Effects of food deprivation and high fat diet on immunoreactive dynorphin A(1–8) levels in brain regions of Zucker rats

The levels of immunoreactive dynorphin A(1–8) (ir-DYN8) were measured in discrete brain regions of lean Zucker rats subjected to food deprivation for 72 hr and to a high fat diet, and in fatty Zucker rats after food deprivation for 72 hr. Fatty rats showed higher concentrations of ir-DYN8 in the cortex and midbrain, when compared to lean rats fed a stock diet ad lib. Food deprivation increased ir-DYN8 levels in the cortex of lean rats and fatty rats and in the hippocampus of fatty rats, but decreased its content in the striatum of lean rats and in the midbrain of fatty rats. The high fat diet increased ir-DYN8 levels in the cortex and midbrain of lean rats. These results suggest that ir-DYN8 levels in extrahypothalamic structures of Zucker rats could be differentially modified under conditions of hereditary obesity and dietary manipulations.     

Influence of the subfornical organ on meal-associated drinking in rats

A lesion of the subfornical organ (SFO) may disrupt drinking after a meal of dry chow as it does drinking after intragastric administration of hypertonic saline. Food and water intakes of SFO-lesioned (SFOX) and sham-lesioned rats were measured during 90-min tests following various lengths of food deprivation. During the tests, all rats began eating before they began drinking. After 20-24 h of food deprivation, latency to begin drinking after eating had started was longer for SFOX than for sham-lesioned rats. Plasma osmolality was elevated by 2-3% in both lesion groups at 12 min, the latency for sham-lesioned rats to drink, but SFOX rats nevertheless continued eating and delayed drinking. Eating after shorter 4-h food deprivations and ad libitum feeding produced more variable drinking latencies and less consistent effects of SFO lesion. During 24 h of water deprivation, SFO lesion had no effect on the suppression of food intake and did not affect food or water intakes during the first 2 h of subsequent rehydration. These findings indicate that the SFO is involved in initiating water intake during eating and in determining drinking patterns and the amount of water ingested during a meal.     

Drinking,but not feeding,is opiate-sensitive in hamsters

The long-lasting opiate antagonist, naltrexone (NTX), was examined for its effects on various types of consummatory behavior in male golden hamsters and rats. Rat, but not hamster, 24 hr food and water intakes were significantly decreased by four daily NTX (10.0 mg/kg) injections. Hamsters displayed a minimal night to day feeding ratio compared to rats. hamsters increased food intake following insulin (50 U/kg) administration, but not after 24 hr food deprivation (FD) or 2-deoxy-D-glucose (2-DG; 800 mg/kg) injections. NTX (1.0 and 10 mg/kg) had no effect on feeding, but markedly attenuated hamster drinking induced by 48 hr water deprivation or hypertonic saline injection. Dexamethasone (DEX), a glucocorticoid which depletes pituitary β-endorphin and produces anorexia in rats, had no effect on daily hamster intake. Since the normal feeding profile of the hamster is similar to that of naloxone and DEX-treated rats, hamsters appear to lack an opiate-sensitive feeding system. In contrast, stimulated drinking behavior of hamsters operates through an opiate-sensitive mechanism. Thus, there are marked species differences concerning the involvement of endogenous opioids is consummatory behavior.     

Dynorphin A (1-13), microinjected into the preoptic area, stimulates water intake in rats

The effects of dynorphin A (1-13) (DYN), injected into the preoptic area, was investigated on water intake in rats. DYN at both doses of 2 and 10 nmoles significantly increased water intake for two and four hours after the injection in a dose related fashion. However, no significant change was observed in food intake. Naloxone pretreatment (0.3 mg/kg, s.c.) completely attenuated the DYN-induced stimulation of water intake. The present studies suggest that DYN in the preoptic area may play an important role in the regulation of drinking behavior, but have no effect on food intake.     

