Feeding regulation by endogenous sugar acids through hypothalamic chemosensitive neurons

Analysis of blood of fasted rats revealed two endogenous sugar acids, 3,4-dihydroxybutanoic acid (2-deoxytetronic acid; 2-DTA) and 2,4,5-trihydroxypentanoic acid (3-deoxypentonic acid; 3-DPA), that might be related to food intake control. Injection of 2-DTA into the third cerebral ventricle reduced food intake for 24 hr in 72 hr deprived rats and depressed single neurons activity in the lateral hypothalamus (LHA). The same amounts of 3-DPA elicited feeding in a dose-related fashion, and increased LHA single neuron activity with 6 to 8 min latency. Intravenous injection of 3-DPA, but not 2-DTA, was effective. Liposome encapsulation of 2-DTA enhanced its potency after intraperitoneal injection, probably by allowing passage across the blood-brain barrier. Electrophoretic application of 2-DTA significantly and specifically suppressed, and 3-DPA facilitated activity of glucose-sensitive (GS) neurons in the LHA. Neither affected glucose insensitive LHA neurons. Both sugar acids affected glucoreceptor (GR) neuron activity oppositely in the ventromedial hypothalamic nucleus (VMH). Intracellular recordings verified that the effect of 2-DTA on the GS and GR neurons was the same as glucose. Hyperpolarization of GR neurons with a membrane conductance increase was brought about by 3-DPA. The levels of plasma glucose and insulin changed oppositely by 2-DTA and 3-DPA, respectively when these were applied into the third cerebral ventricle. Feeding behavior and LHA and VMH neuron activity changes after injection suggest 2-DTA may be an endogenous satiety substance and 3-DPA a hunger substance, with effects mediated by GS neurons in LHA and GR neurons in VMH. Effects of 3-hydroxybutyric acid were also verified and discussed.     

Hypothalamic control of gastric acid secretion

Study of hypothalamic control of gastric acid scretion (GAS) has revealed GAS-related neurons, their location in the lateral hypothalamic area (LHA), their characteristics, and implications of their relations to feeding and other functions. Some LHA glucose-sensitive neurons are referred to as gastric type because of their effects on gastric oxyntic cells via specific gastric related neurons of the medulla oblongata and the vagus. The 2-deoxy-D-glucose (2-DG), or insulin induced GAS was completely abolished by bilateral subdiaphragmatic vagotomy, or micro-lesions in specific sites of the LHA. These gastric type glucose-sensitive neurons were thus believed to contribute to control of GAS. The paraventricular nucleus (PVN) was also found to affect GAS. GAS-related PVN neurons were observed in the rostral PVN. Electrophoretic application of various chemicals, especially glucose, also affected neurons in the rostral PVN. Electrophoretically applied norepinephrine (NE) increased PVN single neuron activity and suppressed GAS. Results suggest that the rostral PVN may be another site to modulate LHA control of GAS, and NE may be a transmitter or modulator.     

Effects of endogenous sugar acids on the ventromedial hypothalamic nucleus of the rat

Effects of certain endogenous sugar acids such as 2-deoxytetronic acid (2-DTA) and 3-deoxypentonic acid (3-DPA) were investigated on the neuronal activity of the ventromedial hypothalamic nucleus (VMH) in the rat. Electrophoretically applied 2-DTA significantly and specifically facilitated the activity of glucoreceptor neurons in the VMH, while 3-DPA suppressed their activity. However, non-glucoreceptor neurons were not affected by these sugar acids. These results reinforces the previous suggestion that 2-DTA and 3-DPA also might act as endogenous satiety and hunger substances, respectively.     

Direct effects of 3,4-dihydroxybutanoic acid gamma-lactone and 2,4,5-trihydroxypentanoic acid gamma-lactone on lateral and ventromedial hypothalamic neurons

The mechanism of central actions of endogenous sugar acids, 3,4-dihydroxybutanoic acid gamma-lactone (3,4-DB) and 2,4,5-trihydroxypentanoic acid gamma-lactone (2,4,5-TP) which have been newly identified as satiety and hunger substances respectively, was investigated. Intracellular recordings were made from neurons in the lateral hypothalamic area (LHA) of rats and ventromedial hypothalamic nucleus (VMH) of guinea pigs, brain areas referred to as feeding and satiety centers, respectively. The LHA neurons hyperpolarized by 3,4-DB show no change in membrane input resistance while the depolarized VMH neurons are associated with an increase in membrane resistance. The mechanisms related to the action of 3,4-DB on these hypothalamic neurons are similar to those in case of glucose on the glucose-sensitive neuron in the LHA and the glucoreceptor neuron in the VMH. 2,4,5-TP depolarized LHA neurons but hyperpolarized VMH neurons with a decrease in the membrane resistance. Our findings indicate that 3,4-DB and 2,4,5-TP have reciprocal effects on each LHA and VMH neurons, with regard to neuronal excitability.     

