Food Intake In Hamsters Research Articles

Food restriction attenuates oxidative stress in brown adipose tissue of striped hamsters acclimated to a warm temperature

It has been suggested that the up-regulation of uncoupling proteins (UCPs) decreases reactive oxygen species (ROS) production, in which case there should be a negative relationship between UCPs expression and ROS levels. In this study, the effects of temperature and food restriction on ROS levels and metabolic rate, UCP1 mRNA expression and antioxidant levels were examined in the brown adipose tissue (BAT) of the striped hamsters (Cricetulus barabensis). The metabolic rate and food intake of hamsters which had been restricted to 80% of ad libitum food intake, and acclimated to a warm temperature (30°C), decreased significantly compared to a control group. Hydrogen peroxide (H2O2) levels were 42.9% lower in food restricted hamsters than in the control. Malonadialdehyde (MDA) levels of hamsters acclimated to 30°C that were fed ad libitum were significantly higher than those of the control group, but 60.1% lower than hamsters that had been acclimated to the same temperature but subject to food restriction. There were significantly positive correlations between H2O2 and, MDA levels, catalase activity, and total antioxidant capacity. Cytochrome c oxidase activity and UCP1 mRNA expression significantly decreased in food restricted hamsters compared to the control. These results suggest that warmer temperatures increase oxidative stress in BAT by causing the down-regulation of UCP1 expression and decreased antioxidant activity, but food restriction may attenuate the effects.

Photoperiodic regulation of the orexigenic effects of ghrelin in Siberian hamsters

Animals living in temperate climates with predictable seasonal changes in food availability may use seasonal information to engage different metabolic strategies. Siberian hamsters decrease costs of thermoregulation during winter by reducing food intake and body mass in response to decreasing or short-day lengths (SD). These experiments examined whether SD reduction in food intake in hamsters is driven, at least in part, by altered behavioral responses to ghrelin, a gut-derived orexigenic peptide which induces food intake via NPY-dependent mechanisms. Relative to hamsters housed in long-day (LD) photoperiods, SD hamsters consumed less food in response to i.p. treatment with ghrelin across a range of doses from 0.03 to 3 mg/kg. To determine whether changes in photoperiod alter behavioral responses to ghrelin-induced activation of NPY neurons, c-Fos and NPY expression were quantified in the arcuate nucleus (ARC) via double-label fluorescent immunocytochemistry following i.p. treatment with 0.3 mg/kg ghrelin or saline. Ghrelin induced c-Fos immunoreactivity (-ir) in a greater proportion of NPY-ir neurons of LD relative to SD hamsters. In addition, following ghrelin treatment, a greater proportion of ARC c-Fos-ir neurons were identifiable as NPY-ir in LD relative to SD hamsters. Changes in day length markedly alter the behavioral response to ghrelin. The data also identify photoperiod-induced changes in the ability of ghrelin to activate ARC NPY neurons as a possible mechanism by which changes in day length alter food intake.

Effect of ShanZha, a Chinese herbal product, on obesity and dyslipidemia in hamsters receiving high-fat diet

Aim The present study is designed to investigate the effect of ShanZha ( Crataegus pinnatifida) on obesity or dyslipidemia induced by high-fat diet in hamsters and characterize the role of PPARα in this action of ShanZha. Materials and methods We induced dyslipidemia and obesity in hamsters using high-fat diet and treated hamsters with ShanZha or vehicle for 7 days. We measured the body weight, adipose tissue weights, and food intake of hamsters. Plasma total cholesterol (TC), triglyceride (TG), LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) were determined at the beginning and end of this treatment. Effect of ShanZha on adipogenesis was examined in vitro and change of PPARα was analyzed using Western blot. Results The food intake, body weights, and weights of both brown and white adipose tissues were markedly reduced in hamsters receiving ShanZha as compared with the vehicle-treated control. Plasma levels of TC, TG and LDL-C were decreased by this ShanZha treatment while HDL-C was elevated. The effects of ShanZha were reversed by the combined treatment with PPARα antagonist, MK886. ShanZha inhibited the fat droplet accumulation in 3T3-L1 adipocytes in a dose-dependent manner and this effect was abolished by MK886. Western blot results showed activation of PPARα by ShanZha in hamster adipose tissue. Conclusion We suggest that ShanZha could activate PPARα to improve dyslipidemia or obesity.

