Peptide YY (PYY), a potent orexigenic agent

Neuropeptides, food intake and body weight regulation: a hypothalamic focus

Energy homeostasis is controlled by a complex neuroendocrine system consisting of peripheral signals like leptin and central signals, in particular, neuropeptides. Several neuropeptides with anorexigenic (POMC, CART, and CRH) as well as orexigenic (NPY, AgRP, and MCH) actions are involved in this complex (partly redundant) controlling system. Starvation as well as overfeeding lead to changes in expression levels of these neuropeptides, which act downstream of leptin, resulting in a physiological response. In this review the role of several anorexigenic and orexigenic (hypothalamic) neuropeptides on food intake and body weight regulation is summarized.

Peptide YY: a key mediator of orexigenic behavior

Peptide YY (PYY) is the most potent orexigenic peptide or substance known. However, neither the underlying physiology of this hyperphagia nor PYY's natural role in brain are well understood. Thus, this review details the neuroanatomical sites, the neurochemical and systemic interactions, the food-related properties and the motivational factors that characterize hyperphagia elicited by central PYY. Emphasis also is given to evidence that central PYY has properties functionally distinct from neuropeptide Y. Finally, future research directions are outlined that aim at accelerating our understanding of the roles that brain PYY and PYY-preferring receptors occupy in normal and abnormal feeding behavior.

Peptide YY and cancer: current findings and potential clinical applications

Peptide YY (PYY) is a naturally occurring gut hormone with mostly inhibitory actions on multiple tissue targets. PYY has been identified in several carcinoid tumors and a decreased expression of PYY may be relevant to the development and progression of colon adenocarcinoma. Treatment with PYY decreases growth in pancreatic and breast tumors, most likely through a reduction in intracellular cAMP. In cancer patients, PYY may also improve malnutrition that results from iatrogenic causes or cachexia associated with advanced disease. PYY plays a significant role in multiple aspects of cancer from regulation of cell growth to potential therapeutic applications.

Feeding after fourth ventricular administration of neuropeptide Y receptor agonists in rats

Neuropeptide Y (NPY) and peptide YY (PYY) stimulate food intake after injection into the fourth cerebral ventricle, suggesting that NPY receptors in the hindbrain are targets for the stimulatory effect of these peptides on food intake. However, the NPY/PYY receptor subtype mediating the feeding response in the hindbrain is not known. To approach to this question we compared dose-effect of several NPY receptor agonists to stimulate food intake in freely-feeding rats 60- and 120-min after injection into the fourth cerebral ventricle. At the 120-min time point, PYY was 2- to 10-times as potent as NPY over the dose-response range and stimulated twice the total intake at the maximally effective dose (2-fold greater efficacy). NPY was 2-times as potent as the Y1, Y5 receptor agonist, [Leu(31)Pro(34)]NPY but acted with comparable efficacy. The Y5-, Y2-differentiating receptor agonist, NPY 2-36, was comparable in potency to PYY at low doses but equal in efficacy NPY and [Leu(31)Pro(34)]NPY. The Y2 receptor agonist, NPY 13-36, produced only a marginal effect on total food intake. The profile of agonist potency after fourth cerebral ventricle administration is similar to the profile obtained when these or related agonists are injected in the region of the hypothalamus. Agonists at both Y1 and Y5 receptors stimulated food intake with a rank order of potency that does not conclusively favor the exclusive involvement of a single known NPY receptor subtype. Thus it is possible that the ingestive effects of NPY and PYY are mediated by multiple or novel receptor subtypes in the hindbrain. And the relatively greater potency and efficacy of PYY raises the possibility that a novel PYY-preferring receptor in the hindbrain is involved in the stimulation of food intake.

Long-term orexigenic effects of AgRP-(83---132) involve mechanisms other than melanocortin receptor blockade

Overexpression of agouti-related peptide (AgRP), an endogenous melanocortin (MC) 3 and 4 receptor antagonist (MC3/4-R), causes obesity. Exogenous AgRP-(83---132) increases food intake, but its duration and mode of action are unknown. We report herein that doses as low as 10 pmol can have a potent effect on food intake of rats over a 24-h period after intracerebroventricular injection. Additionally, a single third ventricular dose as low as 100 pmol in rats produces a robust increase in food intake that persists for an entire week. AgRP-(83---132) completely blocks the anorectic effect of MTII (MC3/4-R agonist), given simultaneously, consistent with a competitive antagonist action. However, when given 24 h prior to MTII, AgRP-(83---132) is ineffective at reversing the anorectic effects of the agonist. These results support a critical role of MC tone in limiting food intake and indicate that the orexigenic effects of AgRP-(83---132) are initially mediated by competitive antagonism at MC receptors but are sustained by alternate mechanisms.

Geriatric cachexia: the role of cytokines

Weight loss in elderly patients is a common clinical problem. Wasting and cachexia are associated with severe physiologic, psychologic, and immunologic consequences, regardless of the underlying causes. Cachexia has been associated with infections, decubitus ulcers, and even death. Multivariate analyses of risk and prognostic factors in community-acquired pneumonia in the elderly have found that age by itself is not a significant factor related to prognosis. Among the significant risk factors, only nutritional status is amenable to medical intervention. Cachexia in the elderly may have profound consequences: medical, cognitive, and psychiatric disorders may diminish self-reliance in activities of daily living, thus reducing quality of life and increasing the frequency of secondary procedures, hospitalizations, and the need for skilled care. Cachexia is associated with higher-than-normal concentrations of tumor necrosis factor alpha (TNF-alpha), interleukin (IL) 1, IL-6, serotonin, and interferon gamma. The role of these proinflammatory cytokines has been established in the cachexia seen in cancer and AIDS patients. Reduction in the concentrations of these cytokines is associated with weight gain. Drugs that promote appetite stimulation and weight gain, such as progestational agents, cyproheptadines, pentoxifylline, and thalidomide may work by down-regulating these proinflammatory cytokines. An understanding of the relation between cachexia and negative regulatory cytokines may point to effective treatment of geriatric cachexia as well.

