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

Neuropeptide Y and Peptide YY in Association with Depressive Symptoms and Eating Behaviours in Adolescents across the Weight Spectrum: From Anorexia Nervosa to Obesity

Neuropeptide Y (NPY) and peptide YY (PYY) are involved in metabolic regulation. The purpose of the study was to assess the serum levels of NPY and PYY in adolescents with anorexia nervosa (AN) or obesity (OB), as well as in a healthy control group (CG). The effects of potential confounders on their concentrations were also analysed. Eighty-nine adolescents were included in this study (AN = 30, OB = 30, and CG = 29). Anthropometric measurements and psychometric assessment of depressive symptoms, eating behaviours, body attitudes, and fasting serum levels of NPY and PYY were analysed. The AN group presented severe depressive symptoms, while the OB group held different attitudes towards the body. The levels of NPY were lower in the AN and OB groups as compared with the CG. The PYY levels were higher in the OB group than in the AN group and the CG. The severity of eating disorder symptoms predicted fasting serum concentrations of NPY. Lower levels of NPY in AN, as well as in OB suggests the need to look for a common link in the mechanism of this effect. Higher level of PYY in OB may be important in explaining complex etiopathogenesis of the disease. The psychopathological symptoms may have an influence on the neurohormones regulating metabolism.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Orosensory stimulation is sufficient and postingestive negative feedback is not necessary for neuropeptide Y to increase sucrose intake

Although central administration of neuropeptide Y (NPY) has a potent orexic effect, it is not clear how NPY changes the potency of peripheral feedbacks from the gut to prolong eating and increase meal size. It has been suggested that NPY increases the stimulating effect of orosensory sweet stimuli or that it decreases the inhibitory effect of postingestive stimuli. To clarify this issue, we compared the orexic effect of NPY (2 microg) injected into the third ventricle of the brain on the volume and microstructure of intake of 0.8M sucrose during sham feeding (SF) and real feeding (RF) in male Sprague Dawley rats. The rationale for this comparison is that orosensory stimulation occurs in SF and RF, but postingestive negative feedback is present only in RF. NPY increased the volume ingested and the rate and number of clusters of licking significantly more in SF than in RF. This demonstrates that orosensory sucrose stimulation is sufficient and postingestive negative feedback is not necessary for the orexic effect of NPY under these experimental conditions.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

Is there appetite after GLP-1 and PACAP?

Anitobesity drugs must increase the sensitivity of the hypothalamic satiety center towards leptin and antagonize the synthesis and action of NPY. The array of pharmacologic tools available is vast and presently ineffective. Among peptide analogs considered for evaluation [NPY-5 antagonists and CCK-A, bombesin, amylin and melanocyte-stimulating hormone-4 (or melanin-concentrating hormone?) agonists], is there a place for GLP-1 and PACAP? GLP-1 receptors present in ARC, PVN, VMN, and SON are the target for both central and blood-borne GLP-1 in those hypothalamic neurons endowed with GLUT-2 and glucokinase. GLP-1, hypersecreted by L-cells after a meal, is a potent insulinotropic agent and, together with glucose, reduces food intake and induces c-fos in the ARC. PACAP is present in the ARC, PVN, and SCH, and its hypothalamic type I receptor elevates cAMP and inositol triphosphate in the PVN, where it may perhaps antagonize NPY-induced food intake and hyperinsulinemia. However, irrelevant neuroendocrine, autonomic, and circadian functions are also activated by this peptide, making it a less than ideal base on which to build an obesity treatment.

