Noradrenaline and “Chemical Coding” of Hypothalamic Neurones

FIRING rates of single neurones in the “feeding system”—the perifornical and ventromedial areas of the hypothalamus—are altered by the systemic administration of an anorexigenic agent, such as amphetamine or glucose^1–4. Using the micro-iontophoretic technique which involves releasing chemicals directly on individual neurones, Oomura et al. confirmed that glucose can alter the spontaneous firing rates of some neurones in the hypothalamus of the rat⁵. We wish to report that micro-iontophoretic applications of glucose, amphetamine and noradrenaline to hypothalamic neurones yield a pattern of results not readily reconcilable with the current views of the role of adrenergic substances as “transmitters” in the regulation of hypothalamic feeding function.     

Facilitation of Recovery after Lateral Hypothalamic Damage by Prior Ablation of Frontal Cortex

BILATERAL lesions of the lateral hypothalmus in the rat produce aphagia and adipsia¹, but if the animals are kept alive by intragastric feeding they may begin to eat and drink spontaneously again after a few days^1–4. It has been suggested⁵ that recovery of feeding depends on the recovery of an adrenergic reward system, partial denervation of which may account for less severe deficits in feeding behaviour after other lesions of the central nervous system. For example, ablation of frontal cortex in the rat results in progressive loss of weight for 3–4 days, followed by recovery⁶ and also in changed sensitivities to drugs affecting noradrenergic synapses^7,8. It seems possible that denervation supersensitivity may be the explanation of the recovery of function^8,9. We suggest that lateral hypothalamic lesions may partially denervate hypothalamic neurones as a result of the destruction of intrahypothalamic connexions. Thus if lateral hypothalamic neurones were partially denervated by ablation of frontal cortex at some time before damage to the lateral hypothalamus itself, delayed supersensitivity from the cortical lesion should result in facilitated recovery. We now present data to support this hypothesis.     

Gastrin in the mechanisms of genetic determination of feeding behavior in rabbits

Spreading of a dominant motivation to the molecular intracellular mechanisms of genetic memory was studied. Blockage of protein synthesis in the nervous system selectively abolishes food motivation in rabbits during stimulation of the lateral hypothalamus but exerts no noticeable effect on avoidance responses during stimulation of the ventromedial hypothalamus. During protein synthesis blockage, food motivation returns to normal upon pentagastrin intracerebroventricular (i.c.v.) injection. Intracerebroventricular administration of antigastrin immunoglobulin inhibits feeding reaction to lateral hypothalamic stimulation but not avoidance response to ventromedial hypothalamic stimulation. It was concluded that feeding motivation translates into feeding behavior in the following stages: motivational excitation, gene activation, mRNA synthesis, formation of a gastrin-like peptide, and expression of feeding behavior.     

Substance P and the ethanol-evoked changes in the independent motivated behavioral reactions of rabbits

Ethanol (0.5 g/kg) administered intravenously led to alterations in central mechanisms of feeding and escape, elicited by threshold electrical stimulation either of lateral or of ventromedial hypothalamic centers of the rabbit. Subsequent intravenous injection of substance P (30 mcg/kg) restored the excitability of the ventromedial hypothalamus and facilitatory effects on this motivational center of the midbrain reticular formation. The restoration of both inhibitory influences of the dorsal hippocampus and facilitatory ones of the midbrain reticular formation on the excitability of the lateral hypothalamus was also observed after SP administration. Data obtained suggest that oligopeptides could be used to increase the tolerance to ethanol or to cure the negative acute effects of alcohol in motivated behaviours.     

