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Biomedical subjects

I Zucker

Publications and source records attributed to I Zucker.

At least 145 records · Page 8Linked to original sources
PubMed1980

Regulation by the pituitary gland of circadian rhythms in the hamster.

Locomotor activity of male hamsters was recorded during long-term exposure to constant light (LL), constant darkness (DD) and during entrainment (modification of a circadian rhythm) to a 14 h light : 10 h darkness photoperiod (14L : 10D). In LL the period of the activity cycle was substantially longer in hypophysectomized than in control animals. This difference persisted during tests in DD. Although hypophysectomy reduced the duration of the active phase in some hamsters, overall the difference between the groups was not significant. The phase angle of onset of activity in 14L : 10D was not affected by hypophysectomy. Hypophysectomized female hamsters tested in DD had activity rhythms whose periods were longer than those of control animals; they were also significantly less active than corresponding controls during the first 4 h of the subjective night but the duration of the active phase did not differ significantly between the groups. These results suggest that hormones of the pituitary-gonadal axis modulate the period of circadian oscillation.

Activity Cycles↗
PubMed1978

Photoperiodic regulation of the hamster testis: dependence on circadian rhythms.

The testes of hamsters exposed to short days (10 hr of light per day) regress within 13 weeks. Administration of 7.5% deuterium oxide to hamsters lengthens the period of free running circadian activity rhythms by 2.2% and prevents testicular regression during short-day exposure. This consistent with predictions derived from an external coincidence model for photoperiodic time measurement: Deuterium oxide changes phase relationships between the light-dark cycle and the circadian system, the hamster's daily photosensitive phase is stimulated with light during short days, and the testes remain large. Conservation of the period of circadian rhythms within narrow limits has adaptive significance for hamster photoperiodism and for the occurrence and phasing of the annual reproductive cycle.

Animals↗
PubMed1978

Photoperiodic regulation of copulatory behaviour in the male hamster.

The influence of daylength on copulatory behaviour was assessed by comparing male hamsters exposed to long or short photoperiods (14 or 2 h light/24 h). Copulation declined in animals transferred from long to short days; 13 out of 14 hamsters ceased to ejaculate within 9 weeks and many no longer intromitted in tests with sexually receptive female hamsters. The decline in copulation in hamsters experiencing short days was associated with atrophy of the gonads and flank glands. Behavioural changes in these animals were far more gradual than those observed in hamsters after surgical castration. There was significantly more mating behaviour in tests during the subjective night of the hamsters than during their subjective day. Exogenous testosterone was more effective in restoring copulation in castrated hamsters exposed to long days than in castrated animals experiencing short days. This suggests that in short days the substrate for copulatory behaviour is relatively refractory to androgens. Photoperiodically mediated changes in behaviour, physiology and morphology may each contribute directly to the reproductive quiescence presumed to occur in the field during the short days of autumn and winter.

Animals↗
PubMed1977

Estradiol shortens the period of hamster circadian rhythms.

Continuous administration of estradiol benzoate by means of subcutaneously implanted capsules shortened the free-running circadian period of locomotor activity of blind hamsters (Mesocricetus auratus) that had had their ovaries removed. Estradiol also advanced the phase of the wheel running of sighted female hamsters without ovaries that were entrained to a photoperiod with 12 hours of light and 12 of darkness. These results, and findings from hamsters undergoing natural estrous cycles, indicate that endogenous estradiol is involved in the regulation of circadian periodicity.

Animals↗
PubMed1976

Circadian organization of the estrous cycle of the golden hamster.

In constant dim illumination the hamster estrous cycle free-runs with a period that is a quadruple multiple of the concurrently recorded rhythm of wheel-running activity; both activity and estrous cycles are generated by biological clocks. Maintenance of stable phase angle differences between heat onset and running onset before and after treatment with deuterium oxide suggests that a common circadian system generates periodicities in estrus and activity. An organization of the estrous cycle is proposed in which the stimulus for the ovulatory surge of luteinizing hormone is generated by a circadian system that includes the suprachiasmatic nuclei of the hypothalamus. Various possible interactions of estradiol and photoperiod with the neurogenic stimulus for the luteinizing hormone surge are described and implications of different types of circadian organization of the estrous cycle for theories of sexual differentiation are considered.

Animals↗
PubMed1976

Light, behavior, and biologic rhythms.

The most potent environmental synchronizer of "biologic clocks" in mammals is the light-dark cycle. The author describes experiments that identify a particular pathway--a derect connection between retina and hypothalamus--as the main route by which such biologic rhythms as the daily activity cycle, the estrous cycle, and the annual reproductive cycle are entrained to the external environment.

Animals↗