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Biomedical subjects

D A Damassa

Publications and source records attributed to D A Damassa.

At least 37 records · Page 2Linked to original sources
PubMed1984

Luteinizing hormone-releasing hormone (LH-RH) cells and their projections in the forebrain of the bat Myotis lucifugus lucifugus.

Luteinizing hormone-releasing hormone (LH-RH) neurons and their projections were studied by immunocytochemistry in the brains of little brown bats (Myotis lucifugus lucifugus: Chiroptera: Vespertilionidae ) as a first step in the study of relationships between these neurons and the seasonal reproductive events characteristic of this species. The majority of immunoreactive neurons in adult male, adult female, and fetal bats were ovoid bipolar cells with one thin and one thicker process, both of which gave rise to fine varicose fibers. LH-RH-immunoreactive perikarya were concentrated in the region of the arcuate nuclei in all bats examined. Perikarya were also consistently found dispersed in the mammillary region, anterior hypothalamus, preoptic areas, septum, diagonal band of Broca, and olfactory tracts; they were occasionally observed in the dorsal hypothalamus, organum vasculosum of the lamina terminalis (OVLT), habenula, amygdala, and cingulate gyrus. LH-RH-immunoreactive fibers projected heavily to the median eminence, infundibular stalk, and posterior pituitary. In extrahypothalamic areas, these fibers were especially abundant in the stria medullaris/habenula and stria terminalis/amygdala, but also contributed to the diagonal band of Broca and the olfactory tracts. Immunoreactive fibers that may be components of many different pathways clustered in the rostral septum and permeated the medial hypothalamus. LH-RH-containing fibers frequently entered the subfornical organ, but were observed less often in the OVLT and only occasionally in the pineal. The organization of the LH-RH system in the little brown bat resembles that of primates, but differs considerably from that in the rat. Anatomical characteristics of the LH-RH system in bats thus suggest that this animal may be a particularly suitable species for further study of neuroendocrine control of reproductive function as it may relate to primates, including humans.

Amygdala↗
PubMed1984

Perinatal and postnatal patterns of plasma sex steroid-binding protein and testosterone in relation to puberty in the male little brown bat.

The little brown bat (Myotis lucifugus lucifugus) possesses a specific plasma sex steroid-binding protein (SBP) which exhibits high affinity for both testosterone (T) and estradiol. To examine the peri- and postnatal patterns of plasma androgen binding in relation to puberty, concentrations of SBP and total T levels were measured in males at various intervals throughout the first year of life. In addition, reproductive organs were examined histologically over this period. SBP levels were low (less than 7 nM) in near-term fetuses (mid-June) but increased more than 30-fold by 1 week of age (range, 245-602 nM). Elevated titers of this protein were present until 3 weeks of age. By 4 weeks of age (onset of puberty, initiation of the first spermatogenesis), SBP concentrations had fallen significantly, and by 12 weeks, just before the first winter hibernation period, plasma SBP levels had returned to low prenatal-like values (3-12 nM). These levels were maintained throughout winter dormancy. The total plasma T concentrations were also elevated during the early postnatal period and were comparable to or even exceeded those previously measured in spermatogenically active adults. Plasma T levels then declined in parallel to those of SBP and reached a nadir (less than 0.6 ng/ml) by 12 weeks of age. As with SBP, T also remained low throughout hibernation. Although a complete spermatogenic cycle was found to occur in postnatal bats during the summer of their birth, this cycle was greatly reduced compared to that which occurs in sexually mature adults during the same period. Maximal testicular weights from the postnatal males were only one fifth of those previously measured in adult males. In addition, the epididymides in the young bats remained virtually devoid of sperm, and the accessory glands showed little evidence of stimulation. Thus, this first spermatogenic cycle in Myotis does not result in the attainment of sexual maturity and, therefore, appears to be "silent." Since sexual maturity is reached during the following summer when the bats are approximately 1 yr of age, the pubertal process in Myotis is prolonged and appears to be biphasic. Nevertheless, the existence of a perinatal rise in SBP levels (which is repeated in this species when the pubertal process is reinitiated during the second summer) as well as a decline in SBP levels during the onset of puberty resembles that previously described for other mammals.

Animals↗
PubMed1984

Control of plasma sex steroid-binding protein (SBP) in the little brown bat: effects of photoperiod and orchiectomy on the induction of SBP in immature males.

Immature male little brown bats (Myotis lucifugus lucifugus) exhibit striking increases in plasma levels of sex steroid-binding protein (SBP) when aroused prematurely from the latter half of hibernation. To identify some of the factors that control this induction, the effects of castration, photoperiod manipulation, and season (early vs. late hibernation) were studied. During the latter half of hibernation, the elevation of plasma SBP levels induced by premature arousal was found to be similar in intact and castrated males. Since castration completely abolished the postarousal rise in plasma testosterone levels, and estradiol concentrations remained low (less than 10 pg/ml) in both groups, changes in gonadal steroids are apparently not responsible for these increases in SBP. The induction of SBP in males aroused late in hibernation also appeared to be independent of whether animals were maintained under long [16 h of light, 8 h of darkness (16L:8D)] or short (8L:16D) photoperiods. Three weeks after arousal, plasma SBP concentrations in the intact groups were 228 +/- 17 nM (mean +/- SE; 16L:8D) and 271 +/- 5 (8L:16D), while in the castrated groups, SBP levels were 256 +/- 43 (16L:8D) and 231 +/- 19 (8L:16D). In addition, comparable degrees of gonadal activation, including increases in testicular weight, rises in circulating testosterone, and initiation of spermatogenesis, were observed in both the long and the short photoperiod groups. During the first half of hibernation, the induction of SBP was similarly unaffected by castration. However, at this time, photoperiod had a marked effect on SBP induction. Only males maintained under a long photoperiod after arousal from early hibernation exhibited increased levels of SBP (158 +/- 51 nM) and evidence of gonadal activity. The animals housed under a short photoperiod had lower levels of SBP (44 +/- 22 nM) and exhibited no gonadal activation. In general, responses seen in animals aroused during the first half of hibernation were reduced compared to those observed after arousal during the second half of hibernation. Thus, the postarousal increase in SBP appears to be independent of gonadal secretions, but can be influenced by photoperiod during early hibernation.