The role of histamine 3 receptors in the control of food intake in a seasonal model of obesity: the Siberian hamster

Siberian hamsters develop hypophagia and increase catabolism of fat reserves in response to short photoperiods resulting in a natural loss of body weight in winter. We previously found that histamine 3 receptor (H3R) mRNA in the posterior hypothalamus is significantly decreased in short photoperiods. We hypothesized that this lower expression of H3R might contribute to the winter hypophagic state, therefore we examined the effects of the H3R agonist imetit and inverse agonists clobenpropit and thioperamide on food intake. We expressed the Siberian hamster H3R receptor in vitro and confirmed that imetit, clobenpropit and thioperamide are bound specifically, thus validating them as tools to investigate the role of H3R in vivo. Intracerebroventricular administration of histamine decreased food intake in hamsters in the fat summer state. Administration of imetit to hamsters in the lean state increased food intake, whereas administration of inverse agonists decreased food intake, though this was associated with decreased locomotor activity. Both H3R inverse agonists prevented the nocturnal rise in body temperature indicating additional effects on energy expenditure. In summary, our results suggest that increased availability of central histamine or the reduction of H3R activity decrease food intake. These effects are similar to those observed in hamsters in short photoperiods.

Feeding and behavioural effects of central administration of the melanocortin 3/4-R antagonist SHU9119 in obese and lean Siberian hamsters

Siberian hamsters accumulate fat reserves in long photoperiods, but show a long-term decrease in food intake and body weight when exposed to a short winter photoperiod. The aim of this study was to determine the role of central melanocortin 3/4 receptors (MC3/4-R) in generating this chronic catabolic state by investigating the effects of SHU9119, a MC3/4-R antagonist, on food intake and associated behaviours. In adult male hamsters, intra-cerebroventricular infusions of SHU9119 significantly increased food intake in a dose-dependent manner. The time course of action was slow, food intake being increased between 4 and 24 h after intra-cerebroventricular administration. A similar degree of increase in food intake occurred in fat hamsters in long days and in lean hamsters chronically exposed to short days. Intra-cerebroventricular treatment with MTII (a MC3/4-R agonist) significantly decreased food intake for up to 24 h after treatment, and SHU9119 reversed these suppressive effects between 4 and 24 h after treatment, a similar time course to that observed when SHU9119 was administered alone. We conclude that endogenous melanocortin peptides acting via MC3/4-R are involved in the regulation of food intake in hamsters in both anabolic and catabolic states, but these acute studies do not provide evidence that increased activity of this hypothalamic system underlies the seasonal decrease in food intake that contributes to the long-term catabolic state in short days.

Decrease of food intake by MC4-R agonist MTII in Siberian hamsters in long and short photoperiods.

We investigated the role of the hypothalamic melanocortin system in the regulation of food intake in the Siberian hamster, which shows a profound seasonal decrease in food intake and body weight in short photoperiod (SP). In male hamsters maintained in long photoperiod (LP), intracerebroventricular injection of melanotan II (MTII) just before lights off significantly decreased food intake relative to vehicle treatment over the 6-h observation period. Similar effects were observed in age-matched hamsters after exposure to a short daylength for 9 wk, when body weight had significantly decreased. There was no clear difference in either the magnitude of response or the dose required for half-maximal inhibition of food intake in hamsters in SP compared with those in LP. MTII significantly increased grooming in both LP and SP. Our results indicate that the melanocortin system is a potent short-term regulator of food intake. However, the lack of differential response or sensitivity to MTII treatment in the obese (LP) vs. lean (SP) states does not support the hypothesis that changes in this melanocortin pathway underlie the long-term decrease in food intake that occurs in this seasonal model.

Photoperiod Modulates Torpor and Food Intake in Siberian Hamsters Challenged With Metabolic Inhibitors

Siberian hamsters, Phodopus sungorus, exposed to a short photoperiod (SP) were challenged with 2-deoxy- d-glucose (2DG), which disrupts glycolysis and induces torpor in animals maintained in long photoperiods (LP), or mercaptoacetate (MA), which disrupts fatty acid oxidation. SP decreased rather than facilitated the induction of torpor by 2DG; decreased torpor in response to 2DG coincided with onset of spontaneous torpor in SP hamsters. In contrast, MA induced hypothermia in hamsters kept in SP but not LP, but did not induce full torpor. We conclude that short day lengths do not induce spontaneous torpor by increasing responsiveness to glucose availability; instead, responsiveness to glucoprivation is, if anything, blunted in SP. The occurrence of spontaneous torpor may be unrelated to concurrent metabolic fuel availability. Although 2DG and MA had different effects on thermoregulation in short vs. long day lengths, each treatment decreased 24-h food intake in hamsters in both photoperiods.

