Biomedical subjects

I Zucker

Publications and source records attributed to I Zucker.

At least 109 records · Page 6Linked to original sources

PubMed1985

Pineal gland influences period of circannual rhythms of ground squirrels.

Female golden-mantled ground squirrels were pinealectomized (Pinx) or Sham-Pinx at 70 days of age and maintained for more than 2 yr at 23 degrees C in a 10:14 light-dark photoperiod. Reproductive condition and body weight were recorded weekly and bi-weekly, respectively. Pinx and Sham-Pinx squirrels displayed circannual rhythms in body weight; the groups did not differ with respect to absolute magnitudes of annual peaks and troughs in body mass. The period of the circannual body weight cycle (measured peak to peak) was 27 and 58 days shorter in Pinx than in Sham-Pinx squirrels during the 1st and 2nd yr, respectively, after surgery. The onset of estrus during the second postoperative cycle occurred significantly earlier in Pinx than in Sham-Pinx squirrels. The pineal gland is not essential for the generation or expression of circannual or circadian cycles but may affect the period of some circannual rhythms.

Animals↗

PubMed1985

Recovery of lipid mass after removal of adipose tissue in ground squirrels.

Male golden-mantled ground squirrels subjected to surgical removal of substantial portions of inguinal, retroperitoneal, and epididymal adipose tissue [lipectomy (Lipx)] or to sham lipectomy (Sham) during the early prehibernatory fattening phase did not differ in body mass 4 mo later at the time of their annual body weight peaks. Body mass restoration by Lipx squirrels was achieved without compensatory increases in food intake. There was little or no regeneration of epididymal adipose tissue, complete regeneration of the retroperitoneal depot, and an increase in mass of subcutaneous fat of Lipx animals. Epididymal and retroperitoneal adipocytes were equivalent in size in Sham and Lipx squirrels; adipocytes in subcutaneous fat were 20% larger in Lipx than in Sham animals. Generation of the annual body mass cycle of this ground squirrel involves active regulation of the lipid mass.

Adipose Tissue↗

PubMed1985

Chemosensory and neural influences on photoperiodic responsiveness of laboratory rats.

Olfactory bulbectomy unmasks photoperiodic responsiveness in normally nonphotoperiodic rats. We assessed whether the photoperiodic effects of bulbectomy reflect disruption of chemosensory input. At 26-28 days of age, male Sprague-Dawley rats were subjected to removal of their vomeronasal organ (VNO) complex, a sham-VNO ablation or large electrolytic lesions aimed at the pyriform cortex or corticomedial nuclei of the amygdala. Other rats were infused with (1) 7.5% ZnSO4, a treatment that destroys the olfactory neuroepithelium, (2) 0.09% saline, or (3) air in each external nare every 4 days; rats from each treatment condition were assigned either to a long (LD 14:10) or short (LD 8:16) day lighting regimen and were autopsied at 90 days of age. Seminal vesicle and paired testes weights did not differ significantly among long-day groups. Mean seminal vesicle and paired testes weights were decreased only in short-day rats treated with ZnSO4. These results indicate that the VNO does not mediate the effects of photoperiod on rat reproduction. Olfactory information, not transduced by the amygdala, or nonsensory components of the olfactory bulbs appear to mask photoperiodism in intact rats.

Amygdala↗

PubMed1985

Circannual rhythms of ground squirrels: role of the hypothalamic paraventricular nucleus.

Female golden-mantled ground squirrels, maintained in an LD 14:10 photoperiod at 23 degrees C, sustained lesions of the paraventricular nucleus (PVN) or sham operations. Body weight and reproductive status were recorded weekly pre- and postoperatively. Bilateral lesions of the PVN did not eliminate, phase-shift, or otherwise disrupt the circannual rhythms of body mass or reproduction. Absolute levels of body weight were unaffected by PVN ablation. The PVN is not an essential component of the oscillatory system that generates circannual cycles in ground squirrels.

Animals↗

PubMed1985

Photoperiodic regulation of reproductive development in male white-footed mice (Peromyscus leucopus) born at different phases of the breeding season.

Male white-footed mice were maintained from birth in chambers equipped with latitudinal timers programmed to simulate the natural progression of daylengths at 42 degrees N latitude. Mice were born into photoperiods starting on 1 April, 15 July, 15 September or 27 October. Testes and seminal vesicles of April- and July-born mice were mature at 60 days of age; puberty was delayed by several months in animals born into the September and October photoperiods but these mice became fecund at about 3.5 months of age, independent of current photoperiod. Therefore, increasing daylengths of late winter do not appear to synchronize the reproductive development of overwintering juveniles born at different times during the previous breeding season.

