Naloxone suppresses food/water consumption in the deprived cat

Food cravings, endogenous opioid peptides, and food intake: a review

Extensive research indicates a strong relationship between endogenous opioid peptides (EOPs) and food intake. In the present paper, we propose that food cravings act as an intervening variable in this opioid-ingestion link. Specifically, we argue that altered EOP activity may elicit food cravings which in turn may influence food consumption. Correlational support for this opioidergic theory of food cravings is provided by examining various clinical conditions (e.g. pregnancy, menstruation, bulimia, stress, depression) which are associated with altered EOP levels, intensified food cravings, and increased food intake.

Feeding and drinking behavior problems

The physiologic and behavioral basis of normal canine and feline feeding is given in detail. Abnormalities of ingestive behavior include obesity and anorexia in both species, flank or blanket sucking in Doberman Pinschers, coprophagia and stone chewing in dogs, and wool chewing in cats. Drinking behavior is discussed briefly, and the abnormalities of hypernatremia (a failure of thirst) and psychogenic polydipsia and polyphagia are reviewed.

The opioid antagonist, MR2266, specifically decreases saline intake in the mouse

The effects of the opioid antagonist, Mr2266 [(-)-(1R,5R,9R)-5,9-diethyl-2-(3-furyl-methyl)-2'-hydroxy-6,7-benzomo rph an] on the intake of water and saline (0.9%) were investigated in the mouse, deprived of water for 24 hr. In an attempt to evaluate motor functions, the behavior after treatment with Mr2266 was also examined by using multi-dimensional behavioral analyses. Although smaller doses (1.0, 3.0 and 10.0 mg/kg) of Mr2266 failed to affect significantly the intake of water, a larger dose (30.0 mg/kg) elicited a significant attenuation in the intake of water. During a 30 min observation, Mr2266 (30.0 mg/kg) depressed markedly linear locomotion, while other behavioral responses, such as rearing and grooming, remained unchanged. In contrast, 1.0-30.0 mg/kg doses of the drug produced a significant reduction in the intake of saline. The drug Mr2266 had no significant effects on the latency to start drinking at any doses tested. These results suggest that Mr2266 specifically blocks the intake of saline of the mouse through the mediation of opioid systems.

Apomorphine markedly potentiates naltrexone-induced hypodipsia in the rat

This article describes the effects of apomorphine on naltrexone-induced decreases in water intake of the rat deprived of water for 24 h. Apomorphine alone at reasonable doses (0.03, 0.1, 0.3 and 1.0 mg/kg) failed to affect water intake of the rat, but a higher dose (3.0 mg/kg) abolished water intake completely, accompanied by marked stereotypy. Naltrexone (0.1, 1.0 and 10.0 mg/kg) produced a dose-dependent reduction in water intake. A 0.3-mg/kg dose of apomorphine which is considered to activate preferentially presynaptic dopamine autoreceptors enhanced markedly naltrexone (1.0 and 10.0 mg/kg)-induced decreases in water intake. Only apomorphine at 1.0 mg/kg caused a significant prolongation of the latency to start drinking. Apomorphine (0.3 mg/kg), naltrexone (0.1, 1.0 and 10.0 mg/kg) or their combinations did not produce a marked effect on locomotor activity in the rat. These results suggest that apomorphine is capable of potentiating naltrexone-induced decreases in water intake through the mediation of presynaptic dopamine autoreceptors without causing motor dysfunction.

Failure of naloxone to attenuate fasting induced hyperphagia in broiler chicks

Subcutaneous administration of naloxone at 1 to 10 mg/kg produced a dose-related decrease in feed intake of broiler chicks. Food deprivation for 3, 6, 12, and 24 hours produced a significant increase in feed intake compared to non-food deprived birds. Subcutaneous administration of naloxone at 1 to 10 mg/kg failed to attenuate hyperphagia of broiler chicks, deprived of food for 12 hrs. These data suggest that opiate receptors are involved in the regulation of spontaneous feeding behavior in broiler chicks. However, in contrast to other mammals and pigeons, a mechanism, other than endorphinergic system, not sensitive to naloxone blockade, might be involved in food deprivation induced hyperphagia in broiler chicks.

