Behavioral consequences of hormonal deprivation on the responsiveness of female rats to estradiol

Female rats which had been ovariectomized either 7 days earlier (short-term deprivation, N = 11) or 35 days earlier (long-term deprivation, N = 11) were tested for their response to treatments of estradiol benzoate (6.0 micrograms/kg body weight) and progesterone (1.2 mg/kg). The long-term deprived females showed less sexual behavior than females deprived for only 7 days prior to treatment. In particular, lordosis quotients after treatment with estradiol alone were significantly lower in the long-term deprived females, t(20) = 3.194, p less than 0.01. Following a supplemental progesterone injection, the lordosis scores and the number of proceptive behaviors displayed by long-term deprived females were also significantly lower than these measures in short-term deprived females, t(20) = 3.481, p less than 0.01 and t(20) = 3.737, p less than 0.01, respectively. In contrast, the two groups did not differ in the degree to which estradiol treatment suppressed food intake, F(1,20) = 2.306, N.S. Likewise, the changes in water intake and body weight produced by estradiol treatment did not differ significantly between the two groups, F(1,20) = 0.118, N.S. and F(1,20) = 0.452, N.S., respectively. The results obtained from the sex behavior tests are generally consistent with the notion that hormonal deprivation alters the responsivity or sensitivity of female rats to estradiol. However, these changes do not appear to involve a general decline in receptor sensitivity or number, because the ability of estradiol to suppress ingestive behaviors was not diminished in the long-term deprived females.     

The effects of liver denervation on food and water intake in the rat

In Experiment 1, liver denervations or sham operations were performed on rats in two separate trials. Food and water intakes and body weights of denervated rats did not deviate significantly from their sham operated controls. Male and female rats responded similarly. In Experiment 2, in addition to daily food and water intakes, initial daily meal size was investigated in two groups of liver denervated and sham operated rats. Initial daily meal size was determined during a one hour test at the start of the dark period of the light:dark cycle. In one group of rats a chow diet was used for testing, while a liquid diet was utilized in the second group. According to the “liver glucoreceptor preabsorptive satiety and general food intake control hypothesis” the denervated rats should have experienced a depression of daily food intake and preabsorptive satiety. No differences were found in either preabsorptive satiety or daily food and water intakes and body weights when denervated rats were compared to sham operated control animals. The results question whether liver glucoreceptors have any detectable influence on the control of feeding behavior. Certainly the data does not support the role of liver glucoreceptors as a major controller of feeding behavior in the rat.     

Effects of stereoisomers of estradiol on food intake, body weight and hoarding behavior in female rats

The effects of 17-alpha and 17-beta estradiol on food intake, body weight and hoarding behavior in ovariectomised rats were investigated. For five days, ten animals received subcutaneous injections of both isomers (10 micrograms/kg/day) in a counterbalanced design. Hoarding tests were conducted on the last three days of each 5-day injection period. 17-Alpha estradiol significantly reduced food intake but was without effect on body weight. 17-Beta estradiol reduced food intake significantly more than the alpha form and also significantly reduced body weight. These differential effects suggest that stereoisomers of estradiol may be acting on separate regulatory systems. The treatments did not change hoarding activity compared to pre-treatment levels.     

The effects of long warm and cold ambient exposures on food intake water intake and body weight in the capsaicin desensitized rat

Seventeen Sprague Dawley rats received, subcutaneously, 250 mg·kg^–1 of capsaicin divided into 10 increasing doses (10–50 mg·kg^–1) and administered on 7 successive days. Nine controls were treated with an isotonic saline solution using the same protocol. The rats spent, in succession, 5 weeks at 20° C, 6 weeks at 33.5° C, 6 weeks at 8° C, 4 weeks at 30° C and, finally, 5 weeks at 20° C ambient temperature. Their mean food intake (FI), water intake (WI) and body weights were recorded daily. In the 2 groups of rats, FI was inversely related to ambient temperature. However, during the first few days of the exposures, FI in treated rats was greater than controls in the warm environment and less in the cold environment. In controls, WI increased linearly with ambient temperature in the warm environment. This relation was not found in treated rats: they drank less water than controls and lost body weight. During the first days at 8° C ambient temperature, rectal temperature decreased in treated rats and two animals died.The results are similar to those described for rats with hypothalamic lesions. They may also be related to a peripheral effect of the drug.This work was supported by the Centre National de la Recherche Scientifique (C.N.R.S. L.A. 181) and by the Institut National de la Santé et de la Recherche Médicale (I.N.S.E.R.M., A.T.P. 80-79-112)     