Animals↗

PubMed1985

Neuroendocrine responsiveness to oestradiol and male urine in neonatally androgenized prairie voles (Microtus ochrogaster).

The influence of neonatal androgenization on behavioural receptivity was tested by treating female voles on the 3rd day of life with testosterone propionate or with the oil vehicle. After treatment in adulthood with urine or with oestradiol benzoate, androgenized voles were less likely than normal females to display behavioural oestrus and were more likely to engage in agonistic behaviour in tests with stud males. Uteri of androgenized and control females treated with oestradiol benzoate in adulthood manifested similar increases in weight; however, only normal females treated with male urine showed increased uterine weights. Males castrated in adulthood did not display lordosis after treatment with oestradiol benzoate. Sexual differentiation induced by neonatal testicular secretions appears to limit responsiveness of the adult neuroendocrine axis to chemosensory stimuli in male urine.

Animals↗

PubMed1984

Ovarian modulation of lipoprotein lipase activity in white adipose tissue of ground squirrels.

Golden-mantled ground squirrels were ovariectomized (OVX) or Sham-OVX during the weight gain phase of the circannual body weight cycle. Other squirrels, OVX or Sham-OVX during the weight loss phase, were subcutaneously implanted with estradiol-filled or empty Silastic capsules. The mass of several fat pads as well as adipose tissue lipoprotein lipase (LPL) activity were determined at autopsy. Ovariectomy at either phase of the annual cycle was without effect on body weight. However, LPL activity of the parametrial fat pad was increased in OVX as compared to Sham-OVX squirrels. Fourteen days of estradiol treatment during the weight loss phase decreased the mass and LPL activity of the retroperitoneal fat depot but did not affect these parameters in perirenal adipose tissue. Although estradiol exerts different or opposite effects on body mass and food intake of rats and ground squirrels, ovariectomy and estrogen treatment affect LPL activity in a similar fashion in both species.

Adipose Tissue↗

PubMed1984

Rapid recovery of body mass after surgical removal of adipose tissue in ground squirrels.

A substantial proportion of total adipose tissue mass was surgically removed from female ground squirrels during weight gain or weight loss phases of the circannual body weight cycle. Within 2 months of fat removal, squirrels had restored body mass to levels appropriate to the stage of the annual body weight cycle. These findings suggest that ground squirrels may use feedback from body lipids in controlling body weight.

Acclimatization↗

PubMed1984

Photoperiodic influences on testicular development of deer mice from two different altitudes.

Onset of breeding activity tends to occur later in the year for deer mice from progressively higher elevations. We tested the hypothesis that the critical day length for development and maintenance of the reproductive system is longer for mice from higher elevations. Offspring of deer mice trapped at elevations of 1219 and 3048 m were raised from birth to 55 days of age in photo-periods that provided 10, 11, 12, 13 or 16 h light/day. Short day lengths (less than 13 h light/day) retarded maturation of the reproductive apparatus of juveniles from both elevations. The critical photoperiod for development of the reproductive apparatus was 1 h shorter for mice derived from stock trapped at 3048 m as compared to 1219 m. The gonads of adult mice from each elevation were unresponsive to photoperiod and remained functional in all day lengths tested (10-13 h light/day). Photoperiod does not appear to be a proximate factor underlying the altitudinal gradient in reproduction of male deer mice.

Altitude↗

PubMed1984

Short photoperiods counteract the effects of ovariectomy on energy balance of voles.

Adult female meadow voles maintained from birth in a long photoperiod (14 h light, 10 h darkness; LD 14:10) were ovariectomized or sham-ovariectomized and housed subsequently in long or short (LD 10:14) photoperiods for 10 wk. Absolute and relative daily food intake, body mass, carcass lipid and water content, and lipoprotein lipase activity of white adipose tissue were reduced in voles housed in short photoperiods. Ovariectomy resulted in increases in food intake and body weight and altered carcass composition in long-day voles, but these changes were negated in voles kept in short photoperiods. Responsiveness to short photoperiods promotes winter weight loss and subsequent energy intake savings and counteracts the body weight increases normally associated with gonadal quiescence and diminished hormone secretion.

Animals↗

PubMed1984

Circannual rhythms of body weight in pallid bats.

