Ingestion in the satiated rat: role of alpha and beta receptors in mediating effects of hypothalamic adrenergic stimulation

Peptides that regulate food intake: norepinephrine is not required for reduction of feeding induced by cholecystokinin

CCK octapeptide (CCK-8) is released by the gut in response to a meal and acts via CCK(A) receptors on vagal afferents to induce satiety. However, the central neural pathways by which peripheral CCK-8 affects feeding are poorly understood. In the present study, we tested the hypothesis that norepinephrine (NE) is necessary for satiety induced by peripheral CCK-8 by using mice lacking dopamine beta-hydroxylase (Dbh(-/-)), the enzyme responsible for synthesizing NE and epinephrine from dopamine. We found that Dbh(-/-) mice are as responsive to the satiating effects of CCK-8 as their normal littermates.

Symptoms of hypoglycaemia in people with diabetes

The symptoms of hypoglycaemia are fundamental to the early detection and treatment of this side-effect of insulin and oral hypoglycaemic therapy in people with diabetes. The physiology of normal responses to hypoglycaemia is described and the importance of symptoms of hypoglycaemia is discussed in relation to the treatment of diabetes. The symptoms of hypoglycaemia are described in detail. The classification of symptoms is considered and the usefulness of autonomic and neuroglycopenic symptoms for detecting hypoglycaemia is discussed. The many external and internal factors involved in the perception of symptoms are reviewed, and symptoms of hypoglycaemia experienced by people with Type 2 diabetes are addressed. Age-specific differences in the symptoms of hypoglycaemia have been identified, and are important for clinical and research practice, particularly with respect to the development of acquired hypoglycaemia syndromes in people with Type 1 diabetes that can result in impaired awareness of hypoglycaemia. In addition, the routine assessment of hypoglycaemia symptoms in the diabetic clinic is emphasized as an important part of the regular review of people with diabetes who are treated with insulin.

Effects of subtypes alpha- and beta-adrenoceptors of the lateral hypothalamus on the water and sodium intake induced by angiotensin II injected into the subfornical organ

The present experiments were conducted to investigate the role of the alpha(1A)-, alpha(1B), beta(1)- and beta(2)-adrenoceptors of the lateral hypothalamus (LH) on the water and salt intake responses elicited by subfornical organ (SFO) injection of angiotensin II (ANG II) in rats. 5-methylurapidil (an alpha(1A)-adrenergic antagonist), cyclazosin (an alpha(1B)-adrenergic antagonist) and ICI-118,551 (a beta(2)-adrenergic antagonist) injected into the LH produced a dose-dependent reduction, whereas efaroxan (an alpha(2)-antagonist) increased the water intake induced by administration of ANG II into the SFO. These data show that injection of 5-methylurapidil into the LH prior to ANG II into the SFO increased the water and sodium intake induced by the injection of ANG II. The present data also show that atenolol (a beta(1)-adrenergic antagonist), ICI-118,551, cyclazosin, or efaroxan injected into the LH reduced in a dose-dependent manner the water and sodium intake to angiotensinergic activation of SFO. Thus, the alpha(1)- and beta-adrenoceptors of the LH are possibly involved with central mechanisms dependent on ANG II and SFO that control water and sodium intake.

Participation of alpha-1 and alpha-2 adrenoceptors of the lateral hypothalamic area in water intake, and renal sodium, potassium and urinary volume excretion induced by central administration of angiotensin II

The circumventricular structures and the lateral hypothalamus (LH) have been shown to be important for the central action of angiotensin II (ANGII) on water and electrolyte regulation. Several anatomical findings have demonstrated neural connection between circumventricular structures and the LH. The present experiments were conducted to investigate the role of the alpha-adrenergic antagonists and agonistic injected into the LH on the water intake, sodium and potassium excretion elicited by injections of ANGII into the lateral ventricle (LV). The water intake was measured every 30 min over a period of 120 min. The sodium, potassium and urinary volume were measured over a period of 120 min in water-loaded rats. The injection of ANGII into the LV increased the water intake, which was reduced by previous injection of clonidine (an alpha-2-adrenergic agonist) into the LH. The injection of yohimbine (an alpha-2-adrenergic antagonist) and prazosin (an alpha-1-adrenergic antagonist) into the LH, which was done before injecting ANGII into the LV, also reduced the water intake induced by ANGII. The injection of ANGII into the LV reduced the sodium, potassium and urinary volume. Previous treatment with clonidine attenuated the action of ANGII in reducing the sodium, potassium and urinary volume, whereas previous treatment with yohimbine attenuated the effects of ANGII but with less intensity than that caused by clonidine. Previous treatment with prazosin increased the inhibitory effects of ANGII in those parameters. The injection of yohimbine and prazosin, which was done before the injection of clonidine, attenuated the effect of clonidine on the ANGII mechanism. The results of this study led us to postulate that when alpha-2-adrenergic receptors are blocked, the clonidine may act on the imidazoline receptors to produce its effects on the ANGII mechanism. We may also conclude that the LH is involved with circumventricular structures, which present excitatory and inhibitory mechanisms. Such mechanisms are responsible for regulating the renal excretion of sodium, potassium and water.

Food intake after adrenaline and noradrenaline injections into the hypothalamic paraventricular nucleus in pigeons

The effects of local injections of adrenaline (Adr, 6 nmol) or noradrenaline (Nor, 16 nmol) into the paraventricular nucleus (PVN) and into other anterior hypothalamic districts on feeding behavior were examined in satiated pigeons bearing a chronically implanted cannula. When infused into the PVN, both Adr and Nor reliably elicited feeding responses during the first hour after the injection. Feeding responses to Adr injections were significantly higher than those evoked by Nor. Other behavioral measurements (sleep, exploratory, and preening) were not affected by these treatments. Local pretreatment with phentolamine (20 nmol) but not with propranolol (20 nmol) abolished the feeding response induced by both Adr and Nor into the PVN. Lateral hypothalamic sites were also shown to respond to catecholamine injections with an increase in feeding, followed also by an increased sleep-like behavior duration. Together with other evidence, the present results indicate that adrenergically mediated circuits into the avian PVN play an important role in the mechanisms of food intake control, equivalent to that observed in mammalian species.