Suppression of deprivation-induced water intake in the rat by opioid antagonists: central sites of action

The effects of naltrexone methobromide, a quaternary derivative of the opioid antagonist naltrexone, were investigated on deprivation (24 h)-induced water intake in the unilaterally cannulated rats. Naltrexone methobromide reduced post-deprivational water intake with an ED50 of 7.3 micrograms when tested at 30 min (peak effect) after intracerebroventricular administration. It also dose-dependently (0.3-10 micrograms) depressed water intake, with peak effects at 15 min, after microinjection into the paraventricular hypothalamic nucleus and into the supraoptic hypothalamic nucleus. The drug did not produce any other effects on behaviors. The ED50S were 1.4 micrograms when given into the paraventricular nucleus, and 3.3 micrograms when given into the supraoptic nucleus, respectively. Although injections of higher doses (1.0, 3.0 and/or 10 micrograms) of the drug into the preoptic area, zona incerta, and corpus callosum significantly suppressed water intake, other behavioral manifestations, such as rotational behaviors, convulsions, body shakes, head swaying, and/or backward locomotion were manifested simultaneously with the reduction in drinking. When injected into the lateral hypothalamic area, water intake was not significantly affected by the drug. These findings suggest that the paraventricular and supraoptic hypothalamic nuclei are important sites of action in the naltrexone-induced suppression of water intake.

Drinking and subsequent suppression of vasopressin is unaltered by naloxone in dogs

The effect of the opioid antagonist naloxone on drinking and the subsequent suppression of plasma vasopressin were evaluated in seven dogs following 24 hr of water deprivation. Each animal underwent an intravenous injection of vehicle as a control and a low (0.05 mg/kg) and high (1 mg/kg) dose of naloxone. Plasma vasopressin was significantly (p less than 0.05) increased from a control value of 4.6 +/- 1.9 microU/ml to 9.9 +/- 3.1 microU/ml after the high dose of naloxone. Fluid intake was not altered by naloxone; 42 +/- 6 ml/kg for the control, 45 +/- 8 ml/kg at the low dose, and 49 +/- 7 ml/kg for the high dose. Six minutes after the onset of drinking vasopressin was reduced by 48% for the control, 41% for the low dose and 45% for the high dose, with no significant difference among treatments. Thus, in dehydrated dogs naloxone presumably blocks endogenous opioids, elevates vasopressin following dehydration, but does not affect drinking behavior or the subsequent suppression of vasopressin after drinking.

Naloxone and fluid consumption in rats: dose-response relationships for 15 days

Rats were given daily intraperitoneal injections of 10.0, 1.0, 0.1, 0.01, 0.001 or 0.0 mg/kg naloxone for 15 days. Each day after the injections, animals were allowed access to a 20% sucrose solution for two hours and to tap water for the subsequent 10 hours. Consumption of the sucrose solution by the group that received 1.0 mg/kg was reliably decreased on Day 1 and 2, reflecting the suppressive effect of naloxone at that dose. By Day 3 until the end of the experiment, however, the suppression was no longer significant, suggesting that tolerance had developed. A similar effect was seen with the group given the highest dose, 10.0 mg/kg; although drinking was significantly less than the control in each of the 15 sessions, this group showed a trend to increase intake over the days of the experiment, thus also indicating possible tolerance to the effect of naloxone. Drinking patterns of the other groups did not differ statistically from the control. Thus, the low doses had no ability to suppress consumption, and the lowest dose that did lower it soon lost that ability; the highest dose continued to suppress drinking throughout the study but with decreasing efficacy. High performance liquid chromatography (HPLC) demonstrated that the naloxone remained intact over the 15 days of the experiment, supporting the suggestion that tolerance to naloxone might have developed.

Naloxone induced suppression of feeding in tigers

Naloxone suppresses, but does not eliminate feeding in Siberian tigers. Naloxone administration paired with novel foods appeared to induce emesis.

Opioid modulation of ingestive behaviors in woodchucks and racoons

We have examined the effect on feeding of opioid blockade with naloxone in two species which demonstrate a marked seasonality in their feeding patterns, the racoon (Procyon lotor) and the woodchuck (Marmota monax). Naloxone suppressed food intake in the woodchuck which is a true hibernator. Naloxone failed to suppress food intake in the racoon and, in fact, enhanced intake of a preferred sucrose solution. In the racoon, ir-dynorphine concentrations were extremely high in the hypothalamus compared to the values obtained in rats and woodchucks. We suggest that possible explanations for the lack of responsiveness to opiates in racoons may be their extremely high daily food intake relatively to body mass when compared to woodchucks and rats and the high levels of ir-dynorphin may be sufficient to overcome the inhibitory effect of naloxone. These studies stress the occurrence of species diversity in the response to opioid antagonism.

