Monoamine transmitter activity in lateral hypothalamus during its perfusion with insulin or 2-DG in sated and fasted rat

Role of neuropeptide F in regulating filter feeding of Manila clam, Ruditapes philippinarum

Endogenous signals which may be involved in the regulation of filter feeding in bivalves have never been examined. NPY/NPF homologue has been proved to play an important role in the regulation of food intake in vertebrate and several invertebrates. In this study, a NPF homologue was cloned from visceral ganglia of clam Ruditapes philippinarum. The full-length cDNA sequence was 892bp in length and encoded a precursor of 82 amino acid residues. We then examined the effects of fasting and refeeding on the filtration rates (FR), plasma glucose concentration (PGC), 5-HT, DA and the expression level of the rp-NPF and insulin transcript. The mRNA expression level of rp-NPF in visceral ganglion was increased during fasting, and rose to highest level on 72h after starvation and declined immediately after food had been supplied. Hemocoel injection of rp-NPF(5μg/g)significantly increased FR of clams within 2h. Compared to the controls, a significant increase in insulin mRNA levels was observed at 8h after injection. Contents of 5-HT and DA also increased in the 5μg/grp-NPF administrated clams at 8 and 24h after injection. These results suggest that, similar to vertebrates, NPF, insulin, 5-HT and DA may play a role in the regulation of feeding in R. philippinarum.

High-fructose diet during periadolescent development increases depressive-like behavior and remodels the hypothalamic transcriptome in male rats

Fructose consumption, which promotes insulin resistance, hypertension, and dyslipidemia, has increased by over 25% since the 1970s. In addition to metabolic dysregulation, fructose ingestion stimulates the hypothalamic-pituitary-adrenal (HPA) axis leading to elevations in glucocorticoids. Adolescents are the greatest consumers of fructose, and adolescence is a critical period for maturation of the HPA axis. Repeated consumption of high levels of fructose during adolescence has the potential to promote long-term dysregulation of the stress response. Therefore, we determined the extent to which consumption of a diet high in fructose affected behavior, serum corticosterone, and hypothalamic gene expression using a whole-transcriptomics approach. In addition, we examined the potential of a high-fructose diet to interact with exposure to chronic adolescent stress. Male Wistar rats fed the periadolescent high-fructose diet showed increased anxiety-like behavior in the elevated plus maze and depressive-like behavior in the forced swim test in adulthood, irrespective of stress history. Periadolescent fructose-fed rats also exhibited elevated basal corticosterone concentrations relative to their chow-fed peers. These behavioral and hormonal responses to the high-fructose diet did not occur in rats fed fructose during adulthood only. Finally, rats fed the high-fructose diet throughout development underwent marked hypothalamic transcript expression remodeling, with 966 genes (5.6%) significantly altered and a pronounced enrichment of significantly altered transcripts in several pathways relating to regulation of the HPA axis. Collectively, the data presented herein indicate that diet, specifically one high in fructose, has the potential to alter behavior, HPA axis function, and the hypothalamic transcriptome in male rats.

Brain glucose and insulin: effects on food intake and brain biogenic amines of rainbow trout

The effects of central (intracerebroventricular, 9 microg fish(-1)) and peripheral (intraperitoneal, 4 mg kg(-1)) administration of bovine insulin, as well as the effect of hyperglycemia (oral administration of 1 g glucose fish(-1)) and brain glucodeprivation (intracerebroventricular administration of 2-deoxy-D-glucose) on food intake and levels of brain (telencephalon, preoptic area, and hypothalamus) biogenic amines (serotonin, dopamine, noradrenaline and their metabolites 5-hydroxyindoleacetic acid, and dihydroxyphenylacetic acid) were assessed on rainbow trout ( Oncorhynchus mykiss). Treatment with insulin inhibited food intake after 26 or 52 h of administration, central or peripheral, respectively. This effect was still apparent after 74 h of central treatment. When assessing changes in the levels of biogenic amines after 26 h of central insulin administration, there was a significant increase in the levels of 5-hydroxyindoleacetic acid, and in the ratio of dihydroxyphenylacetic acid/dopamine of insulin-treated fish, in telencephalon and hypothalamus, respectively. These results suggest that peripherally administered insulin is involved in a feedback regulatory loop with food intake and body weight. Moreover, at least part of the effects of insulin could be mediated by hypothalamic dopaminergic activity. The strong hyperglycemia induced by oral administration of glucose did not induce significant changes either on food intake (control versus treated), or in brain levels of biogenic amines. The intracerebroventricular administration of 2-deoxy-D-glucose induced an increase in food intake without altering plasma glucose levels, suggesting that fish brain possesses a control system for detecting hypoglycemia in plasma and therefore keep brain glucose levels high enough for brain function.