Leptin, neuropeptide Y, and peptide YY in long-term recovered eating disorder patients

BACKGROUND

Disturbances of leptin, neuropeptide Y (NPY), and peptide YY (PYY) have been found in women who are ill with anorexia or bulimia nervosa. It is not certain whether peptide disturbances are cause or consequence of eating disorders.

METHODS

Plasma leptin and cerebrospinal fluid leptin, NPY, and PYY concentrations were measured in women who were recovered from anorexia or bulimia nervosa to determine whether alterations persisted after recovery.

RESULTS

NPY, PYY, and leptin concentrations were similar across all diagnostic groups.

CONCLUSIONS

Alterations in NPY, PYY, and serum leptin concentrations are probably secondary to pathological eating behaviors. Alterations of these peptides are unlikely to be trait-related disturbances that contribute to the etiology of eating disorders.

Thioperamide, a histamine H3 receptor antagonist, powerfully suppresses peptide YY-induced food intake in rats

BACKGROUND

Whether or not peptide YY (PYY)-induced hyperphagia is modified by the histaminergic system in the brain is not yet known.

METHODS

We investigated the effect on feeding of intracerebroventricular (ICV) administration of a specific histamine H3 receptor antagonist prior to ICV administration of PYY in rats.

RESULTS

PYY (1, 3, and 10 micrograms/10 microL) strongly induced feeding behavior in a dose-dependent manner in sated rats. The 4-hour food intake induced by 3 micrograms/10 microL of PYY was equal to that induced by a 16-hour fast. The ICV administration of thioperamide (40.8, 122.4, and 408.5 micrograms/10 microL) did not suppress the 4-hour food intake induced by 16-hour fasting; however, thioperamide produced dose-dependent and strong inhibition of hyperphagia induced by a 3-microgram dose of PYY.

CONCLUSIONS

These results suggest that the effect of PYY on appetite is different than that induced by fasting and may involve a histaminergic mechanism.

Effects of single and chronic intracerebroventricular administration of the orexins on feeding in the rat

Two novel hypothalamic neuropeptides, orexin-A and -B, are suggested to regulate feeding. A single intracerebroventricular injection of orexin-A (23.4 nmol), administered 3 h into the light phase, increased feeding in satiated rats and prolonged feeding in fasted rats; it also increased feeding when given 6 h into, but not at the start of, the dark phase. An 8-day intracerebroventricular infusion with orexin-A (18 nmol/day) increased daytime feeding on days 2 and 8, but nocturnal feeding was reduced and there was no change in 24 h intake. Orexin-B had no effects. These results demonstrate a circadian variation in feeding responses to orexin-A.

Thioperamide, a histamine H3 receptor antagonist, suppresses NPY-but not dynorphin A-induced feeding in rats

Whether or not neuropeptide Y (NPY)-induced feeding in rats is influenced by the histaminergic system in the brain was investigated by intracerebroventricular (i.c.v.) administration of a selective histamine H3 receptor antagonist prior to i.c.v. administration of NPY. NPY (10 microg/10 microl) strongly induced feeding in sated rats during the light phase of the day. Dynorphin A1-17 (10 microg/10 microl), a kappa-opioid agonist, and rat pancreatic polypeptide (rPP, 30 microg/10 microl) also stimulated ingestive behavior in sated rats, but food intake in both cases was less than that induced by NPY. Thioperamide maleate, a specific histamine H3 receptor antagonist (408.5 microg/10 microl) reduced the feeding response to NPY by 52% (P < 0.0001), but not to dynorphin A1-17 and rPP. Thioperamide at i.c.v. doses of 40.8-408.5 microg/10 microl had no effect on food intake in sated rats. These results suggest that the thioperamide may have a specific effect on NPY receptor-mediated neuronal systems related to feeding.

The pharmacology of neuropeptide Y (NPY) receptor-mediated feeding in rats characterizes better Y5 than Y1, but not Y2 or Y4 subtypes

Thirteen neuropeptide Y (NPY) agonists were administered intracerebroventricularly (i.c.v.) in rats (full dose-response curves) to estimate their half-effective dose (ED50) on feeding. These values were compared to their binding affinities (IC50) for rat NPY receptor subtypes Y1, Y2, Y4 and Y5 in vitro. Correlations between in vivo ED50 and in vitro IC50 were strong for the Y5 (r = 0.87; P < 0.01), weak for the Y1 (r = 0.48; P < 0.04) and non-significant for the Y2 and Y4 receptor subtypes. In vitro, h[D-Trp32]NPY was found to be a Y5-selective ligand and a full agonist in Y5-expressing cells. In vivo, it dose-dependently stimulated feeding, but failed to induce the full maximal response observed with pNPY. It did not antagonize pNPY-induced feeding and overfeeding in 24 h fasted rats. These findings demonstrate a role for the Y5, or possibly Y5 in combination with Y1, but not Y2 or Y4 receptor subtypes in feeding. No evidence was found for the existence of an additional, as yet undescribed, NPY feeding receptor.

Characterisation of the neuropeptide Y receptor that mediates feeding in the rat: a role for the Y5 receptor?