The central efferent mechanism of brown adipose tissue thermogenesis induced by preoptic cooling

This study was performed to investigate central efferent mechanisms for brown adipose tissue thermogenesis. In unanesthetized rats, the effects of local anesthesia of the ventromedial hypothalamus, anterior hypothalamus, and lateral hypothalamus were observed on the brown adipose tissue thermogenesis induced by preoptic cooling. Rats had a thermode, thermocouple, and bilateral injection cannulae chronically implanted in the hypothalamus and a thermocouple beneath the interscapular brown adipose tissue. The experiments were done at an ambient temperature of 24-25 degrees C. Preoptic cooling increased brown adipose tissue and colonic temperatures without shivering. Injecting lidocaine bilaterally into the ventromedial hypothalamus during preoptic cooling reduced brown adipose tissue temperature (Tbat). The mean maximum decrease of Tbat was 0.51 +/- 0.26 degrees C and occurred 5-8 min after lidocaine injection. When lidocaine was injected into the anterior hypothalamus, Tbat increased. The mean maximum increase of Tbat was 0.85 +/- 0.29 degrees C and occurred 4-9 min after lidocaine injection. In the lateral hypothalamus, lidocaine had no effect on Tbat. Tbat was not influenced by injection of saline into the ventromedial, anterior, or lateral hypothalamus. The efferent pathway from preoptic to brown adipose tissue may thus traverse the medial part of hypothalamus. The ventromedial hypothalamus facilitates and anterior hypothalamus inhibits brown adipose tissue thermogenesis induced by preoptic cooling.     

Nitric oxide synthase and interferon-gamma receptor immunoreactivities in relation to ascending spinal pathways to thalamus,hypothalamus, and the periaqueductal grey in the rat

The retrograde tracer fluoro-gold was injected into the periaqueductal grey, thalamus or hypothalamus, and spinal cord sections were processed for neuronal nitric oxide synthase (nNOS) immunohistochemistry to investigate the relationships of nNOS immunoreactive, and spinomesencephalic, spinothalamic and spinohypothalamic projection neurones. In addition, in the lateral spinal nucleus the relationship between spinomesencephalic, -thalamic and -hypothalamic projection neurones, and nNOS and interferon-gamma receptor immunoreactive structures was investigated at the lumbar level. No single retrogradely labelled spinomesencephalic, -thalamic or -hypothalamic neurone showed nNOS immunoreactivity. In the lateral spinal nucleus, however, many fluoro-gold-labelled neurones were closely apposed by both nNOS and interferon-gamma receptor immunoreactive structures, especially prominent in the hypothalamic injection cases. This study gave no evidence for nNOS immunoreactivity in spinal neurones projecting to the periaqueductal grey, thalamus or hypothalamus, but suggests that in the lateral spinal nucleus such neurones are contacted by both nNOS- and interferon-gamma receptor-containing axon terminals.     

Nitric oxide synthase and interferon-gamma receptor immunoreactivities in relation to ascending spinal pathways to thalamus, hypothalamus, and the periaqueductal grey in the rat

The retrograde tracer fluoro-gold was injected into the periaqueductal grey, thalamus or hypothalamus, and spinal cord sections were processed for neuronal nitric oxide synthase (nNOS) immunohistochemistry to investigate the relationships of nNOS immunoreactive, and spinomesencephalic, spinothalamic and spinohypothalamic projection neurones. In addition, in the lateral spinal nucleus the relationship between spinomesencephalic, -thalamic and -hypothalamic projection neurones, and nNOS and interferon-gamma receptor immunoreactive structures was investigated at the lumbar level. No single retrogradely labelled spinomesencephalic, -thalamic or -hypothalamic neurone showed nNOS immunoreactivity. In the lateral spinal nucleus, however, many fluoro-gold-labelled neurones were closely apposed by both nNOS and interferon-gamma receptor immunoreactive structures, especially prominent in the hypothalamic injection cases. This study gave no evidence for nNOS immunoreactivity in spinal neurones projecting to the periaqueductal grey, thalamus or hypothalamus, but suggests that in the lateral spinal nucleus such neurones are contacted by both nNOS- and interferon-gamma receptor-containing axon terminals.     