Behavioral effects of iron deficiency in the adult rat

Adult hooded rats were placed on an iron deficient diet for 2 (Stage 1), 8 (Stage 2) or 12 (Stage 3) weeks. Iron levels were monitored by a number of indices, including hemoglobin concentration, serum iron level, transferrin saturation, total and latent iron binding capacity and brain and liver nonheme iron level. All three dietary conditions yielded depressed hemoglobin levels. The most significant observation was a marked reduction in liver and brain iron levels for Stage 1 animals. All animals were trained on a single trial taste-aversion task. The taste of saccharin solution was paired with either an immediate or delayed intragastric injection of lithium chloride. Memory for the association was measured 24 hr or 4 days after training and was found to be significantly below normal for Stage 1 and not significantly different from normal for either Stage 2 or Stage 3 animals. Learning remained at normal levels and was even enhanced at some stages of deficiency (Stages 2 and 3). Activity levels decreased with increasing iron deficiency. There appeared to be a direct association between memory for the taste aversion task and liver and brain iron levels.     

The ingestion of food and the recovery of body weight following fasting in the naive rat

The total food consumption of experimentally naive rats following 24, 48, 72, and 96 hr fasts was observed during the period of the recovery of body weight. The total amount of food consumed in excess of prefast food consumption was found in all groups to be equivalent to 24 hr intake and was, therefore, independent of degree of fast and body weight lost. Moreover, it was found that rats recover lost body weight following a fast even when intake is held to prefast levels. These findings suggest that the regulation of body weight may be under the control of mechanisms in addition to the control of food intake.     

Food intake, body weight and lordosis in male and female mongolian gerbils: effects of ovarian steroids

The effects of gonadectomy and ovarian hormone treatment on food intake, body weight, and lordosis in male and female Mongolian gerbils were examined. In female gerbils, a significant decrease in food intake and body weight was observed after ovariectomy, with estradiol benzoate (1, 10, or 100 micrograms/day) increasing food intake in a dose dependent fashion. However, the dose of estrogen (1 microgram) that restored food intake and body weight to control levels in ovariectomized animals was lower than that required to elicit maximal sexual receptivity. Progesterone, when given in conjunction with estrogen, significantly facilitated the effect of estrogen on food intake without further altering body weight. In male gerbils, castration produced a significant but transient increase in body weight and a delayed increase in food intake. Unlike female gerbils, male gerbils exhibited no significant alterations in food intake, body weight, or lordosis in response to treatment with ovarian steroids. The present results are compared to those obtained in other species.     

Nocturnal feeding pattern in the prepubertal rat: influence of the ventromedial hypothalamus (VMH)

Daily feeding patterns, food intake and changes in body weight of male and female prepubertal rats were observed across a period from 21 to 50 days of age. Light/dark differences in feeding were found for both males and females throughout the recorded period, with feeding occurring predominantly during the dark period. The light/dark difference in feeding behavior gradually increased as the animals developed. Bilateral lesions placed in the VMH of female rats at 21 days of age disrupted the light/dark differences in feeding behavior primarily by decreasing dark period feeding. These lesions further resulted in a period of hypophagia and retarded body weight gain as well as a delay in pubertal onset. These data indicate that prepubertal rats regulate their feeding behavior so that food intake occurs principally during the dark period and that the integrity of the VMH is necessary for this regulation.     

Flavor,forced choice and deprivation affect corticosterone selection by the adrenalectomized rat

Adrenalectomized rats were given access to corticosterone-supplemented (20 μg/ml) and-unsupplemented saline (0.9% NaCl) in two separate bottles and preferences were measured for each. Half of the rats received corticosterone in maple-flavored saline (MAPLE group), while the other half received corticosterone in anise-flavored saline (ANISE group). Each rat also received unsupplemented saline in the alternate flavor. After an initial preference test, preferences were measured again following a period of forced choice (where rats were given the supplemented saline only) and again following a period of deprivation (where rats were given the unsupplemented saline only). All three independent variables (flavor, forced-choice and deprivation) played roles in determining self-administration of corticosterone. Results from the initial preference test demonstrated that both groups preferred the maple-flavored saline whether it contained corticosterone or not. However, consumption of corticosterone-supplemented saline regardless of flavor increased following both forced-choice and deprivation suggesting that the adrenalectomized rats were controlling their corticosterone levels. Strong negative correlations were found between intake of corticosterone-supplemented saline and body weight suggesting that the adrenalectomized rat may be controlling corticosterone levels based on some correlate of body weight.     