Role of the adrenergic pathways of the lateral hypothalamus on water intake and pressor response induced by the cholinergic activation of the medial septal area in rats

In the present experiments, we investigated a possible involvement of noradrenergic receptors of the lateral hypothalamus (LH) in the water intake and pressor response induced by cholinergic stimulation of the medial septal area (MSA) in rats. The cholinergic agonist carbachol (2 nmol) injected into the MSA induced water intake and pressor response. The injection of an alpha 2-adrenergic agonist, clonidine (20 and 40 nmol), but not of an alpha 1-adrenergic agonist, phenylephrine (80 and 160 nmol), into the LH inhibits the water intake induced by carbachol injected into the MSA. The injection of clonidine or phenylephrine into the LH produced no change in the MAP increase induced by carbachol injected into the MSA. The present results suggest that adrenergic pathways involving the LH are important for the water intake, but not for the pressor response, induced by cholinergic activation of the MSA.

Effects of adrenalectomy and deprivation condition on food intake after phenylpropanolamine or clonidine

alpha-Adrenergic receptors within the paraventricular hypothalamus (PVN) modulate feeding such that activation of alpha 2-adrenoceptors by drugs such as clonidine (CLON) increase feeding; whereas activation of alpha 1-adrenoceptors by drugs such as phenylpropanolamine (PPA) suppress feeding. Prior studies suggest that the feeding-stimulatory effect of alpha 2-adrenergic activation is a function of drug dose as well as the deprivation condition and adrenal status of the animal. Specifically, CLON's effects on feeding are greatest at low doses in food-satiated adrenally intact rats. Whether a similar profile is produced by alpha 1-adrenoceptor agonists such as PPA has not previously been explored. Thus, the present study provides a comparison of the effects on food intake of drug dose, deprivation condition, and adrenalectomy induced by these alpha 2- and alpha 1-adrenergic drugs. Accordingly, both adrenalectomized (ADX) as well as sham-control (SHAM) adult male rats underwent a series of 1-h feeding tests following administration of PPA (5, 10, 20 mg/kg, IP) as well as CLON (0.0125, 0.025, 0.05, 0.1 mg/kg, IP) under both deprived and nondeprived testing conditions. The results suggest that the deprivation condition, but not the surgical condition (ADX vs. SHAM), exerts the greatest overall effect on food intake following administration of alpha-adrenergic drugs.

Role of the alpha 1- and alpha 2-adrenoceptors of the lateral hypothalamus in the dipsogenic response to central angiotensin II in rats

The present experiments were conducted to investigate the role of the alpha 1- and alpha 2-adrenergic receptors of the lateral hypothalamus (LH) on the drinking response elicited by intracerebroventricular (i.c.v.) injections of carbachol and angiotensin II (AII) in rats. Clonidine (an alpha 2-adrenergic agonist) injected into the LH produced a dose-dependent reduction of the drinking responses elicited by i.c.v. administration of carbachol and AII. The alpha 1-adrenergic agonist phenylephrine injected into the LH reduced the dipsogenic response to i.c.v. AII, but not to carbachol. Injection of yohimbine (an alpha 2-adrenergic antagonist) and prazosin (an alpha 1-adrenergic antagonist) into the LH also reduced the water intake produced by i.c.v. injection of AII. Previous injection of alpha 1- or alpha 2-adrenergic antagonists into the LH increased the antidipsogenic effect of clonidine or phenylephrine injected into the same area on the water intake induced by i.c.v. AII. These results show that the alpha 1- and alpha 2-adrenergic receptors of the LH are involved in the control of drinking responses elicited by i.c.v. injection of AII in rats. They also show that clonidine, but not phenylephrine, suppresses the drinking induced by i.c.v. carbachol. The data suggest that the discharge of central alpha-adrenergic receptors has a dual (inhibitory and excitatory) effect on water intake induced by central AII.

Noradrenergic neurons modulate lateral hypothalamic chemical and electrical stimulation-induced feeding by sated rats

The lateral hypothalamus (LHA) is important in feeding behavior. Functions of neurotransmitters and receptors in the control of feeding behavior elicited by electrical and chemical stimulation in the bilateral LHA were studied using electrodes and cannulae chronically implanted in sated rats. Experiments were performed in the daylight (0700-1900). Chemical stimulation with norepinephrine (NE), epinephrine (E) or dopamine (DA) dose-dependently (1-10 nmol) increased food intake (g/8 h). Neither E nor DA affected LHA-electrical stimulation-induced feeding (ESIF), but small doses (0.5-10 nmol) of NE significantly (p less than 0.05) enhanced LHA-ESIF. Pretreatment with larger doses (50-500 nmol) of NE significantly (p less than 0.05-0.01) inhibited LHA-ESIF. The results indicate that catecholaminergic input to feeding-related neurons in the LHA is noradrenergic. Pretreatment with 10-160 nmol phenoxybenzamine (PBZ) or 5-80 nmol propranolol (PNL) dose-dependently inhibited ESIF. PBZ was slightly more potent than PNL, which indicates that the feeding-related adrenergic receptors in the LHA are predominantly alpha-receptors. Electrophysiological data support these behavioral results which, when taken together, suggest that LHA-ESIF might be caused by electrically driven release of NE from feeding-related neurons.

