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  • Springer  (127)
  • Canadian Science Publishing  (21)
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  • 1
    Electronic Resource
    Electronic Resource
    Extraocular light perception in photoperiodic responses of the White-crowned sparrow (Zonotrichia leucophrys) and of the Golden-crowned sparrow (Z. atricapilla) (1971)
    Springer
    Journal of comparative physiology 75 (1971), S. 323-331 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Testicular maturation, migratory restlessness (Zugunruhe) and fattening are induced in many species of birds by long day-lengths in Spring. We have tested the hypothesis that extraocular photoreceptors located in the brain are involved in mediating these photoperiodic responses in White-crowned sparrows (Zonotrichia leucophrys) and Golden-crowned sparrows (Z. atricapilla). Our approach consisted in reducing the amount of light penetrating to the brain with either black India ink injected under the skin of the head (Golden-crowned sparrows) or by covering the entire head (except eyes and beak) with a black collodion hood (White-crowned sparrows). Birds treated in these ways showed significantly less testicular growth, Zugunruhe and premigratory fattening when placed under a 16L-8D photoperiod than control birds which did not have their brains shielded from light. However, even when the bird brains were shielded from light and although light intensity was close to threshold level, some testicular growth, Zugunruhe and fattening did occur. We conclude that extraocular photoreceptors are involved in the control of the three photoperiodic responses studied, but that the eyes are possibly of significance as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00340684
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  • 2
    Electronic Resource
    Electronic Resource
    Extraretinal photoreception during the gonadal photorefractory period in the golden-crowned sparrow (1975)
    Springer
    Journal of comparative physiology 96 (1975), S. 27-36 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Extraretinal photoreception is involved in the perception of light used to measure photoperiodic time during the initiation of gonadal growth in a number of birds. Evidence is presented which demonstrates that extraretinal photoreceptors are also involved in measuring photoperiodic time during the gonadal photorefractory period in the goldencrowned sparrow (Fig. 3). Untreated sparrows were able to terminate the refractory condition while being exposed to long dim days (16DL:8D; DL=0.2 lux). However, birds which had their head feathers clipped to allow more light to penetrate through to the brain were maintained in the refractory state under the same lighting conditions. These results demonstrate that extraretinal photoreception is involved in the maintenance of photorefractoriness in birds. It has been suggested that the eyes and extraretinal photoreceptors may both be involved in the initiation of gonadal growth in golden-crowned sparrows (Gwinneret al., 1971). This conclusion was based on the observation that a reduced rate of gonadal growth occurred in sparrows with shielded brains as compared to unshielded controls when both groups of birds were exposed to the same light treatment (i.e. 16L:8D; L=6 lux). The results presented here suggest that at a light intensity of 6 lux, light may have been reaching extraretinal photoreceptors even in birds with shielded brains. Therefore, the eyes may not be involved in testicular recrudescence in this species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00611960
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  • 3
    Electronic Resource
    Electronic Resource
    Circadian rhythmicity and the initiation of gonadal growth in sparrows (1974)
    Springer
    Journal of comparative physiology 92 (1974), S. 59-64 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary White-crowned and golden-crowned sparrows were held under a variety of light cycles in which a main 8-hour light period was combined with dark periods of varying durations. Gonadal growth was not observed in birds under cycles of 24-(8L∶16D), 48-(8L∶40D) or 72-hours (8L∶64D). Growth was initiated in sparrows under cycles of 36-(8L∶28D) and 60-hours (8L∶52D). These results are consistent with the hypothesis that circadian rhythmicity is involved in photoperiodic time measurement during the initiation of gonadal growth in birds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696526
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  • 4
    Electronic Resource
    Electronic Resource
    Central administration of muscimol phase-shifts the mammalian circadian clock (1989)
    Springer