Effects of intracerebroventricular injection of naloxone on operant feeding and drinking in pigs

Operant feeding and drinking to satiation were studied in prepubertal pigs deprived of food or water for 18 hours and then given intracerebroventricular (ICV) injections of a solution of naloxone hydrochloride. In feeding tests there was no difference in the amount of food consumed, or in the rate at which reinforcements were obtained, between pigs given ICV injections of 0.4 or 0.8 mg naloxone and those receiving a control injection of saline. However, in drinking tests, injection of both 0.2 and 0.4 mg naloxone significantly (p less than 0.01) reduced the quantity of water drunk and slowed the rate at which reinforcements were obtained. No significant effects on operant water intake were seen after intravenous injection of 0.4 mg naloxone.

Suppression of food and water intake after intracerebroventricular infusion of morphine and naloxone in rabbits

The effect of intracerebroventricular infusion of morphine and naloxone on food and water intake was investigated in rabbits. Morphine hydrochloride at a dose of 120, 10 and 5 micrograms produced statistically significant suppression of 24-h food and water intake. The same effect ensued after infusion of naloxone at dose of 120 and 10 micrograms. Postmorphine aphagia was accompanied by a rise in blood free fatty acids and normal glucose levels. No changes were seen after naloxone.

Effect of naltrexone on food intake and hoarding in white-footed mice (Peromyscus)

Increases in food consumption and hoarding in mammals have been shown to be immediate and preparative adjustments to the energetic stresses of temperate winters. The sensitivity of these behaviors to the opiate antagonist naltrexone was tested in non-deprived white-footed mice (Peromyscus leucopus). Mice received naltrexone hydrochloride intraperitoneally (10 mg/kg in saline vehicle) once daily for four consecutive days subsequent to an equivalent period of injection with saline as control. Daily food intake was significantly (p less than 0.05) lower after naltrexone treatment. Hoarding, as assessed by logarithmic hoarding scores and the weight of cached food, was not affected by administration of this drug at this dosage. These results suggest that hoarding, a complex behavioral pattern that does not immediately affect internal energy stores, may not fall within the opiate regulatory scheme.

Naloxone suppresses fluid consumption in tests of choice between sodium chloride solutions and water in male and female water-deprived rats

The effects of naloxone on fluid consumption by water-deprived rats trained to choose between a saline solution and water in a 15-min drinking test were examined. Rats of each sex were allocated to three groups and given access to 0.125% NaCl, 0.6% NaCl, and 1.7% NaCl, respectively, as the alternative to water. Under control conditions they drank substantially more of the hypotonic salt solutions than water, but drank slightly more water than hypertonic salt solution. Naloxone generally reduced fluid consumption, dose-dependently (0.01-10 mg/kg). In the cases of the two hypotonic solutions, the suppressant effect of naloxone was limited to saline solution. The usually low levels of water consumption were unaffected. In the case of the hypertonic solution, naloxone suppressed salt and water intakes by equivalent amounts. The effects of naloxone in the tests with the two higher salt concentrations depended upon sex. There was on example of a significant naloxone-induced reduction in saline preference (females; 0.125% NaCl v H2O). In other instances, saline preferences were not significantly modified. The results are briefly discussed in relation to current suggestions that naloxone may affect fluid consumption in ways which are taste-dependent (e.g., taste sensitivity, palatability, reward). An alternative view is also considered, that the effects of naloxone may be taste-independent, at least in the particular case of drinking in a two-choice test with saline and water.