Stimulation of feeding by galanin: anatomical localization and behavioral specificity of this peptide's effects in the brain

The neuropeptide galanin (GAL) has been found to elicit eating after injection into the hypothalamic paraventricular nucleus (PVN). To determine whether GAL's effect in the brain is anatomically specific, this peptide (0.1 or 0.3 nmol) was microinjected into one of 14 different brain areas of rats, and its impact on subsequent food intake was measured. Among the hypothalamic sites tested, only the PVN and the adjacent periventricular region yielded a significant eating response to GAL. With injection into the PVN, a feeding response was observed without apparent changes in other food-associated behaviors, e.g., drinking, grooming, resting and sleeping, or low and high levels of activity. All other hypothalamic and extrahypothalamic sites tested were unresponsive to GAL, with the exception of the amygdala where a significant eating response was observed. These findings suggest that central GAL elicits feeding by acting in an anatomically localized and behaviorally specific manner. In light of other pharmacological and anatomical evidence, it is suggested the PVN GAL, in modulating feeding behavior, may work in association with the catecholamine norepinephrine (NE) which is known to coexist with GAL in PVN neurons.

Intrahypothalamic injections of norepinephrine facilitate feline affective aggression via alpha 2-adrenoceptors

The purpose of this study was to investigate the effects of noradrenergic agents infused into the anterior hypothalamus on feline affective defense responses elicited by electrical stimulation of the ventromedial hypothalamus. Anterior hypothalamic sites which are known to receive inputs from both the ventromedial hypothalamus and ascending noradrenergic pathways were selected for pharmacological analysis. Intracerebral infusions of NE (1.2-2.4 nmol) into the anterior hypothalamus significantly reduced the threshold current required to elicit the hissing component of affective defense via electrical stimulation of the ventromedial hypothalamus. Maximal threshold reductions (17 +/- 3% to 20 +/- 3%) were observed 30 min following infusion. Anterior hypothalamic infusions of clonidine facilitated feline affective defense by reducing hissing current thresholds by 18 +/- 4%. Clonidine-induced changes in response thresholds parallel those obtained with NE. Both NE-induced and clonidine-induced reductions in current thresholds were reversible by pre- and post-treatment of the anterior hypothalamic sites with yohimbine. These results demonstrate that the reductions in response thresholds are mediated by post-synaptic alpha 2-adrenoceptors located within the anterior hypothalamus. Thus the noradrenergic system may play an important role in the regulation of affective aggressive behavior.

Clonidine and phenylephrine injected into the lateral hypothalamus inhibits water intake in rats

It has been demonstrated that peripheral or intracerebroventricular (i.c.v.) administration of the alpha 2-adrenoceptor agonist, clonidine, blocks the water intake induced by several dipsogenic stimuli in rats. In the present investigation we studied the effect of the injection of clonidine, phenylephrine, prazosin or yohimbine into the lateral hypothalamic area (LHA) on the water intake induced by water deprivation or central angiotensin II (AII) in rats. Rats with chronic cannulas implanted into the lateral ventricle and LHA were used. Injection of clonidine or phenylephrine into the LHA reduced the water intake produced by both water deprivation and i.c.v. injection of AII. Previous injection of the alpha 1- or alpha 2-adrenoceptor antagonists, prazosin or yohimbine, into the LHA reduced the antidipsogenic effect of clonidine or phenylephrine injected into the same area. These results suggest that the alpha 1- and alpha 2-adrenergic receptors of the hypothalamus are part of the central inhibitory system for the thirst produced by dehydration or central AII.

Pertussis toxin inhibits neuropeptide Y-induced feeding in rats

Neuropeptide Y (NPY) is the most powerful peptide drug stimulating feeding in rats. Rats with paraventricular hypothalamic (PVH) cannulae were used to investigate the mechanisms involved in NPY-induced feeding. Consistent with previous reports, injection of 2 micrograms of NPY into the PVH significantly increased the cumulative food intake over 1-, 2- and 4-hr periods. Ad lib feeding decreased significantly two days after pertussis toxin (PT) administration, but recovered to nearly normal levels on the fourth day. PT had no immediate effect on NPY-induced feeding; however, four days after PT was injected NPY (2 micrograms) did not increase the food intake compared to control. In vitro investigations showed that isoproterenol-stimulated adenylate cyclase activity in the hypothalamus of control rats was inhibited by NPY. In PT-treated rats, however, no inhibition of cAMP production was observed. These results suggest that cAMP may mediate NPY-induced feeding and that a PT-sensitive G protein may be involved in this signal transduction.

Effects of norepinephrine infused in the paraventricular hypothalamus on energy expenditure in the rat

The metabolic effects of norepinephrine (NE), when infused into the paraventricular nucleus of the hypothalamus (PVN), were examined using indirect calorimetry. In two separate experiments, it was found that NE infused into the PVN reduced energy expenditure in freely moving rats. While NE also reduced motor activity, these reductions were not statistically significant. Reductions in voluntary motor activity were not necessary for a reduction in energy expenditure, as NE still reduced energy expenditure in rats that were lightly sedated. Clonidine, but not L-phenylephrine, mimicked the hypometabolic effect of NE, suggesting an action at alpha 2 receptors. Infusions of NE were also found to increase blood glucose shortly after infusion, although the specificity of this effect is questionable. Taken together, these data suggest that activation of noradrenergic neurons within the PVN results in a metabolic shift towards energy conservation.