    Journal of comparative physiology 164 (1989), S. 805-814 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The suprachiasmatic nucleus (SCN) of the hypothalamus contains a neural oscillatory system which regulates many circadian rhythms in mammals. Immunohistochemical evidence indicates that a relatively high density of GABAergic neurons exist in the suprachiasmatic region. Since intraperitoneal injections of the benzodiazepine, triazolam, have been shown to induce phase shifts in the free-running circadian rhythm of locomotor activity in the golden hamster, the extent to which microinjections of muscimol, a specific agonist for gamma-aminobutyric acid (GABA), may cause phase-shifts in hamster activity rhythms was investigated. Stereotaxically implanted guide cannulae aimed at the region of the SCN were used to deliver repeated microinjections in individual animals. A phase-response curve (PRC) generated from microinjections of muscimol revealed that the magnitude and direction of permanent phase-shifts in the activity rhythm were associated with the time of administration. The PRC generated for muscimol was characterized by maximal phase-advances induced 6 h before activity onset and by maximal phase-delays which occurred 6 h after activity onset. The PRC for muscimol had a shape similar to a PRC previously generated for the short-acting benzodiazepine, triazolam. Single microinjections of different doses of muscimol given 6 h before activity onset induced phase-advances in a dose-dependent fashion. Histological analysis revealed that phase shifts induced by the administration of muscimol were associated with the proximity of the injection site to the SCN area. These data indicate that a GABAergic system may exist within the suprachiasmatic region as part of a central biological clock responsible for the regulation of the circadian rhythm of locomotor activity in the golden hamster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616752
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  • 5
    Electronic Resource
    Electronic Resource
    Changes in locomotor activity associated with the photoperiodic response of the testes in male golden hamsters (1979)
    Springer
    Journal of comparative physiology 132 (1979), S. 277-284 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Male golden hamsters were exposed to either 14 h of light per 24 h (LD 14∶10) or LD 6 ∶18 for 210 days, in order to assess the effects of the light-dark cycle and changes in the reproductive system upon locomotor activity. Wheel-running activity was recorded continuously, and testicular size and serum testosterone concentrations were measured periodically throughout the study. 2. The short photoperiod induced a decrease in testicular width, serum levels of testosterone, and the number of wheel revolutions per 24-h period, when compared to the levels of these variables exhibited by LD 14∶10 hamsters. Prolonged exposure to LD 6∶18 resulted in a spontaneous increase in these three parameters to levels indistinguishable from those observed in LD 14∶10 animals. Neither testicular width, serum testosterone concentration, nor quantity of activity changed significantly in LD 14∶10 hamsters throughout the study. 3. LD 6∶18 exposure also induced an expansion of the daily activity time; this increased duration of the daily active phase persisted, even after the spontaneous increase in testicular width, serum testosterone concentration, and number of wheel revolutions per day. The duration of the daily active phase was unchanged in LD 14∶10 animals through the course of the experiment. 4. The onset of activity in all hamsters exposed to LD 14∶10 occured between 0–1 h after lights-off and did not vary appreciably for individual animals during the 210 days of LD 14∶10. The time required for stable reentrainment following a shift from LD 14∶10 to LD 6∶18 varied between 30 and 120 days among individual hamsters, and the phase relationship of activity onset to lights-off after 200 days of LD 6∶18 ranged between -1 and — 6 h. The time course of reentrainment to short days did not appear to be affected by changing testosterone levels. 5. Coincident with LD 6∶18-induced testicular regression was an increased lability of the time of activity onset each day. A return to stability in the day-to-day time of activity onset was coincident with spontaneous testicular recrudescence in LD 6∶18 hamsters. Hamsters maintained on LD 14∶10 exhibited a stable time of daily activity onset throughout the investigation. 6. These results indicate that the number of wheel revolutions per day and the lability of daily activity onset are correlated with light-induced changes in the hamster reproductive system. In contrast, the duration of the daily active phase and the phase relationship between activity onset and lights-off are relatively independent of changes in the reproductive system and are a function of the entraining light-dark cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00614498
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  • 6
    Electronic Resource
    Electronic Resource
    Splitting of the circadian rhythm of activity in hamsters: Effects of exposure to constant darkness and subsequent re-exposure to constant light (1982)
    Springer