Body weights of pallid bats collected in the field were substantially greater during October and December than between April and September. When maintained in the laboratory under constant conditions of photoperiod and temperature, bats manifested circannual rhythms in body weight. These endogenous cycles were observed in adult and juvenile individuals of both sexes and in bats housed in long or short photoperiods (14 or 10 h of light/day). The period of the cycle averaged 10 mo. Photoperiod influenced the timing and magnitude of the body weight cycle; bats kept in short photoperiods achieved peak body weights earlier than animals housed in long day lengths. We propose that day length is one of the proximate factors for synchronization of circannual cycles of pallid bats.

Acclimatization↗

PubMed1984

Gonadal and photoperiodic control of seasonal body weight changes in male voles.

After 15 wk in a short photoperiod (10 h of light/day), adult male voles weighed 25% less and consumed 33% less food than did voles in a long photoperiod (14 h light/day). Neither body weight nor food intake differed among long- and short-day castrated voles. After 19 wk, castrated long-day voles weighed less than did intact animals. Voles reduced their body weight during the first 15 wk in the short photoperiod and increased their body mass during the succeeding 15 wk. Body mass of short-day voles was positively correlated with combined testes weight. Voles in the short photoperiod collected less nesting material than did their long-day counterparts at week 31. Pelage characteristics at week 32 were not affected by castration or by photoperiod. We conclude that the decreased body mass of male voles during the late summer, fall, and early winter reflects a decrease in circulating levels of testicular hormones; gonadal recrudescence and increased circulating androgen levels are in part responsible for the subsequent seasonal increase in body weight. Part of the increased body mass in late winter in field populations or in laboratory voles after 15 wk in the short photoperiod is independent of the resumption of gonadal activity. Fluctuations in neural and endocrine processes, rather than availability of food, are the principal factors underlying seasonal changes in energy balance.

Adaptation, Physiological↗

PubMed1984

Photoperiod influences the annual reproductive cycle of the male pallid bat (Antrozous pallidus).

Adult pallids bats collected in April or May, were maintained in short or long photoperiods (10 or 14 h light/day) for 3-6 months. In August, the short-day bats had regressed testes, epididymal spermatozoa and fully developed accessory sex glands, corresponding to the autumnal reproductive condition of field animals; long-day bats had testes undergoing spermatogenesis, few epididymal spermatozoa and undeveloped accessory sex glands (summer reproductive condition). Bats in each photoperiod manifested the expected autumnal reproductive pattern in October. We suggest that photoperiod influences the reproductive physiology of male pallid bats by affecting an endogenous circannual reproductive rhythm.

Animals↗

PubMed1983

Short photoperiods reduce winter energy requirements of the meadow vole, Microtus pennsylvanicus.

Adult male voles were maintained for 10 weeks in long or short photoperiods (14 or 10 hr light/day) at 23 degrees C and then for 6 days at 10 degrees C. Short photoperiod voles weighed approximately 20% less and consumed 36% and 42% fewer calories than did long-day animals at 23 degrees C and 10 degrees C, respectively. Relative energy intake (kcal/g body mass) was lower for short-than long-day voles at 10 degrees C. Short-day animals gathered more nesting material than their long-day counterparts at both ambient temperatures. Absolute as well as relative wet weights of interscapular brown adipose tissue were reduced in short-day voles and their testes were regressed. Two types of dorsal pelage hairs were longer in short- than in long-day voles; a dense undergrowth of light gray hairs, present in all short-day voles, was completely absent or only sparsely represented in the pelage of long-day animals. Photoperiod is a major proximate factor mediating winter adaptations of meadow voles: By decreasing body mass and reducing food requirements, short photoperiods presumably diminish winter foraging activity and energy devoted to thermoregulation. Increases in nest-building activity, growth of a winter pelage, and testicular regression are other changes induced by short daylengths that facilitate survival of over-wintering voles.

Animals↗

PubMed1983

Circannual and seasonal variations in plasma luteinizing hormone levels of ovariectomized ground squirrels (Spermophilus lateralis).

Plasma luteinizing hormone (LH) levels were determined at monthly intervals in intact and ovariectomized squirrels maintained in a constant 14L:10D photoperiod at a temperature of 23 +/- 2 degrees C. LH was undetectable (less than 0.9 ng/ml) in plasma of intact females at all times of year. Females ovariectomized (OVX) at 9.5 months of age in March showed substantial increases in plasma LH in May and June but LH was undetectable between July and November. Females ovariectomized at 13 months of age in July first manifested detectable LH levels the following January and February (6-7 months post-ovariectomy). Very few adult females trapped in May and ovariectomized in August had detectable LH levels within 2 months of ovariectomy; however, females ovariectomized the following February had detectable LH titers 1 month later. Long-term studies of individual OVX squirrels indicated peak LH levels between March and June, 1980, relatively low or undetectable titers between August and December and elevated LH levels between January and March, 1981. The results are suggestive of a circannual rhythm of LH secretion which appears restricted to one season of the year and occurs independently of steroid feedback from the ovaries; ovarian steroids only modulate the levels of plasma LH during the brief annual period of hypothalamo-hypophysial activity. We suggest that onset and termination of LH release are mediated by central nervous system circannual clocks.