Binding specificity and presynaptic action of anaphylatoxin C5a in rat brain

Human anaphylatoxin C5a injected directly to the perifornical hypothalamus (PFH) of the rat elicits food intake in sated rats, an effect which mimics that of norepinephrine (NE) at the PFH. The ability of C5a to induce food intake is selectively blocked by the alpha-adrenergic antagonist phentolamine, confirming that C5a exerts its effects via an alpha-adrenergic receptor system. In this study specific C5a binding sites on rat brain slices were detected using 125I-C5a at 2.4 nM in the presence of unlabeled noncompeting C3a and competing C5a at 0.5 microM. To determine whether the in vivo activity of C5a was due to direct stimulation of an alpha-adrenergic receptor system or to indirect modulation via a specific C5a receptor, rats were pretreated at the PFH with C5ai, the "inactive" 74-desarginated derivative of C5a. C5ai blocked stimulation of feeding by C5a but had no effect on food intake elicited by NE, suggesting a presynaptic site for C5a activity. To determine whether C5a anaphylatoxin acts at presynaptic or postsynaptic sites, the ability of C5a and of NE to induce food intake in sated rats was compared before and after injection of the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMPT) to the PFH. AMPT would produce focal depletion of endogenous catecholamines by inhibition of catecholamine biosynthesis. Rats treated with AMPT failed to respond to C5a but ate excessively following NE, suggesting that C5a acts presynaptically, possibly to release NE. We propose that C5a acts at a specific C5a/C5ai receptor to modulate catecholamine activity at the brain site.

Neuropeptide Y, epinephrine and norepinephrine in the paraventricular nucleus: stimulation of feeding and the release of corticosterone, vasopressin and glucose

The paraventricular nucleus (PVN) is known to have an important function in mediating a variety of behavioral and endocrine responses. In the present study, the responsiveness of the PVN to the effects of the coexisting neurotransmitters, neuropeptide Y (NPY), epinephrine (EPI) and norepinephrine (NE), was examined. Albino rats were each chronically implanted with a swivel brain-cannula that permits chemicals to be infused without disturbing the animals' ongoing behavior. When infused into the PVN, each of these neurotransmitters elicited a reliable feeding response during the first hour after injection. The response to EPI was significantly stronger than that of NE and NPY, while the latency to eat after injection was considerably longer for NPY as compared to the catecholamines. In tests with food absent, each of these substances also increased blood levels of corticosterone (EPI greater than NE = NPY) and vasopressin (NPY greater than EPI greater than NE) and revealed a significant positive correlation between circulating levels of these two hormones. In addition, EPI and NE, in contrast to NPY, caused a simultaneous rise in blood glucose, producing levels that were positively correlated with the hormones. No relationship, however, was detected between these endocrine changes and the rats' feeding-stimulatory responses. Together with other evidence, these results suggest that adrenergic as well as noradrenergic innervation to the PVN has a key role in the behavioral and endocrine systems of this nucleus and, moreover, that NPY generally mimics the effects of these catecholamines in the PVN.

[Pharmacological and molecular aspects of the regulation of eating behavior. With special reference to the role of catecholamines and effects of amphetamine]

Among the numerous endogenous substances involved in the regulation of feeding behaviours, the catecholamines are in the front rank. The numerous studies devoted to this aspect of catecholamines emphasize the importance and complexity of their intervention. Depending on the cerebral structures on which they act and on whether noradrenaline or dopamine are concerned, orexigenic or anorexigenic effects have been described. Alpha-2 and beta adrenergic receptors as well as D1 and D2 dopaminergic receptors participate in these effects. Amphetamine, which is an indirect catecholaminergic agonist, mobilizes neuronal catecholamines and fosters their various effects. Moreover, it exercises direct effects by its association with sites borne by glycaemia-sensitive neurons. This target seems to be common to a wide variety of anorectic agents. They are thought to reproduce on this hypothalamic "glucostat" the effect of a high blood glucose level, thus triggering off signals of satiety. In this unifying hypothesis, the diverse pharmacological profiles these agents are known to possess would result from associated properties.

Alpha 2-adrenoceptor blockade attenuates feeding behavior induced by neuropeptide Y and epinephrine

Neuropeptide Y (NPY, 0.47 nmol) and epinephrine (28.9 nmol) evoked robust, and quantitatively similar, increments in food intake and local eating rate following administration into the third cerebral ventricle (IIIV). Whereas IIIV pretreatment with phentolamine (71 nmol), a nonselective alpha-adrenoceptor antagonist, or prazosin (9.5 nmol), a selective alpha 1-adrenoceptor antagonist, was without effect on NPY-induced feeding behavior, pretreatment with the alpha 2-adrenoceptor antagonist yohimbine (15 nmol) dramatically attenuated the stimulatory effects of NPY or epinephrine on both food intake (by over 50%) and local eating rate. Additionally, yohimbine administered alone was associated with a stimulatory effect on food intake for the periods of 80-110, and 110-140 minutes posttreatment. These data demonstrate that feeding behavior induced by IIIV administration of NPY or epinephrine is attenuated by prior blockade of alpha 2-adrenoceptors and suggest that, as in other systems innervated by neurons displaying NPY and adrenergic transmitter colocalization, the effects of NPY on feeding behavior may, at least in part, be mediated via alpha 2-adrenoceptors.

Selection for growth alters the feeding response to injections of biogenic amines

Two experiments were conducted to determine if selection for growth altered the response to intracerebroventricular (ICV) injections of methoxamine and 5-hydroxytryptamine (5-HT). Lines of chickens divergently selected over 25 generations for 8-week body weight were used. The ICV injection of methoxamine into fully fed birds significantly increased food intake in the high-weight line but had no effect on food intake in the low-weight line. Conversely, the ICV injection of 5-HT had no effect in fully fed birds but significantly decreased food intake in 24-hr fasted birds in both weight-lines. Food intake was affected by 5-HT for a much longer period in the high-weight line than in the low-weight line. These results suggest that selection for growth alters the brain response to biogenic amines.