Central control of gastric acid secretion by extralateralhypothalamic nuclei

Whether secretion of gastric acid (GAS) is in response to peripheral and/or central administration of chemical or electrical stimuli can be differentiated by vagotomy. GAS has been shown to be controlled by specific lateral hypothalamic (LHA) neurons. Application of 2-deoxy-D-glucose (2-DG) or insulin to the LHA by microinjection or iontophoresis has experimentally induced GAS. The paraventricular nucleus (PVN) has now been found to also affect GAS. GAS was produced more copiously and more quickly by rostral PVN lesion than by lesion of the ventromedial (VMH) or dorsomedial (DMH) nucleus, and nearly as much by caudal PVN lesion. Microinjection of 2-DG into the LHA induced GAS more potently in animals with rostral PVN lesions than in those with caudal PVN, VMH or DMH lesions, or in intact animals. Results indicate that the PVN may be an additional central site from which GAS is affected.     

Lateral hypothalamus neuron responses to electroosmotic 2-deoxy-D-glucose

SHIRAISHI, T. AND A. SIMPSON. Lateral hypothalamus neuron responses to electroosmotic 2-deoxy-D-glucose. BRAIN RES. BULL. 8(6) 645–651, 1982.—Electroosmotic applications of 2-deoxy-D-glucose (2-DG) were made in the lateral hypothalamus (LHA). Changes in LHA unit activity and concomitant gastric acid secretion were then observed. 2-DG responsive neurons tended to form two clusters in the LHA. Electroosmotic application induced four patterns of activity change in different LHA neurons. Gastric acid secretion increased when LHA unit activity increased. Results presented here agree with prior reports of hypophagia after precise lesions in this LHA region and other reports of 2-DG induced hyperphagia which might be mediated through central neurons.     

Effects of lateral hypothalamic stimulation on medulla oblongata and gastric vagal neural responses

Recordings were made of neural activity in the medial to lateral region of the dorsal nucleus of the vagus in the medulla oblongata (NDV), and from the gastric branch of the vagal nerve (gastric vagus) in rats. Gastric acid secretion following lateral hypothalamic (LHA) stimulation was observed, and NDV neurons were identified by stimulation of the peripheral end of the gastric vagus. NDV-neurons responded to LHA stimulation with latencies of about 5 msec, and about 6.5 msec to the peripheral stimulation of the gastric vagus. Out of 274 NDV neurons, which were located by their spontaneous discharge, 186 (67.9%) responded to LHA stimulation. Gastric acid secretion (with either short or long latency) occurred in 8.6% (16/186) of these cases. These 16 neurons were considered to be ‘gastric secretory’ neurons and are discussed as such. The results imply that some LHA neurons, which are either concerned with or directly control gastric acid secretion, communicated by at least one path (probably polysynaptic) to the medulla oblongata and then via the vagus to the oxyntic cells of gastric glands.     

Orexin-A signaling in the paraventricular nucleus promote gastric acid secretion and gastric motility through the activation neuropeptide Y Y1 receptors and modulated by the hypothalamic lateral area

ObjectiveAbnormal gastric acid secretion and gastric dyskinesia are common gastroenterological ailments. Our study aims to investigate the effect of orexin-A in the paraventricular nucleus (PVN) gastric motility and gastric acid secretion.MethodsThe source of orexin-A neuronal projections to the PVN were explored by retrograde tracing and fluorescence immunohistochemistry experiments. Neuronal discharge recordings of single cells were taken within the PVN. Gastric motility was recorded using a force transducer implanted into the stomach, and gastric acid secretion measured through a pyloric catheter.ResultsOrexin-A-positive neuronal projections from LHA to PVN were found. Administration of orexin-A to PVN activated the firing of 63.2% NPY-excited/GD-excitatory (GD-E) neurons but suppressed the firing of 55.9% NPY-inhibited/GD-inhibitory (GD-I) neurons, promoted gastric motility and gastric acid secretion in a dose-dependent manner. Responses produced by orexin-A could be partially blocked by Y₁ receptor antagonist GR-231118; Electrical stimulation to the the hypothalamic lateral area (LHA) altered NPY-sensitive/GD neuronal activity in the PVN, stimulated gastric motility and gastric acid secretion. Additionally, these effects induced by LHA electrical stimulation were blocked by administration of the OX1R antagonist SB-334867 to the PVN.ConclusionOrexin-A from LHA neurons act on the PVN to enhance gastric motility and gastric acid secretion, with Y₁ receptor signaling playing a critical role.     