Analysis of Variance↗
PubMed1983

Control of plasma sex steroid-binding protein in the bat Myotis lucifugus lucifugus: induction of steroid-binding activity in immature males.

Concentrations of sex steroid-binding protein (SBP) in plasma of immature male little brown bats (Myotis lucifugus lucifugus) were found to be low (15 +/- 2.8 (S.E.M) nmol/l) and stable throughout the period of hibernation which immediately precedes the onset of the first spermatogenic cycle (sexual maturity). In contrast, plasma SBP titres in spermatogenically active adults (summer) were markedly raised (238 +/- 26 nmol/l). When immature males were removed from hibernation and maintained on a long photoperiod of 16 h light: 8 h darkness at a constant temperature of 25 degrees C to accelerate the onset of sexual maturity, these animals exhibited a rapid rise in circulating SBP. Plasma levels of SBP in immature males maintained on a long photoperiod increased significantly after 2 weeks, and by 3 weeks reached values (234 +/- 20 nmol/l) that were indistinguishable from those seen in spermatogenically active adults. These high plasma SBP titres at 3 weeks were accompanied by increases in testicular and epididymal weights and the onset of spermatogenesis. However, no stimulation of the sex accessory glands was observed, possibly reflecting the effects of increased plasma SBP on the biological activity of circulating androgens. The ability of immature male Myotis to exhibit a pubertal increase in plasma SBP following simple environmental manipulation should provide a valuable model for the study of the control and action of sex steroid-binding protein.

Animals↗
PubMed1982

Effects of testosterone, dihydrotestosterone, or estradiol administered neonatally on sexual behavior of female ferrets.

Groups of female ferrets born in the laboratory received sc Silastic capsules containing testosterone (T), 5 alpha-dihydrotestosterone (DHT), 17 beta-estradiol (E), or no steroid for 15 days beginning on the day of birth; an additional group of male ferrets received empty sc capsules neonatally. All ferrets were gonadectomized at 11 weeks of age and were subsequently tested for masculine and feminine sexual behaviors while being treated consecutively over an 8-month period with several different gonadal steroids. The ability to display masculine sexual behavior was studied in the absence of replacement hormones and during a counterbalanced sequence of treatments with Silastic capsules containing T, E, or DHT. The maximal amount of neck grip, mount, and pelvic thrusting behavior displayed, regardless of adult endocrine treatment, was significantly greater in control male and neonatally T-treated females than in females that had received no hormone, E, or DHT neonatally. Animals in all five groups displayed equivalent increments in sexual receptivity in response to daily sc injections of increasing dosages of estradiol benzoate. Polyacrylamide gel electrophoresis of plasma collected from newborn female ferrets revealed no binding of either [3H]E or [3H]T, whereas two binding peaks were found for [3H]DHT. After the administration of androgen in adulthood, equivalent clitoral growth and ossification occurred in females given either T or DHT neonatally. These results suggest that in ferrets, behavioral masculinization occurs in response to neonatal exposure to T itself and not to its major neural metabolites, E and DHT. They also show that behavioral defeminization fails to occur in ferrets even after neonatal exposure to pharmacological amounts of E, T, or DHT.

Animals↗
PubMed1980

Effects of centrifugation stress on pituitary-gonadal function in male rats.

The effects of centrifugation for various lengths of time were investigated on circulating levels of luteinizing hormone (LH) and testosterone in male rats. In a chronic 52-day experiment, centrifugation at 4.1 G significantly reduced LH and testosterone levels for the entire period. Centrifugation at 2.3 G had less effect inasmuch as LH levels were not significantly decreased and testosterone levels were significantly reduced only during the first few days of centrifugation. In more acute experiments, centrifugation at 4.1 G for 4 h resulted in reduced testosterone levels, whereas centrifugation for 15 min did not significantly alter the hormone levels. These results indicate that centrifugation can decrease circulating LH and testosterone levels if the gravitational force is of sufficient magnitude and is maintained for a period of hours. Chronic centrifugation may also inhibit the acute excitatory response of LH to handling and ether stress.

Animals↗
PubMed1978

Neuroendocrine mechanisms mediating the suppression of circulating testosterone levels associated with chronic stress in male rats.

Neuroendocrine mechanisms involved in the reduction of testosterone (T) levels induced by the chronic surgical stress of s.c. gauze implantation were investigated in male rats. The reduction resulted from a decline in T secretion and not an increase in clearance of the hormone from the circulation. In most cases, the decrement was accompanied by a reduction in LH levels, indicating that decreased LH stimulation is the primary factor mediating the drop in T levels. The suppressive effect of surgical stress on LH and T levels was apparently not mediated by the pituitary-adrenal system.

Adrenal Glands↗