Metabolic action of neuropeptide Y in relation to its effect on feeding

Because energy homeostasis depends on a continuous balance between food intake, energy expenditure, and energy storage, it was expected that neuropeptide Y (NPY) could act not only on food intake but also on metabolic parameters. Using an original calorimetric device that allows the computation of the background metabolism (energy expenditure free from the cost of locomotor activity), we assessed the effect of a microinjection of NPY upon the quantitative (background metabolism, thermic effect of food) and qualitative (respiratory quotient) components of energy metabolism. NPY was injected into the juxtafornical hypothalamus at a dose that promotes feeding behavior (1 microg/0.5 microL) and enhances locomotor activity. Although total metabolism was increased proportionally to locomotion, no effect of NPY on background metabolism was observed when no food was available. Only following a calibrated meal given 30 min after the microinjection did NPY induce a delayed decrease in respiratory quotient whereas the postprandial background metabolism remained unaffected. In conclusion, only the new-generation calorimeters can show that the NPY-induced rise in overall metabolic rate is entirely accounted for by the unavoidable enhancement in locomotor activity and that the only metabolic effect of NPY is the delayed postprandial respiratory quotient decrease, suggesting a postabsorptive orientation toward more lipid utilization.

Brain peptides and obesity: pharmacologic treatment

Obesity results from an imbalance between nutrient ingestion and metabolism, with more calories being ingested than utilized. The brain plays an important role in coordinating these complex behavioral and physiological functions, operating through multiple neurochemical systems with distinct properties. This review focuses on two hypothalamic peptide systems, neuropeptide Y (NPY) and galanin (GAL), that illustrate how the brain operates through different mechanisms to control the body's nutrient stores, in different states or conditions. These peptides have different behavioral and physiological effects and are, themselves, differentially responsive to feedback signals from circulating steroids, peptides, and nutrients. They can be distinguished by their relation to natural feeding patterns and endogenous hormones and by their specificity of action in relation to natural biological rhythms. The neuroanatomical substrates involved in these actions of NPY and GAL are also distinct. The neurocircuit mediating NPY's actions originates in the arcuate nucleus and terminates in the medial portion of the paraventricular nucleus; the GAL-containing neurons, in contrast, are concentrated in the lateral portion of the paraventricular nucleus, in addition to the medial preoptic area, which contribute to local GAL innervation as well as projections to the median eminence. Regarding their distinct functions, the evidence suggests that the NPY system is more closely related to patterns of carbohydrate ingestion and carbohydrate utilization, channeling nutrients towards the synthesis of fat. It is most strongly activated at the start of the active feeding cycle or after weaning, in close association with the adrenal steroid, corticosterone. The GAL system, in contrast, is more closely associated with patterns of fat consumption and signals related to fat oxidation. This peptide system is most active during the middle of the feeding cycle or immediately after puberty, in close association with the gonadal steroids. The gene expression and synthesis of these peptides in their respective neuronal cell groups is inhibited by circulating insulin and altered by dietary nutrients. Disturbances in sensitivity to insulin and steroid feedback regulation in the brain are believed to be involved in producing abnormal patterns of peptide function that result in overeating and body weight gain.

Intracerebroventricular injection of dibutyryl cyclic adenosine 3',5'-monophosphate increases hypothalamic levels of neuropeptide Y

This investigation examined in vivo the relationship between the nucleotide cAMP and hypothalamic levels of two peptides, neuropeptide Y (NPY) and galanin (GAL), which are known to potentiate feeding behavior. In brain-cannulated rats, third ventricular injections of N6,2'-O-dibutyryl cyclic adenosine 3',5'-monophosphate ((Bu)2cAMP, 25 micrograms), compared to saline, caused a significant increase in NPY levels in the arcuate nucleus (ARC) and medial parvocellular portion of the paraventricular nucleus (mPVN), while having no impact in other hypothalamic areas. These site-specific changes in NPY occurred in the absence of any alteration in circulating levels of insulin, corticosterone, aldosterone or glucose, or of changes in hypothalamic levels of GAL. These findings implicate cAMP as having regulatory functions within specific hypothalamic NPY-synthesizing neurons, projecting from the ARC to the mPVN, that are believed to be involved in energy homeostasis.