Food intake was measured in freely fed rats following intracerebroventricular administration of neuropeptide Y (NPY) and several of its analogues and antagonists to investigate the hypothesis that the NPY Y5 receptor mediates feeding. Rat NPY (rNPY), rNPY(2-36) and rNPY(3-36) produced similar feeding responses over the dose range 0.7-7.0 nmol. Rat peptide YY (rPYY) was more potent and at least as efficacious as rNPY. [Leu31 Pro34]-rNPY (agonist potency: Y1 > Y5 > Y4 = y6) and human pancreatic polypeptide (hPP) produced flatter dose-response curves, suggesting partial agonism at the receptor(s). rNPY(13-36) (agonist potency: Y2 > Y5) had little activity and rPP was inactive. [D-Trp32]-NPY was a weak orexigenic agent given alone and, consistent with partial agonism, it markedly antagonised the response to porcine NPY (pNPY). Similarly, the receptor antagonist (Y1 > Y4) 1229U91 stimulated feeding slightly, and markedly inhibited rNPY-induced feeding. In contrast to a previous report, BIBP 3226 (70 nmol), another Y1 receptor antagonist, failed to inhibit the response to rNPY. Our data in vivo are inconsistent with findings that hPP, [Leu31 Pro34]-rNPY and [D-Trp32]-rNPY are full agonists at the rat cloned Y5 receptor. Thus, whilst the Y5 receptor may be involved, its participation as the sole receptor mediating the orexigenic action of NPY in the rat remains unproven.

The effect of hypothalamic peptide YY on hippocampal acetylcholine release in vivo: implications for limbic function in binge-eating behavior

Central injection of peptide YY (PYY) in sated rats produces the most powerful stimulating effect of food intake known to date. The neural mechanisms by which PYY regulates appetite are not clear but may be important because abnormal levels of PYY have been implicated in the neurobiology of bulimia nervosa. Interactions between brain acetylcholine (ACh) and PYY had not been studied. Therefore, the present experiments were designed to explore the in vivo release of ACh from the hippocampus (HPC) of rats in response to hypothalamic infusion of PYY. Hippocampal ACh release was found to increase 400% in response to 10 microg PYY. In a separate experiment, blockade of the same area of the HPC with bilateral intracerebral injections of 3.5 microg scopolamine did not affect intake stimulated by intrahypothalamic injection of 4 microg PYY. Furthermore, a third experiment showed, for the first time, that PYY (2.5-10.0 microg) can elicit robust feeding when infused directly into the HPC. The significance of these findings to the activation of limbic functions such as memory, reinforcement, and obsessional processes that accompany human binge-eating syndromes is discussed.

The role of the central nervous system in the psychoneuroendocrine disturbances of anorexia and bulimia nervosa

It has been well-recognized that starvation in anorexia and bulimia nervosa causes endocrine disturbances. Such disturbances may help understand why many people with eating disorders cannot easily reverse their illness since people with eating disorders often enter a downward spiraling circle with malnutrition sustaining and perpetuating the desire for more weight loss and dieting. Symptoms, such as obsessions and dysphoric mood, and altered appetitive behavior, may be exaggerated by neuropeptide alterations and thus contribute to this downward spiral. While neuropeptide disturbances do not appear to be a permanent feature or cause or anorexia nervosa, these disturbances are strongly entrenched, and are not easily corrected by improved nutrition or short-term weight normalization. This suggests that therapy should be sustained for months after nutritional normalization.

Neurobiological and psychopharmacological basis in the therapy of bulimia and anorexia

1. Eating disorders can be found in several psychiatric pathologies: schizophrenia, delusional disorder (somatic type), bipolar disorders, major depressive disorder, borderline personality disorder, generalized anxiety disorder, body dysmorphic disorder, somatization disorder and conversion disorder. 2. Although their clinical features have been defined, relatively little is known about the role of neurobiological patterns in the pathogenesis of these disorders. Several CNS neurotransmitters and neuromodulators are involved in the regulation of eating behavior in animals and have been implicated in symptoms such as depression and anxiety often observed in patients with eating disorders. The authors will review some studies on NA, DA, 5-HT, beta-endorphins, CRH, VP, OT, CCK, NPY and PYY involved in eating disorders. Furthermore, we will highlight some of the studies on drug therapy of eating disorders taking into account the effects of these agents on neurotransmitters and neuromodulators. 3. Antidepressant drugs have long been used for anorexia nervosa and bulimia, these disorders been claimed to be affective equivalent. Antidepressant agents seem to be effective in reducing the frequency of binge-eating episodes, purging behavior and depressive symptomatology. It is notable that antidepressant agents have been proved to be effective in patients with chronic bulimic symptoms, even in cases persisting for many years and in patients who had repeatedly failed courses of alternative therapeutic approaches. In all of the positive studies, antidepressant agents appeared effective even in bulimic subjects who did not display concomitant depression. 4. Few controlled studies on use of medications for anorexia nervosa have been published. Central serotonergic receptor-blocking compounds such as cyproheptadine cause marked increase in appetite and body weight. Zinc supplementation or cisapride could be a therapeutic option in addition to psychological and other approaches in anorexia nervosa. 5. There is no therapy as yet which is fully effective in alimentary disorders. Psychotropic drugs give some relief from symptoms, but they cannot cure the disorders. An integrated approach, either pharmacological or psychological, is still recommendable.

Melatonin disturbances in anorexia nervosa and bulimia nervosa

The pineal gland releases melatonin into the blood stream in response to sympathetic noradrenergic stimulation of pinealocytes. This process is inhibited by light via the retino-hypothalamic-pineal pathway. Hence melatonin is predominantly released in darkness. Because serotonin is a precursor of melatonin, the intake of dietary tryptophan may also influence melatonin levels. Although the exact physiological role of melatonin in humans is unclear, it appears to be implicated in reproductive physiology, especially in terms of the onset of menarche. Low levels of melatonin also occur in depression. In this review, studies of melatonin in patients with anorexia nervosa and bulimia nervosa are considered in relation to potential abnormalities of noradrenergic function and circadian rhythm. The influence of weight loss, binging and purging, and depression on melatonin is discussed. Other studies involving the assessment of melatonin in relation to menstrual function are required.