Administration of D-glucosamine into the third cerebroventricle induced feeding accompanied by hyperglycemia in rats

D-glucosamine, 2-amino-2-deoxy-D-glucose, is known to be an endogenous glucose analogue and to antagonize glucose uptake and metabolism. The present experiments were aimed to clarify effects of glucosamine and related chemical substances on ingestive behavior, as well as its direct effects on hypothalamic neurons. Infusion of 24 mumole glucosamine into the third cerebroventricle induced feeding within 30 min in 5 rats out of 7 tested, accompanied by increased ambulatory activity. No periprandial drinking was observed. Plasma glucose level increased, peaking at 30 min after the injection. Plasma insulin level tended to increase, but not significantly. Electrophoretic application of glucosamine activated glucose-sensitive neurons in the lateral hypothalamus and suppressed glucoreceptors in the ventromedial hypothalamus. These facts, together with other reported results, suggest that glucosamine can modulate physiological feeding and that carbon 2 of the glucose molecule is important in feeding modulation by glucose analogues.     

下丘脑外侧区注入胃泌素对大鼠胃酸分泌的影响

本工作观察了下丘脑外侧区(LHA)、腹内侧核(VMH)或侧脑室(LCV)注射17肽胃泌素(G17)或五肽胃泌素(G5)对清醒大鼠胃酸分泌的影响。结果表明,将 G17或 G5注入 LHA可引起胃酸分泌明显增加,而将 G5注入 VMH、LCV 或静脉则不影响胃酸分泌;切断迷走神经可以阻断在 LHA 注入 G5引起胃酸分泌增加的效应;在阿托品背景下,将 G5注入 LHA仍能引起胃酸分泌明显增加;静脉注射酚妥拉明,心得安或纳洛酮均不影响 G5对 LHA 刺激胃酸分泌的作用。这些结果提示:LHA 是胃泌素作用的一个特异性部位,由 LHA 发出的冲动可能通过迷走神经内的两种传出纤维引起胃酸分泌,一为胆碱能纤维,另一为非胆碱能非肾上腺素能纤维。     

Central structures involved in opioid-induced feeding

This paper summarizes efforts to identify structures involved in the opioid regulation of feeding. Many opioid agonists and antagonists increase or decrease food intake when injected centrally, which suggests, but alone does not prove, that the opioid feeding system is located within the brain. Some conditions of hunger and feeding cause changes in opioid peptide levels in certain brain areas, notably the hypothalamus, which may indicate that the areas are components of this opioid system. Lesion studies have also identified some potentially important structures, inasmuch as lesions of these structures reduce the effectiveness of opioid agonists or antagonists to alter food intake. Finally, microinjection studies have mapped the brain in terms of the effects on feeding of opioid agonists and antagonists. Results of different types of studies are consistent in suggesting that parts of the hypothalamus, particularly the paraventricular and ventromedial nuclei and the lateral hypothalamic area, are important components of the opioid feeding system.     

Glucagon-related peptides in the rat hypothalamus

Summary Immunohistochemically, nerve fibers and terminals reacting with anti-N-terminal-specific but not with anti-C-terminal-specific glucagon antiserum were observed in the following rat hypothalamic regions: paraventricular nucleus, supraoptic nucleus, anterior hypothalamus, arcuate nucleus, ventromedial hypothalamic nucleus and median eminence. Few fibers and terminals were demonstrated in the lateral hypothalamic area and dorsomedial hypothalamic nucleus. Radioimmunoassay data indicated that the concentration of gut glucagon-like immunoreactivity was higher in the ventromedial nucleus than in the lateral hypothalamic area. In food-deprived conditions, this concentration increased in both these parts. This was also verified in immunostained preparations in which a marked enhancement of gut glucagon-like immunoreactivity-containing fibers and terminals was observed in many hypothalamic regions. Several immunoreactive cell bodies were found in the ventromedial and arcuate nuclei of starved rats. Both biochemical and morphological data suggest that glucagon-related peptides may act as neurotransmitters or neuromodulators in the hypothalamus and may be involved in the central regulatory mechanism related to feeding behavior and energy metabolism.     