Gastrin related peptide effects in lateral hypothalamus depend on food deprivation

Gastrin related peptides (PG) affected neurons in the lateral hypothalamus (LHA) differently in food deprived than in non-deprived rats. Electroosmosis and intravenous (IV) results agreed. Gastric acid secretion was also measured. Neural responses to PG were: transiently increased discharge rate followed by desensitization occurred equally in deprived and non-deprived rats; dose related decrease in discharge rate occurred significantly more often in non-deprived than in deprived rats. Observed LHA changes and gastric acid secretion occurred pari passu. It was concluded that PG could contribute to LHA control of feeding behavior. It was not determined whether the effects attributed to systemic injection and those attributed to electroosmotic application both had the same origin. The significant differences which were observed could have been either different reactions by one neuron type, or responses of different neuron types.     

Functional correlations between lateral hypothalamic glucose-sensitive neurons and hepatic portal glucose-sensitive units in rat

The effects of glucose injection into the hepatic portal vein on neural activity of the lateral hypothalamic area (LHA) were studied in rats. A majority of identified glucose-sensitive neurons in the LHA were inhibited by portal injection of glucose. This was found to be mediated through the alpha-noradrenergic pathways. Most of the glucose-insensitive neurons did not respond to the same procedure. Portal injection of hypertonic saline increased neural activity of some glucose-insensitive neurons but no glucose-sensitive neurons responded. Convergence of hepatic vagal afferent glucose-sensitive units on LHA glucose-sensitive neurons was clarified by this study.     

Effects of mazindol on rat lateral hypothalamic neurons

In order to elucidate the mechanism of action of the anorectic drug, mazindol, effects of electrophoretically applied mazindol were examined on glucose-sensitive and non glucose-sensitive neurons in the rat lateral hypothalamic area (LHA), which is functionally important in food intake control. Mazindol was found to significantly suppress the firing rate of glucose-sensitive neurons. Ouabain a Na-K pump inhibitor, attenuated mazindol induced suppression of neuronal firing rate. Intracellular recordings revealed hyperpolarization of the membrane with no change in membrane conductance by perfusion of brain slice with 0.1 mM mazindol in bath. This was similar to the effect of 30 mM glucose. Results suggest that the inhibitory action of mazindol is mediated by activation of the Na-K pump. Spiroperidol, a dopamine antagonist, did not affect the inhibitory response to mazindol, suggesting direct action of mazindol on LHA neurons, independent of dopamine.     

Calcitonin-induced anorexia in rats: Evidence for its inhibitory action on lateral hypothalamic chemosensitive neurons

Effects of a synthetic derivative of eel calcitonin, [Asu1,7]ECT on feeding behavior, and its direct action on the neuronal activity of lateral hypothalamic area (LHA) were studied in rats. Food intake was significantly reduced in a dose-dependent manner after intra-third ventricular injection of [Asu1,7]ECT (0.2-1.0 U/rat). The neuronal activity of LHA neurons, especially the glucose-sensitive neurons, was inhibited by electrophoretic application of [Asu1,7]ECT. The inhibition was accompanied by a hyperpolarization of the membrane by about 5-7 mV with an increase in the membrane resistance (5.0-8.7%). This effect was also shown to be independent of noradrenergic or serotonergic mechanisms. Phosphodiesterase inhibitors, such as 3-isobutyl-1-methylxanthine and papaverine augmented the inhibitory response, whereas nicotinic acid blocked it. These results suggest that the anorexia caused by [Asu1,7]ECT is mediated through a direct inhibition of chemosensitive neuronal activity in the LHA, caused by an increase in the intracellular level of cyclic 3',5'-adenosine monophosphate.     