Altered action of dopamine and cholecystokinin on lateral hypothalamic neurons in rats raised under different feeding conditions

Single-unit activity was recorded in the lateral hypothalamus (LH) of adult Wistar rats anaesthetized with urethane. The rats were differently nourished till weaning by raising in small (SL), control (CL) or large litters (LL). They gained significantly different body weight leading to overweight in SL (mean: 428.4 g on day 90) and underweight in LL rats (mean 399.5 g) compared to CLs (414.5 g). The mean basal firing rate of LH neurons differed, it was lowest in SL and highest in LL rats. The proportion of neurons changing their firing rate by more than 30% in response to iontophoretically administered dopamine (DA) was significantly greater in SL (76%) than LL rats (54%). Effects of DA were significantly more often blocked by a D1 receptor antagonist in LL than CLs. The responsiveness to cholecystokinin (CCK) alone and coadministered with DA was also greater in SL than LL. Furthermore, the proportion of neurons inhibited by DA alone and in the presence of CCK was significantly greater in SL than LL rats. In conclusion, litter size and difference in nourishment during early postnatal development of rats seem to determine LH basal firing rate. The increased neuronal responsiveness to exogenous DA and CCK in neonatally overfed SL rats may indicate a decreased activity of these endogenous signals which normally contribute to limitation of energy intake.

2-deoxy-D-glucose attenuates harmaline induced tremors in rats

Neuronal hyperactivity in essential tremor is accompanied by high energy demand in cerebellum, medulla and the thalamus. It has been suggested that brain regions that have increased metabolic demands are highly vulnerable to interruptions in glucose metabolism. In the present investigation attempt was made to study the effect of 2-deoxyglucose (2DG) a glycolytic pathway inhibitor on harmaline induced tremor in rats. Wistar rats of either sex weighing 100+/-3 g were given harmaline (10 mg/kg, i.p.) alone or along with 2DG (15 min before harmaline) in doses of 300, 600 and 900 mg/kg, respectively. The latency of onset, intensity and duration of tremor following harmaline administration were recorded. Neurobehavioral responses, electromyography (EMG) and levels of blood glucose and cerebellar serotonin (5HT) were determined after 40 min of harmaline administration. 2DG significantly and dose dependently attenuated severity of harmaline induced tremors and amplitude of EMG. Treatment of rats with 2DG alone reduced the locomotor activity, however, no significant change was observed in grip strength, landing foot splay, air righting reflex and response to tactile stimuli. Harmaline alone and along with 2DG had no effect on behavioral parameters except a decrease in landing foot splay. 2DG produced a dose-dependent hyperglycemia and attenuated harmaline induced increase in cerebellar 5HT levels. Our results clearly suggest the protective effect of 2DG in harmaline induced tremor. Further studies are warranted to assess the role of glucoprivation in the suppression of neuronal excitability in tremors.

