Reactivity to aversive stimuli as a function of alterations in body weight in normal and gonadectomized female rats

Two studies compared the quinine aversion and shock thresholds of intact and gonadectomized female rats. Using food deprivation to modify body weight, the first study measured the reactivity of gonadectomized and intact rats at the same weight level and compared their behavior to a food deprived, but heavier, gonadectomized group. While maintained at the same weight levels, no differences in either shock thresholds or quinine aversion were found between gonadectomized and intact animals. The heavier gonadectomized group showed decreased reactivity on both measures. The second study manipulated body weight with gonadal hormones. Estrogen and the combination of estrogen and progesterone maintained the body weight of gonadectomized rats at the level of the intact control group. During this period the reactivity of both estrogen injected groups was not different from the control group. Progesterone had no effect on weight gain and the progesterone injected group did not differ in reactivity from an oil injected gonadectomized group. Both the progesterone and oil injected gonadectomized groups were heavier and showed less reactivity to both shock and quinine. These results were interpreted as direct support for previous work suggesting that the effects of alterations in gonadal hormones are mediated by the weight changes attendant on hormone level changes and are not direct effects of gonadal hormones, themselves.     

Postneonatal testosterone treatment fails to alter hormonal regulation of body weight and food intake of female rats

Daily injections of testosterone propionate (2 mg/da) from 30–50 days of age failed to affect any of the aspects of food intake or body weight that have previously been shown to be altered by a single dose of testosterone during the first five days of postnatal life. Specifically, postneonatal testosterone did not: (1) increase body weight; (2) reduce the sensitivity of weight control mechanisms to estradiol; or, (3) enhance the sensitivity of these mechanisms to testosterone. These results support the position that the sensitivity of these regulatory mechanisms to gonadal hormones is organized prior to puberty.     

Sex differences in the activational effects of gonadal hormones on food intake and body weight

Estrogens have been shown to decrease, and androgens to increase body weight (BWt) of guinea pigs (GPs). The magnitude of the BWt sex difference shown by intact adult GPs is due primarily to these concurrent, or activational, effects of gonadal steroids. However, a small but significant sex difference in BWt persists in animals gonadectomized at birth, indicating that early hormonal exposure may permanently influence certain steroid sensitive weight regulatory mechanisms in the two sexes. Three experiments were therefore designed to investigate the short term effects of estradiol and testosterone on food intake (FI) and BWt of gonadectomized adult male and female GPs. In the first experiment, GPs gonadectomized in adulthood were given a single injection of 6 micrograms estradiol benzoate (EB). Although EB treatment reduced FI and BWt of both females and males, significantly larger reductions occurred in females. In the second experiment, GPs gonadectomized at birth received treatments of oil or 2 micrograms EB for 7 days. EB treatment also produced significantly larger effects on FI and BWt in the neonatally gonadectomized females. The third experiment involved GPs gonadectomized as adults who were injected with either oil or 1 mg/day testosterone propionate in oil (TP) for 32 days. Compared to changes in oil injected controls, TP produced significantly larger increases in male BWt than female BWt. Therefore, although GPs show only minor sex differences in BWt which might relate to prenatal gonadal hormonal exposure, significant sex differences remain in their responsiveness to the activational effects of gonadal steroids on FI and BWt in adulthood.     

Eating as a function of body weight and of hours deprivation

Five pigeons were allowed one hour of access to food after variable intervals of deprivation averaging 23 hours. Five other pigeons were allowed one hour of food after fixed 23 hour intervals. It was found that the amount eaten by birds in an environment continually alternating between deprivation and one-hour ad lib feeding could be better predicted as a linear function of their body weights than as a 2nd degree polynomial function of the number of hours they were deprived.     

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.     

Sexual dimorphism in the regulation of caloric intake and body weight of rats fed different diets

Female, androgenized female (AF), and male rats were given access to 1 of 3 diets—chow (C), high-dextrose (D-chow:dextrose, 2:1), and high-fat (F-chow:Crisco, 2:1) for 2 months. Caloric intake (CI), water intake, and body weights were monitored daily. Responses to gonadectomy and a single injection of estradiol benzoate (EB) were also studied. For females, F- and C-fed rats had comparable CI's, whereas D-fed rats chronically ate much less. For males, F-fed rats overate, whereas C- and D-fed rats had comparable CI's. The pattern of CI of AF rats fed the 3 diets was intermediate between that of males and females. Male rats were less responsive to the anorexic effects of EB than were the other two groups, and the F-diet potentiated the anorexic effects of EB in all three groups. Results are discussed in terms of a sex difference in the hypothalamic regulation of feeding behavior which is modulated by gonadal hormones.     