Forebrain and hindbrain involvement of neuropeptide Y in ingestive behaviors of rats

Neuropeptide Y (NPY) is an extremely potent orexigenic agent. These studies demonstrate that the effect of NPY on food and water intake are seen after infusion into either the third (3V) or fourth (4V) ventricle and that this is a specific effect, as it was not seen with the deaminated form. There was a nonsignificant tendency for lateral midbrain knife cuts to food intake. Both 3V and 4V NPY infusions showed an attenuated increases in food intake at 1 but not 2 h following NPY infusion in the lateral knife cut rats compared to the sham controls. Medical knife cuts resulted in significantly greater food intake in the basal state and a lesser increase in food intake in response to NPY infused into the 3V. These midbrain data suggest a role for both medical and lateral fibers in mediating the effects of NPY on food intake. Lateral fibers appear to be more important, but their transection only delays the time of onset of the stimulating effect of NPY to the second hour. Lateral knife cuts virtually abolish the effect of 4V NPY on stimulating water intake. 3V NPY in the presence of NPY has a less clear effect at 1 h, but mildly attenuated the NPY effect on water intake at 2 h in lateral knife cut rats. Medial knife cuts slightly attenuate the effect of 3V NPY on water intake. However, medial knife cuts markedly increased basal water ingestion. These studies demonstrate the importance of neuronal communications between third and fourth ventricle associated structures in the modulation of ingestive behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of Tyr-MIF-1, MIF-1, and naloxone on peptide YY-induced hyperphagia

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and MIF-1 (Pro-Leu-Gly-NH2) act as opiate antagonists in various behavioral systems including ingestion. Central injection of peptide YY (PYY) elicits a powerful feeding response in satiated rats, and the opioid antagonist naloxone decreases eating in a variety of conditions including PYY-stimulated eating. Therefore, the aim of this study was to examine the effects of Tyr-MIF-1 and MIF-1 as opiate antagonists on a naloxone-sensitive PYY model of hyperphagia. Naloxone at doses of 1.0 and 10.0 mg/kg, SC, decreased hyperphagia induced by 2.4 micrograms PYY injected in the PVN. MIF-1 and Tyr-MIF-1 had no effect on PYY-induced eating at doses comparable to naloxone (0.1 to 10.0 mg/kg, IP). These results suggest that in this model of eating behavior, Tyr-MIF-1 and MIF-1 do not act as opiate antagonists.

[Leu31,Pro34]neuropeptide Y (NPY), but not NPY 20-36, produces discriminative stimulus effects similar to NPY and induces food intake

Rats were trained to discriminate between an intracerebroventricular injection of 1.15 nmol of Neuropeptide Y (NPY) and a sham injection. Rats rapidly learned to press the appropriate lever during training. NPY's discriminative stimulus effects were compared to those of saline, and 1.15-3.45 nmol [Leu31,Pro34]NPY, a Y1 receptor agonist and NPY 20-36, Y2 receptor agonist. [Leu31,Pro34]NPY resulted in NPY-appropriate responding, whereas saline and NPY 20-36 did not. [Leu31,Pro34]NPY also increased food intake, but NPY 20-36 did not. This suggests that NPY's discriminative stimulus and orexigenic effects involve the Y1, but not the Y2, receptor.

Suppression of peptide YY-induced hyperphagia by terbutaline

Central administrations of neuropeptide Y and peptide YY (PYY) produce robust increases in food intake, and this response may be contingent upon the availability of insulin. In contrast, beta 2-adrenergic agonists decrease food intake, and this effect also appears to be dependent on circulating insulin. To investigate a possible interaction between PYY and beta 2-adrenergic function, rats were given systemic injections of terbutaline, a beta 2 agonist, at doses of 0, 5, 10, and 50 mg/kg prior to injections of 0.57 nmol PYY in the paraventricular nucleus of the hypothalamus. Terbutaline pretreatment significantly decreased feeding elicited by PYY in a dose-dependent fashion. This suggests that beta 2-adrenoreceptor activity is involved in PYY-induced feeding.

Effect of naloxone and antidepressants on hyperphagia produced by peptide YY

Central injection of peptide YY (PYY) elicits a powerful feeding response with a short latency in satiated rats. Because of this effect, PYY has been implicated as a neurochemical signal in bulimia nervosa. Serotonin agonists and opioid antagonists induce anorectic effects upon feeding behavior in humans and animals. Therefore, to investigate a possible interaction between PYY-induced eating and these anorexigenic agents rats were given injections of either naloxone (100 micrograms/3 microliters, ICV, and 10 mg/kg, SC), fluoxetine (3-30 micrograms/3 microliters and 5-10 mg/kg, IP), or clomipramine (3-30 micrograms/3 microliters and 5-10 mg/kg, IP) prior to fourth ventricular injections of PYY (15 micrograms/18 microliters). Central and peripheral naloxone and IP but not central injections of fluoxetine blocked PYY-induced intake. Clomipramine had no effect. This suggests that PYY-stimulated feeding may require the action of endogenous opioids and may be inhibited by serotonergic function.

Nonamphetamine awakening agent modafinil induces feeding changes in the rat

In rats, modafinil, an alpha1 adrenergic receptor dependent, that has been shown to increase wakefulness without subsequent rebound effect, decreases feeding and reduces body weight. However, modafinil does not show a monotonic dose-related decrease in food intake. The dose-response curve for modafinil is U-shaped; feeding decreases after doses of 20 and 40 mg/kg, but no effects were seen after doses of 10 and 80 mg/kg. When feeding is resumed, no compensatory effect is seen, and body weight remains lower during the 24-h session. The drinking-to-feeding ratio remains unchanged, showing that modafinil has no effect on water intake. These results are discussed with reference to the possible mechanisms underlying the relation between sleep, feeding, and metabolism.

