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Biomedical subjects

F H Bronson

Publications and source records attributed to F H Bronson.

At least 55 records · Page 3Linked to original sources
PubMed1987

Scent marking in the musk shrew (Suncus murinus).

The hormonal regulation of scent marking was examined in male and female musk shrews. In males castration depressed flank, perineal, and throat marking frequencies, and a physiological dose of testosterone restored perineal and throat marking to intact levels. Females exhibited high levels of marking whether tested in a non-pregnant state, late in gestation, or when post-partum. Moreover, ovariectomy had no influence on marking behavior. Adrenalectomy, in addition to ovariectomy, caused a significant decline in two of the three marking behaviors examined, flank and perineal marking. These results demonstrate that these sexually monomorphic scent marking behaviors are under gonadal control in male musk shrews, but not in females. Furthermore, two of the three different types of scent marking examined in female musk shrews appear to require adrenal hormones. Throat marking in the female musk shrew apparently is not regulated by steroidal hormones.

Adrenal Glands↗
PubMed1987

Role of the ovary and adrenal gland in the sexual behavior of the musk shrew, Suncus murinus.

The contributions of the ovary and the adrenal gland to sexual behavior were examined in the female musk shrew (Suncus murinus). Ovariectomy eliminated sexual behavior, and treatment with estradiol or testosterone restored it in almost all shrews. Progesterone was ineffective in this regard. Adrenalectomy, likewise, blocked sexual behavior in most females with intact ovaries. Taken together, these results suggest that sexual behavior in this primitive eutherian mammal is normally modulated by secretions of both the ovary and the adrenal gland.

Adrenal Glands↗
PubMed1987

Puberty in female rats: relative effect of exercise and food restriction.

Reproductive development in relation to growth and fat deposition was compared in three groups of female rats: a group that was allowed to grow only slowly by requiring them to work hard on a running wheel for their food; a group in which the same slow rate of growth was imposed by restricting their food intake, but without an exercise requirement; and a normally growing, nonexercising, ad libitum-fed, control group. Animals forced to run for their food experienced vaginal opening at a significantly lower body weight than either of the other two groups. The same trend was apparent for the first ovulation, but not significant. Thus the present results suggest that, under some conditions, intense exercise may actually accelerate rather than decelerate reproductive development, at least relative to body weight. With the possible exception of body weight, none of the whole-body parameters measured in this experiment (body weight, growth rate, or amount of fat) were found to be critically related to the first ovulation when all three groups of females were considered as a unit. Thus the present results also argue against some of the current hypotheses, all developed using dietary manipulation, that the onset of fertility is somehow dependent on one of these factors.

Animals↗
PubMed1987

Reproductive response of a tropical mammal, the musk shrew (Suncus murinus), to photoperiod.

Musk shrews (Suncus murinus) were maintained for 8 weeks in long (16 h light:8 h darkness) or short (8 h light:16 h darkness) daylengths. Males housed in short daylength had significantly lighter androgen-dependent sex accessory organs than did males kept in long daylengths. This same trend was noted in male sexual behaviour. However, the weights of the testes and epididymides and sperm numbers did not differ. Females housed in short daylengths had significantly lighter cervices and were less likely to demonstrate sex behaviour than animals kept in under long daylengths. Ovarian and uterine weights did not differ. These results suggest that the ability to respond to photoperiod can exist in tropical mammals, even if it is not used as a cue to time seasonal breeding.

Animals↗
PubMed1986

Effects of food restriction and restoration on gonadotropin and growth hormone secretion in immature male rats.