Water intake induced by water deprivation in the quail,Coturnix coturnix japonica

Mechanisms inducing drinking after water deprivation, and mechanisms terminating drinking after rehydration, were investigated in the quail, Coturnix coturnix japonica. 1. Water intake was induced after 4 h of water deprivation, and the amount of water drunk increased in proportion to the period of water deprivation. Drinking occurred immediately after deprivation. Drinking occurred immediately after deprived birds were given access to water, and continued for periods proportional to the period of water deprivation. 2. Plasma angiotensin II concentration increased, as did plasma osmolality and Na+ concentration, and blood volume decreased after water deprivation. The increase in plasma angiotensin II concentration and decrease in blood volume occurred soon after the start of water deprivation, whereas plasma osmolality and Na+ concentration did not increase until at least 4 h after the start of water deprivation. 3. These results indicate that extracellular dehydration and angiotensin II are responsible for the significant drinking that follows 4 h of water deprivation, and that cellular dehydration is also involved in the stimulation of drinking that occurs after longer periods of water deprivation. 4. Plasma osmolality and Na+ concentration in birds deprived of water for 48 h quickly returned to normal levels after the birds were allowed access to water. Plasma angiotensin II levels and blood volume also approached the values measured prior to water deprivation. However, the rate and degree of restoration of normal values were reduced, and normal values were not restored even after 1.5 h or rehydration when drinking terminated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peptides and transmitter enzymes in hypothalamic magnocellular neurons after administration of hyperosmotic stimuli: comparison between messenger RNA and peptide/protein levels

Summary In situ hybridization histochemistry and indirect immunofluorescence histochemistry were used to study changes in the expression of vasopressin (VP), oxytocin (OXY), tyrosine hydroxylase (TH), galanin (GAL), dynorphin (DYN) and cholecystokinin (CCK) in hypothalamic magnocellular neurons of the paraventricular (PVN) and supraoptic (SON) nuclei of rats. After prolonged administration of 2% sodium chloride as drinking water (salt-loading), the treatment increased the levels of VP, OXY, TH, GAL, DYN and CCK mRNA in the PVN and SON. The increase in CCK mRNA was, however, proportionally higher in the PVN than in the SON. Within cell bodies of the PVN and SON of salt-loaded rats, a depletion of VP- and OXY-like immunoreactivity (LI) and an increase in TH-LI were seen. In salt-loaded/colchicine-treated rats, a marked decrease in GAL- and DYN-LI, but no specific changes in CCK-LI were observed. Within nerve fibers of the posterior pituitary of salt-loaded rats, a marked depletion of VP-, GAL- and DYN-LI was found. Less pronounced depletion was observed in OXY- and CCK-LI, and no specific changes in TH-LI were seen. The results show that high plasma osmolality induces increased mRNA levels for VP, OXY, TH, GAL, DYN and CCK, presumably indicating increased synthesis, an increased export from cell somata of VP, OXY, GAL and DYN, and a decrease in levels of these peptides in the posterior pituitary, suggesting increased release. The catecholamine-synthesizing enzyme TH, however, which has a cytoplasmic localization and is not released from nerve endings, remains high in the cell bodies and nerve endings during this state of increased activity.     

Effect of stress,adrenalectomy and changes in glutathione metabolism on rat kidney metallothionein content: comparison with liver metallothionein

Eighteen hours of immobilization stress, accompanied by food and water deprivation, increased liver metallothionein (MT) but decreased kidney MT levels. Food and water deprivation alone had a significant effect only on liver MT levels. In contrast, stress and food and water deprivation increased both liver and kidney lipid peroxidation levels, indicating that the relationship between MT and lipid peroxidation levels (an index of free radical production) is unclear. Adrenalectomy increased both liver and kidney MT levels in basal conditions, whereas the administration of corticosterone in the drinking water completely reversed the effect of adrenalectomy, indicating an inhibitory role of glucocorticoids on MT regulation in both tissues. Changes in glutathione (GSH) metabolism produced significant effects on kidney MT levels. Thus, the administration of buthionine sulfoximine, an inhibitor of GSH synthesis, decreased kidney GSH and increased kidney MT content, suggesting that increased cysteine pools because of decreased GSH synthesis might increase kidney MT levels through an undetermined mechanism as it appears to be the case in the liver. However, attempts to increase kidney MT levels by the administration of cysteine or GSH were unsuccesful, in contrast to what is known for the liver. The present results suggest that there are similarities but also substantial differences between liver and kidney MT regulation in these experimental conditions.     