Postsynaptic alpha 2-noradrenergic receptors mediate feeding induced by paraventricular nucleus injection of norepinephrine and clonidine

This study examines the feeding response induced by hypothalamic noradrenergic stimulation, in terms of the type and synaptic position of its mediating receptor. Tests with norepinephrine or the alpha 2 receptor agonist clonidine, injected into the area of the paraventricular nucleus (PVN), revealed a potent feeding response in satiated animals. This response by either agonist was blocked, in a dose-dependent fashion, by local injection of the alpha 2-noradrenergic antagonists, rauwolscine and yohimbine. It was also blocked by the general antagonist, phentolamine. In contrast, it was unaffected by hypothalamic injection of the alpha 1-noradrenergic antagonists, prazosin and corynanthine. These results indicate that feeding elicited by noradrenergic stimulation in the region of the PVN is mediated through alpha 2-type receptors. These alpha 2 receptors appear to be located postsynaptically, since the effectiveness of clonidine in eliciting eating was undisturbed by prior injection of the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine.

Anaphylatoxin C5a modulation of an alpha-adrenergic receptor system in the rat hypothalamus

C5a anaphylatoxin injected via implanted cannulae into the perifornical region of the hypothalamus stimulated eating in sated rats. C5a also attenuated carbamyl choline-induced drinking, and carbamyl choline inhibited C5a-induced eating, a mutual inhibition characteristic of the adrenergic-cholinergic interactions at this site. The increased food intake induced by C5a was also reversed by phentolamine, an alpha-adrenergic antagonist. Granulocytes infiltrating as a result of C5a-mediated leukotaxis did not arrive at the site in time to influence C5a activity. We propose that C5a in some way activates an alpha-adrenergic receptor system in the hypothalamus, and that anaphylatoxins could mediate neuropsychiatric symptoms sometimes associated with immune complex diseases affecting the central nervous system.

Effect of immune complex-forming reactants on catecholamine-modulated behaviors in the rat hypothalamus

Injection of immune complex-forming reactants via implanted cannulae to the perifornical hypothalamus stimulated eating in sated rats and increased the eating response to exogenous norepinephrine (NE). Immune complex-induced eating was not seen after carbamyl choline injection, and immune complex treatment had no effect on water intake under any of the test conditions. The effects of immune complex activity occurred only 6 hours after administration, a time associated with heavy polymorphonuclear leukocyte infiltration of the cannula site. Immune complex activity mimics that following NE injection of this site. Because the immune complex-forming reactants are not specific to any neural antigen, we propose that their effects are indirectly mediated by anaphylatoxins produced by activation of the complement cascade.

Autonomic and endocrine factors in the regulation of food intake

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

Dopamine-beta-hydroxylase inhibitors, feeding and locomotor activity: reinstatement of feeding following central norepinephrine

The effects of two dopamine-beta-hydroxylase (DBH) inhibitors, FLA-63 and fusaric acid (FA) on feeding behaviour and locomotor activity were examined. In Experiment 1 activity was measured over 7 hr in 48 rats treated with FLA-63 (0, 1.25, 2.50, 5.00 mg/kg) or FA (0, 20.0, 40.0, 80.0 mg/kg). While FA produced no significant effect on activity, FLA-63 produced an increase at the highest doses. In Experiment 2 the same doses of the two DBH inhibitors were administered to 48 rats and food intake over 7 hr was measured; both FA and FLA-63 produced decreases in food intake. In a third experiment, rats were stereotaxically implanted with microinjection guide cannulae extending to the ventromedial hypothalamus and, following peripheral treatment with either 5.0 mg/kg FLA-63, 40 mg/kg FA, or their respective vehicles were injected centrally with morphine (5.3 nmoles in 0.5 microliter), norepinephrine (NE; 60 nmoles in 0.5 microliter for the FLA-63 pre-treated group and 30 nmoles in 0.5 microliter for the FA pre-treated group) or saline. Central NE was found to reinstate feeding only in the hr following injection in both groups, while morphine reinstated feeding only in the FA group and only in the third hr following injection. Results support the involvement of hypothalamic NE in feeding.

Tolerance to or facilitation of pharmacological effects induced by chronic treatment with the beta-adrenergic stimulant clenbuterol

The effect in mice of chronic administration of the beta-adrenergic agonist clenbuterol was studied using four pharmacological tests, two of which are predictive of antidepressant activity in man. The suppressive effect of acute administration of the beta-adrenergic agonist in two tests unrelated to antidepressant activity, locomotor activity and investigation of food, was attenuated after chronic treatment. However, in the two tests which are predictive of antidepressant activity, antagonism of reserpine induced hypothermia and potentiation of yohimbine toxicity, the effect of clenbuterol was greater following chronic treatment.

Dietary obesity: effects of drugs on food intake in S 5B/P1 and Osborne-Mendel rats

The effect of several drugs on food intake has been examined in two strains of rats, one (S 5B/P1) which is resistant to developing obesity when eating a high fat diet, and one (Osborne-Mendel) which readily develops obesity when eating the same diet. Insulin and 2-deoxy-D-glucose increased food intake in a dose dependent manner in both S 5B/P1 and Osborne-Mendel rats. However, the S 5B/P1 rats showed a greater response, with a shorter latency period, to both agents than did the Osborne-Mendel rats. Conversely, d-amphetamine at the higher doses produced a dose dependent suppression of food intake with maximal suppression being similar for both strains. At a lower dose, however, d-amphetamine significantly increased food intake in the Osborne-Mendel rats, but not in the S 5B/P1 rats. The S 5B/P1 rats were also slightly more sensitive to the anorexic effects of lower dose adenosine than were the Osborne-Mendel rats whereas the reverse was true following higher dose adenosine. Naloxone suppressed food intake equally in both strains and D-glucose did not alter food intake in either strain. These studies identify three drugs, all stimulatory, to which the two strains of rat respond differently.