Macronutrient-induced cascade of events leading to parallel changes in hypothalamic serotonin and insulin

Extracellular serotonin (5-HT) and insulin from hypothalamic PVN-VMH region follow parallel changes in response to specific macronutrient ingestion. Possible independent or causal mechanisms have been investigated. A common primary event might be pancreatic insulin secretion for both insulin entry into the brain and 5-HT synthesis through variations in the ratio of tryptophan over competitor amino acids. The steps of this cascade were found to account only partly for the changes in hypothalamic 5-HT and insulin. The central consequences of these metabolic effects may be modulated directly at the hypothalamic level. For instance, we observed a positive relation between the changes in insulin and 5-HT and the satiating potency of each nutrient. In addition, a direct action of dexfenfluramine on insulin has been found at the hypothalamic level showing that an activation of the serotonergic system immediately enhances insulin levels. This central event may be an important step in a cascade of events triggered by macronutrient ingestion leading to common hypothalamic insulin and 5-HT changes involved in feeding regulation.

Norepinephrine mediates glucoprivic-induced increase in GABA in the ventromedial hypothalamus of rats

Noradrenergic mechanisms in the hypothalamus may be involved in counterregulatory responses to glucoprivic episodes. After 2-deoxy-D-glucose (2-DG; 1.2 mmol/kg iv), extracellular norepinephrine (NE) concentration in the ventromedial hypothalamus (VMN) increased in a bimodal fashion to 251 +/- 39% (P < 0.001) and 150 +/- 17% (P < 0.001) of baseline during the first 30 min. In the lateral hypothalamus (LHA), NE decreased by 30 min (61 +/- 4%, P < 0.001) and no consistent changes were measured in the paraventricular nucleus (PVN). Because the NE response in the VMN after 2-DG followed the same pattern as GABA, the interaction between NE and GABA was evaluated. In the VMN, GABA had little effect on extracellular NE concentrations but NE increased GABA concentrations 166 +/- 13%, (P < 0.01). In the presence of yohimbine (alpha(2)-adrenoceptor antagonist) the first GABA peak after 2-DG was absent, and the second GABA peak was absent in the presence of timolol (beta-adrenoceptor antagonist). These results support an interaction among noradrenergic and GABAergic systems in the VMN during glucoprivation and that increased NE mediates the increase in extracellular GABA after 2-DG.

Activation of hypothalamic insulin by serotonin is the primary event of the insulin-serotonin interaction involved in the control of feeding

In previous experiments, we reported a close parallelism in the responses of both serotonin (5-HT) and insulin in the hypothalamic PVN-VMH region of freely-moving rats during feeding. Thus, hypothalamic 5-HT and insulin may participate, independently or in interaction, in the control of carbohydrate and fat ingestion. The precedence of the activation of one or the other substance remained to be investigated. In adult male Wistar rats, (a) dexfenfluramine was administered to the PVN-VMH region by reverse microdialysis (80 microM for 10 min) while local insulin was assessed; (b) insulin was locally infused (400 mU for 10 min) through the tip of the dialysis probe while 5-HT was measured. Dexfenfluramine immediately increased 5-HT release, and also extracellular insulin levels (+102%). This activation of insulin by serotonin is actually a central effect since neither insulinemia nor glycemia were affected. Conversely, insulin enhanced 5-HT release (+81%), but only 45 min after the beginning of its infusion. Noradrenaline, dopamine and metabolites were slightly or not at all modified by insulin. These data demonstrate that an interaction does exist between insulin and 5-HT in the VMH-PVN area. Because of the delay of 5-HT response to insulin, an activation of the serotonergic system would be the causal event acting immediately on insulin, and not the contrary. Whatever the exact mechanism of this interaction, it seems to be a link in a larger cascade of events involving numerous neurotransmitters and peptides leading to the regulation of feeding.

Feeding-related dopamine in the amygdala of freely moving rats

Extracellular levels of dopamine (DA) were measured in the central part (the central and intercalated nuclei) of the amygdala (AMY) using microdialysis at 20 min intervals before, during and after 1 h of feeding in 12 h food-deprived rats. The results were compared with the effects of peripheral injections of glucose or a low dose (200 mU) of insulin in non-deprived animals. Feeding caused a 130% increase in extracellular DA. Glucose resulted in an increase in DA levels (+86%). In contrast, insulin caused a decrease of DA (-50%) and metabolites. The results show that natural feeding is associated with an increase in DA turnover in the amygdala, and that peripheral glucose and insulin can affect DA metabolism in the amygdala presumably in response to changes in glucose utilization.