Modulation of deprivation-induced food intake by D-phenylalanine

D-phenylalanine has been shown to possess opiate-like effects upon pain perception. The present study examined whether it would have similar opiate-like effects upon food intake in deprived rats. The first experiment demonstrated that food intake of rats deprived for 24 h prior to injection was significantly reduced for 2 h following a 250 mg/kg dose of D-phenylalanine. However, intake over a 24 h period following injection was significantly increased following a 125 mg/kg dose of D-phenylalanine. The second experiment revealed that 0.3, 1.0, 3.0 and 10.0 mg/kg doses of naloxone dose-dependently reduced intake for 2 h in deprived rats when paired with a vehicle injection. However, the inhibitory actions of the two lower naloxone doses were significantly attenuated when paired with an injection of a 250 mg/kg dose of D-phenylalanine. These results are discussed in terms of whether D-phenylalanine possesses direct or indirect opiate-like effects upon ingestion.

Patterns of drinking in the rat following the administration of opiate antagonists

Durations of drinking were recorded for water-deprived rats as they drank to satiety, following SC injections of naloxone (0.1-10.0 mg/kg), naltrexone (0.1-10.0 mg/kg) or saline vehicle. The results provided evidence for the effects of opiate antagonists on the temporal pattern of drinking exhibited by water-deprived animals. A separate, time-sampling procedure was used to supplement the drinking duration data, and showed that the opiate antagonists may suppress water consumption during a period 2.5-7.5 min after the start of the initial drinking bout. A second experiment confirmed that the pattern of drinking displayed during schedule-induced polydipsia in the rat is resistant to any suppressant effect of a moderate dose of an opiate antagonist. The similarity between opiate receptor blockade and water preloading in their effect on drinking in response to water deprivation, and lack of effect on schedule-induced polydipsia is discussed. Opiate antagonists may affect drinking principally by imposing a thirst satiety signal.

Hormones and feed intake

During the several decades that hormones have been considered for roles in the control of feeding, certain ones have gained special attention, although the role assigned to any one hormone has varied from time to time. Three classes of hormones have been considered in this review: gastrointestinal, brain, and pancreatic. Of these classes, two have obtained the most compelling evidence for a physiological role in the control of feeding. CCK, an intestinal and brain hormone, appears to be involved in satiety. Glucagon of pancreatic origin appears also to play an important role in satiety. These hormones, when sequestered by a specific antibody, cause a delay in satiety and thus increase food intake. Insulin, another pancreatic hormone, has been considered for several roles in the control of feeding. Recently, attention has been given to the possibility that insulin of the CSF provides an integrated link between the metabolic state of the adipose tissue and the brain structures concerned with the control of feeding. Thus, insulin may be a primary hormone involved in the maintenance of energy balance or of body-weight. Finally, brain opiate peptides, e.g. dynorphin, are very likely involved in the transmission of information concerned with the interaction of feeding and maintenance of energy balance. Clearly, hormones play primary roles in the control of feeding behaviour and the regulation of energy balance, but much remains to be done to establish their specific actions or components of the associated physiological systems.

Opioid modulation of appetite

The discovery of opiate receptors and endogenous opioid peptides within the central nervous system has resulted in a number of speculations concerning the physiological significance of these peptides. In the present article, we review the evidence suggesting a primary role for some of the opioid peptides as regulators of ingestive behavior. In particular, we elaborate a hypothesis in which we suggest that in some species opioid peptides may play a role as a tonic inducer of ingestive behaviors, held in check by a variety of neuropeptides and monoamines. This review explores in detail the role of the opioid peptides as major mediators of the reward system and as a link between reward and feeding behaviors. Finally, a teleological role for opioid peptides in species preservation, which may explain the discrepancies in the role of the opioid peptides in feeding behavior in different species is proposed. It is suggested that the feeding profile of the animal provides important clues as to whether or not the animal has an opiate-sensitive feeding system. We stress that interactions with ingested nutrients and the milieu interieur provide an important means by which animals modulate the opiate-entrained feeding drives.

Naloxone blocks exercise-stimulated water intake in the rat

To examine whether opiate receptors modulate exercise-induced water intake, we measured water intake during four consecutive hours after a one-hour swim stress in male, Sprague-Dawley rats. Increased cumulative water intake was found four hours following exercise and this response was naloxone-reversible (P = 0.06). Suppression of water intake in the naloxone-treated, exercised group was most marked in the first two hours after exercise (P less than 0.05). Non-exercised rats consumed water at a constant, linear rate (P less than 0.05) whether treated with naloxone or saline. These results indicate an endogenous opioid role in regulating exercise-induced water intake in the rat, but do not delineate whether this role reflects a non-specific stress behavior or specific physiological processes related to thirst.