Food intake control in birds

The regulation of food intake has been a topic of intense investigation for several decades. Most investigators have used the rat in such studies while considerably fewer studies have been conducted using birds. Research concerned with the control of food intake in birds is discussed herein. In most instances, birds and mammals have similar control mechanisms. The alimentary tract and the liver are peripheral structures which function in the control of feeding in birds but much remains to be studied as to their role. Many brain loci, including the lateral hypothalamus, ventromedial hypothalamus, striatum and olfactory bulbs are also involved in controlling food intake. Studies with birds have revealed marked breed and line differences in the response to factors modulating food intake. The bird appears to provide an excellent model for studies designed to investigate how selection for growth can alter the mechanisms involved in food intake control.

Hypophysectomy disturbs the noradrenergic feeding system of the paraventricular nucleus

Injection of norepinephrine (NE) into the hypothalamic paraventricular nucleus (PVN) of satiated rats is known to stimulate eating behavior. In addition, drinking behavior is potentiated just prior to the onset of eating, followed by a strong inhibition of water intake. To understand the relationship between these PVN noradrenergic phenomena and endocrine processes associated with the PVN, chronically hypophysectomized animals were tested for their behavioral responsiveness to PVN NE injection. Pituitary ablation was found to abolish the NE-elicited eating response and the NE drinking suppressive effect. However, hypophysectomy had no impact on the NE-elicited preprandial drinking response, nor did it affect drinking produced by carbachol, angiotensin, and histamine, or the feeding and drinking responses induced by insulin. These results demonstrate that hypophysectomy disturbs PVN noradrenergic mechanisms in a behaviorally and pharmacologically specific specific manner.

Chronic norepinephrine injection into the hypothalamic paraventricular nucleus produces hyperphagia and increased body weight in the rat

A single injection of norepinephrine (NE) into the paraventricular nucleus (PVN) is known to elicit a feeding response in the satiated rat. Through repeated NE injections, the present study set out to determine whether chronic noradrenergic stimulation of the PVN is effective in producing changes in total daily food intake, as well as in body weight gain. The results indicate that repeated injections of NE (20 nmoles/injection given 4 times/day) cause a stimulation of eating with each injection and consequently produce a significant increase in total daily food intake. This stimulatory effect on feeding behavior occurs under food-restricted conditions, where food is available only at times (in the daytime) when NE is injected, and also under food-satiated conditions were food is available essentially ad lib. This hyperphagia results in a gradual increase in body weight which develops over the course of a 5-day sequence of repeated NE injections. There is some evidence to suggest that the overeating produced by NE throughout the day may be attributed specifically to an increase in meal size rather than to a change in meal frequency. This evidence suggests that medial hypothalamic NE, particularly within the PVN, may play a role in long-term feeding behavior and body weight regulation.

Chronic infusion of norepinephrine and clonidine into the hypothalamic paraventricular nucleus

Previous experiments have shown that acute injection of NE and CLON into the PVN initiates a short-term feeding response in satiated rats. This study examined, in brain-cannulated rats, the impact of remote, chronic injections of NE, CLON, or saline on daily food intake and body weight gain. Over a period of 14 days, NE was infused into the PVN, either continuously at a rate of 12 nm/microliter/hr, or discretely at a rate of 6 nm/microliter/sec. In addition, the alpha 2-adrenergic agonist CLON was infused into the PVN discretely at a rate of 3 nm/0.5 microliter/30 sec. Relative to saline infusion, chronic (continuous or discrete) stimulation of the PVN with either of these drugs was effective in potentiating daily food intake by 12-19% and in increasing body weight gain, from approximately 1.5 g/day to 3.3 g/day. This evidence indicates that medial hypothalamic NE, especially within the PVN, is sufficiently robust to alter long-term feeding patterns and body weight regulation.

Clonidine-induced feeding: analysis of central sites of action and fiber projections mediating this response

Clonidine (CLON), an alpha-adrenergic agonist, was used in conjunction with norepinephrine (NE) to elicit feeding in satiated rats that had sustained hypothalamic electrolytic lesions, or coronal knife cuts at the hypothalamic, midbrain or pontine level of the brainstem. Electrolytic lesions of the paraventricular nucleus (PVN) of the hypothalamus significantly attenuated feeding normally stimulated by intraperitoneal injection of CLON. This contrasts with lesions in the dorsomedial or perifornical hypothalamic regions which had no effect on CLON-elicited eating. Knife cuts placed in the posterior hypothalamus and throughout the midbrain tegmentum also left intact the CLON eating response, in contrast to specific cuts in the dorsal pontine tegmentum which disrupted feeding elicited by PVN injections of NE and CLON, as well as by peripheral administration of CLON. Analyzed together, these results with effective and ineffective cuts relative to CLON and NE feeding provide evidence for an alpha-adrenergic feeding circuit which originates in the PVN and descends from this nucleus, via a dorsal periventricular course, through the diencephalon and midbrain. Further caudally, these fibers mediating NE and CLON feeding then appear to traverse ventrolaterally into the dorsolateral pontine tegmentum on their way to the dorsal medulla.