Gastric related properties of rat paraventricular neurons

Central control of gastric acid secretion (GAS) was formerly attributed to specific neurons in the lateral hypothalamus (LHA), but the rostral part of the paraventricular nucleus (r-PVN) of the hypothalamus was shown to be another site that modulates central control of GAS. In the present study, the characteristics of 145 spontaneously firing r-PVN neurons were investigated in 22 rats. Discharges were: high frequency regular or irregular, low frequency regular or irregular. About half of the regular discharges were phasic. Electrical stimulation in the r-PVN evoked responses in 407 LHA units. Response latencies ranged from 4.7 to 78.1 msec; indicating mono- and polysynaptic, and myelinated and nonmyelinated fiber connections. Gastric related and non-related r-PVN neurons were observed. It was also shown, for the first time, that electrophoretic application of various chemicals, especially glucose, affected chemosensitive neurons in the r-PVN. PVN neuron responses to LHA repetitive stimulation were classified as excitatory (E), excitatory-inhibitory (E-I), I and I-E. PVN neuronal discharges might be modulated by gastric type LHA neurons. Electrophoretically applied norepinephrine (NE) increased PVN neuronal activity and suppressed GAS. Results suggest that rostral PVN neurons might affect LHA control of GAS, with NE as the probable transmitter or modulator.     

Responses of rat lateral hypothalamic neuron activity to vestibular nuclei stimulation

Effects of lateral vestibular nucleus (LVN) stimulation on neuronal activity in the rat lateral hypothalamic area (LHA), including specific glucose-sensitive neurons, were investigated by extracellular and intracellular recordings in vivo. Stimulation of the contralateral LVN evoked 3 types of response in 46% (111/240) of the neurons recorded extracellularly: long latency (38.1 +/- 23.6 ms) excitation (62/111, 56%), short latency (6.9 +/- 3.1 ms) excitation-inhibition (33/111, 30%), and inhibition with 20.1 +/- 11.1 ms latency (16/111, 14%). Glucose-sensitive neurons, which were identified by electrophoretic application of glucose, did not respond specifically to such stimulation. Neuronal activity was recorded intracellularly from 31 LHA neurons, of which 13 responded to LVN stimulation. Seven of the 13 neurons showed a long latency EPSP (10.4 +/- 5.5 ms) and the remaining 6 exhibited an EPSP-IPSP sequence with shorter latency (4.5 +/- 3.0 ms). The amplitude of these responses was graded with a change in stimulus intensity. The EPSPs of both types of response were considered to be polysynaptic because of shortening of latencies by higher current stimulation. Since the LHA is implicated in the regulation of autonomic nerve activity, the present results showing polysynaptic pathways from the LVN to the LHA suggest functional involvement of the LHA in vestibulo-autonomic responses.     

Responses of rat lateral hypothalamic neurons to periaqueductal gray stimulation and nociceptive stimuli

The effects of dorsal periaqueductal gray (D-PAG) stimulation and noxious stimuli on neural activity in the lateral hypothalamic area (LHA) were investigated in 56 adult male anesthetized rats. Strong tail pinch was used as noxious stimulation. We examined 234 extracellular and 75 intracellular recordings of LHA responses to electrical stimulation of D-PAG. To determine neurotransmitter candidates, the effects of the opioid agonist, morphine, and its antagonist, naloxone were investigated by systemic administration and microelectrophoresis. Of 234 spontaneously firing LHA neurons, 70 (30%) were inhibited by D-PAG stimulation. Of these 70 neurons, 26/40 tested (65%) were glucose-sensitive, 16/19 (84%) were inhibited by morphine and 12/18 (67%) were inhibited by tail pinch. Glucose-sensitive neurons were selectively inhibited by morphine and tail pinch. Naloxone attenuated inhibitory responses to D-PAG stimulation, tail pinch and electrophoretic morphine. From intracellular recordings these polysynaptic inhibitory responses to D-PAG stimulation were considered to be inhibitory postsynaptic potentials (IPSPs) with 6.1 +/- 3.2 ms (mean +/- S.D.) latency and reversal membrane potential of about -78 mV. Since LHA glucose-sensitive neurons receive, selectively, both inhibitory opioid inputs from the D-PAG and inhibitory inputs through noxious stimulation, we suggest that D-PAG might be an intermediate site for transmission of noxious stimuli to the LHA.     

Excitatory stimulation of neurons in the arcuate nucleus inhibits gastric acid secretion via vagal pathways in anesthetized rats