[Leu31-Pro34] neuropeptide Y identifies a subtype of 125I-labeled peptide YY binding sites in the rat brain

Subtypes of the neuropeptide Y (NPY) receptor in the rat brain were identified by the use of the selective Y-1 analog, [Leu34-Pro34] NPY. In rat brain homogenate binding studies, [Leu31-Pro34] NPY was found to produce a partial inhibition of 100 pM 125I-labeled peptide YY (PYY) binding with a plateau at 50-1000 nM [Leu31-Pro34] NPY resulting in a 70% inhibition of binding. The C-terminal fragment NPY 13-36, a putative Y-2 agonist, exhibited very little selectivity in rat brain homogenates. Scatchard analysis of 125I-labeled PYY binding to rat brain homogenate yielded biphasic plots with Kd values of 40 and 610 pM. Inclusion of 100 nM [Leu31-Pro34] NPY was found to eliminate the low affinity component of 125I-labeled PYY binding leaving a single, high affinity binding site with a Kd of 68 pM. In autoradiographic studies, displacement curves indicated that [Leu31-Pro34] NPY completely inhibited binding in the cerebral cortex with little effect on the binding in the hypothalamus. On the other hand NPY 13-36 inhibited binding in the hypothalamus at low concentrations but required higher concentrations to inhibit binding in the cerebral cortex. Other brain regions such as the hippocampus, appeared to contain both subtypes. Subsequent to these studies, a quantitative autoradiographic map was conducted using 50-100 pM 125I-labeled PYY in the presence and absence of [Leu31-Pro34] NPY which produced a selective displacement of binding in certain distinct brain regions. These areas included the cerebral cortex, certain thalamic nuclei and brainstem while ligand binding was retained in other brain regions including the zona lateralis of the substantia nigra, lateral septum, nucleus of the solitary tract and the hippocampus. Numerous brain regions appeared to contain both receptor subtypes. Therefore, the Y-1 and Y-2 receptor subtypes exhibited a somewhat distinct distribution in the brain. In addition, 125I-labeled PYY appears to label the Y-2 receptor with relatively higher affinity when compared to the Y-1 receptor.

Evidence for neuropeptide Y mediation of eating produced by food deprivation and for a variant of the Y1 receptor mediating this peptide's effect

Neuropeptide Y (NPY) elicits eating when injected directly into the paraventricular nucleus (PVN) or perifornical hypothalamus (PFH). To identify the essential regions of the NPY molecule and the relative contributions of Y1 and Y2 receptors, the eating stimulatory potency of NPY was compared to that of its fragments, analogues, and agonists when injected into the PVN or PFH of satiated rats. Additionally, antisera to NPY was injected into the cerebral ventricles (ICV) to determine whether passive immunization suppresses the eating produced by mild food deprivation. Tests with NPY fragments revealed that NPY(2-36) was surprisingly potent, nearly three times more so than intact NPY. In contrast, fragments with further N-terminal deletions were progressively less effective or ineffective, as was the free acid form of NPY. Collectively, this suggests that both N- and C-terminal regions of NPY participate in the stimulation of eating. Tests with agonists revealed that the putative Y1 agonist [Pro34]NPY elicited a strong dose-dependent feeding response, while the putative Y2 agonist, C2-NPY, had only a small effect at the highest doses. Although this suggests mediation by Y1 receptors, the uncharacteristically high potency of NPY(2-36) may additionally suggest that the receptor subtype underlying feeding is distinct from that mediating other responses. Additional results revealed that ICV injection of antisera to NPY, which should inactivate endogenous NPY, produced a concentration-dependent suppression of eating induced by mild food deprivation. This finding, along with published work demonstrating enhanced levels of hypothalamic NPY in food-deprived rats, suggests that endogenous NPY mediates the eating produced by deprivation.

The discriminative stimulus effects of neuropeptide Y

Neuropeptide Y (NPY), an endogenous peptide which strongly induces food intake, is demonstrated to have discriminative stimulus properties when administered intracerebroventricularly. Rats rapidly learned to press the appropriate lever during training. NPY discrimination was dose-dependent. NPY's discriminative stimulus properties were compared to those of two doses of Peptide YY (PYY) and 24 and 48 h of food deprivation, conditions which also increase feeding. Both doses of PYY generalized to NPY, supporting previous findings that PYY has effects similar to NPY. Although food deprivation increases feeding in a manner similar to NPY, food deprivation did not result in NPY-appropriate responding.

Structure-function analysis of stimulation of food intake by neuropeptide Y: effects of receptor agonists

Neuropeptide Y (NPY) is a potent natural orexigenic signal in the rat. In this study, we have compared the effects of several COOH-terminal fragments of NPY and NPY receptor agonists on cumulative food intake in male rats. Rats were implanted with permanent cannulae either into the third cerebroventricle or paraventricular nucleus (PVN). NPY1-36 and various COOH-terminal fragments of NPY, two agonist analogues [Leu31, Pro34]NPY and NPY 1-4-Aca (epsilon-amino-caproic acid)-25-36, were administered intracerebroventricularly (ICV) or directly into the PVN, and the cumulative 2-h food intake response was compared. We observed that peptides that were effective by ICV were also effective when administered into the PVN, but smaller amounts of the peptides were required after PVN injection to evoke an equivalent food intake response. Injection of NPY1-36 induced a dose-dependent increment in food intake. Surprisingly, deletion of NH2-terminal tyrosine residue did not adversely affect feeding behavior. In fact, NPY2-36 was consistently more effective than NPY1-36; the enhancement in feeding by NPY2-36 was dose-related and was higher than evoked by NPY1-36 at each dose tested. Further serial deletion of aminoacids at NH2-terminal resulted in complete loss of activity. In addition, NPY agonist analogue, NPY 1-4-Aca-25-36, failed to stimulate feeding. However, NPY Y1 receptor agonist, [Leu31, Pro34]NPY, but not Y2 receptor agonist, NPY13-36, stimulated feeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Enteroglucagon and peptide Y-Y response after construction of a pelvic reservoir in humans