High density and food deprivation affect arginine vasotocin, isotocin and melatonin in gilthead sea bream (Sparus auratus).

Arginine vasotocin (AVT) and isotocin (IT) levels in plasma and pituitary, and melatonin (MEL) levels in plasma were determined in gilthead sea bream (Sparus auratus) subjected to two different types of stress: i) high density (HD) and ii) food deprivation (NF: non-fed). Fishes were randomly assigned to one of 4 treatments that lasted for 14 days: 1) fed fish under normal low density (ND, 4 kg m(-3)); 2) non-fed (NF) fish under ND; 3) fed fish under high density (HD, 70 kg m(-3)); and 4) non-fed fish under HD. Ten fish from each tank were anaesthetized, weighed and plasma and pituitary samples were taken. Plasma and pituitary AVT and IT content were determined by HPLC, while plasma MEL was assayed by RIA. Plasma AVT and IT values were enhanced in all fish kept at high density. The response of AVT was much stronger than that of IT. The highest pituitary AVT and IT levels were shown in NF fish kept at normal density. The significantly higher plasma MEL levels were measured in fed fish kept at HD. These results suggest a role of AVT, IT and MEL in response of sea bream to a common stress factor, high density. Although food deprivation does not influence AVT and IT plasma levels, it seems to affect hypothalamic synthesis of nonapeptides. Further studies are required to elucidate the complex role of AVT, IT and MEL in the sea bream's response to different stress stimuli.     

High density and food deprivation affect arginine vasotocin, isotocin and melatonin in gilthead sea bream (Sparus auratus)

Arginine vasotocin (AVT) and isotocin (IT) levels in plasma and pituitary, and melatonin (MEL) levels in plasma were determined in gilthead sea bream (Sparus auratus) subjected to two different types of stress: i) high density (HD) and ii) food deprivation (NF: non-fed). Fishes were randomly assigned to one of 4 treatments that lasted for 14 days: 1) fed fish under normal low density (ND, 4 kg m(-3)); 2) non-fed (NF) fish under ND; 3) fed fish under high density (HD, 70 kg m(-3)); and 4) non-fed fish under HD. Ten fish from each tank were anaesthetized, weighed and plasma and pituitary samples were taken. Plasma and pituitary AVT and IT content were determined by HPLC, while plasma MEL was assayed by RIA. Plasma AVT and IT values were enhanced in all fish kept at high density. The response of AVT was much stronger than that of IT. The highest pituitary AVT and IT levels were shown in NF fish kept at normal density. The significantly higher plasma MEL levels were measured in fed fish kept at HD. These results suggest a role of AVT, IT and MEL in response of sea bream to a common stress factor, high density. Although food deprivation does not influence AVT and IT plasma levels, it seems to affect hypothalamic synthesis of nonapeptides. Further studies are required to elucidate the complex role of AVT, IT and MEL in the sea bream's response to different stress stimuli.     

Liver, Brain, and Heart Metallothionein Induction by Stress

To date, stress has been reported to induce metallothionein (MT) synthesis in the liver only. In the present experiment, the effects of food and water deprivation alone or of immobilization stress plus food and water deprivation on liver, brain, and heart MT have been studied in adult male rats. Liver and brain MT levels were increased by immobilization stress as soon as 6 h after the onset of stress. Eighteen hours of immobilization, which is accompanied by food and water deprivation, further increased liver and brain MT levels and significantly increased heart MT content. A specific effect of immobilization was evident in all three tissues, because the effect of food and water deprivation alone was significantly lower than that of immobilization plus starvation. Changes in MT apparently were not related to changes in cytosolic Zn.     

Effects of food deprivation and high fat diet on immunoreactive beta-endorphin levels in brain regions of Zucker rats

The levels of immunoreactive beta-endorphin (ir-beta-EP) were measured in the brain and pituitary of lean Zucker rats subjected to food deprivation for 72 h and to a high fat diet, and in fatty Zucker rats after food deprivation for 72 h. Ir-beta-EP was increased in the neurointermediate (NI-) pituitary lobe but reduced in the medulla-pons of fatty rats when compared to lean littermates fed ad libitum. Food deprivation decreased ir-beta-EP in the cortex and medulla-pons of lean rats and in the cortex, midbrain and NI-pituitary of fatty rats. In contrast, ir-beta-EP was increased in the anterior pituitary of lean rats and in the striatum of fatty rats after deprivation. The high fat diet produced a decrease in ir-beta-EP in the cortex, midbrain and NI-pituitary with an increase in the striatum and hypothalamus of lean rats. These results suggest that the ir-beta-EP concentration could be differentially affected in different brain regions of Zucker rats by changes in the energy balance.     