Role of neuropeptides in the regulation of feeding behavior: a review of cholecystokinin, bombesin, neuropeptide Y, and galanin

The purpose of this report is to provide a review of four peptides (cholecystokinin, bombesin, neuropeptide Y, galanin) and their role in feeding behavior. Cholecystokinin (CCK) and bombesin (BBS) are considered satiety peptides, and neuropeptide Y (NPY) and galanin (GAL) have been proposed as appetite peptides. For the purposes of this review, satiety refers to the physiological cessation of feeding, and appetite refers to the drive to eat and exists in gradations.

Neuropeptide Y and energy balance: one way ahead for the treatment of obesity?

Obesity is a vast and ever-expanding problem in affluent societies, which we have so far failed to confront. Over 20% of Western European and North American adults are overweight to a degree which may potentially shorten their life expectancy. Obesity has well-known associations with non-insulin-dependent diabetes (NIDDM), hypertension, dyslipidaemia and coronary heart disease, as well as less obvious links with diseases such as osteoarthrosis and various malignancies; it also causes considerable problems through reduced mobility and decreased quality of life. The overall financial burden of obesity is impossible to calculate precisely, but may account for 6-8% of total health-care expenditure in North America [1] (similar estimates probably apply to Western Europe). Obesity is difficult to treat and many patients remain obstinately overweight despite our best efforts. The available options range from behavioural therapy to gastrointestinal surgery and include numerous drugs designed to suppress appetite or increase energy expenditure. As in many other areas of medicine, the length and diversity of this list are reliable signs that effective treatment is still beyond our reach. This article argues that new anti-obesity drugs may emerge from recent advances in understanding the control of energy balance in rodents. The discussion is structured around neuropeptide Y (NPY), a major brain peptide which at present appears to be important in regulating energy balance and seems a promising candidate for therapeutic exploitation.

Neuropeptide Y attenuates satiety: evidence from a detailed analysis of patterns ingestion

Centrally injected neuropeptide Y (NPY) is a potent stimulant of ingestive behavior capable of augmenting both food and fluid intake in fully satiated animals. To gain further insight into NPY's mechanism of action, we recorded patterns of licking behavior in rats drinking sweetened condensed milk solutions immediately after lateral ventricular injection of NPY (10 micrograms) or vehicle. In a separate study, we examined licking patterns after 23 h food deprivation (FD) that produced approximately the same total intake as NPY. Consistent with previous reports, we found NPY stimulated intake by increasing total ingestion time and total volume consumed during a 1-h test. Although NPY increased the number of bouts of licking and shortened pauses between bouts, it also decreased mean bout size, bout duration and within-bout lick rate (local rate). It had no significant effect on start latency or lick efficiency (licks/ml). Further analyses revealed that NPY attenuated satiety (reduced slope of lick-rate functions with session time) but had no significant effect on the beginning lick rate, a measure related to orosensory excitation. In contrast to NPY, FD increased both the beginning lick rate and individual bout size without changing either the mean number of bouts or the pause between bouts. In general, NPY stimulated an intermittent pattern of licking and delayed satiation whereas FD increased the initial rate of licking and the size of individual bouts without changing the basic licking pattern. The increase in initial lick rate suggests that FD, unlike NPY, enhances orosensory stimulation. These data compliment previous results showing that NPY increases the motivation to eat.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermoregulatory effect of intracerebral injections of neuropeptide Y in rats at different environmental temperatures

1. In order to characterize the thermoregulatory actions of brain neuropeptide Y (NPY), the effects of intra-third ventricular (I3V) injection of NPY on temperatures of colon (Tco), brown adipose tissue (TBAT) and tail skin (Ts) were observed at ambient temperatures (Ta) of 19 and 8 degrees C. 2. The injection of NPY in a dose of 8 mcg/100 g body wt evoked a fall of Tco by about 2 degrees C in both neutral and cold environments. NPY (4 and 8 mcg/100 g body wt) induced dose-dependent Tco falls in rats at thermoneutral environment. The thermolytic reactions induced by I3V administration of NPY were associated with a fall in TBAT but no changes in Is were observed. 3. The results suggest that NPY may mediate hypothermic response in neutral and cold environments mainly by its effects on the brown adipose tissues in the rat.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Neuropeptide Y: a central regulator of energy homeostasis