Neuropeptide Y perfused in the preoptic area of rats shifts extracellular efflux of dopamine, norepinephrine, and serotonin during hypothermia and feeding

This study examined the localized action of neuropeptide Y (NPY) on monoamine transmitter activity in the hypothalamus of the unrestrained rat as this peptide induced hypothermia, spontaneous feeding or both responses simultaneously. A guide tube was implanted in the anterior hypothalamic pre-optic area (AH/POA) of Sprague-Dawley rats. Then either control CSF vehicle or NPY in a dose of either 100 ng/microliter or 250 ng/microliter was perfused by push-pull cannulae in this structure in the fully sated, normothermic rat. Successive perfusions were carried out at a rate of 20 microliters/min for 6.0 min with an interval of 6.0 min elapsing between each. Samples of perfusate were assayed by HPLC for their levels of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their respective metabolites. Whereas control CSF was without effect on body temperature (Tb) or feeding, repeated perfusions of NPY over 3.0 hr caused dose-dependent eating from 4 to 39 g of food, hypothermia of 0.9 to 2.3 degrees C or both responses concurrently. As the rats consumed 11-39 g of food, the efflux of NE, MHPG, DOPAC and 5-HT was enhanced significantly, whereas during the fall in Tb the efflux of NE, DOPAC and 5-HIAA from the AH/POA increased. When the Tb of the rat declined simultaneously with eating behavior, the levels in perfusate of DOPAC and HVA increased significantly while MHPG declined. During perfusion of the AH/POA with NPY the turnover of NE declined while DA and 5-HT turnover increased during hypothermia alone or when accompanied by feeding. These results demonstrate that the sustained elevation in NPY within the AH/POA causes a selective alteration in the activity of the neurotransmitters implicated in thermoregulation, satiety and hunger. These findings suggest that both DA and NE comprise intermediary factors facilitating the action of NPY on neurons involved in thermoregulatory and ingestive processes. The local activity of NPY on hypothalamic neurons apparently shifts the functional balance of serotonergic and catecholaminergic neurons now thought to play a primary role in the control of energy metabolism and caloric intake.

The lateral hypothalamic area revisited: ingestive behavior

This article discusses the role of the lateral hypothalamic area (LHA) in feeding and drinking and draws on data obtained from lesion and stimulation studies and neurochemical and electrophysiological manipulations of the area. The LHA is involved in catecholaminergic and serotonergic feeding systems and plays a role in circadian feeding, sex differences in feeding and spontaneous activity. This article discusses the LHA regarding dietary self-selection, responses to high-protein diets, amino acid imbalances, liquid and cafeteria diets, placentophagia, "stress eating," finickiness, diet texture, consistency and taste, aversion learning, olfaction and the effects of post-operative period manipulations by hormonal and other means. Glucose-sensitive neurons have been identified in the LHA and their manipulation by insulin and 2-deoxy-D-glucose is discussed. The effects on feeding of numerous transmitters, hormones and appetite depressants are described, as is the role of the LHA in salivation, lacrimation, gastric motility and secretion, and sensorimotor deficits. The LHA is also illuminated as regards temperature and feeding, circumventricular organs and thirst and electrolyte dynamics. A discussion of its role in the ischymetric hypothesis as an integrative Gestalt concept concludes the review.

Effects of repeated 2-deoxy-D-glucose administration on ingestive, psychological, and 5-HT-related behaviours in the rat