Separating food and water deprivation in locusts: effects on the patterns of consumption, locomotion and growth

Abstract. In a factorial experiment, fifth-instar Locusta migratoria (L.) (Orthoptera: Acrididae) were given either dry food (lyophilized grass) and drinking water, food only, water only, or neither food nor water.Food consumption and insect weight were measured daily, and the behaviour of each locust was recorded for 5 h on each of four consecutive days and for 2.5 h on the fifth.Consumption declined progressively in locusts given food only, and those given water only were not observed to drink after the first day of food deprivation.The decline in food consumption on the first day was accounted for by a decrease in the average duration of feeds, which remained constant thereafter.The further decline in consumption over subsequent days was due to a progressive decline in the number of feeds.Although food availability did not slow weight loss relative to locusts given neither food nor water, the availability of water without food did.The proportion of time locomoting increased in all deprivation treatments, but the pattern of change across the five observation days differed markedly between treatments.Locusts given food but no water increased locomotion from 20% of the time budget (the value for controls) to 30% on the first day of deprivation, and by the second day had reached a plateau of approximately 65%.which was maintained until the experiment was terminated on day 5.In contrast, locusts given water but no food approached the 65% level of locomotion on the first day, which was stutistically greater than the 55% observed in those deprived of both food and water.This increase was due both to an increase in the number of locomotion bouts initiated and an increase in the average duration of locomotion bouts.On the second and third days, all deprivation treatments maintained locomotion at around 65%.By day 4, locomotion had decreased to approximately 15% in locusts deprived of both food and water, but not in those deprived of food only or water only.Unlike those given only food, locusts given only water showed a reduction in locomotion of c. 15% on the fifth day.     

Role of the non-opioid dynorphin peptide des-Tyr-dynorphin (DYN-A2−17) in food intake and physical activity,and its interaction with orexin-A.

Food intake and physical activity are regulated by multiple neuropeptides, including orexin and dynorphin (DYN). Orexin-A (OXA) is one of two orexin peptides with robust roles in regulation of food intake and spontaneous physical activity (SPA). DYN collectively refers to several peptides, some of which act through opioid receptors (opioid DYN) and some whose biological effects are not mediated by opioid receptors (non-opioid DYN). While opioid DYN is known to increase food intake, the effects of non-opioid DYN peptides on food intake and SPA are unknown. Neurons that co-express and release OXA and DYN are located within the lateral hypothalamus. Limited evidence suggests that OXA and opioid DYN peptides can interact to modulate some aspects of behaviors classically related to orexin peptide function. The paraventricular hypothalamic nucleus (PVN) is a brain area where OXA and DYN peptides might interact to modulate food intake and SPA. We demonstrate that injection of des-Tyr-dynorphin (DYN-A₂₋₁₇, a non opioid DYN peptide) into the PVN increases food intake and SPA in adult mice. Co-injection of DYN-A₂₋₁₇ and OXA in the PVN further increases food intake compared to DYN-A₂₋₁₇ or OXA alone. This is the first report describing the effects of non-opioid DYN-A₂₋₁₇ on food intake and SPA, and suggests that DYN-A₂₋₁₇ interacts with OXA in the PVN to modulate food intake. Our data suggest a novel function for non-opioid DYN-A₂₋₁₇ on food intake, supporting the concept that some behavioral effects of the orexin neurons result from combined actions of the orexin and DYN peptides.     