Neuropeptide Y (NPY) is a 36 amino acid peptide belonging to the pancreatic polypeptide family of neuroendocrine hormones. It is the most abundant peptide yet discovered in the mammalian brain and is widely expressed by neurons in the central and peripheral nervous systems as well as adrenal medullary cells. Recently, a large number of studies have focussed on the potential roles played by NPY within the hypothalamus and pituitary with respect to the control of food intake and energy homeostasis. It is now clear that NPY is a potent stimulator of food intake in models of hyperphagia, that hypothalamic NPY also regulates sympathetic neural activity and it appears that NPY may also influence the glucocorticoid, growth hormone and thyroid hormone axes. Taken together, current data suggest that hypothalamic and pituitary NPY-expressing cells represent an important and critical site of integration of peripheral hormonal signals with regulation of energy homeostasis.

Neuropeptide Y in the arcuate nucleus is modulated by alterations in glucose utilization

This study examined the response of hypothalamic neuropeptide Y (NPY) to specific metabolic challenges. After intraperitoneal administration of 2-deoxy-D-glucose, which blocks glucose utilization, NPY levels measured via radioimmunoassay were significantly potentiated in the arcuate (ARC) and suprachiasmatic nuclei of the rat hypothalamus. The antimetabolite mercaptoacetate, in contrast, which blocks fatty acid oxidation, produced no significant change and actually tended to reduce NPY levels in the ARC. It is concluded that glucose utilization, in particular, may constitute an important signal, either direct or indirect, in the modulation of NPY production in the hypothalamus.

Neuropeptidergic regulation of feeding behavior Neuropeptide Y

Neuroendocrine control of feeding behavior is multifactorial, involving a variety of peripheral and central signals. Neuropeptides, catecholamines, and serotonin constitute the signals of the feeding circuitry acting primarily in the brain, especially at the hypothalamic level. In this review, an attempt is made to summarize the recent progress made in our continuing effort to understand the regulation of feeding behavior by neuropeptides, particularly those that stimulate feeding. A special emphasis has been placed on a neuropeptide of the pancreatic polypeptide family-neuropeptide Y (NPY).

Regulation of hypothalamic neuropeptide expression by peripheral metabolism

The mechanisms of appetite and body-weight regulation by peripheral signals are highly complex in vertebrates and remain poorly understood. It is intuitively apparent that such regulation must involve interactions between peripheral metabolic status and the brain, but what are the signals recognized by the brain to initiate feeding? The hypothalamus has long been recognized as central in "recognition" of peripheral nutrient and metabolic signals (and, perhaps, body weight status) and in "regulation" of hunger and satiety responses and, therefore, is a logical site on which to focus research aimed at understanding interactions between and regulation of the periphery and central nervous system. Recent studies demonstrating modulation of hypothalamic neurotransmitter expression by peripheral metabolic status may yield insights into regulation of appetite and metabolism in obesity and aberrant metabolic homeostasis. This review concentrates on summarizing data regarding regulation of expression of neuropeptide Y and growth hormone-releasing hormone as model peptide systems for addressing questions relating peripheral metabolism and hypothalamic neuropeptide expression.

