Wet Mash Diet Research Articles

Estradiol suppresses ingestive response evoked by activation of 5-HT1A receptors in the lateral hypothalamus of ovariectomized rats.

The present study investigated the effects of estradiol (E2) on ingestive behavior after activation of 5-HT1A receptors in the lateral hypothalamus (LH) of female rats habituated to eat a wet mash diet. Ovariectomized rats treated with corn oil (OVX) or estradiol cypionate (OVX+E) received local injections into the LH of vehicle or an agonist of 5-HT1A receptors, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT; at a dose of 6 nmol). To determine the involvement of these receptors in food intake, some animals were pretreated with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY-100635, a 5-HT1A receptor full antagonist, at a dose of 0.37 nmol), followed by the injection of the agonist 8-OH-DPAT or its vehicle. The results showed that the injection of 8-OH-DPAT into the LH of OVX rats significantly increased food intake, and the duration and frequency of this behavior. The pretreatment with E2 suppressed the hyperphagic response induced by 8-OH-DPAT in OVX animals. The inhibition of 5-HT1A receptors after pretreatment with WAY-100635 blocked the hyperphagic effects evoked by 8-OH-DPAT in OVX. These results indicate that the activity of LH 5-HT1A receptors could be affected by blood E2 levels.

WAY100635 blocks the hypophagia induced by 8-OH-DPAT in the hypothalamic nuclei

This study examined the influence of pretreatment with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY100635, full 5-HT1A receptor antagonist, 37 nmol) on feeding effects evoked by local injections of 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT, 5-HT 1A and 5-HT 7 receptor agonist, 6 nmol) into the LH and into the ARC of female rats adapted to a wet mash diet (enriched with 10% sucrose), during diestrus or estrus. The results showed that the LH-pretreatment with WAY100635 suppressed the hypophagic effects evoked by 8-OH-DPAT during estrus as well as diestrus. The ARC pretreatment with WAY100635 blockaded the hypophagia evoked by 8-OH-DPAT in estrus rats. The previous treatment with WAY100635 in the ARC also suppressed the feeding duration decrease evoked by 8-OH-DPAT in estrus. The latency to start feeding, the drinking behavior and the durations of other non-ingestive behaviors were not affected by the different treatments, hypothalamic regions (LH or ARC), and/or estrous cycle stages (diestrus and estrus), except for the locomotion duration increase after 8-OH-DAPT in LH-pretreated rats in diestrus. The present findings confirm our previous suggestion that ARC- and the LH-5-HT 1A receptors participate in the serotonergic control of feeding and that these feeding-related serotonergic circuits in LH are affected by ovarian hormones, since the treatment with WAY100635 evoked a hypophagia response during the diestrus phases.

The effects of metergoline and 8-OH-DPAT injections into arcuate nucleus and lateral hypothalamic area on feeding in female rats during the estrous cycle

The present study examined the effects of local injections of metergoline (MET, an antagonist of 5-HT1/2 receptors, 2 and 20 nmol) and 8-hydroxy-2-(di- n-propylamino)-tetralin (8-OH-DPAT, selective 5-HT1A receptor agonist, 0.6 and 6 nmol) into the arcuate nucleus (ARC) and the lateral hypothalamus (LH), on ingestive and non-ingestive behaviors of female rats. These effects were examined during the diurnal periods of diestrus and estrus in rats adapted to eat a wet mash diet (enriched with 10% sucrose) during 1h for 3 consecutive days at the recording chamber. The results showed that 8-OH-DPAT injected into the LH significantly reduced food intake at all doses and both cycle stages, while in the ARC these treatments evoked hypophagia only at the highest 8-OH-DPAT dose and only at the estrous phase. MET administered into the ARC (at all doses) failed to affect food intake during both estrous stages. On the other hand, food intake decreased after injection of both doses of MET into the LH of rats during estrous and diestrus phases. In estrus stage, injections of the higher dose of 8-OH-DPAT into the ARC and into the LH decreased the duration of feeding. Latency to start feeding, drinking, and non-ingestive behaviors were not affected by 8-OH-DPAT or MET treatments in the ARC or the LH in both cycle phases. These results indicated that 5-HT1A receptors participate in the serotonergic control of feeding-related mechanisms located at the ARC and the LH. These feeding-related serotonergic circuits in both areas are possibly affected by ovarian hormones that could increase sensitivity of ARC neurons to the hypophagic effects of 8-OH-DPAT or increase the efficacy of satiety signals that terminate feeding. In addition, the present data indicated that serotonergic inputs do not exert a tonic inhibitory activity on the ARC and the LH feeding-related circuits.