Reduced feeding during water deprivation depends on hydration of the gut

Removal of drinking water at the start of the dark period reduced food intake in freely feeding rats within 45 min. Both first and later meals were smaller during 7.5 h of water deprivation, but meal frequency did not change. Ingestion of a normal-sized meal (3 g) rapidly increased plasma tonicity when drinking water was withheld, but intravenous infusions of hypertonic NaCl causing similar increases in plasma tonicity did not reduce feeding. Feeding during 6 h of water deprivation was restored by slowly infusing the volume of water normally drunk into the stomach, jejunum, or cecum, but not in the vena cava or hepatic portal vein. The infusions did not alter water or electrolyte excretion or affect food intake in rats allowed to drink. We conclude that the inhibition of feeding seen during water deprivation is mediated by a sensor that is located in the gastrointestinal tract or perhaps in the mesenteric veins draining the gut, but not the hepatic portal vein or the liver. In the absence of drinking water, signals from this sensor provoke the early termination of a meal.     

The in vitro release of immunoreactive dynorphin and alpha-neoendorphin from the perfused rat duodenum

The release of immunoreactive (ir) dynorphin (DYN) and alpha-neoendorphin (ir-ANEO) from the isolated perfused rat duodenum was demonstrated using specific radioimmunoassays (RIAs). Depolarization of the tissue by increasing the potassium (K+) concentration up to 108 mM enhanced the release of ir-DYN and ir-ANEO in Ca2+-dependent manner. Administration of the serotonin-releasing agent fenfluramine (10(-6) M) and the serotonin receptor agonist m-chlorophenylpiperazine (m-CPP, 10(-6) M) stimulated the release of ir-DYN and ir-ANEO from the duodenum. A subsequent study revealed that serotonin (5-HT, 10(-6)-10(-4) M) induced a dose-dependent increase in the release of ir-DYN and ir-ANEO from the duodenum. The effect of 5-HT on the release of ir-DYN and ir-ANEO from the duodenum was antagonized by 5-HT antagonist cyproheptadine (10(-6) M). The presence of dynorphin and the related peptides in the gastrointestinal tract (GIT) and their release from the duodenum in vitro indicate that these peptides may act as transmitters involved in some GIT functions. Furthermore, our results suggest that at least part of 5-HT effects on the GIT may be mediated by the release of dynorphin and the related peptides.     

Day–Night Differences in Membrane‐Bound Pyroglutamyl‐2‐Naphthylamide‐Hydrolyzing Activity in Rat Hypothalamus,Pituitary, and Retina

Membrane‐bound pyroglutamyl‐2‐naphthylamide‐hydrolyzing enzyme activity was analyzed fluorometrically in the anterior hypothalamus, pituitary, and retina of adult male rats to investigate day–night differences. Six groups (n=6 per group) were assessed—three during the light span and three during the dark span—under a standard 12 h–12 h light–dark cycle (light on from 07:00 to 19:00 h) and controlled temperature environment, with food and water available ad libitum. In the hypothalamus, enzyme activity levels were higher for time points of the dark than the light period. In contrast, the pituitary and retina exhibited the highest levels at the time points of the light period. The pituitary and retina also exhibited significant differences between the clock‐hour means of the light period. Day–night differences in membrane‐bound pyroglutamyl‐2‐naphthylamide‐hydrolyzing activity may reflect differences in its susceptible endogenous substrates.     

NaCl concentration alters temporal patterns of drinking and eating by rats

To obtain an understanding of the role of taste in NaCl preference-aversionunder standard laboratory feeding conditions, we characterizedthe eating and drinking patterns of rats maintained on powderedfood, water, and NaCl solution. The concentration of NaCl wasvaried systematically from 0.01 to 0.4 M with a single concentrationpresent for four consecutive days. In addition to daily intake,the number and duration of ingestion bouts, and the number ofswitches between food and fluid and between water and salinewere recorded throughout the day/night cycle. The availabilityof NaCl solution did not alter the typical pattern of night-timefeeding and prandial (drinking after a meal) drinking. As shownpreviously, NaCl intake was highest for 0.15 M NaCl and declinedat both stronger and weaker concentrations. Variations in drinkingbout number and duration determined amount consumed. Drinkingbout duration was highest for 0.2 M NaCl then declining progressivelyat both stronger and weaker concentrations. The number of drinkingbouts was highest for 0.04 M NaCl, a concentration slightlyabove the adapting salivary sodium concentration, declininglinearly thereafter with stronger NaCl concentrations. The availabilityof NaCl solution influenced the amount of food consumed, aswell as the number and duration of food bouts. Food bout numberwas highest in the presence of the weakest 0.01 M NaCl solution,while food bout duration was highest in the presence of hypertonicNaCl concentrations. Most switching behavior occurred betweenmeal consumption and drinking and little between drinking fluids.When 0.01–0.08 NaCl solutions were available, the ratsdrank saline after a meal; when hypertonic 0.3–0.4 M NaClsolutions were available, they drank water after a meal. Inthe presence of intermediate NaCl concentrations (0.15–0.20),the choice of fluid consumed after a meal was more equivocalto the extent that there was increased switching between waterand saline and vice versa. The significance of these differencesin the micromolar features of eating and drinking are discussedin relationship to taste and postingestional control mechanismsof ingestion.     