Brain neuropeptide Y: an integrator of endocrine, metabolic and behavioral processes

Neuropeptide Y (NPY), acting through various medial hypothalamic nuclei, is found to have potent effects on a variety of endocrine, physiological and behavioral systems that modulate energy balance. This peptide affects the release of various hormones, such as corticosterone, insulin, aldosterone and vasopressin, which modulate energy metabolism, as well as food intake. It also has direct impact on energy metabolism through an effect on substrate utilization and lipogenesis. Finally, NPY has a remarkably potent stimulatory effect on feeding behavior, which is characterized by a selective increase in carbohydrate ingestion that is strongest at the beginning of the active feeding cycle and is dependent upon circulating levels of corticosterone. This evidence has led to the proposal that NPY exerts anabolic effects to restore energy balance at specific times of energy depletion. Increased NPY activity may occur at the beginning of the active cycle or after a period of food deprivation. Further evidence, that chronic NPY stimulation produces profound hyperphagia and obesity and that endogenous NPY concentration is increased in genetically obese animals, strongly suggests that hypothalamic NPY may contribute to the development of eating disorders and obesity.

[The regulation of feed intake and selection with special reference to poultry]

Feed intake is regulated in a dialogue between the animal and the feed, which is influenced by numerous factors. The hypothalamus has a central integrative function. Furthermore, caudal brain areas (medulla oblongata, pons) are of importance because these areas are relays of peripheral signals and gustatory afferents. All peripheral informations are integrated by various neurotransmitters and neurohormones. The function of this neuronal system is not exactly known yet. Sensorial informations, mechano-, chemo- and osmoreceptors of the gastrointestinal tract and gastrointestinal hormones are discussed as influences of the periphery. The physiological satiety function of cholecystokinin is questionable in poultry. Hepatic chemoreceptors, which are activated by various metabolites, influence the amount of feed ingested. The feed choice appears to be regulated by the same mechanisms. Our knowledge about the translation of peripheral signals into choice behaviour by changes of neurotransmitter systems is limited.

Unchanged hypothalamic neuropeptide Y concentrations in hyperphagic, hypoglycemic rats: evidence for specific metabolic regulation of hypothalamic NPY

Hypothalamic concentrations of neuropeptide Y (NPY), a potent central appetite stimulant, increase dramatically in food-restricted and insulin-deficient diabetic rats. This suggest that NPY may drive hyperphagia in these conditions, which are characterized by weight loss and insulin deficiency. To test the hypothesis that insulin deficiency and weight loss are specific stimuli to hypothalamic NPY, we measured NPY concentrations in individual hypothalamic regions in rats with hyperphagia caused by insulin-induced hypoglycemia. Groups of 8 male Wistar rats were injected with ultralente insulin (20-60 U/kg) to induce either acute hypoglycemia (7 h after a single injection) or chronic hypoglycemia (8 days with daily injections). In hypoglycemic rats, plasma insulin concentrations were increased 6- to 7-fold compared with saline-injected controls; food intake was significantly increased with acute and chronic hypoglycemia and weight gain was significantly increased in the chronically hypoglycemic group. NPY concentrations were measured by radioimmunoassay in 8 hypothalamic regions microdissected from fresh brain slices. NPY concentrations were not increased in any region in either acute or chronic hypoglycemia. NPY therefore seems unlikely to mediate hyperphagia in hyperinsulinemia-induced hypoglycemia, supporting the hypothesis that weight loss is a specific stimulus to hypothalamic NPY and that insulin deficiency may be the metabolic signal responsible.

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

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

Full amino acid sequence of centrally administered NPY required for maximal food intake response

Central administration of NPY (1-36) potently increases food intake and it has been hypothesized that biological activities of NPY are related to its ability to form an alpha-helix, represented by the fragment NPY (14-31). In this experiment the necessity of N-terminal fragments for increasing food intake was evaluated. Two-h fasted male rats were administered 0, 0.2, 1.0 or 5.0 nmol NPY (1-36) or NPY fragments in 5 microliters saline ICV and intake of lab chow pellets was measured for 22 h. Fragments containing all or part of the polyproline-like helix [NPY (1-8)] antiparallel to the alpha-helix dose-relatedly increased food intake for 4 hours after injection. Five nmol NPY (1-36) and NPY (2-36) increased 4-hour food intake 486 and 219%, respectively (p less than 0.05). Fragments excluding the first 8 amino acids but including all of the alpha-helix also increased food intake, but the response was much reduced. Five nmol NPY (9-36) and NPY (14-36) increased 4-hour food intake 128% (p = 0.02) and 62% (NS), respectively. When all or part of the alpha-helix was excluded, no activity was detected, i.e., NPY (21-36) and NPY (32-36). Substitution of dPro for lPro in position 2 increased potency but not efficacy of NPY since food intake was increased at the 0.2 and 1.0 but not 5.0 nmol doses and the percent increase was not more than to 5 nmol NPY (1-36). Thus the maximum food intake response to NPY requires both C-terminal and N-terminal fragments as well as the alpha-helix.