Ovarian influences on food intake and body weight regulation in lactating rats

In the following experiments, an attempt was made to determine the role of the ovary in the control of food intake and body weight regulation during lactation. In the first study, it was found that concentrations of estradiol benzoate effective in suppressing food intake and body weight in nonlactating animals were not effective during lactation. In the second experiment, ovariectomy during lactation was shown not to produce the usual increases in food intake and body weight or change in meal patterns known to occur after ovariectomy in the nonlactating rat. These results suggested that lactating animals behave the as though functionally ovariectomized and that the removal of the ovaries is of no additional consequence. The further observation that animals nursing small litters gained weight considerably more rapidly than animals nursing large litters led to the prediction that these animals would also be more responsive to the suppressive effects of EB. In the third study, EB in concentrations which are not effective in suppressing body weight in animals nursing large litters was found to suppress body weight in mothers with small litters. However, since these animals also showed a decline in milk yield, a number of alternative interpretations of these results were considered. These results, together with data concerning levels of ovarian hormones during gestation and lactation led to the hypothesis that pregnant and lactating animals undergo an elevation in body weight set-point, similar in magnitude and quality to elevations following ovariectomy in the nonlactating animal.     

Melatonin and lighting condition: Absence of long-term effects on food intake and body weight regulation in the albino rat

In contrast to photoperiodic rodents, the nonphotoperiodic laboratory rat's food intake and body weight was unaffected by melatonin treatment (Silastic implants). Constant dark and constant light were equally ineffective as well in disturbing these regulatory behaviors.     

The effects of agouti-related protein gene transfer in vivo by electroporation in mice

In the present study, the cDNA encoding agouti-related protein (AGRP) gene known as an orexigenic factor was transferred in vivo to test whether food intake and body weight gain is improved in mice. When the expression plasmid of AGRP gene driven by mouse β-actin, pActAGRP, was transferred into leg muscle by electroporation, body weight of gene-transferred mice was significantly increased at 14 days and afterwards compared with that of control counterparts (p < 0.05). Likewise, daily food intake was also significantly higher in the AGRP gene-transferred mice than in the control mice at 4 days and afterwards (p < 0.05). A significant increase in serum AGRP concentration of the AGRP gene-transferred group was detected compared with the control group at 1 week (p < 0.01), but the difference quickly disappeared at 3 weeks. However, the hypothalamic NPY mRNA abundance of AGRP gene-transferred mice was significantly higher than that of the control mice at 3 weeks (p < 0.05). These results suggested that instead of hormone administration per se, in vivo AGPR gene transfer into skeletal muscle was found to mimic hormonal effects. The present methodology of in vivo gene transfer by electroporation might be useful to promote growth and food intake in farm livestock as well as experimental animals.     

Sexually dimorphic effects of forced exercise on food intake and body weight in the rat

The food intake (FI), body weight (BWt) and water intake (WI) of adult male and female rats were compared during a seven day period of forced exercise in a treadmill. Work loads for the exercised groups were gradually increased across the seven-day test period, whereas work loads for the sedentary controls were maintained at the same level used during a previous three-day training period. Relative to their respective control groups, male rats showed a decrease in FI and BWt in response to the exercise challenge, but female rats showed an increase in FI sufficient to maintain their BWt at control levels. Both male and female rats showed a reliable increase in WI during the period of forced exercise. These sexually dimorphic changes in FI and BWt in response to forced exercise indicate that female rats are capable of demonstrating a more vigorous defense of BWt than are male rats and suggest that there is a sex difference in the long-term control of feeding behavior in the rat.     

Effects of bulbectomy on hibernation,food intake and body weight in the european hamster,Cricetus cricetus

Bulbectomy was performed on European male wild hamsters in autumn, habitual phase of weight decline and entrance into hibernation. Total bulbectomy suppresses both nest building behavior and hibernation, and is followed by an immediate increase in food intake and obesity. The body weight curve of totally bulbectomized animals is in opposition of phase with that of the controls. Incomplete bulbectomy suppresses nest building behavior but hibernation is present with a diminution of periodic arousals. Hyperphagia starts in spring after the terminal arousal; it is similar to that of the total bulbectomized animals. Anosmic animals do not differ from the control animals.     