Feeding behavior induced by central norepinephrine injection is attenuated by discrete lesions in the hypothalamic paraventricular nucleus

Extensive brain-cannula mapping studies in the rat have demonstrated that the hypothalamic paraventricular nucleus (PVN) is the most sensitive brain site for eliciting eating behavior with central norepinephrine (NE) injection. The present experiments examined the impact of lesions aimed at the PVN on this NE-elicited eating response. In rats with NE injection cannulas aimed at the lateral ventricle, bilateral lesions of the PVN significantly attenuated, by 60 to 70%, the eating effect induced by NE, at doses ranging from 20 to 160 nmoles. PVN lesions which extended ventrally to damage tissue lying within the periventricular region were more effective in abolishing the NE response than were lesions that remained confined to the dorsal aspects of the PVN. Large lesions located just dorsal to the PVN had no impact on the NE response. This evidence supports the primary role of the PVN in mediating the eating behavior elicited by central noradrenergic activation.

Changes in brain amines associated with cancer anorexia

Analysis of indole amine metabolism within acute (Walker 256 carcinosarcoma) and chronic (methycholanthrene-induced sarcoma) animal models of cancer anorexia demonstrated elevated levels of plasma free tryptophan, whole brain tryptophan, serotonin and 5-hydroxyindoleacetic acid in anorectic tumor-bearing rats. Whole brain levels of catecholamines were not changed within either tumor line. Regional central nervous system determination of tryptophan metabolism in rats bearing Walker 256 tumors revealed elevated tryptophan in the hypothalamus, corpus striatum, mesencephalon, diencephalon, cerebellum and cortex, increased serotonin in the diencephalon and cerebellum and elevated 5-hydroxyindoleacetic acid in the diencephalon, hippocampus, pons-medulla, cerebellum and cortex. Although tryptophan was significantly increased only in the corpus striatum and diencephalon of the more chronic methycholanthrene tumor model, serotonin concentration was elevated in the corpus striatum, diencephalon, hippocampus, pons-medulla, cerebellum and cortex, while levels of 5-hydroxyindoleacetic acid were significantly increased in all these areas as well as in the mesencephalon. Since similar changes in indole activity were not observed in pair-fed control rats, it is concluded that the elevated serotonin and 5-hydroxyindoleacetic acid levels in tumor-bearing rats did not result from undernutrition alone. Assay of regional catecholamines revealed few food-relevant changes, with norepinephrine being elevated in the corpus striatum and decreased in the pons-medulla of tumor-bearing rats. Therefore, these experiments suggest that the increased serotonin metabolism observed in tumor-bearing rats may be involved in the etiology of the anorexia of cancer.

Psychopharmacological activity of anaphylatoxin C3a in rat hypothalamus

C3a anaphylatoxin injected into the perifornical hypothalamic region of sated rats increased the eating response to norepinephrine and the drinking response to carbamyl choline but had no effect on food or water intake in sated, saline control animals. This potentiation of drug-stimulated intakes was reversible by intrahypothalamic injection of catecholamine receptor antagonists haloperidol and phentolamine. We propose that C3a acts as a catecholamine agonist in the central nervous system. The results suggest that C3a may play a role in mediating the neuropsychiatric manifestations associated with immune complex formation or deposition in the central nervous system.

Monoamine involvement in the overeating caused by muscimol injection in the rat nucleus raphe dorsalis and the effects of d-fenfluramine and d-amphetamine

Injections of 5,7-dihydroxytryptamine in the nucleus raphe dorsalis did not significantly modify the eating caused by muscimol (100 ng) injected in the same area of freely fed rats 11 days later. Eating caused by muscimol, like food intake in starved rats, was significantly reduced by phenoxybenzamine (5, 10 and 20 mg/kg i.p.). Penfluridol (2.5 and 5 mg/kg p.o.), a dopamine receptor blocker, markedly reduced muscimol-induced eating, but had no effect on the food intake of starved rats. d-Fenfluramine (2.5 mg/kg i.p.), a releaser of serotonin from nerve terminals, significantly reduced eating in muscimol-injected and starved animals whereas d-amphetamine 1.25 and 2.5 mg/kg i.p. only inhibited the food intake of starved rats. Eating elicited by muscimol injected in the nucleus raphe dorsalis appears to constitute a catecholamine-mediated model of hyperphagia selectively inhibited by agents which increase serotonin transmission.

Food intake and temperature response to injections of catecholamines into the lateral ventricle of the turkey brain

The effects of dopamine, norepinephrine, and epinephrine on food intake, water intake, and colonic body temperature (Tc) were investigated in adult Medium White turkey hens. Solutions containing dopamine, L-norepinephrine, or L-epinephrine were prepared in concentrations of 0, 33, and 67 micrograms/10 microliters in artificial cerebrospinal fluid and injected into the lateral cerebral ventricles. Dopamine, norepinephrine, and epinephrine significantly decreased Tc. Food intake was significantly decreased by norepinephrine and epinephrine whereas dopamine had no effect. These results suggest that brain catecholamines are involved in the neural control of food intake and body temperature of turkeys.

Serotonin depletion by 5,7-dihydroxytryptamine or para-chloroamphetamine does not affect cancer anorexia

Anorectic tumor-bearing rats exhibited increased brain levels of the 5-HT precursor, tryptophan, and metabolite, 5-hydroxyindoleacetic acid (5-HIAA). In an effort to determine whether indoleamine systems had any role in the etiology of cancer anorexia the anorectic effects of cancer (Walker 256 carcinosarcoma) were investigated in immature female rats that had been depleted of brain serotonin (5-HT) by the intracisternal injection of 5,7-dihydroxytryptamine (5,7-DHT) or the systemic injection of para-chloramphetamine (PCA). Although both 5,7-DHT and PCA significantly reduced brain concentrations of 5-HT and 5-HIAA by approximately 50%, no effects on the onset or severity of the anorectic response to cancer were observed. Similarly, neither drug affected eating in non-tumor-bearing control animals. Therefore, these data do not support increased brain 5-HT activity as a primary mediator of cancer anorexia.