Validation of the DLW method in Japanese quail at different water fluxes using laser and IRMS

In Japanese quail (Coturnix c. japonica; n = 9), the doubly labeled water (DLW) method ((2)H, (18)O) for estimation of CO(2) production (l/day) was validated. To evaluate its sensitivity to water efflux levels (r(H(2))O(e); g/day) and to assumptions of fractional evaporative water loss (x; dimensionless), animals were repeatedly fed a dry pellet diet (average r(H(2))O(e) of 34.8 g/day) or a wet mash diet (95.8 g/day). We simultaneously compared the novel infrared laser spectrometry (LS) with isotope ratio mass spectrometry. At low r(H(2))O(e), calculated CO(2) production rate exhibited little sensitivity to assumptions concerning x, with the best fit being found at 0.51, and only little error was made employing an x value of 0.25. In contrast, at high r(H(2))O(e), sensitivities were much higher with the best fit at x = 0.32. Conclusions derived from isotope ratio mass spectrometry and LS were similar, proving the usefulness of LS. Within a threefold range of r(H(2))O(e), little error in the DLW method is made when assuming one single x value of 0.25 (recommended by Speakman JR, Doubly Labelled Water. Theory and Practice. London: Chapman & Hall, 1997), indicating its robustness in comparative studies.

Comparison of growth performance, carcass yield and composition, and fatty acid profiles of Pekin and Muscovy ducklings fed diets based on food wastes

Pekin and Muscovy male ducklings were raised on diets based on food wastes. Three feeding systems were offered: commercial pellets (control), partial food waste (PFW) and 100% food waste (FW). For the starting, growing and finishing periods, respectively, the control system provided 25, 23 and 21% crude protein (CP) on a dry matter (DM) basis. The two experimental systems each had a dry pelleted diet and a wet mash diet offered free choice. The PFW system had two rations for the dry diet containing 23 and 22% CP for the starting and growing–finishing periods, respectively, whereas the wet diet had a single ration with 17% CP on a DM basis. The FW also had two forms of diets: dry pellets (18% CP) and wet mash (20% CP). The PFW ducks had higher (P < 0.05) body weights than those of the control system. Both breeds consumed less feed of PFW and FW than those on the control. Feed efficiency was significantly improved for PFW and FW relative to control for both breeds. The birds fed food waste diets consumed higher proportions of fat and less protein. Pekins had higher (P < 0.05) content of skin and fat, whereas the Muscovies had a higher (P < 0.05) content of meat and bone. Both breeds had a preference for wet over dry diets as a percentage of the total feed consumption. Fatty acid profiles of the subcutaneous fat showed significant breed but no feeding system differences. These results suggest industrial food wastes have potential nutritional value as alternative feedstuffs. Key words: Food waste, duck, performance, carcass, fatty acid

Hyperphagia in pre-fed rats following oral δ 9-THC

WILLIAMS, C.M., P.J. ROGERS AND T.C. KIRKHAM. Hyperphagia in pre-fed rats following oral Δ 9-THC. PHYSIOL BEHAV 65(2) 343–346, 1998.—Using a pre-feed paradigm, the effects of orally-administered Δ 9- tetrahydrocannabinol (THC) on low baseline levels of nocturnal feeding were assessed. Following 2-h access to a palatable wet mash diet at dark onset, adult male Lister hooded rats (Charles River) were treated with either sesame seed oil vehicle or Δ 9- tetrahydrocannabinol (0.063, 0.12, 0.25, 0.5, 1.0, or 2.0 mg/kg). One hour later, rats were allowed ad libitum access to standard chow, and intakes were monitored over the subsequent 24 h. Doses of 0.5, 1.0, and 2.0 mg/kg produced substantial hyperphagia during the first hour of testing. Subsequently, rats compensated for their overconsumption so that 24-h intakes were similar in all conditions. The data confirm anecdotal reports of the orexigenic actions of exogenous cannabinoids and suggest a critical role for endogenous cannabinoid systems in the regulation of appetite .

Hyperphagia induced by direct administration of midazolam into the parabrachial nucleus of the rat

Benzodiazepine receptor agonists increase food intake in many different species, yet there has been little investigation of the central site of actions of these drugs on ingestive behaviour. In the present experiments, direct administration of the benzodiazepine receptor agonist midazolam (3–30 μg/μl) into the parabrachial nucleus of the pons significantly increased the consumption of a wet mash diet and a 3% sucrose solution in adult non-deprived rats. The hyperphagic response was blocked by pre-treatment with the selective benzodiazepine receptor antagonist flumazenil. Injection of midazolam into the parabrachial nucleus had no effect on locomotor activity, despite the fact that in the same animals an increase in mash intake was observed following intra-parabrachial midazolam. These data suggest that benzodiazepine receptors located in the parabrachial nucleus may be an important site of action for the effects of benzodiazepines specifically on ingestive behaviour.