DISTRIBUTION OF GAMMA-AMINOBUTYRIC ACID (GABA) IN THE RAT HYPOTHALAMUS: FUNCTIONAL CORRELATES OF GABA WITH ACTIVITIES OF APPETITE CONTROLLING MECHANISMS

—In the hypothalamus, the highest GABA content (approx. 26 nmol/mm³) was constantly observed in the lateral hypothalamic area (LHA). In other parts of the hypothalamus uneven distribution of GABA was also observed, but areas showing high concentration of GABA did not coincide with the locations of various hypothalamic nuclei. In the LHA, which is known to contain a feeding centre, the anterior part (6.4 and 6.0 mm anterior (A 6.4 and A 6.0) respectively to the vertical zero plane of de Groot) showed a remarkably high content of GABA. The GABA content in the LHA at A 6.4 was decreased during the initial phase of insulin hypoglycemia and, in contrast, showed a significant increase following hyperglycemia induced by alloxan administration. In the ventromedial nucleus (VMH) of the hypothalamus, which is known to contain a satiety centre, the GABA content was increased during the initial phase of insulin hypoglycemia. The results suggest that both certain parts of the LHA and VMH contain or receive GABA-inhibitory neurons and that these neurons may play important physiological roles in controlling functional states of the feeding and satiety centres in the hypothalamus.     

Glucagon-Like Peptide 1 (GLP-1) Can Reverse AMP-Activated Protein Kinase (AMPK) and S6 Kinase (P70S6K) Activities Induced by Fluctuations in Glucose Levels in Hypothalamic Areas Involved in Feeding Behaviour

The anorexigenic peptide, glucagon-like peptide-1 (GLP-1), reduces glucose metabolism in the human hypothalamus and brain stem. The brain activity of metabolic sensors such as AMP-activated protein kinase (AMPK) responds to changes in glucose levels. The mammalian target of rapamycin (mTOR) and its downstream target, p70S6 kinase (p70S6K), integrate nutrient and hormonal signals. The hypothalamic mTOR/p70S6K pathway has been implicated in the control of feeding and the regulation of energy balances. Therefore, we investigated the coordinated effects of glucose and GLP-1 on the expression and activity of AMPK and p70S6K in the areas involved in the control of feeding. The effect of GLP-1 on the expression and activities of AMPK and p70S6K was studied in hypothalamic slice explants exposed to low- and high-glucose concentrations by quantitative real-time RT-PCR and by the quantification of active-phosphorylated protein levels by immunoblot. In vivo, the effects of exendin-4 on hypothalamic AMPK and p70S6K activation were analysed in male obese Zucker and lean controls 1 h after exendin-4 injection to rats fasted for 48 h or after re-feeding for 2–4 h. High-glucose levels decreased the expression of Ampk in the lateral hypothalamus and treatment with GLP-1 reversed this effect. GLP-1 treatment inhibited the activities of AMPK and p70S6K when the activation of these protein kinases was maximum in both the ventromedial and lateral hypothalamic areas. Furthermore, in vivo s.c. administration of exendin-4 modulated AMPK and p70S6K activities in those areas, in both fasted and re-fed obese Zucker and lean control rats.     

Differential effects of central administration of relaxin‐3 on food intake and hypothalamic neuropeptides in male and female rats

Relaxin‐3 (RLN3) is an orexigenic neuropeptide that produces sex‐specific effects on food intake by stronger stimulation of feeding in female compared with male rats. This study determined which hypothalamic nuclei and associated neuropeptides may be involved in the sex‐specific orexigenic effects of RLN3. Relaxin‐3 (800 pmol) or vehicle was injected into the lateral ventricle of female and male rats. Food and water intake were measured after the first injection, and rats were euthanized after the second injection to determine the mRNA expression of the hypothalamic neuropeptides. Food but not water intake showed sex‐specific effects of RLN3. Stimulation of food intake by RLN3 was significantly higher in female than in male rats. No effect of RLN3 injection was found on c‐fos mRNA expression in the arcuate, dorsomedial and ventromedial hypothalamic nuclei. Increased c‐fos mRNA expression was observed in the paraventricular hypothalamic nucleus (PVN) in both sexes and in the lateral hypothalamic area (LHA) in female rats. Relaxin‐3 injections led to a sex‐nonspecific increase in the expression of oxytocin mRNA in the magnocellular PVN. Conversely, RLN3‐induced expression of anorexigenic neuropeptide arginine vasopressin (AVP) was significantly higher in the parvocellular PVN in male compared with female rats. Finally, RLN3 administration significantly increased the expression of orexin (ORX) mRNA in the LHA in female but not in male rats. Stronger expression of anorexigenic AVP in the PVN in male rats and increased expression of ORX in the LHA in female rats may contribute to stronger orexigenic effects of RLN3 in female rats compared with male rats.     