It is well established that autonomic control of gastrointestinal function is modulated by central autonomic neurotransmission. In this context it has been shown that gastrointestinal motility and secretion can be modulated by exogenous neuropeptides microinjected into the paraventricular nucleus of the hypothalamus (PVN). Furthermore, there is considerable evidence suggesting that neurons projecting from the arcuate nucleus (Arc) to the PVN may be the source of endogenous neuropeptide release in the PVN. This poses the question whether stimulation of neurons in the arcuate nucleus, e.g. by an excitatory amino acid, alters gastrointestinal function. In the present study, we investigated the effect of an excitatory amino acid, kainate, microinjected into the arcuate nucleus on gastric acid secretion in urethane-anesthetized rats. Kainate (140 pmol/rat) bilaterally microinjected into the Arc induced an significant inhibition of pentagastrin (PG) stimulated (16 mg/kg per h) gastric acid secretion throughout an observation period of 120 min after microinjection. Microinjection of kainate into hypothalamic areas outside the arcuate nucleus did not modify gastric secretion. Bilateral cervical vagotomy blocked the effect of kainate injected into the Arc on PG-stimulated gastric acid secretion. These data show that gastric secretory function can be modulated by stimulation of neuronal activity in the Arc via efferent vagal pathways. The results suggest that the arcuate nucleus is a forebrain area involved in the CNS regulation of gastrointestinal function.     

Lateral hypothalamic area orexin-A influence the firing activity of gastric distension-sensitive neurons and gastric motility in rats

The orexins system consists of two G-protein coupled receptors (the orexin-1 and the orexin-2 receptor) and two neuropeptides, orexin-A and orexin-B. Orexin-A is an excitatory neuropeptide that regulates arousal, wakefulness and appetite. Recent studies have shown that orexin-A may promote gastric motility. We aim to explore the effects of orexin-A on the gastric -distension (GD) sensitive neurons and gastric motility in the lateral hypothalamic area (LHA), and the possible regulation by the paraventricular nucleus (PVN). Extracellular single unit discharges were recorded and the gastric motility was monitored by administration of orexin-A into the LHA and electrical stimulation of the PVN. There were GD neurons in the LHA, and administration of orexin-A to the LHA could increase the firing rate of both GD-excitatory (GD-E) and GD-inhibited (GD-I) neurons. The gastric motility was significantly enhanced by injection of orexin-A into the LHA with a dose dependent manner, which could be completely abolished by pre-treatment with orexin-A receptor antagonist SB334867. Electrical stimulation of the PVN could significantly increase the firing rate of GD neurons responsive to orexin-A in the LHA as well as promote gastric motility of rats. However, those effects could be partly blocked by pre-treatment with SB334867 in the LHA. It is suggested that orexin-A plays an important role in promoting gastric motility via LHA. The PVN may be involved in regulation of LHA on gastric motility.     

Fibroblast Growth Factor Receptor-1 in the Lateral Hypothalamic Area Regulates Food Intake

Previous studies have shown that acidic and basic fibroblast growth factor (aFGF and bFGF) and certain fragments of the aFGF N-terminal suppress food intake in rats due to their inhibitory actions on the glucose-sensitive neurons in the lateral hypothalamic area (LHA). The present study was planned to determine the role of FGF receptor-1 (FGFR-1), which was found in the LHA neurons of rats, on feeding regulation. The structure–activity relationship of aFGF fragments in feeding suppression was also investigated. An injection of anti-FGFR-1 antibody (250 and 350 ng) into the bilateral LHA significantly increased food intake. Synthesized aFGF fragments were infused into the III ventricle to elucidate the structure–activity relationship on the inhibition of feeding. Although aFGF-(1–29) did not affect food intake, [Ser¹⁶]aFGF-(1–29) (400 ng) and [Glu¹⁶]aFGF-(1–29) (400 ng), in which the cysteine residue at position 16 of aFGF-(1–29) was replaced with structurally similar serine and glutamic acid, were observed to significantly inhibit food intake. These findings suggest that endogenous FGFR-1 in the LHA plays an important role in FGF-induced feeding suppression, while, in addition, the dissolving disulfide bond formation in aFGF fragments enhances their inhibitory effects on feeding.     

Quinolinic acid toxicity on orexin neurons blocked by gamma aminobutyric acid type A receptor stimulation

Selective degeneration of hypothalamic orexin neurons, a hallmark of pathology in narcolepsy patients, is in part reproduced in hypothalamic slice cultures by application of an endogenous excitotoxin quinolinic acid. Depolarized membrane potential may be responsible for the vulnerability of orexin neurons to excitotoxicity. We show that stimulation of gamma-aminobutyric acid type A receptors, which is known to hyperpolarize orexin neurons, by muscimol or isoguvacine potently inhibits quinolinic acid cytotoxicity on orexin neurons. In addition, the protective effect of gamma-aminobutyric acid and a gamma-aminobutyric acid uptake blocker nipecotic acid is abolished by a gamma-aminobutyric acid type A antagonist picrotoxin. Norepinephrine and serotonin do not provide a neuroprotective effect. Thus, GABAergic inhibitory control may be a decisive factor regulating survival of orexin neurons under excitotoxic insults.