This experiment concerned the changing patterns in secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and growth hormone (GH) under conditions of food restriction and subsequent catch-up growth. Weanling male rats were given either restricted (4 g food/day) or unrestricted access to food until 60 days of age. At this age, food-restricted rats weighed only 25% as much as rats fed ad libitum. Food restriction resulted in a dramatic decrease in the frequency of LH and GH pulses, and in the amplitude of GH pulses. It also slightly but significantly decreased mean blood levels of FSH (which was not secreted in a pulsatile manner in 60-day-old controls fed ad libitum). When restricted rats were given unrestricted access to food, frequency of LH and GH pulses and mean levels of FSH increased significantly and simultaneously within 2 days in half of the animals. Only an additional 8-10% of their body weight decrement was recovered at this time. After 10 days of food restoration, when restricted rats still weighed 50% less than controls, their secretory patterns of all three hormones were not significantly different from those of controls. Thus, recovery of gonadotropin and GH secretion was relatively rapid. Except for the quantitatively lesser impact of food restriction on FSH secretion, there was no evidence of any priorities in the secretion of the three hormones. Under conditions of rapid catch-up growth, the secretory patterns of LH, FSH, and GH appeared to develop simultaneously.

Animals↗
PubMed1986

Food restriction and reproductive development: male and female mice and male rats.

The effect of food restriction on reproductive development was compared in male and female mice. This was accomplished using an experimental design that allowed us to assess the amount of reproductive development that could occur in the total absence of body growth, when growth was stopped at each of three different body weights. Our results demonstrate that reproductive development has much more inertia in males than in females. Specifically, the final stages of reproductive development can proceed largely independently of body growth in males but not in females. This same design was also employed in an abbreviated study of male rats. When its results are coupled with the existing literature for female rats, it appears as though the sex differences noted above are characteristic of both species.

Animals↗
PubMed1986

Physical and metabolic correlates of sexual inactivity in aged male mice.

The object of this study was to identify specific syndromes of sexual loss in aged male mice. Emphasis was placed on uncovering syndromes that involve physical as opposed to motivational deterioration. To this end, 30-mo-old CBF1 male mice were subjected to a large battery of tests, each of which was designed to detect sensory, neuromuscular, metabolic, or sexual deficits. Over 50 measures were obtained on each of 63 males. A group of 23 6-mo-old males were studied simultaneously to establish base lines of normal performance. Old males routinely showed evidence of deterioration in some tests but not in others. Some old males actually performed as well as young males in some tests, including an exhaustive test of sexual capacity. Ten nonsexual measures were significantly correlated with sexual activity. Further analyses then suggested seven distinct syndromes of reproductive loss, each with its own specific cause and unique manifestation. Six of these syndromes manifested themselves as behavioral deficits; one was related to a failure to eject sperm. Our data also suggest the possible existence of two more syndromes, but these remain to be verified more fully. Although additional syndromes undoubtedly will be found in male mice, the present testing paradigm can be exploited to isolate and study the functional bases of each of these specific facets of reproductive loss.

Aging↗
PubMed1986

Food-restricted, prepubertal, female rats: rapid recovery of luteinizing hormone pulsing with excess food, and full recovery of pubertal development with gonadotropin-releasing hormone.

Prepubertal female rats were maintained continuously at 45% of their expected 50-day body weight by restricting their food intake. Uteri and ovaries declined in weight under these conditions. No evidence of pulsatile LH release was seen when these animals were examined at 50 days of age. Allowing unlimited access to food at this time caused rapid pubertal development. LH pulsing began in some females within 12 h; strong LH pulsing was seen in most females within 24 h, and all ovulated after only 2 1/2 or 3 1/2 days of ad libitum feeding. These were fertile ovulations, accompanied by mating and resulting in pregnancy. Administering GnRH in a pulsatile manner to 50-day-old, food-restricted animals also yielded full pubertal development. Uteri and ovaries gradually increased in weight, and ovulation occurred in 3 1/2 to 5 1/2 days. These findings support a contention that the major reproductive deficit resulting from food restriction relates to the control of GnRH secretion. In toto they also suggest a close metabolic coupling between some dimension of nutrient and/or energy processing and the GnRH pulse generator in the normally growing female.

Animals↗
PubMed1985

Behavioral and physiological responses of female house mice to foraging variation.