Radiofrequency lesions of the PVN fail to modify the effects of serotonergic drugs on food intake

Past research has suggested that the paraventricular nucleus (PVN) of the hypothalamus is an important brain site mediating changes in feeding induced by drugs that modify 5-hydroxytryptamine (5-HT; serotonin) neurotransmission. To test this possibility, several experiments examined the impact of lesions of the PVN on both decreases and increases in feeding following treatment with 5-HT-acting drugs. Rats with free access to standard lab chow were given access also to a wet mash diet for 1 h each day. When intakes of this diet had stabilised, rats were divided into two groups: one group received bilateral radiofrequency lesions of the PVN, the other served as a sham-operated control group. The PVN-lesioned group consumed more lab chow and gained significantly more weight over a 10-week period than the control group. Clonidine stimulated feeding in the sham-operated group, but did not do so in the lesioned group. These findings confirmed that the PVN lesions disrupted the control of food intake, as well as body weight regulation. The indirect 5-HT agonists d-fenfluramine (0.63, 1.25 and 2.5 mg/kg) and fluoxetine (2.5, 5 and 10 mg/kg ), and the 5-HT 1 agonist 1(m-trifluoromethylphenyl)piperazine (TFMPP, 0.63, 1.25 and 2.5 mg/kg) dose dependently reduced the intake of the wet mash diet in sham-operated animals. This action was not modified by the PVN lesions. The highest doses of d-fenfluramine and fluoxetine also suppressed intake of chow over the 23-h period subsequent to the wet mash presentations, but the magnitude of this effect was similar in sham-operated and PVN-lesioned animals. Peripheral injection of the 5-HT 1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 62.5, 125 and 250 μg/kg) stimulated the intake of chow over a 2-h period, and this effect was observed in both sham-operated and lesioned rats. Thus, PVN lesions failed to modify either the feeding suppressant or stimulant actions of drugs that alter 5-HT neurotransmission. These results demonstrate that the PVN is not a critical site mediating the effects of peripherally injected serotonergic drugs on feeding behaviour.

A comparison of the effects of the 5-HT 1 agonists TFMPP and RU 24969 on feeding following peripheral or medial hypothalamic injection

Experiments were conducted to compare the food intake suppressant effects of the 5-hydroxytryptamine (5-HT) 1 agonists 1-3-trifluoro-methylphenylpiperazine hydrochloride (TFMPP) and 5-methoxy-3-(1,2,3,6-tetrahydropyridinyl)1H indole (RU 24969) following either peripheral or medial hypothalamic injections. The effects of these manipulations were examined in 3 different paradigms involving the stimulation of feeding by: (1) infusion of 25 nmol noradrenaline (NA) into the medial hypothalamus, (2) adaptation to a 20 h food deprivation schedule, and (3) the presentation of a palatable wet mash diet for 1 h each day to ad libitum-fed rats. In all 3 paradigms TFMPP and RU 24969 (0.31–5 mg/kg, i.p.) induced dose-dependent reductions of food intake. Both drugs were somewhat less potent at inhibiting feeding that resulted from food deprivation. In contrast to these results medial hypothalamic infusion of TFMPP or RU 24969 (12.5–50 nmol) failed to affect food intake in any of the 3 tests. This occured in spite of the fact that both 5-HT (12.5–50 nmol) and fluoxetine (12.5–50 nmol) mildly attenuated the feeding that resulted from NA infusion into the same site. The results provide clear evidence that the food intake suppressant effects of peripherally injected TFMPP and RU 24969 are not mediated in the medial hypothalamus. They also suggest that even though manipulations of serotonergic function within the medial hypothalamus can alter food intake, this probably does not involve selective activation of 5-HT 1C and/or 5-HT 1B receptors.

Bombesin-induced behavior in infant rats

The behavioral effects of bombesin in 5-, 10- and 20-day-old rat pups have been investigated and the peptide was found to induce scratching (1, 10 mg/kg IP) and grooming (10 mg/kg IP) as early as 5 days after birth. Bombesin did not produce any other overt activities in the developing pups in doses of up to 10 mg/kg, however, lower doses of the peptide (0.1, 1 mg/kg IP) reduced intake of a wet mash diet in deprived 15-day-old rat pups resulting in significant decreases in body weight compared with control animals. These behavioral responses agree with the well-documented effects of bombesin in adult rats and are also in accordance with results from biochemical studies which have shown the existence of receptors for bombesin-like peptides in the rat central nervous system from an early age.