Animals↗

PubMed1983

Latitude of origin influences photoperiodic control of reproduction of deer mice (Peromyscus maniculatus).

Three subspecies of Peromyscus maniculatus originating from different latitudes were maintained from birth in light dark cycles that provided between 10 and 18 h of light per day. At 50 days of age, Chihuahua, Mexico mice (latitude of origin 27 degrees N) and South Dakota, U.S.A. mice (44 degrees N) kept in the 10L:14D photoperiod had reduced gonadal and seminal vesicle weights and a lower spermatogenic index than corresponding mice kept in a 14L:10D photoperiod. Some Chihuahua and South Dakota mice, apparently constituting nonphotoperiodic subpopulations, developed their gonads while kept in the short-day photoperiod. The critical day length for stimulation of sexual maturation was greater for mice from Manitoba, Canada (55 degrees N) than for mice from the lower latitudes. At 70 days of age, testes and seminal vesicle weights, and the spermatogenic index of Manitoba mice in the 14L:10D photoperiod, were lower than those of animals maintained in 16L:8D and 18L:6D photoperiods. Responsiveness to short day lengths was greater among adult South Dakota than adult Chihuahau mice and melatonin treatment significantly reduced testes weights of South Dakota but not of Chihuahua adult mice. Photoperiodic regulation of the reproductive system varies with latitude of origin. Differences in the critical day length necessary for stimulating development of functional reproductive activity and variations in the percent of photoperiodic animals within each subspecies, appear to contribute to latitudinal gradients in reproduction.

Animals↗

PubMed1983

Seasonal variations in plasma luteinizing hormone levels of gonadectomized male ground squirrels (Spermophilus lateralis).

Plasma luteinizing hormone (LH) levels were determined at monthly intervals in intact and orchidectomized ground squirrels maintained in a constant 14L:10D photoperiod at a temperature of 23 +/- 2 degrees C. Animals were orchidectomized or sham operated at different ages and at different stages of the annual reproductive cycle. LH levels were elevated in orchidectomized as compared to intact males within 1 month, and often within 48 h, after orchidectomies performed either before or after the normal breeding season. LH levels tended to remain chronically elevated in long-term orchidectomized males. Although negative feedback regulation of LH by the testes was evident at most stages of the reproductive cycle, effects of orchidectomy on LH were most pronounced during the nonbreeding season when plasma LH titers of intact males were at their annual nadirs, and less pronounced or absent during the breeding season when levels were normally elevated in intact males. For most of the year male gonadal hormones exert negative feedback on LH release. We hypothesize that under the influence of a circannual timing mechanism, sensitivity to steroid feedback is reduced as the breeding season approaches and LH secretion increases despite the attendant rise in plasma androgen levels. These results contrast with data for female squirrels in which there is a seasonally restricted and characteristically brief elevation of plasma LH after ovariectomy; in females, but not in males, onset and termination of LH secretion appear to be regulated by a circannual clock that functions independently of gonadal secretions.

Animals↗

PubMed1983

Lability and diversity of circadian rhythms of cotton rats Sigmodon hispidus.

Cotton rats (Sigmodon hispidus) were maintained from birth in constant LD 14:10 photoperiods and temperatures. Wheel running was diurnal for 6 of 13 juvenile rats and nocturnal for most others. Most diurnal rats eventually added nocturnal activity components. In constant darkness the activity rhythms of adult rats free-ran with a period of 23.2 +/- 0.3 h; in constant illumination the period was 24.7 +/- 0.1 h, in conformation to Aschoff's rule for nocturnal rodents. Some previously nocturnal adult rats eventually adopted stable diurnal activity cycles and other were successively nocturnal, diurnal for 6 mo, and then nocturnal again while maintained in the LD 14:10 photoperiod. The existence of multiple activity types, as well as the spontaneous inversions from nocturnal to diurnal status substantiate and extend field observations of this species. Seasonal inversions from nocturnal to diurnal activity, previously attributed to fluctuating environmental conditions, may also be subject to regulation by endogenous processes. It is suggested that spontaneous phase reversals in activity reflect changes in entrainment of circadian pacemakers by the light-dark cycle or altered relations between such pacemakers and the overt activity rhythm.

Animals↗