The effects of repeated treatment with the metabolic stressor 2-deoxy-D-glucose (2-DG: 500 mg/kg/day, 7 days) upon some ingestive and psychological behaviours were investigated, and compared with those elicited by repeated immobilization or cold exposure (2 hr/day, 7 days). Because all these stressors affect central serotonergic systems, 5-HT1A and 5-HT2A receptor-mediated behaviours were also analysed. Both 2-DG administration and immobilization decreased daily food intakes and increased the weight of the adrenals, while all stressors reduced body weight gain. In addition, 2-DG triggered hyperphagia (and reduced body weight loss) throughout the 7 light phases, and hypophagia (and reduced body weight gain) throughout the 7 dark phases. However, the other stressors had only temporary effects during the light phases. These results suggested that immobilized and cold exposed rats, but not 2-DG-treated rats had progressively adapted to their stressors. Furthermore, 2-DG-treated rats exhibited decreased ambulation when placed in the open field, but no change in social interaction. Forepaw treading and flat body posture responses to the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) were not altered by the stressors, but both of them slightly amplified 8-OH-DPAT-induced hypothermia. This change was associated with a decreased head shake response to the 5-HT2A agonist 1-(4-iodo-2,5-dimethoxy-phenyl)-2-aminopropane (DOI) in 2-DG-treated rats, compared with that measured in the other groups. This study opens the possibility that alterations in feeding rhythms has functional consequences on 5-HT2A receptors.

Acetylcholinesterase and Na+,K(+)-ATPase activities in different regions of rat brain during insulin-induced hypoglycemia

The activities of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7), responsible for hydrolysis of acetylcholine and Na+,K(+)-ATPase (Mg(2+)-dependent ATP phosphohydrolase, EC 3.6.1.3), which plays a crucial role in neurotransmission, were determined in four brain regions after 1, 2, and 3 h of insulin administration. Significant decrease in the acetylcholinesterase and Na+,K(+)-ATPase activities was observed in the soluble and total particulate fractions from cerebral hemispheres, cerebellum, brain stem, and diencephalon + basal ganglia after 1, 2, and 3 h of insulin-induced hypoglycemia. Blood glucose level decreased significantly after 1 h of insulin administration and remained at low level for 2 h thereafter, whereas, the protein content in different subcellular fractions from four brain regions did not show any significant change under this physiological stress.

Catecholaminergic projections from the solitary tract nucleus to the perifornical hypothalamus

The source of adrenergic and other catecholaminergic fibers innervating the perifornical lateral hypothalamus was localized in the medulla after combination of Fluoro-Gold retrograde tracing and immunohistochemistry for either tyrosine-hydroxylase or phenylethanolamine-N-methyltransferase. Following perifornical injections, Fluoro-Gold-labeled neurons were observed mainly in regions including the noradrenergic and adrenergic cell groups. In the caudal solitary tract nucleus, two kinds of doubly labeled neurons were found: a) numerous noradrenergic neurons in the A2 group at the level of, or caudal to the area postrema; b) some adrenergic neurons in the C2 group at a level immediately rostral to the area postrema. These catecholaminergic neurons connecting the caudal solitary tract nucleus to the perifornical hypothalamus might convey feeding relevant information such as glycemic level or satiety signals.

Insulin and glucose-induced changes in feeding and medial hypothalamic monoamines revealed by microdialysis in rats

Microdialysis from the ventromedian (VMH) and paraventricular (PVN) regions and simultaneous infusion of insulin alone (orexigenic) or with glucose (anorexigenic) was performed in the free-feeding rat. Intravenous insulin infusion (1 IU in 1 ml over 1 h) resulted in the expected glucoprivic feeding and a decrease in dopamine (DA) and serotonin (5-hydroxytryptamine [5-HT]) with an increase in their respective metabolites, dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA). These data are quite different from those observed in spontaneous ad lib feeding: increase in DA, 5-HT and 5-HIAA and decrease in DOPAC. These last changes were not superimposed on insulin effects when insulin-induced meals occurred. When food was not available, insulin infusion induced the same changes except an increase in DA levels which could probably be ascribed to stress. When insulin was infused together with a sufficient amount of glucose to prevent hypoglycemia, we observed the usual anorexigenic effect. Although this treatment had an effect on induced-feeding opposite to that following insulin alone, the changes in hypothalamic monoamines were similar. The only consistent overall change is finally the rise in 5-HIAA found in both spontaneous and induced feeding conditions. These data suggest that monoaminergic changes in the VMH and PVN are not directly implicated in the control of feeding but they rather reflect metabolic events that accompany this behavior.