A comparison of the effects of tryptamine and 5-hydroxytryptamine on feeding following injection into the paraventricular nucleus of the hypothalamus

The effects of 5-hydroxytryptamine (5-HT) and tryptamine injected into the paraventricular nucleus of the hypothalamus (PVN) on food intake, and on noradrenaline- (NA) induced feeding were examined. In nondeprived rats, 12.5–100 nmol 5-HT reduced the intake of palatable wet mash diet over a 30-minute period. Tryptamine (50 and 100 nmol) was without effect in this paradigm. However, when tryptamine was injected into the PVN of rats pretreated with the monoamine oxidase inhibitor, pargyline, a strong anorectic effect was observed. The action of tryptamine in pargyline-treated rats was not affected by depletion of 5-HT levels in the PVN with PCPA. This indicates that the effect of tryptamine is not mediated by a release of endogenous 5-HT. Tryptamine injected into the PVN potentiated the effect of a low dose of 5-HT on food intake. This effect may be due to a prolongation of the activity of 5-HT resulting from tryptamine competing with 5-HT for the same reuptake system. Tryptamine and 5-HT attenuated the feeding response elicited by injection of 25 nmol NA into the PVN. Both tryptamine and 5-HT were more potent at attenuating the effects of NA than in reducing the intake of the palatable wet mash diet. Overall, the results suggest that tryptamine may act via the serotonergic system in the PVN to affect food intake, but it is a weaker compound than 5-HT in this respect.

Increased food intake in satiated rats induced by the 5-HT antagonists methysergide, metergoline and ritanserin.

Two series of experiments examined whether 5-hydroxytryptamine (5-HT) antagonists induce feeding in rats. In the first series of experiments separate groups of rats were injected with various doses of methysergide, cyproheptadine, metergoline or ritanserin prior to a 2 h period of access to a wet mash diet which induced vigorous feeding under control conditions. None of the antagonists increased food intake in this paradigm. Rather, at certain doses, methysergide, cyproheptadine and ritanserin induced slight decreases in food intake. Since 5-HT may be involved in controlling satiety, it may be that a more appropriate test of the efficacy of these compounds involves administering them to maximally satiated rats. Consequently, the effects of these drugs were investigated in groups of rats which had fed to satiety immediately prior to drug treatment. In this paradigm methysergide, metergoline and ritanserin, but not cyproheptadine, induced definite increases in food intake. It is suggested that this effect occurs via a dissipation of satiety signals, and that these results further support the hypothesis that 5-HT is involved in controlling satiety. The possibility that these antagonists act on peripheral 5-HT systems is discussed.

Regeneration may mediate the sparing of VMH obesity observed with prior vagotomy.

The extent to which the vagus nerve is involved in mediating the development of obesity in animals with lesions of the ventromedial hypothalamus (VMH) was determined. Female rats were given either VMH lesions or sham lesions 100 days after they had received vagotomy with pyloroplasty, sham vagotomy with pyloroplasty, or sham vagotomy with sham pyloroplasty. For the first 7 postlesion wk, the animals were fed a wet mash diet, then they were maintained on a high-fat diet for 10 wk, and finally they were fed a highly palatable supermarket diet for 4 wk. VMH-lesioned animals with prior vagotomy and pyloroplasty displayed 65% of the obesity observed in lesioned animals with prior sham vagotomy. This expression was increased to 72% of the full VMH obesity during the supermarket diet phase. Assessment of vagotomy suggested that vagal regeneration and, in some cases, recovery of vagally stimulated insulin secretion had occurred. This reorganization may have contributed to the residual obesity expressed in VMH-lesioned animals with prior vagotomy.

Developmental study of adipose cellularity in lateral hypothalamic-lesioned Zucker obese rats.