Peripubertal female house mice were required to work for their food at either 23 degrees C or 9 degrees C. We used a special caging system in which animals had to emerge from a thermally-buffered burrow and run a programmable number of running wheel revolutions to obtain a pellet of food. Of concern here were the behavioral and physiological adjustments necessary to accommodate growth and reproductive development when faced with the need to forage for different lengths of time at different temperatures. When female house mice are confronted with poor foraging at cool temperatures they allot their highest priorities to maintaining energy balance; body growth is next, and reproductive development and nonforaging activity have the lowest priorities. Our results also demonstrate that the time spent foraging while exposed to low ambient temperature is critical for this species. This relationship probably determines whether or not house mice will breed continuously or seasonally in a particular habitat.

Animals↗
PubMed1985

Mammalian reproduction: an ecological perspective.

The objectives of this paper are to organize our concepts about the environmental regulation of reproduction in mammals and to delineate important gaps in our knowledge of this subject. The environmental factors of major importance for mammalian reproduction are food availability, ambient temperature, rainfall, the day/night cycle and a variety of social cues. The synthesis offered here uses as its core the bioenergetic control of reproduction. Thus, for example, annual patterns of breeding are viewed as reflecting primarily the caloric costs of the female's reproductive effort as they relate to the energetic costs and gains associated with her foraging effort. Body size of the female is an important consideration since it is correlated with both potential fat reserves and life span. Variation in nutrient availability may or may not be an important consideration. The evolutionary forces that have shaped the breeding success of males usually are fundamentally different from those acting on females and, by implication, the environmental controls governing reproduction probably also often differ either qualitatively or quantitatively in the two sexes. Mammals often live in habitats where energetic and nutrient challenges vary seasonally, even in the tropics. When seasonal breeding is required, a mammal may use a predictor such as photoperiod or a secondary plant compound to prepare metabolically for reproduction. A reasonable argument can be made, however, that opportunistic breeding, unenforced by a predictor, may be the most prevalent strategy extant among today's mammals. Social cues can have potent modulating actions. They can act either via discrete neural and endocrine pathways to alter specific processes such as ovulation, or they can induce nonspecific emotional states that secondarily affect reproduction. Many major gaps remain in our knowledge about the environmental regulation of mammalian reproduction. For one, we have a paucity of information about the annual patterns of breeding and about the mechanisms controlling these patterns in the most common mammals on the planet-the small to average-sized mammals living in the tropics. We probably have only a shallow conceptualization of the way available energy and nutrients control reproduction and, likewise, we may have only a narrow view of the potential kinds and uses of seasonal predictors. Finally, we have little appreciation of the way environmental cues interact with each other to control reproduction.

Animals↗
PubMed1985

Food restriction and reproductive development in wild house mice.

Reproductive development was examined in wild house mice who had either unlimited or severely restricted access to food. The degree of food restriction was set at a level that allowed no body growth after 24 days of age. This treatment completely blocked reproductive development in females. In contrast, it had only minor effects on the reproductive development of males. Despite their stunted condition, food-restricted males developed normal numbers of sperm in their testes and vasa deferentia. They developed almost normal accessory tissues, and 8 of 10 inseminated test females when challenged at 8 wk of age. These results are considered primarily in relation to the opportunistic reproductive strategy of this species.

Animals↗
PubMed1985

Effect of short-term food deprivation on reproduction in female mice.

CF-1 female mice were subjected to 24 or 48 h of food deprivation beginning when they were in estrus or diestrus, or when they were 2 or 12 days pregnant, or on Days 2 or 12 of lactation. Ovulation was delayed by a week or more when 48 h of food deprivation was initiated when the female was in diestrus; lesser delays occurred when food deprivation began in estrus. There was little effect of acute food deprivation on pregnancy. Most females deprived of food beginning on Day 2 of lactation ate their young, but females deprived on Day 12 of lactation rarely did so. These results are discussed in terms of the complexity of interacting factors that determine the degree to which each stage of the female's reproductive cycle is susceptible to disruption by acute food deprivation.

Adipose Tissue↗
PubMed1984

Energy allocation and reproductive development in wild and domestic house mice.