Cannabinoid (CB)1 receptor antagonist, AM 251, causes a sustained reduction of daily food intake in the rat

Cannabinoid (CB)(1) receptors are present throughout the nervous system, including several areas implicated in the control of food intake. Central and peripheral administration of CB(1) agonists increase food intake while CB(1) receptor antagonists reduce food intake. However, in some previous studies, tolerance to the anorectic effects of CB(1) antagonists develops within days. To further delineate the role of endogenous cannabinoid signaling in energy intake, we studied the effects of the CB(1) antagonist AM 251 (1.25, 2.5 and 5 mg/kg ip), the anandamide membrane transporter inhibitor VDM 11 (10 mg/kg ip), and the CB(1) agonists anandamide (1 mg/kg ip), and methanandamide (1 mg/kg ip), on food intake. A single administration of the CB(1) antagonist AM 251 significantly reduced food intake for a total of 6 days (P<.05). Reductions in food intake brought about by AM 251 were accompanied by reductions in weight gain for 6 days (P<.05). Contrary to expectations, VDM 11 did not increase food intake in this study. Anandamide was also unable to increase food intake; however, the more stable agonist methanandamide significantly increased food intake 3 h after administration (P<.05). These results support the role of CB(1) receptor antagonists in the treatment of obesity and suggest that the anorectic effect of AM 251 may last longer than previously reported.     

Melatonin and estradiol effects on food intake, body weight, and leptin in ovariectomized rats

OBJECTIVE: The study in ovariectomized (Ovx) rats, as a model of menopausal status, of the effects of melatonin (M) and/or estradiol (E), associated or not with food restriction, on body weight (BW) and serum leptin levels. METHODS: Female SD rats (200-250 g) were Ovx and treated with E, M, E+M or its diluents. Control sham-Ovx rats were treated with E-M diluents. After 7 weeks being fed ad libitum, the animals were exposed for 7 more weeks to a 30% food restriction. We measured: food intake, BW, nocturnal and diurnal urinary excretion of sulphatoxymelatonin (aMT6s), leptin in midday and midnight blood samples, glucose, total cholesterol, LDL, HDL and triglycerides. RESULTS: Day/night rhythm of aMT6s excretion was preserved in all cases. The increase of aMT6s excretion in M-treated animals basically affected the nocturnal period. In animals fed ad libitum, E fully prevented Ovx-induced increase of BW, leptin and cholesterol. Melatonin reduced food intake and partially prevented the increase of BW and cholesterol, without changing leptin levels. Under food restriction, M was the most effective treatment in reducing BW and cholesterol. Leptin levels were similar in M, E or E+M treated rats, and lower than in untreated Ovx rats. CONCLUSIONS: Our result gives a preliminary experimental basis for a post-menopausal co-treatment with estradiol and melatonin. It could combine the effectiveness of estradiol (not modified by melatonin) with the positive effects of melatonin (improvement of sleep quality, prevention of breast cancer, etc.). The possible beneficial effects of melatonin which could justify its use, need to be demonstrated in clinical trials.     

Long-term effects of caudate nucleus lesions on body weight in the rat

Lesions placed bilaterally in the caudate nucleus of albino rats produced only small transient depressions in body weight immediately after the operation. However over the following 240 days the lesioned animals grew more slowly and achieved lower and premature asymptotic weights compared to their matched controls. Logical and empirical considerations mitigate against sensory or motor interruption of feeding as a basis of these changes. Rather striatal influences on mechanisms which regulate and control growth are indicated.     

Effects of guanethidine sympathectomy on feeding, drinking, weight gain and amphetamine anorexia in the rat

Adult female rats that underwent sympathectomy induced by guanethidine treatment (10, 20 or 40 mg/kg) exhibited markedly increased water intake, but did not display significant alterations of either food intake, body weight, or the Lee Index of obesity. Guanethidine treatment did not attenuate amphetamine anorexia as evidenced by comparable dose-dependent reductions in food intake to d-amphetamine sulfate (0.25, 0.50, 1.0, and 2.0 mg/kg) in sympathectomized and control rats. These data are not consistent with the hypothesis that amphetamine anorexia is partially mediated via enhanced BAT thermogenesis.     

Spillage behavior and thiamin deficiency in the rat

Food spillage, food intake and body weight of four groups of adult rats were monitored daily as they were fed varying sequences of deficient, marginal, or high thiamin (B₁) diet. Food spillage was a more sensitive index of the level of dietary B₁ than either food intake or body weight change. Animals fed the deficient B₁ diet exhibited the greatest levels of food spillage followed by the animals fed the marginal B₁ diet. Hypophagia and weight loss occurred only among animals fed the marginal B₁ diet. Feeding the high B₁ diet to animals previously given the deficient and marginal B₁ diets completely eliminated the excessive food spillage, and food intake and body weight returned to control levels. These data support the use of spillage behavior as a useful screening tool for detecting behavioral effects of inadequate nutrient intake or chemical intoxication.