Hypothalamic galanin is up-regulated during hyperphagia and increased body weight gain induced by disruption of signaling in the ventromedial nucleus

Disruption of signaling in the ventromedial nucleus (VMN) by colchicine (COL) produces transient (4 days) hyperphagia and weight gain. Microinjection of galanin into various hypothalamic sites stimulates feeding, so we tested the hypothesis that galanin is up-regulated in COL-treated rats by analyzing galanin concentrations in micropunched hypothalamic sites. Galanin was increased in the paraventricular nucleus on Days 1 through 4 after COL-injection. Galanin was also elevated in three other hypothalamic sites, the dorsomedial nucleus, lateral hypothalamic area, and perifornical hypothalamus, on Days 2-4 and in the lateral preoptic area, on Day 1 only. In the median eminence-arcuate nucleus and amygdala an initial decrease on Day 1 was followed by a then progressive increase through Day 4. These increases occurred despite marked elevations in blood insulin and leptin, hormones known to suppress hypothalamic galanin. When COL- or saline-treated rats were injected intracerebroventricularly with galanin, it stimulated feeding further in the hyperphagic COL-treated rats, but the relative response over basal consumption was similar in both COL-treated and control rats. These results in VMN disrupted rats suggest that neurochemical rearrangements, including increased availability of galanin, may contribute to the hyperphagia and increased weight gain; additionally, it seems that neurons in the VMN normally exert a restraint on galanin signaling.     

Neuroendocrine regulatory peptide-1 and neuroendocrine regulatory peptide-2 influence differentially feeding and penile erection in male rats: sites of action in the brain

The effect of NERP-1 and NERP-2, two recently discovered VGF-derived peptides, on feeding and penile erection was studied after injection into the lateral ventricles, the lateral hypothalamus, the arcuate nucleus or the paraventricular nucleus of the hypothalamus. NERP-2 (1-5 nmol), but not NERP-1 (2-4 nmol), increased feeding in a dose-dependent manner when injected into the lateral ventricles or bilaterally into the lateral hypothalamus but not into the arcuate or the paraventricular nucleus. The effect of NERP-2 given into the lateral ventricles was found in the first, but not in the second 60 min after treatment, and was antagonized by SB-408124, an orexin-1 receptor antagonist given into the lateral ventricles or the arcuate nucleus, but not into the paraventricular nucleus. However, SB-408124 was unable to reduce NERP-2-induced feeding when injected bilaterally into the lateral hypothalamus before NERP-2 given also bilaterally into the lateral hypothalamus. In contrast, NERP-1, but not NERP-2, induced penile erection in a dose-dependent manner when injected into the lateral ventricles or the arcuate nucleus, but not into the paraventricular nucleus or the lateral hypothalamus. The pro-erectile effect of NERP-1 was not prevented by the prior injection of d(CH(2))(5)Tyr (Me)(2)-Orn(8)-oxytocin or SB-408124 into the lateral ventricles. The present results suggest that while NERP-2 facilitates feeding by acting in the lateral hypothalamus, possibly by increasing orexin activity in the arcuate nucleus, NERP-1 facilitates penile erection by acting in the arcuate nucleus with a mechanism not related to orexin or oxytocin.     

