Learn More
1. Light-induced phase shifts of the circadian rhythm of wheel-running activity were used to measure the photic sensitivity of a circadian pacemaker and the visual pathway that conveys light information to it in the golden hamster (Mesocricetus auratus). The sensitivity to stimulus irradiance and duration was assessed by measuring the magnitude of(More)
Photic information entrains a circadian pacemaker located in the suprachiasmatic nucleus (SCN) of the mammalian hypothalamus to environmental light/dark cycles. To determine whether light regulates c-fos gene expression in the SCN, we have measured c-fos mRNA levels in the SCN of the golden hamster. We report that, during the subjective night, light causes(More)
The suprachiasmatic nuclei (SCN) of the hypothalamus comprise the primary pacemaker responsible for generation of circadian rhythms in mammals. Light stimuli that synchronize this circadian clock induce expression of the c-fos gene in rodent SCN, which suggests a possible role for Fos in circadian entrainment. Appropriate light stimuli also induce the(More)
Visual sensitivity for light suppression of pineal melatonin was measured in golden hamsters using 300 s stimuli of monochromatic light (503 nm) in constant darkness. Increasing stimulus irradiance caused a monotonic decrease in pineal-melatonin content. Irradiance greater than 3.5 X 10(10) photons cm-2.s-1 caused significant reductions of melatonin in the(More)
The ability of social stimuli to act as entraining agents of circadian rhythms was investigated in golden hamsters (Mesocricetus auratus). In a first experiment, pairs of male hamsters (one of them enucleated and the other intact) were maintained under a ligh-dark (LD) cycle with a period of 23.3 h. Running-wheel activity was recorded to determine the(More)
The sensitivity of the visual pathway that subserves circadian entrainment was measured in hamsters after prior stimulation and using trains of multiple pulses. Immediately after subsaturating stimulation in the late subjective night, there was a significant decrease in responsiveness that persisted for at least 1 h. The reduced responsiveness was not due(More)
Despite the well known role of the light-dark cycle in the entrainment of circadian rhythms, very little is known about the neurochemical events that mediate the effects of light on the mammalian circadian clock. Recent anatomical and pharmacological data support the hypothesis that acetylcholine may be involved in relaying light-dark information from the(More)
We have characterized a decrease in photic responsiveness of the mammalian circadian entrainment pathway caused by light stimulation. Phase delays of the running-wheel activity rhythm were used to quantify the photic responsiveness of the circadian system in mice (C57BL/6J). In an initial experiment, the authors measured the responsiveness to single(More)
Muscle strength and proprioception deficits have been recognized in knee OA. Pain is the symptomatic hallmark of knee OA. Indirect evidence suggests that muscle strength and proprioception deficits may be interrelated and that pain may have a confounding influence on the measurement of these factors in knee OA. However, these relationships have never been(More)
Photoperiodic regulation of testicular function was investigated in homozygous tau mutant hamsters; these animals have an innate circadian period of about 20 h. In 20-h light:dark (LD) cycles, the minimum photoperiod required to prevent testicular regression was between 10.0 and 11.5 h per 20-h cycle (equivalent to 12.0-13.8 circadian hours). This was(More)