Search PubMed⌕ Search

Biomedical subjects

I Zucker

Publications and source records attributed to I Zucker.

At least 91 records · Page 5Linked to original sources
PubMed1987

Androgens exert opposite effects on body mass of heavy and light meadow voles.

The influence of gonadal hormones on body mass of adult male meadow voles varied systematically as a function of the animals' baseline body weight; heavier voles decreased and lighter voles increased their body mass after castration. Testosterone replacement reversed the effects of castration; changes in body mass during hormone treatment were negatively correlated with changes observed after castration. Body mass of intact males was not correlated with plasma testosterone titers. Individual differences in body mass of male voles appear to reflect variations among animals in substrate responsiveness to hormones rather than differences in circulating hormone levels.

Androgens↗
PubMed1987

Spontaneous testicular recrudescence of Syrian hamsters: role of stimulatory photoperiods.

The gonads of hamsters maintained in short photoperiods first undergo regression and then spontaneous recrudescence. The latter is indicative of refractoriness of the neuroendocrine axis to short day lengths. We tested the hypothesis that the absence of long-day stimulation contributes to the development of refractoriness to short photoperiods. Male Syrian hamsters were maintained for 26 weeks in a short-day photoperiod (8 hr light/day). Testicular regression was confirmed in all animals at week 10; thereafter different groups of hamsters were stimulated with one long day (16 hr light) every 10, 15, 20 or 30 days until week 26. Control groups were maintained continuously in long or short photoperiods, respectively. The rate of gonadal recrudescence of short-day hamsters was not affected by intermittent stimulation with long photoperiods. After 26 weeks, testes in all short-day groups had undergone recrudescence. Refractoriness to short day lengths is not counteracted by long photoperiods. The role of the pineal gland in the development of refractoriness is considered.

Animals↗
PubMed1987

Influence of daylength experienced by dams on post-natal development of young meadow voles (Microtus pennsylvanicus).

Meadow voles born to dams kept in short days (SD) beginning 5 or 11 weeks before parturition (SD-5, SD-11) had less developed testes, gained weight more slowly and built larger nests than did young gestated and maintained in long days (LD). Pelage development was greater in SD than in LD young at 21 and 45 days of age. At weaning, SD-5 young had less dense fur and shorter guard hairs than did SD-11 young, indicating that the photoperiodic history of dams before insemination affects the post-natal pelage development of their progeny. Short daylengths experienced by dams before mating may facilitate winter preparedness of their offspring.

Animals↗
PubMed1987

Role of photoperiod during pregnancy and lactation in the meadow vole, Microtus pennsylvanicus.

The influence of daylength on body mass and food intake of pregnant and lactating voles was tested by comparing animals housed in long versus short daylengths. Pregnancy rates were approximately 50% in long-day females and in voles kept in short days beginning 2 weeks before mating, but were significantly lower in voles preadapted to short days for 8 weeks before mating. Body mass and food intake increased substantially during pregnancy and lactation and the magnitude of the increase was unaffected by daylength; by contrast, body weight was significantly reduced in non-impregnated voles kept in short as compared to long days. The suppressive effects of short photoperiods on body weight were completely counteracted during pregnancy and lactation. Voles that breed during the short days of winter face extreme energetic challenges but the advantages of early breeding appear to justify the costs.

Animals↗
PubMed1987

Interaction of daylength and lactation in the control of pelage development and nest-building in female meadow voles (Microtus pennsylvanicus).

Pregnancy and lactation inhibited moult into winter pelage in voles maintained in short daylengths; development of a winter pelage was, however, greatly accelerated once the short-day dams weaned their litters. The presumed elevation of prolactin titres during lactation appears to mask full development and expression of pelage changes induced by short daylengths. Nest-building behaviour, by contrast, was increased in response to short photoperiods and was further augmented during lactation and may thereby facilitate thermoregulation in short-day dams that do not develop a winter pelage.

Animals↗
PubMed1986

Influence of deuterium oxide on circadian activity rhythms of hamsters: role of the suprachiasmatic nuclei.

The period of the free-running circadian activity rhythm of Syrian hamsters was measured before and during treatment with 10% deuterium oxide (D2O). Deuteration increased period length by approximately 0.5 h per cycle both pre- and postoperatively in hamsters sustaining complete, incomplete or no unilateral lesions of the suprachiasmatic nuclei (SCN). Neither coupling between the bilaterally paired SCN, nor elimination of 50% of SCN tissue affected period length during D2O treatment. However, variability of the response to D2O was much greater in lesioned than in intact hamsters. We propose that a small percentage of the normal complement of SCN neurons is sufficient to permit full responsiveness of the circadian system to D2O and that there is substantial redundancy in the neural system that responds to deuterium. Stability of the circadian system appears to be increased by the full complement of SCN neurons.

Animals↗
PubMed1986

Photoperiodic regulation of body mass and fat reserves in the meadow vole.