Evidence that neuropeptide Y and dopamine in the perifornical hypothalamus interact antagonistically in the control of food intake

Mapping studies have revealed that the perifornical hypothalamus (PFH) is a primary locus for both the feeding-stimulatory effect of neuropeptide Y (NPY) and the anorectic effect of catecholamines (CAs), suggesting that NPY and CAs may interact antagonistically there. To investigate this, the CA-releasing agent amphetamine (AMPH) was injected through indwelling guide cannulas into the PFH of satiated adult male rats 5 min prior to injection of NPY (78 pmol/0.3 microliters) and food intake was measured 1, 2, and 4 h later. Amphetamine (50-200 nmol) dose-dependently reduced NPY feeding, usually eliminating it at the higher doses. The receptors mediating this effect were investigated by sequential injection of various CA antagonists, AMPH, and NPY into the PFH. Neither the alpha- nor beta-adrenergic receptor antagonists phentolamine (100 nmol) or propranolol (200 nmol) significantly affected AMPH suppression of NPY feeding. In contrast, the dopamine receptor antagonist haloperidol (5 nmol) abolished AMPH suppression of NPY feeding, suggesting that dopamine (DA) mediates the AMPH effect. To examine this, epinephrine (EPI, 50-200 nmol) and DA (25-200 nmol) were tested for suppression of NPY-induced feeding. While EPI had no significant effect, DA at the maximally effective dose (50 nmol) reduced the NPY feeding response by 36% or more. These findings provide convergent evidence for antagonistic interactions between endogenous DA and NPY in the control of eating behavior.

Irreversible suppression of alcohol drinking in cyanamide-treated rats after sustained delivery of the 5-HT2 antagonist amperozide

The purpose of this study was to evaluate the long-term effect of sustained treatment with amperozide, which has been shown to attenuate the volitional drinking of ethyl alcohol in the rat without side effects. Preference for alcohol first was induced pharmacologically in Sprague-Dawley rats by the inhibitor of aldehyde dehydrogenase, cyanamide, administered in a dose of 10 mg/kg twice daily for 3 days. Then following a standard preference test, each rat was offered water and its maximally preferred concentration of alcohol which ranged from 7% to 15%. Following a 4-day pre-drug test, saline control vehicle or amperozide was administered for 7 days by an osmotic minipump implanted in the intrascapular space. A single dose of 208 micrograms/kg/h (i.e., 5.0 mg/kg/day) was selected on the basis of a prior dose response study of amperozide. During the interval of sustained release of amperozide, the consumption of alcohol declined significantly in terms of both absolute g/kg intake and proportion of alcohol to water. When the preference of the rats was retested at 4, 30, 70, 110, and 140 day intervals after the pump had exhausted amperozide, the absolute g/kg consumption of alcohol continued to decline significantly. Unlike other drugs, amperozide did not produce any side effects, particularly on the intake of food or water or on body weight, which suggests a pharmacological specificity of its action.(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrine, dopamine, and 5-HT release from perfused hypothalamus of the rat during feeding induced by neuropeptide Y

In the unrestrained rat, the hyperphagic-like ingestion of food evoked by the sustained elevation of neuropeptide-Y (NPY) in the hypothalamus was correlated with the release and turnover of monoaminergic transmitters in this structure. A single guide tube was implanted stereotaxically in the perifornical region of the hypothalamus for localized push-pull perfusion of an artificial CSF vehicle or NPY1-36 in a concentration of 10, 50, or 100 ng/1.0 microliters. After the rat was fully satiated, a site reactive to NPY was perfused repeatedly at a rate of 20 microliters/min for 6.0 min with an interval of 6.0-12 min elapsing between each perfusion. Samples of perfusate were analyzed by HPLC with coulometric detection for DA, HVA, DOPAC, NE, MHPG, 5-HT, and 5-HIAA. Although control perfusions were without effect on feeding or monoamine activity, NPY evoked mean cumulative intakes of food of 14 +/- 2.4, 25.6 +/- 3.0 and 26.5 +/- 3.2 g in response to 10, 50, or 100 ng/microliter concentrations of NPY, respectively, over the 4.0-5.0 hr test interval. HPLC analyses showed that during feeding the release of both NE and DA was enhanced significantly. The turnover of both catecholamines likewise increased significantly as reflected by the elevated levels of MHPG, DOPAC and HVA. However, neither the basal efflux of 5-HT nor its turnover, as reflected by the output of 5-HIAA, was affected during feeding induced by NPY perfused in the hypothalamus. These results suggest that a sustained elevation of NPY in the hypothalamus causes a perturbation in the basal activity of NE and DA which are both implicated in the neuronal mechanism regulating normal eating behavior. Thus, these catecholamine neurotransmitters are envisaged to comprise an intermediary step in the functional role played by NPY in the hypothalamus in integrating the control of energy metabolism and caloric intake.