The results of an investigation of plasma levels of gastrointestinal hormones in patients after the construction of a pelvic reservoir are reported. Enteroglucagon (EG) and peptide tyrosine-tyrosine (PYY), two hormones believed to play a relevant role in the adaptive response to bowel resection, were investigated using a specific radioimmunoassay in basal conditions and after a standard meal. Pouch patients showed a statistically significant increase in basal levels of both enteroglucagon and PYY compared with control subjects (P less than 0.02 and P less than 0.001, respectively). The response of enteroglucagon to food ingestion, evaluated by means of the total integrated response, was similar in patients and controls. Conversely, the response of PYY was significantly increased in pouch patients compared with control cases (P less than 0.02). Results of this investigation suggest that gut hormones may be involved in mediating the adaptive response of the intestine to pouch construction. Changes of gut peptides may explain, at least in part, the functional results observed after pouch construction.

Suppression of neuropeptide Y-elicited eating by adrenalectomy or hypophysectomy: reversal with corticosterone

Neuropeptide Y (NPY) injected into the paraventricular hypothalamus (PVN) stimulates a robust eating response in the satiated rat. To examine whether the NPY-feeding system interacts with the pituitary-adrenal axis, the eating response to PVN injections of NPY (78 pmol) was tested in adult male rats before and after sham surgery, adrenalectomy (ADX), hypophysectomy (HYPX), and/or corticosterone (CORT) replacement therapy. In unoperated or sham groups, NPY elicited 5.7-8.8 g of food intake in 1 h as compared to 0.4-1.1 g for vehicle-injected animals. In ADX groups, the NPY-elicited response was reduced by 60-71%, to between 2.4 and 2.8 g. Likewise, the average response of the HYPX group was reduced by 69%, to 1.7 g. Corticosterone replacement, via subcutaneous implant of a 100 mg CORT pellet, normalized the NPY-induced feeding response in both the ADX and HYPX groups. These findings suggest that the hypothalamic NPY-feeding system is largely dependent upon circulating CORT and that no other adrenal or pituitary hormone is essential.

The effect of neuropeptide Y on drinking in mice

Neuropeptide Y (NPY) when administered intracerebroventricularly is a potent stimulator of feeding and drinking in rats. In these studies we demonstrated that, in contrast, in mice NPY inhibits drinking induced by water deprivation and that associated with food intake. In addition, we found that mice failed to respond to the rat dipsogen angiotensin II. Old mice demonstrated hypodipsia compared to young mice and NPY failed to inhibit drinking in older mice. Monosodium glutamate (MSG) administered neonatally produces lesions of the arcuate nucleus, an area rich in NPY cell bodies. NPY inhibited drinking and enhanced feeding in MSG treated mice. NPY also significantly inhibited the intake of water flavored with 8% sucrose and 0.1% quinine. NPY failed to alter ingestion of 0.2% or 5% saline. These studies support the contention that marked species differences exist in the regulation of water intake between rats and mice.

Repeated hypothalamic stimulation with neuropeptide Y increases daily carbohydrate and fat intake and body weight gain in female rats

Neuropeptide Y (NPY), repeatedly injected in the hypothalamic paraventricular nucleus (PVN), produces dramatic obesity and overeating in female rats maintained on a single nutritionally complete diet. In the present study, we investigated whether these effects could also be obtained in animals with a choice of three pure macronutrients: protein, carbohydrate, and fat. Female rats with indwelling PVN cannulas were injected with NPY (235 pmol) or its saline vehicle every 8 hr for 6 days. A third group was left undisturbed. Consumption of each macronutrient and body weight were measured every 24 hr for 6 days preinjection, 6 days during injections, and 21 days after the injections were terminated. Relative to vehicle or preinjection rates of body weight gain (approximately 1.5 g/day), NPY dramatically enhanced weight gain to a rate of 9.3 g/day and more than doubled total daily food intake. This augmentation was accounted for by increases in carbohydrate intake (+26.4 kcal/day) and fat intake (+48.5 kcal/day), with no significant potentiation of protein consumption. When the NPY injections were terminated, body weight and macronutrient intake returned to control levels within 1 or 2 weeks. These findings are consistent with a role for NPY in hypothalamic mechanisms of macronutrient intake and body weight regulation and suggest that disturbances in brain NPY may contribute to the development of eating and weight disorders.

Effects of neuropeptide Y on norepinephrine and serotonin metabolism in rat hypothalamus in vivo

A double-barrelled cannula and microdialysis system were used to inject 100 pmoles of neuropeptide Y (NPY) and to collect from the local microenvironment samples of norepinephrine, 3-methoxy-4-hydroxyphenylglycol (MHPG), serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC) a metabolite of dopamine. Following the administration of 100 pmoles of NPY into the ventromedial hypothalamus of conscious rats, there was a significant reduction in the local concentration of norepinephrine and an even greater reduction in the concentration of its metabolite, MHPG, as compared to saline-injected controls. The concentration of serotonin and its metabolite 5-HIAA as well as DOPAC were also reduced in the ventromedial hypothalamus following local injection of NPY. When NPY was injected into the lateral hypothalamus and monoamines measured from areas adjacent to the injection of NPY there was a significant increase in norepinephrine release and a significant increase in the concentration of DOPAC. Serotonin was significantly decreased and there was an increase in the ratio of 5-HIAA to serotonin. NPY is known to stimulate food intake when injected into either area. The present data are consistent with the concept that a reduction in concentration of serotonin is involved in the regulation of food intake following injection of NPY.

