Journal Article10.1177/074873048600100405
Lesions of the thalamic intergeniculate leaflet alter hamster circadian rhythms.
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TL;DR: It is demonstrated that destruction of the GHT in the hamster alters phase shifting in response to periods of light or dark, and a role for the G HT in mediating several photic effects on the circadian system is indicated.
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Abstract: We have investigated the effects of destruction of the geniculo-hypothalamic tract (GHT) on the circadian system of golden hamsters. In the first experiment, intact hamsters were housed in constant darkness, and phase shifts in running-wheel activity rhythms were assessed following 15-min light pulses administered at circadian time (CT) 12 (defined as the beginning of activity), CT 14, CT 18, and CT 20. Responses to light pulses at the same CTs were then reassessed after GHT lesions. Hamsters with complete lesions showed decreases in phase advances caused by light pulses at CT 18 and CT 20. Phase delays elicited by light at CT 12 and CT 14 were not altered. In a second study, intact and GHT-ablated hamsters housed in constant light received 6-hr dark pulses at various CTs. Hamsters with complete GHT ablation showed smaller advances than controls to dark pulses centered on CT 8-10. After 110 days in constant light, 7 of 10 intact hamsters showed splitting of their activity rhythms into two components, while only 1 of the 8 similarly treated ablated hamsters displayed dissociated activity components. Ablated hamsters had significantly shorter free-running periods during the first 35 days of exposure to constant light than did the intact hamsters. These results demonstrate that destruction of the GHT in the hamster alters phase shifting in response to periods of light or dark, and they indicate a role for the GHT in mediating several photic effects on the circadian system.
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TL;DR: In this paper, a model of non-parametric entrainment of circadian pacemakers is tested for the case of nocturnal rodents using 1 or 2 light pulses per cycle, and the model makes use of the available data on freerunning period (τ) in constant darkness and on phase response curves (PRC) for short light pulses.
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A functional analysis of circadian pacemakers in nocturnal rodents
Serge Daan,Colin S. Pittendrigh +1 more
TL;DR: In this article, phase response curves for 15′ bright light pulses of four species of nocturnal rodents are described, and the response to a resetting stimulus at a given phase of the rhythm is correlated with the individual's free-running period.
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Neuropeptide Y: role in light-dark cycle entrainment of hamster circadian rhythms
TL;DR: Microinjection of neuropeptide Y into the suprachiasmatic region of the hypothalamus phase shifted the circadian activity rhythm of hamsters housed in constant light and suggested that NPY functions as a chemical messenger important for the light-dark cycle entrainment of circadian rhythms.
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