the PVN. 8. PVN stimulation evoked significantly more responses in NTS and DMV neurons than VMH stimulation and more responses in DMV neurons than LHA stimulation. This suggests a difference in the number of connections between each hypothalamic site and the dorsomedial medulla. 9. The same dorsomedial medulla neurons were tested with VMH and LHA stimulation. The respective mean latencies of the antidromic and the orthodromic NTS neuron responses were 37.3 +/- 3.2 and 39.6 +/- 12.9 ms for VMH stimulation and 29.8 +/- 5.3 and 31.8 +/- 8.7 ms for LHA stimulation. The mean latencies of the orthodromic DMV neuron responses were 39.4 +/- 8.3 ms for VMH stimulation and 31.1 +/- 5.2 ms for LHA stimulation. The estimated conduction velocity from the VMH to the dorsomedial medulla was approximately 0.25 m/s and from the LHA it was approximately 0.33 m/s, which was significantly faster.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.     

Synchronized release of dopamine and serotonin in the medial and lateral hypothalamus of rats

A positive linear correlation between dopamine and serotonin release was found in the ventromedial hypothalamus and in the lateral hypothalamic area in fasting rats and in fed rats during intermeal intervals. Dopamine release in the ventromedial hypothalamus positively correlated with dopamine and serotonin release in the lateral hypothalamic area, which occurred only during intermeal intervals and was non-significant during the meal consumption periods or during fasting. Meal size correlated significantly only with a decrease in serotonin release in the lateral hypothalamic area. The study was designed to evaluate the relationship between dopamine and serotonin release in these hypothalamic areas and their dependence on feeding status. Microdialysis was performed simultaneously via two probes, one in the ventromedial hypothalamus and the other in the contralateral lateral hypothalamic area, of freely moving male lean Zucker rats over 24h with preserved light and dark phase, either with ad libitum access to food and water, or when no food was available. Dopamine and serotonin concentrations were measured by high-performance liquid chromatography with electrochemical detection in 20-min dialysis samples. Time-series analysis was applied to determine linear correlations between monoamines and in relation to food intake. Data showed that release of dopamine and serotonin is synchronized within the ventromedial hypothalamus and lateral hypothalamic area, particularly in the dark phase and when no food was ingested. However, synchronized release of monoamines between these nuclei occurred only during intermeal intervals: the periods of satiety.These findings suggest a tight relationship between dopaminergic and serotonergic systems of the lateral hypothalamic area and ventromedial hypothalamus, which is influenced by the feeding state and which may be involved in maintaining the balance within and between the centers of the parasympathetic and sympathetic nervous systems. The data also illustate that food intake is coupled unequivocally to the release of dopamine and serotonin in the hypothalamus, suggesting it as a mechanism of activation of postsynaptic neurons associated with new metabolic status.