The effect of naloxone on feeding and spontaneous locomotion in the wolf

The effect of naloxone on food intake and activity levels was studied in the wolf (Canis lupus). Naloxone decreased food intake at both the 1 mg/kg and 5 mg/kg dose. There was no quantitative difference in the magnitude of the decrease in food intake produced by naloxone in winter or summer. Wolves ate significantly greater amounts of deer meat than dog chow after naloxone when expressed on a mass basis but there was no difference when the amounts of food ingested were expressed in calories. This suggests a role for endogenous opiates in the regulation of energy intake. The putative satiety factor, cholecystokinin-octapeptide, had no effect on food intake in wolves. Naloxone decreased spontaneous locomotion and increased time spent resting in wolves. The effects of naloxone on activity were significantly more marked in winter compared to summer.

Effects of opiate antagonists and putative mu- and kappa-agonists on milk intake in rat and squirrel monkey

The effects of a number of relatively pure opiate antagonists (naloxone, naltrexone, diprenorphine), and putative mu- (morphine, etorphine) and kappa- (ketocyclazocine, ethylketocyclazocine) receptor agonists on sweetened condensed milk intake were examined over a broad range of doses in non-deprived rats and squirrel monkeys. The antagonists consistently decreased milk intake in both the rat and squirrel monkey. There were, however, species differences: diprenorphine was 30 times more potent than either naloxone or naltrexone in the squirrel monkey, but was of similar potency in the rat. The effects of the opiate agonists were more variable than those of the antagonists. In both species, all agonists decreased milk intake at high doses that also produced behavioral depression. Significant increases in drinking were produced only by low doses of ketocyclazocine and ethylketocyclazocine in the rat. The suppression of milk intake by the antagonists supports a modulatory role of opiate receptors in the control of drinking behavior, however, the effects of the agonists on drinking are less easily interpreted within this conceptual framework.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.

Novel phenylpiperidine opioid antagonists and partial agonists: effects on fluid consumption

The effects of five opioid antagonists, a racemate partial agonist and its agonist and antagonist optical isomers were studied on deprivation-induced drinking. All compounds had a phenylpiperidine nucleus. The antagonists produced dose-related decreases in drinking, and the potencies for decreasing drinking correlated with morphine-antagonist doses. The racemic partial agonist and its agonist isomer decreased drinking at doses higher than those which produced marked analgesia. Within the class of phenylpiperidine drugs studied, some had less specificity than naloxone for the mu-receptors as compared to the delta-receptor, but the suppression of drinking was not related to changes in mu-to-delta ratios.

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 beta-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 in consummatory behavior.

Naloxone alters alcohol drinking induced in the rat by tetrahydropapaveroline (THP) infused ICV

In male rats of the Sprague-Dawley or Long-Evans strain, intracerebroventricular (ICV) cannulae were implanted permanently using stereotaxic techniques. Tetrahydropapaveroline (THP) was infused ICV for up to 14 days either chronically around the clock or acutely once per day in doses previously found to induce an abnormally high intake of alcohol. During these periods, alcohol preference for individual rats was determined by a self-selection procedure in which the concentration of alcohol was increased from 3 to 30% on each day of a 12-day interval. Those rats which displayed a substantial increase in their intake of alcohol were selected for naloxone treatment and subsequently assigned a fixed concentration of alcohol at which maximum consumption occurred. Naloxone was administered subcutaneously two to six times per day for three consecutive days in total daily doses ranging from 1.5 to 3.0 mg/kg. Each rat served as its own control and was given 0.9% saline isovolumetrically according to the same temporal schedule. Naloxone generally suppressed alcohol intake in animals by 20% to 45%, but the reduction in drinking depended upon the injection regimen as well as the prior level of alcohol consumption. In "high drinking" rats, the mean alcohol intake of 6.2 g/kg/day was reduced to 3.7 g/kg/day by naloxone whereas in "low drinkers" the mean intake of 3.5 g/kg/day was suppressed to 2.8 g/kg/day by the opiate antagonist. These results further support the suggestion of a possible opiate receptor link in the pathogenesis and maintenance of aberrant drinking of alcohol, the mechanism of which may involve the endogenous action of an amine-aldehyde condensation product in the brain.