Peripheral ghrelin participates in the glucostatic signaling mediated by the ventromedial and lateral hypothalamus neurons

Employing immunohistochemistry techniques, we examined the c-fos expression in different hypothalamic areas, when plasma glucose levels were modified by the administration of insulin and 2-deoxyglucose (2-DG) respectively. Subsequently, the hypoglycemia produced by an injection of insulin significantly increased feeding concomitant to higher c-fos expression in the arcuate nucleus (ARC), paraventricular nucleus (PVN), dorsomedial hypothalamus (DMH) and lateral hypothalamus (LH), while no statistical changes in the ventromedial hypothalamus (VMH) were found. Also, the glucopenia induced by 2-DG administration produced similar stimulatory effects on appetite and the neuronal activity affecting all the hypothalamic areas studied, including the VMH. The peripheral blockade of the orexigenic hormone ghrelin with a specific antibody (AGA) significantly decreased food intake as induced from acute hypoglycemia and glucopenia. Curiously, the conjoint AGA and insulin or 2-DG administration produced a differential effect on the hypothalamic neurons analyzed, by increasing the number of c-fos positive neurons in the ARC, PVN and DMH, but not in the VMH and LH. This outcome suggests an interactive effect of the glucostatic pathways involving these two areas with the ghrelin signaling.     

Vasoactive peptides in the structure of defensive motivational excitation

In experiments on rabbits, the action was studied of vasoactive peptides angiotensin-II, bradykinin and lysyl-vasopressin, injected into the brain ventricles, on a passive defensive reaction to electrical stimulation of the ventromedial hypothalamus. It was found that angiotensin-II and lysyl-vasopressin had a pronounced inhibitory influence, while bradykinin had a facilitatory effect on this reaction. Electrical stimulation of the ventromedial hypothalamus predominantly facilitated reactions of individual neurones of the sensorimotor cortex to angiotensin-II and bradykinin. Intraperitoneal injection of P-substance to rats in conditions of an acute conflict situation producing an emotional stress, brought about a significant diminution of sudden death incidence from cardiovascular insufficiency.     

The hypothalamus is involved in the anorexic effect of glucagon-like peptide-1 in chicks

The present study was carried out to investigate whether the hypothalamus is involved in the anorexic effect of glucagon-like peptide-1 (GLP-1) in chicks. To examine this, Fos expression in the chick hypothalamus were immunohistochemically detected after intracerebroventricular (ICV) injection of 30-pmol GLP-1. ICV injection of GLP-1 stimulated the expression of Fos-like immunoreactive (FLI) cells in the ventromedial hypothalamic nucleus (VMN). When 15-pmol GLP-1 was directly injected into the chick VMN, the chick's food intake was significantly decreased compared with the control treatment. Microinjection of GLP-1 into the (LHA) also inhibited feeding in chicks, although ICV injection of GLP-1 did not stimulate FLI expression in the brain area. These results suggest that VMN and some brain regions are involved in the anorexic effect of GLP-1 in chicks.     

Combination unilateral amygdaloid and ventromedial hypothalamic lesions: evidence for a feeding pathway

Previous studies have reported hyperphagia and obesity in female rats with bilateral lesions of the most posterodorsal part of the amygdala. In rats with unilateral posterodorsal amygdaloid lesions, a dense pattern of anterograde degeneration appears in the ipsilateral ventromedial hypothalamus, but not the contralateral nucleus. In the present study, female rats with unilateral ventromedial hypothalamic lesions or sham lesions were given either sham lesions or unilateral lesions of the posterodorsal amygdala (PDA) 20 days later. Unilateral lesions of the ventromedial hypothalamus resulted in hyperphagia and excessive weight gain. Subsequent amygdaloid lesions that were contralateral to the initial hypothalamic lesions resulted in hyperphagia and additional excessive weight gains, but amygdaloid lesions ipsilateral to the initial hypothalamic lesions did not. It is concluded that the effects of the two lesions on body weight are not additive and that the PDA and ventromedial hypothalamus are part of the same ipsilateral pathway regulating feeding behavior and body weight regulation.