Neuropeptide Y (NPY) and the central nervous system: distribution effects and possible relationship to neurological and psychiatric disorders

1. NPY is a 36 amino acid tyrosine-rich peptide. It is one of the most abundant and widely distributed neuropeptides known today within the central nervous system with particularly high concentrations in the hypothalamus and in several limbic regions. 2. NPY seems to coexist with other on neurotransmitters like somatostatin, galanin, GABA and the catecholamines noradrenaline and adrenaline in discrete brain regions. 3. NPY binding sites are widely distributed in the brain. However they do not always overlap with the distribution of NPY-like immunoreactivity. 4. NPY is suggested to be involved in a large number of neuroendocrine functions, stress responses, circadian rhythms, central autonomic functions, eating and drinking behaviour, and sexual and motor behaviour. 5. Psychotropic drugs and neurotoxins can alter the NPY concentrations in discrete brain regions. 6. It is possible that NPY is related to various neurological and psychiatric illnesses, like Huntington's chorea, Alzheimer's disease, Parkinson's disease, eating disorders, and major depressive illness.

Peripheral and central satiety factors in neuropeptide Y-induced feeding in rats

In the first study, injection of NPY into the hypothalamic paraventricular nucleus (PVN) caused a robust feeding effect that was attenuated by intravenous infusions of glucose, but not fructose. It is suggested that increased blood glucose has a direct central effect on NPY feeding mechanisms. In a second study, and contrary to a previous report, peripheral administration of CCK-8 had a marked satiety effect in NPY-treated rats. Thus, NPY-induced feeding is, at least for a short time, possibly subject to the satiating action of prandially-released CCK. In a final study, NPY was shown to be without effect on gastric emptying of a solid test meal.

Peptide YY receptors in the brain

Radiolabelled ligand binding studies demonstrated that specific receptors for peptide YY are present in the porcine as well as the canine brains. Peptide YY was bound to brain tissue membranes via high-affinity (dissociation constant, 1.39 X 10(-10)M) and low-affinity (dissociation constant, 3.72 X 10(-8)M) components. The binding sites showed a high specificity for peptide YY and neuropeptide Y, but not for pancreatic polypeptide or structurally unrelated peptides. The specific activity of peptide YY binding was highest in the hippocampus, followed by the pituitary gland, the hypothalamus, and the amygdala of the porcine brain, this pattern being similarly observed in the canine brain. The results suggest that peptide YY and neuropeptide Y may regulate the function of these regions of the brain through interaction with a common receptor site.

Effect of angiotensin II and peptide YY on cerebral and circumventricular blood flow

Angiotensin II and peptide YY (PYY) are putative neuro/humoral agents acting at several circumventricular regions. These peptides also constrict cerebral vessels. We examined the effect of acute intravenous infusion of saline, angiotensin II and peptide YY on local cerebral blood flow (14C-iodoantipyrine autoradiography) in the circumventricular and non-circumventricular brain regions of 17 conscious rats. No reductions in brain blood flow (28 regions) were observed although angiotensin II and PYY infusion elevated arterial blood pressure 15-25% without influencing heart rate, suggesting an increase in peripheral resistance. However, local blood flow was dependent on the peptide infused. During PYY infusion, blood flow was rather constant in the 20 non-circumventricular regions examined whereas an increase in blood flow and a slight decrease in cerebrovascular resistance occurred in the circumventricular regions. The area postrema exhibited the most pronounced changes--an elevation in blood flow of 44 +/- 11% and a reduction in resistance of 20 +/- 5% in comparison to that in control animals. During angiotensin II infusion, local cerebral blood flow was similar to that in controls and local cerebrovascular resistance was elevated. Thus, the local cerebral circulatory response to peptide administration was dependent on the location of the region examined (circumventricular or non-circumventricular) and on the vasoactive peptide infused.

An investigation of tolerance to the actions of leptogenic and anorexigenic drugs in mice

This study compared the effects of chronic administration of anorexigenic drugs on weight loss in mice. Tolerance to the effects of peripheral anorexigenic peptides, viz. cholecystokinin-octapeptide and bombesin, developed rapidly. Morphine, cocaine and dehydroepiandrosterone-sulfate caused weight loss and appeared similar to d-amphetamine in mechanisms of action. A high dose of fluoxetine (25 mg/kg) proved to be a potent leptogenic agent but was also associated with death in some animals. A lower dose of fluoxetine (5 mg/kg) was associated with the development of tolerance. Calcitonin, a potent anorexigenic agent, did not produce weight loss and tolerance to its anorectic effect had developed by 10 days. Animals varied widely in their individual responsiveness to a given drug. Peripheral administration of peptide YY caused weight loss. We conclude that acute or chronic effects of agents on food intake do not necessarily predict effects on body weight. However, neurotransmitters that enhance feeding centrally appear to cause weight loss when administered peripherally.

Robust feeding following central administration of neuropeptide Y or peptide YY in chicks, Gallus domesticus

Neuropeptide Y (NPY) and peptide YY (PYY) were injected intracerebroventricularly (ICV) in broiler chicks. Both NPY and PYY markedly increased food intake during the first hour post-injection compared to saline (SAL) controls. Food intake doubled in chicks given 5 micrograms NPY. A response surface analysis suggested that following ICV injection of NPY, maximum food intake occurred, using a dose of 9 micrograms. In contrast, an estimated dose between one and 5 micrograms PYY resulted in maximum food intake, giving the latter a slightly higher potency. Time spent drinking was not significantly different among NPY, PYY and SAL groups. Chicks given NPY or PYY also spent significantly less time standing while those given PYY spent significantly less time preening compared to controls.