The stimulation of food intake by selective agonists of mu, kappa and delta opioid receptors

It is known that under some conditions the administration of opioid agonists will stimulate food intake. However, the lack of receptor selectivity of some of the agonists which produce this effect leaves open the question of which receptor types are actually involved. In the experiments presented here, rats were given intracerebroventricular injections of Dynorphin 1-17 (DYN), [D-ala2MePhe4,-Gly-ol5]enkephalin (DAGO), and [D-ser2, leu5]enkephalin-thr6 (DSLET); these peptides are thought to be selective agonists at kappa, mu and delta opioid receptors, respectively. All three peptides stimulated food intake in non-deprived rats at doses in the 3-10 nmol range; water intake was also increased in some cases. Generally, DYN stimulated feeding at a lower dose than DAGO or DSLET and the magnitude of the effect tended to be greater. On the other hand, DAGO more consistently increased water intake. In some cases, DYN also caused episodes of "barrel-rolling" and postural abnormalities, whereas DAGO had sedative and/or cataleptic effects. These results are interpreted as an involvement of more than one opioid receptor types in the regulation of appetite, possibly with separate opioid systems contributing to food and water intake.     

Effect of oral contraceptives on the rat brain and pituitary opioid peptides

This study was designed to explore the hormonal regulation of CNS opioid peptide levels in female Sprague Dawley rats. Forty-eight animals were divided into 2 equal groups for acute and chronic studies. Each group was further divided into 4 subgroups, each containing 6 animals. Each rat in the control group received an inert pill (in 0.25 ml corn oil daily by gavage); the second group, 15 micrograms norethindrone (NE, a potent progestin present in the oral contraceptive Micronor); the third group, 15 micrograms NE and 1 microgram ethinyl estradiol, EE2 (present in the oral contraceptive Modicon) and the fourth group, 10 times the dose of the third group. Rats were treated either acutely for 5 days or chronically for 7 weeks. Opioid peptides were estimated by radioimmunoassay. Acute administration of 150 micrograms NE + 10 micrograms EE2 decreased the levels of methionine-enkephalin (ME), leucine-enkephalin (LE), dynorphin (DYN) and beta-endorphin like immunoreactivity (beta-EI) by about 50% in the pituitary. The same dose on chronic administration also decreased DYN, but increased the levels of ME and LE in the pituitary by 331 and 69%, respectively. In the hypothalamus, chronic administration of NE + EE2 increased the level of ME (155%) and LE (87%) as well as of DYN (97%). In the striatum, the levels of LE (33%) and DYN (115%) were elevated during chronic administration. It is concluded that the acute administration of NE + EE2, in general, reduces the levels of ME, LE, DYN and beta-EI.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hunger on the drinking behaviour of rodents adapted for mesic and xeric environments

Observations of drinking behaviour were taken on six rodent species during fasting. Four of these species were wild-caught and had not previously been examined for food deprivation polydipsia (FDP). These data support an hypothesis that a negative correlation exists between water availability in the natural habitat and the occurrence of FDP. Namely, xerophilous species exhibit an absolute polydipsia during food deprivation while mesically adapted species evidence depressed water consumption. Urine analyses during food deprivation indicated substantial decreases in electrolyte and osmotic pressure concentrations in all species. The drinking patterns of the three desert species investigated are discussed with reference to the availability of green vegetation in the natural habitat; however, there is presently no explanation for the observed polydipsia.