Role of fatty acid oxidation in food intake and hunger motivation in Syrian hamsters

We examined the metabolic control of food intake in Syrian hamsters using methyl palmoxirate (MP), an inhibitor of fatty acid oxidation. If fatty acid oxidation plays a role in the control of food intake in hamsters, as it does in rats, it would be expected that hamsters predisposed toward lipid metabolism would increase food intake in response to inhibition of fatty acid oxidation. To the contrary, female hamsters fed a high-fat diet for several weeks and then treated with MP (0.25–100 mg/kg) did not increase food intake relative to vehicle-treated controls. Furthermore, MP treatment did not enhance food intake in hamsters that had been previously food deprived for 12 hr. Consistent with the inhibition of fatty acid oxidation, plasma levels of total ketone bodies and glucose in the MP-treated hamsters were significantly lower than those of the vehicle-treated controls. Thus, treatment with doses of MP which apparently inhibited fatty acid oxidation did not enhance food intake, even after manipulations which predispose the hamsters toward utilization of fat fuels. The control of food intake in Syrian hamsters is in marked contrast to that of rats and other mammals in which the consequences of glucose and fat metabolism interact to signal changes in food intake.

Inhibition of fatty acid oxidation and glucose metabolism does not affect food intake or hunger motivation in syrian hamsters

We examined the interaction of the metabolic fuels, glucose and free fatty acids (FFA), in the control of food intake in Syrian hamsters. Hamsters were treated with a 2-deoxy-D-glucose (2DG) which inhibits glucose utilization, and methyl palmoxirate (MP), which inhibits fatty acid oxidation. The 2DG and MP, alone or in combination did not enhance food intake in hamsters fed a standard rodent chow diet. Determination of the circulating glucose, FFAs, and ketones confirmed that the drugs were having the intended metabolic effects. The 2DG caused marked hyperglycemia and decreased ketones consistent with an inhibition of glycolysis, and the MP caused increased FFAs and decreased ketones indicating inhibition of fatty acid oxidation. A third experiment examined the hamsters' willingness to ingest a diet made highly unpalatable with NaCl, another measure of hunger motivation. Although food-deprived hamsters ingested more of a salt-adulterated diet than did control animals, hamsters treated with MP and 2DG did not. These experiments provide further evidence that the control of food intake in Syrian hamsters is appreciably different than that of laboratory rats.

Absence of clonidine-induced food intake in hamsters

Previous studies support an interaction between noradrenergic and opiate systems in the control of food intake. For example, in both rats and rabbits, food intake stimulated by the noradrenergic agent clonidine is reduced by opiate antagonists. The purpose of the present study was to determine whether or not clonidine stimulated the food intake of non-food-deprived hamsters, a species which appears to lack an opiate-sensitive feeding system. Hamsters fed a chow diet did not increase their food intake when injected with clonidine in doses ranging from 0.05 to 0.25 mg/kg. Furthermore, the animals did not increase their intake of sunflower seeds, a preferred diet for hamsters.

A comparative analysis of feeding and hoarding in hamsters and gerbils

Male and female hamsters and gerbils were randomly assigned to one of three groups. The animals were tested under ad lib feeding conditions or food deprived until they had lost either 10% or 20% of their predeprivation body weight. They were given a 30-min. hoarding test for three consecutive days. The results indicated that although food-deprived gerbils ate more than control gerbils, deprivation had no significant effect on the food intake of hamsters. A sex difference was also evident in the food intake of gerbils; males ate more than did females. Although there was a sex and species difference in the amount of hoarding, deprivation had no significant effect on the amount of hoarding. The implications of these results for of different models of hoarding are discussed. These models contrast hoarding as a defensive response in the regulation of body weight or as an anticipatory activity that is influenced by other selection pressures.

Hoarding versus the immediate consumption of food among hamsters and gerbils

This project dealt with a comparative analysis of the effects of food deprivation on feeding and hoarding in hamsters and gerbils. The animals were given food in their home cage and their food intake was measured during a 30-min period after which they were transferred to an apparatus in which hoarding behaviour was assessed. The results indicated interesting species differences in the animals' reactions in the test situations. Whereas food-deprived gerbils ate more food than nondeprived gerbils, the food intake of hamsters was not significantly enhanced by deprivation. In the hoarding test, although significant differences were observed between deprived and nondeprived gerbils, the absolute level of hoarding in gerbils was very low in comparison to that of hamsters tested under the same conditions. These results suggest that hamsters and gerbils respond to challenges to their food reserves with different strategies.

Basis for the exercise-induced hyperphagia in adult hamsters

In adult female golden hamsters ( Mesocricetus auratus, Waterhouse) voluntary exercise is associated with increased food intake and accelerated somatic growth. We examined the possible interdependence between increased food intake and accelerated somatic growth by measuring food intake in hamsters whose growth was blocked by hypophysectomy. In a 2 × 2 design, hypophysectomized hamsters (HYPOX, n = 20) and animals with intact pituitaries (INT, n = 24) were either allowed to exercise for 35 days (n = 22) or were maintained in sedentary condition (n = 22). Exercise induced increased food intake in both HYPOX and INT hamsters and somatic growth in INT hamsters only. Hypophysectomy was also associated with a 43% reduction in the activity level and a significant increase in the percentage of body fat estimated indirectly. We conclude that adult hamsters increase their food intake in response to some stimulus related to exercise and not to exercise-induced growth.