Changes in brain neuropeptide Y induced by cholecystokinin peptides

Cholecystokinin (CCK) and neuropeptide Y (NPY) are two peptides with opposite effects on the regulation of feeding behaviour. The possible interaction between these two systems has always been controversial. In this study, rat brain NPY levels were assayed after treatment with CCK 8 S and with a potent CCK agonist (Boc-(Nle 28-Nle 31)-CCK 26-33). CCK 8 S and its agonist analogue (50 micrograms/kg i.p.) both decreased hypothalamic and hippocampal NPY levels. This result suggests a negative relationship between NPY and CCK-peptides which is not surprising given their opposite role in the control of feeding. The hypothalamus and secondarily the hippocampus appear to be the site of this interaction; no change in NPY levels was observed in other brain areas (striatum and cortex). The same pattern of variation was found in the plasma, suggesting a direct release from the brain via a mechanism which remains to be investigated. The effect appeared later with the CCK analogue than with CCK 8 S itself; this is not surprising with regard to other behavioural and biochemical effects of the analogue and provides further characterization of its action.

Changes in hypothalamic neuropeptide Y concentrations induced by cholecystokinin analogues

Neuropeptide Y (NPY) and cholecystokinin (CCK) are two peptides involved in opposite ways in the control of food intake. A possible interaction between NPY and CCK has not yet been well defined. Two CCK derivatives with agonistic and antagonistic properties were studied with regard to their effects on brain and plasma NPY levels. The CCK agonist decreased NPY levels in plasma and in the hypothalamus but not in the other brain areas assayed. The CCK antagonist reversed the agonist-induced decrease in both plasma and hypothalamus. These results suggest a negative relation between NPY and CCK peptides, which is not surprising given their opposite role in feeding regulation. The hypothalamus, a preferential site of this regulation, appears to be the brain area most involved in the NPY-CCK interaction. The plasma NPY level variations closely reflect the hypothalamic profile, suggesting a direct release of NPY by a mechanism that remains to be investigated.

Metabolic effects of neuropeptide Y injections into the paraventricular nucleus of the hypothalamus

The metabolic effects of single injections of neuropeptide Y (NPY) into the paraventricular hypothalamus were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. Over the dose range of 10-156 pmol NPY had large effects on respiratory quotient (RQ) while having no effect on energy expenditure or locomotor activity. The effects of NPY on RQ were unusual both in respect to their dose-response and time-dose-response characteristics. The lowest dose (10 pmol) produced a very low latency reduction in RQ which indicates a decreased utilization of carbohydrates as an energy substrate. The next higher dose (20 pmol) had no effect, whereas the next three doses (39, 78 and 156 pmol) produced increases in RQ which indicate an increased utilization of carbohydrates as an energy substrate. Surprisingly, the latencies of the increased RQs were dose-dependent over the range of 30 min to 20 h with the highest dose producing the longest latency effect. The finding of a positive relation of dose to response latency over a time range of from a few minutes to 20 h is unprecedented and appears to represent a neuromodulatory effect of NPY that acts in concert with its neurotransmitter effects. These data highlight the central role of NPY in modulating energy substrate utilization and indicate the importance of elucidating time-dose-response relationships when investigating the effects of NPY.

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.