The growing mammal has many competing demands for energy, including some that are associated specifically with reproductive development. The concern of the present experiment was with the effect of domestication on energy allocation in relation to puberty. Food consumption, rate of growth, fertility onset, fat deposition and spontaneous locomotor activity were compared during peripubertal development in both sexes of two stocks of house mice, one wild and one domestic. The onset of fertility occurred much earlier in CF-1 females than it did in wild females; in sharp contrast the males of these two stocks achieved fertility at the same time. Food consumption, growth rate and final body weight were greater and locomotor activity was depressed in both sexes of the domestic stock. Proportionately less fat was deposited throughout development in CF-1 females when compared to wild females; fat deposition increased during development in CF-1 males while decreasing in wild males. Most of the energy-related differences noted here are compatible with a hypothesis that selection during domestication has focused on the need for a larger mass of the female mouse which, in turn, has been required to support a larger litter size. With specific regard to the reproductive development of the female, the data presented here are not compatible with the hypothesis that the first ovulation is regulated directly by critical amounts of body fat.

Animal Population Groups↗
PubMed1983

Ambient temperature and reproductive success in rodents living at different latitudes.

The concern of this research was with the susceptibility of rodent reproduction to latitudinal acclimatization. More specifically, the relationship between ambient temperature and reproductive success was examined in house mice and deer mice whose ancestors had been trapped in northern versus southern climates (Alberta vs. Texas). Third generation adults of each of these four populations were paired and challenged to breed at -6 degrees, 3 degrees, 23 degrees or 34 degrees C. A 50-day period of gradual temperature adaptation preceded pairing. House mice, regardless of their geographic origin, were found to be relatively insensitive to extreme temperatures. Many pairs of both the Alberta and Texas stocks of this species still produced offspring when maintained at the experimental extremes of -6 degrees and 34 degrees C. In marked contrast, both northern and southern deer mice exhibited relatively narrow temperature ranges within which maximum breeding occurred: -6 degrees to 3 degrees for Texas deer mice and only at 23 degrees C for Alberta deer mice. Thus there is no evidence in either species that reproduction is either less sensitive to cold in northern latitudes or less sensitive to heat in southern latitudes; indeed, somewhat the reverse situation exists in deer mice. Evolutionarily, latitudinal considerations seem to have been of secondary rather than of primary importance in shaping the relationship between ambient temperature and reproduction in these two species.

Animals↗
PubMed1983

Foraging effort, food intake, fat deposition and puberty in female mice.

A novel caging system was used to study the interrelationships between foraging effort, food intake, growth and sexual maturation of peripubertal female mice. Females housed in these cages were forced to work (forage) at various intensities in order to obtain food pellets. It is argued that this is a biologically more meaningful approach to understanding the energetics of sexual development than the traditional approach of simple underfeeding. Female mice exhibited a cascade of developmental adjustments and deficits when challenged to forage harder for less food. The functions most sensitive to increased foraging effort were sexual development and growth in body length; growth in body weight was intermediate and fat deposition was least sensitive of all. The relative insensitivity of fat deposition to higher foraging costs suggests a strategy for survival during the postweaning dispersal movements of the wild ancestors of the laboratory mouse. Finally, regression analyses suggested that heavier females who had less than average body fat and higher than average food intake achieved their pubertal ovulation most rapidly.

Adipose Tissue↗
PubMed1982

Relative effects of exercise, diet, and female stimulation on sexual aging of male mice.

These experiments examined the effects of several environmental variations on the rate at which sexual activity declines in aging male mice. CF-1 males were reared from 3 to 22 months of age in one of seven experimental conditions: in isolation with or without running wheels and on breeder or low-fat diets, or cohabited throughout this time span with intact or ovariectomized females that were either replaced monthly or not. Monthly replacement of intact females resulted in a pronounced delay in the expected loss of sexual activity of the aging males. Terminal tests of sexual capacity, administered at 23 months of age, however, showed no enduring effect of female replacement. These tests did reveal a larger than expected depression in the sexual activity of isolated males fed the breeder diet. Access to running wheels was totally without on sexual activity. Sexual aging is known to be a highly variable process in male mice. The present results may suggest that much of this variation is ultimately traceable to genetic or early experiential factors, or both.

Aging↗