Ten-week-old lean and obese Zucker rats were sham lesioned or received bilateral, electrolytic lesions of the lateral hypothalamus (LH). They were maintained on a wet mash diet until killing at 15 or 32 wk of age; control lean and obese rats were also killed at 6 and 10 wk. Body composition analyses were performed and adipocyte cellularity of epididymal, retroperitoneal, and subcutaneous depots were calculated. Changes in body composition of LH-lesioned rats, though similar in the two genotypes on an absolute basis, differed on a percentage basis due to the extreme adiposity of the obese rats. Retarded development of protein depots in both lesioned lean and obese rats was apparent at 15 but not 32 wk. Relative to genotypic controls, lesioned lean and obese rats had smaller adipose depots by 32 wk due to decreased adipocyte size in lean rats and reduced adipocyte number in the obese. This genotype-specific response was probably due to the chronic hyperplasia of adipocytes unique to the obese rats. This distinctive developmental pattern of the epididymal depot is discussed.

Weight and regulatory deficits in vagotomized rats: A reexamination

Subdiaphragmatic vagotomy can produce deficits in body weight and regulatory behaviors in rats, but these occur only under specific conditions. Body weight deficits were found in vagotomized male rats eating a liquid diet or a wet mash diet, but did not appear in vagotomized male rats eating pellets. Vagotomized female rats did not show body weight deficits on any of the three diets. However, vagotomized female rats did show a small body weight deficit if access to pelleted food was delayed by 24 hr after surgery. With delayed postsurgical access to food, vagotomized female rats showed no body weight deficits when compared to pair-fed controls. In no case was there a significant reduction in food intake after vagotomy, in contrast to observations made on rabbits. In tests of fluid regulation, female rats were subjected to overnight food deprivation, hypertonic saline injections, or polyethylene glycol injections. Vagotomized female rats consumed less water over a 2-hr period after saline injections, but they failed to show deficits in a 30-min period after saline injections. Further, they showed no deficit on the other two tests. Deficits in body weight and fluid intake regulation reported after vagotomy in rats may be explained most parsimoniously as consequences of gastrointestinal malaise rather than as consequences of metabolic, hormonal, or central neurologic changes.

Dissociation of gustatory and weight regulatory responses to quinine following lateral hypothalamic lesions.

In a two-phase experiment, consummatory (Phase 1) and body weight regulation (Phase 2) responses to quinine adulteration of a wet mash diet were measured in rats recovered from bilateral lateral hypothalamic lesions (LH; n = 16) and in unoperated control rats (C; n = 18). In Phase 1, all rats were fed wet mash adulterated with increasing concentrations of quinine sulfate every other day, and fed unadulterated wet mash on the alternate days. Group LH consumed a significantly lower proportion of quinine-adulterated wet mash relative to unadulterated wet mash, displaying a steeper concentration-response function and a lower rejection threshold than did Group C. In Phase 2, Groups LH and C were maintained exclusively on quinine-adulterated mash for 20 days. This procedure caused equivalent weight loss in the two groups. Therefore, an apparent exaggerated aversion to quinine-adulterated food does not appear to contribute abnormally to the weight regulation exhibited by rats with lateral hypothalamic damage.

Chronically reduced body weight in rats sustaining lesions of the lateral hypothalamus and maintained on palatable diets and drinking solutions.

Male rats sustaining lateral hypothalamic (LH) lesions regulated their body weight at a reduced level when maintained for 1 mo. postlesion upon a wet mash diet. Thereafter, for a period of 84 days, half of these animals were offered a high fat dies whereas the remaining animals continued to receive wet mash. A series of palatable drinking solutions were also offered. Body weight remained at reduced levels relative to intact control animals regardless of the diet offered, even under conditions of high fluid intake generated by the palatable drinking solutions. These results contradict the interpretation of Mufson and Wampler that the lower body weight observed in LH-lesioned animals is secondary to lesion-produced "finickiness" and/or dehydration resulting from hypodipsia. Rather, a primary shift in the set point for body weight appears to underlie the reduced levels of weight maintenance in LH-lesioned animals.

The role of taste preference in the eating behavior of the albino rat

The effects of adding flavoring substances to a standard wet mash diet were tested on twelve male albino rats. The diets, presented singly for ten days each, were 0.15 per cent saccharin sodium, H 2O alone, 0.0375 per cent, 0.075 per cent and 0.12 per cent quinine sulfate. Animals showed intake differences related to diet palatability. Although these differences decrease progressively for the first 8 days there is some evidence that asymptotic steady-state intake would be different for the different diets. Even in the case of achievement of iso-caloric intake across diets, the animal does not ignore taste. This is demonstrated by significant changes in meal-taking which are not attributable solely to total intake differences and, in fact, are greatest at the time that total intake differences are smallest. Specifically, meal size and intermeal-interval size increase as the diet is made less palatable. This change may be necessary for the achievement of stable iso-caloric intake across the diets used in the present experiment. Some implications for finicky animals are discussed.