GABAA receptors in the amygdala: role in feeding in fasted and satiated rats

The purpose of this study was to clarify further the site of action in the amygdala as well as functional characteristics of feeding in response to two GABA receptor agonists. Guide cannulae for microinjection were implanted stereotaxically in the rat just above the central nucleus of the amygdala (CNA). Microinjections of 0.05, 0.25, 0.5 or 1.0 nmol muscimol, a GABAA-selective receptor agonist, produced a dose- and time-dependent decrease of food intake in both the satiated and fasted rat. The bilateral injection of muscimol into the amygdala was more effective than a unilateral injection during the first 2 h, although the overall effects were similar. Microinjection of 0.1 nmol bicuculline methiodide, a GABAA receptor antagonist, into the CNA significantly blocked this inhibitory effect of 0.05 and 0.5 nmol muscimol again in both the satiated and fasted rat. Doses of 0.05, 0.5, 5.0 and 10.0 nmol of the selective GABAB agonist, baclofen, injected into homologous sites in the CNA did not alter food intake. These findings support the viewpoint that the amygdala and its central nucleus comprise a pivotal region involved in the mechanisms underlying the control of feeding behavior. Further, it is envisaged that hypophagic or anorexic responses are induced through the activation of GABAA receptors by the presynaptic release of GABA from neurons which form a component of the anatomical system for hunger and satiety.

Insatiable feeding evoked in rats by recurrent perfusion of neuropeptide Y in the hypothalamus

Hyperphagic-like intake of food was determined in the unrestrained rat during the sustained elevation over time of neuropeptide Y (NPY) within the paraventricular nucleus (PVN) and surrounding hypothalamic regions. A single guide tube was implanted stereotaxically in each of 22 rats for localized, intermittent perfusions of a CSF vehicle, nondeprotected NPY(1-36) or native NPY. Each site in the PVN of the fully sated rat was perfused repeatedly over a 5.0-h interval by means of a standard push-pull cannula system at a rate of 20 microliters/min for 6.0 min in one of three concentrations: 0.2, 1.0 and 2.0 micrograms/min. Two perfusions of 1.0 micrograms/min NPY evoked an intake of 4.6 +/- 1.1 g of food over a 3.0-h period, whereas 4-7 and 8-15 perfusions of this concentration of NPY, distributed over 5.0 h, induced the sated rats to eat a total of 12.0 +/- 1.1 g and 33.2 +/- 3.0 g, respectively. During a fixed number of 10 hypothalamic perfusions distributed over 5.0 h, concentrations of 0.2 and 2.0 micrograms/min NPY caused a cumulative intake of food in the rats of 14.2 +/- 2.0 g and 31.7 +/- 3.3 g, respectively. Under each condition, parallel push-pull perfusions of either control solution in the same hypothalamic sites were without effect on feeding. During the 5.0-h interval of repeated perfusions, successive bouts of eating occurred with individual intakes of food reaching as high as 49.0 g, which exceeded by up to two-fold the entire daily consumption of food. However, ingestion of water was unaffected by perfusion of NPY.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian pattern of large neutral amino acids, glucose, insulin, and food intake in anorexia nervosa and bulimia nervosa