    Journal of comparative physiology 145 (1982), S. 405-411 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The circadian rhythm of wheel running behavior was observed to dissociate into two distinct components (i.e. ‘split’) within 30 to 110 days in 56% of male hamsters exposed to constant light (Figs. 1–2). Splitting was abolished in all 16 animals that were transferred from constant light (LL) to constant darkness (DD) within 1–4 days of DD, and the components of the re-fused activity rhythm assumed a phase relationship that is characteristic of hamsters maintained in DD (Figs. 3–5). Re-fusion of the split activity rhythm was accompanied by a change in period (τ); in 14 animals τ increased while in the other 2 animals τ decreased after transfer to DD. After 10–30 days in DD, the hamsters were transferred back into LL at various time points throughout the circadian cycle. A few of these animals went through two or three LL to DD to LL transitions. The effect of re-exposure to LL was dependent on the phase relationship between the transition into LL and the activity rhythm. A rapid (i.e. 1–4 days) induction of splitting was observed in 7 of 9 cases when hamsters were transferred into LL 4–5 h after the onset of activity (Fig. 5). In the other 2 animals, the activity pattern was ultradian or aperiodic for 20 to 50 days before eventually coalescing into a split activity pattern. In contrast, transfer of animals (n = 13) from DD to LL at other circadian times did not result in the rapid induction of splitting and the activity rhythm continued to free-run with a single bout of activity (Fig. 5). Importantly, a transfer from DD to LL 4–5 h after the onset of activity did not induce splitting if the hamsters had not shown a split activity rhythm during a previous exposure to LL (n=10; Fig. 6). These studies indicate that transfer of split hamsters from LL to DD results in the rapid re-establishment of the normal phase relationship between the two circadian oscillators which underlie the two components of activity during splitting. In addition, there appears to be a history-dependent effect of splitting which renders the circadian system susceptible to becoming split again. The rapid re-initiation of the split condition upon transfer from DD to LL at only a specific circadian time is discussed in terms of the phase response curve for this species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00619345
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of season on circadian activity rhythms of the starling (1971)
    Springer
    Naturwissenschaften 58 (1971), S. 627-628 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01185624
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  • 8
    Electronic Resource
    Electronic Resource
    Daily melatonin injections inhibit short-day-induced testicular regression in hamsters (1980)
    Springer
    Cellular and molecular life sciences 36 (1980), S. 1426-1427 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Daily injections of melatonin were found to retard testicular regression in hamsters exposed to LD 10:14, if the injections occurred in the morning (i.e., 0.5 h after lights on), but not if they occurred in the afternoon (i.e., 6 h after lights on). These results indicate that appropriately timed injections of melatonin can at least partially block the inhibitory effects of short days on gonadal activity in the photoperiodic hamster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01960141
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  • 9
    Electronic Resource
    Electronic Resource
    β-Methyl carboline, a benzodiazepine inverse agonist, attenuates the effect of triazolam on the circadian rhythm of locomotor activity (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 334-337 
    Details
    ISSN: 1420-9071
    Keywords: Benzodiazepine ; circadian rhythm ; gamma-aminobutyric acid ; inverse agonist ; suprachiasmatic nucleus ; triazolam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The benzodiazepine triazolam, the benzodiazepine inverse agonist, β-methyl carboline (β-CCM) or both, were administered to adult male hamsters under conditions of constant light. When given alone, triazolam induced phase advances in the circadian activity rhythm of about 90 min, while β-CCM when given alone, had no effect on phase of the activity rhythm. However, when triazolam and β-CCM were given at the same time, the magnitude of the phase advances induced by triazolam were attenuated to about 30 min. These data, in conjunction with previous results, provide pharmacological evidence for a GABAergic system involved in the regulation of a central circadian pacemaker.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01957468
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of testosterone on the hypothalamic-pituitary-gonadal axis of pinealectomized and pineal-intact male rats (1979)
    Springer
    Cellular and molecular life sciences 35 (1979), S. 705-706 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Previous studies indicate that steroid hormones alter pineal biochemistry, and it has been suggested that at least part of the negative feedback effect of steroid hormones on pituitary gonadotropin release may be mediated by the pineal gland. In this study, pinealectomy did not alter the inhibitory effect of testosterone on neuroendocrine-gonadal activity in the male rat, suggesting that the pineal gland does not mediate the response of the rat hypothalamic-pituitary axis to testosterone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01960410
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