The role of norepinephrine in feeding behavior

When dopamine-beta-hydroxylase is inhibited with FLA-63 (10 mg/kg) free feeding behavior is disrupted in satiated rats. While the average number of meals taken was not different from vehicle injected controls, meal size was decreased 58% in the first 9 hr after treatment with FLA-63. In starved animals, FLA-63, when given alone, produced little effect on feeding behavior, even though norepinephrine depletion was in excess of 40%. When given in combination with RO4-1284 (5 mg/kg), a vesicular reuptake inhibitor, feeding was reduced to 16% of control intake and norepinephrine was specifically depleted 99%. Feeding was reliably reinstated in animals which received FLA-63 plus RO4-1284 with either dl-threo-DOPs, a metabolic precursor to NE, or direct intrahypothalamic injections of NE. These findings suggest that the feeding inhibition observed after treatment with FLA-63 plus RO4-1284 is due to disruption of transmission in brain NE systems. A non-anorectic dosage of L110-140 (3.73 mg/kg), a specific FLA-63. Taken collectively, these findings suggest that the primary role of NE in feeding is maintenance of the consummatory response and that these effects are expressed in relation to activity in other neurochemical systems.

Endorphinergic and alpha-noradrenergic systems in the paraventricular nucleus: effects on eating behavior

Brain cannulated rats were injected with the opioid peptide beta-endorphin (beta-EP) directly into the hypothalamic paraventricular nucleus (PVN) where norepinephrine (NE) is most effective in stimulating eating behavior. Beta-Endorphin (1.0 nmole) reliably increased food intake in satiated animals, and this response was blocked by local administration of the selective opiate antagonist naloxone. The eating induced by beta-EP was positively correlated in magnitude with the NE response and, like NE, was antagonized by PVN injection of the alpha-noradrenergic blocker phentolamine. Naloxone had no effect on NE-induced eating, and the dopaminergic blocker fluphenazine failed to alter either beta-EP or NE eating. When injected simultaneously, at maximally effective doses, beta-EP and NE produced an eating response which was significantly larger than either of the responses elicited separately by beta-EP or NE and was essentially equal to the sum of these two responses. The evidence obtained in this study suggests that beta-EP and NE stimulate food ingestion through their action on PVN opiate and alpha-noradrenergic receptors, respectively, and that beta-EP's action is closely related to, and in part may be dependent upon, the PVN alpha-noradrenergic system for feeding control.

Effects of hypothalamic knife cuts on feeding induced by paraventricular norepinephrine injections

The relationship between the fiber systems involved in the hypothalamic noradrenergic feeding response and the medial hypothalamic (MH) hyperphagia syndrome was appraised in male rats using knife cuts. Parasagittal knife cuts in the perifornical hypothalamus produced hyperphagia and excessive weight gain but failed to disrupt feeding in response to paraventricular hypothalamic injections of norepinephrine (NE). Coronal knife cuts in the posterior hypothalamus which extended from the midline to the lateral perifornical region also failed to disrupt NE feeding. These findings indicate that the output of the noradrenergic feeding system does not follow the feeding pathway implicated in the MH hyperphagia syndrome. They also suggest that the output of the noradrenergic feeding system is not directed laterally beyond the level of the fornix nor caudally into the lower brainstem over the medial forebrain bundle.

Evidence for vagal involvement in the eating elicited by adrenergic stimulation of the paraventricular nucleus

We examined the role of the vagus nerves in mediating the eating and preprandial drinking seen after injection of norepinephrine (NE) into the region of the paraventricular hypothalamic nucleus of satiated rats. Complete subdiaphragmatic vagotomy (confirmed by gastric secretion tests) abolished the NE-elicited eating response, whether the diet used was lab chow, milk, or a milk-chow misture, and attenuated, by 38%, the NE-elicited drinking response. These effects occurred independently of changes in body weight or daily food intake imposed by vagal surgery. The vagotomized rats retained the capacity to rapidly increase eating in response to food deprivation or insulin injection challenges, indicating that the effect of vagotomy on NE-induced eating was not due to some non-specific impairment. Efferent vagal blockade of intact rats with systemic injections of atropine methyl nitrate (0.4 mg/kg) prior to central NE infusions yielded similar results. Finally-selective section of the coeliac branch of the vagus produced a 49% reduction of NE, elicited eating, as compared with a 29% reduction in water intake, while selective section of the gastric plus hepatic vagal branches, leaving only the coeliac branch intact, did not significantly affect either ingestive response. Both of these selectively vagotomized groups displayed an unimpaired capacity to increase food intake in response to systemic insulin injections. These results suggest participation of efferent vagal mechanisms in the adrenergic feeding, and, to a lesser extent, drinking phenomena and are consistent with a particular role for some function under coeliac vagal control (perhaps insulin secretion) in modulating the effects of NE on feeding behavior.

Cholinergic and catecholaminergic interaction and fluid intake in the rat

The effect of simultaneous topical application of adrenergic agonists was investigated on the polydipsia caused by direct carbachol (CCh) stimulation of the rat brain. In addition, fluid selection (4-choice arrangement) was studied. Noradrenaline and isoprenaline fully antagonized the CCh effect after either intracerebroventricular, intraseptal or intrapreoptic application. Phenylephrine inhibited CCh polydipsia after intracerebroventricular or intrahypothalamic but not after intraseptal injection. Previous experiments had shown that adrenergic agonists also exerted a marked modulatory influence on an affective behavioural reaction pattern (rage reaction) of the cat. The results of the present experiments corroborate the assumption that, also in non-striatal brain structures, adrenergic modulation of cholinergic behavioural patterns is perhaps a more general and important phenomenon than had been assumed so far.