Short photoperiods reduce both body mass and food intake of male meadow voles. To help determine whether the primary effect of short day lengths is on regulation of some component of body mass or on the control of food consumption, voles housed in a long photoperiod were provided rations equivalent to those consumed by animals in short day lengths. Animals were transferred to a short photoperiod and after either 3 or 6 weeks of food restriction were fed ad lib. Both groups of voles overate after termination of food restriction and achieved seasonally appropriate body masses that were influenced by the duration of short photoperiod treatment. We conclude that short photoperiods gradually alter the regulated level of one or more components of body mass. We tested and failed to support the hypothesis that the subcutaneous fat depot is selectively spared during seasonal weight loss and thereby increases surface insulation. Thus, the proportion of adipose tissue reduction did not differ significantly among the epididymal, retroperitoneal, and inguinal-subcutaneous fat depots of voles housed in short day lengths.

Adipose Tissue↗
PubMed1986

Short day lengths decrease body mass of overweight female meadow voles.

Groups of adult ovariectomized (ovx) voles and sham-ovx controls were placed in a short photoperiod or left in the original long photoperiod (10 or 14 hr light/day). In the next 12 weeks long-day ovx voles increased their body mass by 11.3%, whereas animals transferred to the short-day photoperiod manifested an 11.9% decline in body mass. Short photoperiods not only reversed pre-existing weight gains attributable to ovariectomy, but also prevented further increases in body mass associated with the withdrawal of ovarian hormones. Fat-free dry carcass mass was increased by ovariectomy and decreased by short photoperiods; lipoprotein lipase activity of white adipose tissue was unaffected by ovariectomy or photoperiod. We suggest that reductions in body mass in voles transferred to the short photoperiod are mediated by changes in pineal melatonin secretion.

Adipose Tissue↗
PubMed1986

Circannual cycles of body mass food intake and reproductive condition in male pallid bats.

Gonadectomy did not eliminate circannual cycles of body mass and food intake in male pallid bats maintained for up to 30 months in short or long photoperiods at a constant temperature of 23 +/- 2 degrees C. Generation and expression of circannual rhythms is independent of the annual testicular cycle. Initial peak body and testicular masses were recorded within one month of each other but the peak in food intake occurred approximately eight months after animals attained peaks in body mass. Increased metabolic efficiency appears to act independently of changes in food intake to effect seasonal increases in body mass of pallid bats.

Animals↗
PubMed1986

Neonatal androgenization in ground squirrels: influence on sex differences in body mass and luteinizing hormone levels.

Female squirrels were injected at birth with 50 or 1000 micrograms testosterone propionate (TP); control males and females were treated with oil vehicle. Squirrels were gonadectomized at 47 days of age. Body mass was recorded weekly and plasma luteinizing hormone (LH) was determined once monthly over the next year. Marked annual cycles in body mass were manifested by 30 out of 31 squirrels. Peak body mass and peak-to-trough differences were greater for control male and TP-female squirrels than for control female squirrels. Trough body weights did not differ among the groups. Luteinizing hormone was detectable in all male and most androgenized females but not in any control female squirrels during the first 4 mo after gonadectomy. Peak LH values were significantly greater for control male than for control female squirrels and were not influenced by neonatal androgenization in females. Testosterone propionate treatment also did not affect sex differences in timing of LH peaks or the total number of months in which LH was detectable. We conclude that testicular hormones secreted during the early postnatal period induce sex differences in the circannual pattern of weight change and some aspects of LH secretion. Complete masculinization, however, either requires more extensive action of gonadal hormones, perhaps both pre- and postnatally, or occurs through some androgen-independent mechanism.

Animals↗
PubMed1986

Fat ablation and food restriction influence reproductive development and hibernation in ground squirrels.

The role of white adipose tissue in development of the reproductive apparatus of male golden-mantled ground squirrels was assessed by surgical removal of fat (lipectomy) immediately prior to onset of hibernation or by manipulation of fat levels through food restriction for 5 wk preceding hibernation. Animals then were maintained without food at 6 degrees C, and they hibernated from November 1983 until April 1984. At that time, blood plasma was assayed for hormone levels, and body mass, body composition, and masses of the testes and seminal vesicle-prostate complex were determined. At autopsy, testes and sexual accessory organs were heavier in Control squirrels than in Food-Restricted or Lipectomized (LIPX) animals. Paired-testes mass was positively correlated with body mass. Testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels were uniformly low in animals sampled during torpor, but were elevated in 2 animals that had regained the euthermic state. The Food-Restricted animals spent more time in torpor than did the other two groups, and the percentage of decrease in body mass over the hibernation season was less for Food-Restricted than for LIPX or Control animals. Adequate lipid stores may be essential for the normal development of the reproductive apparatus of male ground squirrels. In the field, animals with insufficient fat stores may forego reproduction and thereby conserve energy for survival.

