PubMed Health⌕ Search

Biomedical subjects

D M Nance

Publications and source records attributed to D M Nance.

At least 91 records · Page 5Linked to original sources
PubMed1977

Sex and hormone dependent alterations in responsiveness to caloric dilution.

Potential sex differences in the long-term control of feeding behavior in rats was tested by comparing male and female rats in terms of their responsiveness to a 20 and 40 percent diet dilution challenge. During three-day test periods with both levels of diet dilution, female rats increased their daily food intake (FI) significantly more than did male rats. As a further index of greater precision in the long-term control of feeding behavior by female than by male rats, body weight (BWt) was less affected in female than in male rats during the caloric dilution challenges. In a second experiment, gonadectomy was found to attenuate this sexually dimorphic response to a 40% diet dilution test, whereas daily injections of gonadal hormones reestablished the sex difference in FI and BWt changes produced by the dilution challenge. Since responsiveness to the dilution challenge of female rats, but not males, was altered by gonadectomy and steroid treatment, it appears that estrogen shifts the control of feeding behavior in female rats towards more long-term factors.

Animals↗
PubMed1977

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.

Animals↗
PubMed1977

Examination of some factors that control the effects of septal lesions on lordosis behavior.

Various experimental parameters related to the effects of septal lesions on the lordosis behavior of rats have been examined. First, the failure of septal lesions to facilitate lordosis behavior in male rats appears to be related to the degree of exposure to androgens neonatally. The normal facilitation in lordosis behavior associated with septal destruction in adult female rats does not occur if these female rats are treated with 1.0 mg of testosterone propionate (TP) on Day 1 of life. Yet female rats given 270 mug of TP on Day 3 of life respond the same as do normal females to septal lesions. Second, these sexually dimorphic effects of septal lesions can be modified in adult rats by chronic treatment with gonadal hormones following septal destruction. Whereas previous studies indicated that chronic estrogen injections permit a facilitation in lordosis behavior to occur in septal lesioned male rats, the present results showed that chronic injections of TP following a septal lesion attenuates the facilitation in lordosis behavior typically observed in adult female rats following a septal lesion. Third, examination of the time course for the facilitation in lordosis behavior following a septal lesion revealed a four to six day delay before the appearance of heightened female sexual behavior. Fourth, in support of the possibility that modifications in lordosis behavior by septal lesions may be mediated by a depletion or imbalance in brain amines, amphetamine was found to reduce the high levels of lordosis behavior of septal lesioned female rats to control levels. Finally, further evidence of a potential role for brain amines in the effects of septal lesions was provided by the observation of significantly lower content and turnover of dopamine in the amygdala of septal lesioned female rats, relative to sham operated controls.

Animals↗
PubMed1976

Sex-related difference in antral and serum gastrin levels in the rat.

Antral and serum gastrin concentrations were found to be significantly lower in female than in male rats. Following ovariectomy, serum gastrin concentration significantly increased to male levels; tissue gastrin also increased, but not significantly. Daily injections of estradiol benzoate (2 mug/day) abolished the rise in gastrin levels after ovariectomy. Antral and serum gastrin concentrations were significantly higher in lactating rats than in any other group tested. The possible relationships among sex-dependent changes in food intake, gastrin concentration, and gastric secretion are discussed.

Animals↗
PubMed1975

Neurohormonal determinants of sex differences in the hypothalamic regulation of feeding behavior and body weight in the rat.

Androgens produce a permanent organizational effect on the brain of rats during a postnatal period of sexual differentiation. In male rats, this process occurs as a consequence of the endogenous release of androgens; however, exposing female rats to exogenous androgens during this critical period initiates the same process, such that early exposure to androgens results in a dose-dependent increase in body weight. Sex-specific gonadal hormones further modulate this basic organizational difference in that androgens and estrogens have facilitatory and inhibitory effects, respectively, on the regulation of food intake (FI) and body weight (BWt). While the biochemical or anatomical basis of this sexual dimorphism in energy regulation has not been defined, the data presented here support the idea of a functional sex difference in the hypothalamic regulation of FI and BWt. In general, the same kinds of behavioral tests which differentiate between normal animals and rats with lesions of the ventromedial hypothalamus (VMH) or lateral hypothalamus (LH) also differentiate between male and female rats. Male rats respond to regulatory challenges more similar to VMH lesioned animals than do female rats. In addition, it has been shown that the VMH may be a primary neural site for the organizational effects of androgens on the brain. Based upon these data and the fact that rats show a sex difference in exactly those regulatory behaviors which are presumably controlled by the VMH, a model is proposed to account for sex differences in energy regulation.

Animals↗
PubMedDate not supplied

Effects of hypothalamic and preoptic lesions on reproductive behavior in male rats.

Adult male rats, which were selected on the basis of showing complete patterns of male copulatory behavior on two prior tests, were castrated six weeks prior to brain surgery. Animals were divided into three groups and given small bilateral lesions in the dorsomedial preoptic area (POA), ventromedial hypothalamus (VMH), or sham operations. Starting 10 days postsurgery, all animals were injected with estrogen alone and estrogen plus progesterone, and tested twice for lordosis behavior. Ten days following the female behavior tests, animals were injected daily with testosterone propionate for 13 days and tested for masculine sexual behavior on injection 5, 9 and 13. Low levels of lordotic behavior were observed for POA and VMH animals on both tests for female sex behavior and were comparable to sham operated animals. However, in terms of all dependent measures of male copulatory behavior, animals with VMH lesions showed significantly higher levels of male sex behavior with shorter latencies than sham animals across all three behavior tests. In contrast, POA lesioned rats showed little or no male sex behavior on any test and were significantly inferior to sham operated animals. Thus, the POA and VMH appear to exert excitatory and inhibitory control, respectively, over male copulatory behavior in male rats.

Animals↗
PubMedDate not supplied

Alterations by estrogen and hypothyroidism in the effects of septal lesions on lordosis behavior of male rats.

Earlier experiments indicated that chronic exposure to estradiol benzoate (EB) following septal lesions can increase the subsequent levels of female sexual behavior in male rats tested several months later following priming doses of EB. However, the present study demonstrates that a single injection of a large dose of EB (50 microng) two days after septal destruction did not modify subsequent responsiveness to EB priming in male rats relative to sham operated controls. Yet male rats given 10 daily injections of 5.0 microng EB/day immediately following a septal lesion were more responsive to EB than oil treated controls when tested later for lordosis behavior. Therefore, the capacity for EB to alter the behavioral effects of septal lesions on lordosis behavior in male rats is related to both chronic administration and a period of susceptibility to some action of EB during the immediate post-lesion period. In two additional experiments, chronic hypothyroidism induced by propylthiouracil or thyroidectomy was also found to modify the effects of septal lesions on female sexual behavior of male rats. These latter results indicate that EB is not unique in its capacity to alter the behavioral effects of septal lesions in male rats, and are consistent with the view that both EB and hypothyroidism may interact with some dynamic process associated with recovery from brain lesions.

Animals↗