Salicylate as a partial inhibitor of emotional fever and body weight set-point in rats: behavioral and neuroendocrine study

In this article, we report findings from behavioral and neuroendocrine experiments in rats under pharmacologically induced antipyretic conditions. Endpoints included emotional fever, body weight setpoint, and in situ corticotropin-releasing hormone mRNA (CRHmRNA) expression. Nine male Wistar rats were treated with acetylsalicylic acid (ASA) 0.04 g/kg ip in vehicle. On alternating days, all rats received saline (0.9% w/v) as a control. ASA was selected chiefly for its antipyretic and also for effects on metabolism. It has been demonstrated that gentle handling affects body weight and body temperature in rats. In Experiment 1, we investigated whether blocking emotional fever by ASA treatment would inhibit the lowering of the body weight setpoint induced by handling of the rats. Rats were exposed to a daily food-hoarding session under handling stress, and their body weight setpoints were calculated from the hoarding measurements. As rats received ASA and saline in an alternating manner, two setpoints were calculated. In Experiment 2, we performed neuroendocrine analyses of CRHmRNA expression in the same group of animals from Experiment 1. CRHmRNA was determined by in situ hybridization. Results indicated that ASA treatment in rats significantly decreased the body weight setpoint (P=.02) and significantly prevented increases in body temperature due to emotional fever (P=.03) when compared to their control values. Findings also revealed that hypothalamic CRH expression was increased when rats were treated with ASA. ASA did partially block fever induced by handling, but it is difficult to confirm whether emotion was also inhibited by treatment. Taken together, these results indicate that salicylates affect energy balance and might be a good inhibitor of body weight gain in rats.     

Schedule-induced drinking and other behavior in the rat, as a function of body weight deficit

Six rats were presented with food according to a fixed time 60-sec schedule at 80%, 90% and 100% of their initial ad lib body weight, and with food freely available in the home cage. Water was available at all times. Amount of water consumed during test sessions, time spent drinking, number of bouts of drinking, and bout duration of drinking varied inversely with body weight. Visiting the food tray also varied inversely with body weight, while grooming varied directly. In rats fed ad lib in their home cages, more water was drunk when pellets were intermittently scheduled than when the same number of pellets was freely available in a session of equal duration, but time spent grooming did not vary significantly. Thus, drinking is schedule-induced in satiated rats, but grooming is not. It is suggested that the primary effect of satiation is to reduce drinking, and that grooming increases secondarily to fill the time vacated by drinking.     

Paraventricular nucleus lesions in weanling female rats result in normophagia, normal body weight and composition, linear growth and normal levels of several plasma substrates

Female weanling rats received small (1 mAmp for 5 sec) electrolytic lesions in the paraventricular nuclei. Sham-operated rats served as controls. The rats were maintained for 42 days and body weight, linear growth, Lee Index, food intake and efficiency of food utilization were determined throughout the study. Plasma glucose, glycerol, free fatty acids, total protein and carcass fat and protein were determined at sacrifice. There was no significant difference between the lesioned and the sham-operated rats in any of the parameters measured. The findings are interpreted to mean that the PVN of the weanling rat is not functionally mature or alternatively, that there exists a sex difference in weanling rats in response to PVN lesions.     

Sexual dimorphism in passive avoidance behavior of rats: Relation to body weight,age, shock intensity and retention interval

Female rats were inferior to age- and weight-matched males in the retention of a step-through type passive avoidance response 24 and 48 hr after the learning. This sex difference could be observed at different intensities of foot shock which was used as aversive stimulus during the single learning trial. Additionally, unlike in males, retention of the passive avoidance response in the females was not the function of shock intensity. Male and female rats, however, showed similar passive avoidance if tested immediately after the learning trial. The results suggest the existence of sexual dimorphism in memory processes.     

Influence of a diet rich in fish oil on blood pressure,body weight and cardiac hypertrophy in spontaneously hypertensive rats

Summary The effects of a diet rich in fish oil on arterial blood pressure, body weight, left ventricular weight and heart rate have been investigated in 8 month old spontaneously hypertensive male rats (SHR) as compared to age-matched hypertensive controls. A diet containing 10% fish oil decreased blood pressure by about 40 mmHg within 20 days of starting the experiment, and this effect persisted over the observation period of 80 days. Permitting the animals free access to food, the body weight of the diet group increased by 25%. The degree of hypertrophy as evaluated by relating left ventricular weight to tibial length was significantly reduced (10%) in the diet fed group. Heart rate was increased by 53%. The study demonstrates that a diet rich in fish oil can lower arterial blood pressure over several weeks without a recognizable loss in function despite a considerable increase in body weight. It can be assumed that a more marked regression of left ventricular hypertrophy is counteracted by a reflex increase in sympathetic efferentation to the heart.