Insulin, glucose, and large neutral amino acids (LNAA) were studied in 10 patients with anorexia nervosa, 13 patients with bulimia nervosa, and 15 healthy controls. Blood samples were collected at hourly intervals during the day and at two-hour intervals during the night over a 24-hour period. Ad libitum caloric and relative carbohydrate intake was significantly reduced in the anorectic and bulimic patients. Elevated concentrations of beta-hydroxybutyric acid (BHBA) were seen in the bulimic group, and low triiodothyronine (T3) concentrations in the anorectic group. Mean plasma glucose and insulin concentrations were significantly lowered in both groups. The tryptophan (Trp) to LNAA ratio was reduced in anorectic, but not in bulimic patients. These findings suggest that Trp influx into the brain is reduced in anorectic patients, possibly impairing central serotonergic function.

Sensitivity of lateral hypothalamic neurons to glycemic level: possible involvement of an indirect adrenergic mechanism

Most of the lateral hypothalamic neurons responding to moderate changes in blood glucose fail to be affected by direct glucose applications. Therefore their sensitivity to glycemic level must be mediated by an indirect mechanism. In order to test whether adrenergic afferents might be involved, the activity of lateral hypothalamic neurons was recorded during hyperglycemia and local glucose and epinephrine microiontophoresis. A majority of the recorded cells sensitive to local epinephrine responded to this substance with a decrease in activity. While no consistent correspondence was found between the responses of the same cells to local glucose and epinephrine ejections, almost all the neurons sensitive to glycemic alterations responded in the same direction to hyperglycemia and iontophorised epinephrine. These results support the view that the activity of lateral hypothalamic cells can be modulated in relation to changes in glycemic level through adrenergic signals released by some neurons which are sensitive to the blood glucose. The possible localization in the solitary tract area of such neurons projecting to the lateral hypothalamus is discussed.

Profile of NE, DA and 5-HT activity shifts in medial hypothalamus perfused by 2-DG and insulin in the sated or fasted rat

This study was carried out in the unrestrained rat to determine the nature of the in vivo profile of monoamine neurotransmitters within the medial hypothalamus in response to the presence of a glucoprivic or metabolic challenge to neurons within this region. In these experiments, insulin or 2-deoxy-D-glucose (2-DG) was applied locally to the paraventricular nucleus (PVN), dorsomedial nucleus (DMN) and ventromedial hypothalamus (VMH). In each of 11 Sprague-Dawley rats, a guide cannula was implanted stereotaxically to rest just above these structures. Upon recovery, a concentric push-pull cannula system was used to perfuse an artificial CSF within a medial hypothalamic site. The CSF was perfused at a rate of 20 microliters/min with a 5.0 min interval intervening between the collection of each 100 microliters sample. After the rat was fasted for 20-22 hr, either 10 micrograms/microliters 2-DG or 4.0 mU/microliters of insulin was incorporated into the control CSF medium and perfused at the same locus. The aliquots of hypothalamic perfusate were assayed by high performance liquid chromatography with electrochemical detection (HPLC-EC) for the respective concentration in pg/microliter of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and each of their major metabolic products. When the rat was sated, 2-DG enhanced significantly the mean efflux of NE from the medial hypothalamus in comparison to control CSF values. However, under the fasted condition, 2-DG augmented the turnover of both the catecholamine and 5-HT as reflected by elevated levels of MHPG and 5-HIAA, respectively. On the other hand, insulin perfused within the same medial hypothalamic sites evoked a significant increase in the synthesis and release of DA from the sated rat, but did not alter its turnover. Following the interval of fast, insulin produced no immediate alteration in transmitter activity; however, in the interval following insulin's perfusion, DA and 5-HT turnover were enhanced while the efflux of 5-HT was suppressed. An analysis of the proportional values of the levels of the amines to each other revealed marked shifts in the relationships between the catechol- and indoleamine transmitters following local perfusion with both 2-DG and insulin. Overall, NE synthesis and turnover exceeded that of 5-HT following 2-DG, whereas DA predominated over NE and 5-HT during insulin's perfusion.(ABSTRACT TRUNCATED AT 400 WORDS)