The role of cholecystokinin octapeptide in the central control of food intake in the dog

Cholecystokinin octapeptide (CCK-8, 1, 190 pmol/5 min) decreased food intake and water consumption in two models of ingestive behavior, i.e., food deprivation-induced feeding and insulin-induced feeding, when administered into the third (3V) and lateral (LV) cerebral ventricles. In fasted dogs, the suppression of food intake was more prominent after 3V CCK-8, whereas intravenously administered CCK-8 was without effect. Neuropeptide Y (NPY, 1, 190 pmol) had no significant stimulatory effect on food intake and water consumption in fasted as well as satiated dogs, and actually reduced both food and water intake in insulin-treated dogs. There was a slight but significant decrease in food and water intake after 275 nmol naloxone administration in both feeding models, and some of the dogs vomited. In insulin-treated animals, CCK-8 reversed, but NPY potentiated the hypothermic phase of temperature response observed after saline administration, whereas naloxone failed to alter rectal temperature. These results suggest that the effect of CCK-8 on feeding seems to involve central mechanisms in the dog, and that the mechanisms by which CCK-8, NPY and naloxone affect feeding behavior are different.

The effects of adrenergic, opioid and pancreatic polypeptidergic compounds on feeding and other behaviors in neonatal leghorn chicks

The present study examined the effects of intracerebral (IC) administration of pancreatic polypeptide (PP), neuropeptide Y (NPY), norepinephrine (NE), dynorphin and naloxone on food intake in 2-day-old Leghorn chicks. Of the compounds studied, only PP (20 micrograms) and naloxone (10 and 20 micrograms) elevated food intake significantly as compared to saline injections. NPY, a potent orexigenic agent in mammals, did not elevate consumption significantly in a dose-related fashion. This latter finding was attributed to the occurrence of tonic-clonic convulsions following NPY administration. However, for those chicks which did not exhibit behavioral convulsions, food intake appeared to be elevated by 1, 5 and 10 micrograms of NPY. Similarly, NE did not elevate food intake but instead induced sedation and narcolepsy, a behavioral response which could be distinguished from the convulsions observed after NPY. In a separate group of chicks, the effect of NPY on cortical activity was examined. Bipolar electrodes were used to record EEG activity before and after IC injections of saline, NPY or NE. The behavioral convulsions induced by NPY corresponded with an increase in high amplitude sharp-wave activity, which persisted for up to 30 min post-injection. Collectively, these results suggest that the neurochemical substrates for feeding in 2-day-old Leghorn chicks are distinct from those underlying food intake in adult mammals.

Neuropeptide Y (NPY)-induced feeding behavior in female rats: comparison with human NPY ([Met17]NPY), NPY analog ([norLeu4]NPY) and peptide YY

Porcine neuropeptide Y (pNPY) administered into the third ventricle of the brain is known to elicit a powerful feeding response in steroid-treated ovariectomized and intact male rats. The present study compared the effects of pNPY and 3 structurally related peptides, human NPY (hNPY), an analog of NPY (NPY-A, [norLeu4]NPY) and peptide YY (PYY) on feeding behavior in intact female rats. Intraventricular administration of pNPY, hNPY, NPY-A and PYY over a dose range of 0.5 to 10 micrograms evoked feeding behavior to a varying extent. Cumulative food intake during 60 and 120 min was increased in a dose-related fashion at 0.5 and 2.0 microgram for the 4 peptides. Whereas the 10-micrograms dose of pNPY evoked a feeding response smaller than that seen after 2 micrograms, the responses to either 10 micrograms hNPY or 10 micrograms PYY were similar to that seen after 2 micrograms. The effects of these peptides on the time spent eating were quite different: while pNPY increased the time spent eating, this effect was not dose-related, whereas hNPY, NPY-A and PYY produced dose-related increments in the time spent eating. The most dramatic increment in local eating rate was observed after 2.0 micrograms pNPY, with lesser increments seen after 2.0 microgram hNPY and NPY-A. This increased local eating was apparently responsible for the highest cumulative food intake observed. These results demonstrate that (a) 2 micrograms pNPY is equally effective in stimulating feeding behavior in intact female rats as it is in steroid-primed ovariectomized female and intact male rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y chronically injected into the hypothalamus: a powerful neurochemical inducer of hyperphagia and obesity

Neuropeptide Y (NPY), a putative neurotransmitter abundant in the brain, has recently been shown to act within the hypothalamus, inducing a powerful eating response and a specific appetite for carbohydrates. In the present study, NPY (235 pmol) injected bilaterally in the paraventricular nucleus three times a day for 10 days caused approximately a two-fold increase in daily food intake, a six-fold increase in the rate of body weight gain and a three-fold increase in the body fat of female rats. Subsequently, the food intake and body weight of these subjects decreased precipitously, reaching control levels 20 days postinjection. These findings, demonstrating that exogenous NPY is capable of overriding mechanisms of satiety and body weight control, suggest that disturbances in NPY function may play a role in some disorders of eating behavior and body weight regulation.

Paraventricular nucleus injections of peptide YY and neuropeptide Y preferentially enhance carbohydrate ingestion

Neuropeptide Y (NPY) injected into the paraventricular nucleus (PVN) is known to elicit a powerful feeding response in satiated, brain-cannulated rats. The present experiment investigates the effect of peptide YY (PYY), a structurally-related peptide, on feeding behavior and, in addition, the effects of both PYY and NPY on the pattern of macronutrient selection. Injection of PYY directly into the PVN, in doses ranging from 7.8 to 235 pmol/0.3 microliters, caused a strong, dose-dependent stimulation of feeding behavior, as well as a small stimulation of drinking behavior, in satiated rats. The mean latency to eat was 9.3 min, with substantial feeding occurring within 30 min of the injection. At low doses, the increase in feeding was seen predominantly during the first hr. At the highest dose, in contrast, food intake continued to increase progressively over the next few hr. such that by 4 hr postinjection food intake was more than 20 g over vehicle baseline. In 1 hr tests with 3 pure macronutrient (protein, fat and carbohydrate) diets simultaneously available, PYY and NPY (78 pmol/0.3 microliters) both elicited a strong and selective increase in carbohydrate consumption, with little or no effect on protein or fat consumption. These results suggest that hypothalamic receptors sensitive to PYY and NPY may participate in the control of carbohydrate consumption.