Adipose Tissue↗
PubMed1986

The influence of hibernation on testis growth and spermatogenesis in the golden-mantled ground squirrel, Spermophilus lateralis.

Testis size and spermatogenesis were monitored serially in individual golden-mantled ground squirrels before, during, and after the hibernation season. During hibernation, animals spent 81% of days in torpor at body temperatures of 3-4 degrees C. Torpor bouts of 6 days duration were interspersed with brief arousals from torpor during which animals were normothermic. In the 5 mo between December (when animals entered hibernation) and April (when torpor was spontaneously terminated), the estimated mass of testes increased gradually from 500 to 1100 mg, but spermatogenesis did not advance beyond pachytene spermatocytes, which were present before hibernation began. In contrast, during the month after torpor was terminated, testes increased rapidly to 3500 mg and after 31 days, spermatozoa were found in the epididymides. We suggest that the limited testis growth that occurred during the hibernation season was restricted to intervals during which squirrels were aroused from torpor. The major portion of gonadal growth and spermatogenesis in the laboratory, and presumably in the field, occurs after ground squirrels have regained the normothermic state. Since males are reproductively mature when first trapped in spring, these findings suggest that males are normothermic for several weeks before they emerge from their hibernacula in the spring.

Aging↗
PubMed1986

Circannual variations in circadian rhythms of ground squirrels.

There was a circannual rhythm in the times of activity onset (psi o) and activity termination (psi T) and in the duration of the active phase (alpha) in female ground squirrels (Spermophilus lateralis) maintained in a light-dark (LD) 14:10 photoperiod for 22 mo. Activity onset occurred 2.3 h after light onset in the 4 mo before estrus, 0.5 h before light onset during the month encompassing estrus, and progressively later during each of the ensuing 4 mo. Termination of activity occurred later during the month of estrus than in the 4 mo preceding estrus; alpha nearly doubled during the month of estrus and decreased gradually over the next 3 mo. The psi o and psi T remained entrained to the daily illumination cycle, but the phase angles of activity onset and offset and the duration of the active phase varied seasonally and recurred with a circannual period of 9-11 mo. The LD 14:10 photoperiod entrained the circadian activity rhythm throughout the year; however, circannual variations in activity as well as in estrus and body mass were not entrained by this photoperiod but free-ran with periods of less than 12 mo.

Activity Cycles↗
PubMed1986

Circannual rhythms of ground squirrels: a test of the frequency demultiplication hypothesis.

The frequency demultiplication hypothesis (FDH) posits that circannual rhythms are generated from circadian cycles by frequency transformation to the lower-frequency rhythm. To test the FDH, we determined the periods of the circannual body mass and estrous cycles of golden-mantled ground squirrels with circadian locomotor activity rhythms entrained to 23-, 24-, or 25-hr days (T-cycles). Circannual period length did not differ among squirrels entrained to the different T-cycles; intergroup ranges were 298-314 days and 303-312 days, respectively, for body mass and estrus. These results are not consistent with the FDH and suggest instead that separate mechanisms generate circadian and circannual rhythms. In ground squirrels the circannual system influences circadian organization, but a reciprocal influence of circadian on circannual rhythms has yet to be demonstrated.

Animals↗
PubMed1985

Persistence of circannual rhythms in ground squirrels with lesions of the suprachiasmatic nuclei.

Golden-mantled ground squirrels (Spermophilus lateralis) sustained complete ablation of the suprachiasmatic nuclei (SCN) while being maintained under constant conditions of photoperiod, temperature and food availability. After SCN ablation, most squirrels observed for up to 3 years postsurgically underwent normal circannual cycles in body mass. Other squirrels with similar SCN damage evidenced various anomalies in their circannual body weight cycles. Response of squirrels to SCN ablation was not related to the phase of the annual cycle in which lesions were produced. The variable nature of the effect of SCN ablation on circannual body mass cycles suggests that the SCN are non-essential components of the system underlying the generation or expression of circannual rhythms.

Animals↗
PubMed1985

Role of the pineal gland in circadian organization of diurnal ground squirrels.

Golden-mantled ground squirrels, Spermophilus lateralis, pinealectomized (pinx) or sham-pinx at 70 days of age, were maintained in a LD 10:14 photoperiod; phase angles of activity onset were 1.6 +/- 0.3 and 1.9 +/- 0.3 hr in advance of light onset, respectively, and did not differ significantly between the groups. Rates of phase shifting of the activity rhythm after a 6 hr phase advance in the LD cycle also were comparable for the two groups and stable re-entrainment was achieved in 11 days. The period of the free-running activity rhythm in constant light did not differ between the groups. As demonstrated previously in nocturnal rodents, the pineal gland exerts little if any influence on generation or entrainment of the ground squirrel diurnal circadian activity rhythm. The rodent pineal is neither a master circadian oscillator nor a significant component of the transduction process by which light entrains the circadian activity rhythm.

Animals↗