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Golden-mantled ground squirrels (Spermophilus lateralis) undergo seasonal hibernation during which core body temperature (T(b)) values are maintained 1-2 degrees C above ambient temperature. Hibernation is not continuous. Squirrels arouse at approximately 7-day intervals, during which T(b) increases to 37 degrees C for approximately 16 h; thereafter, they(More)
Exposure to low ambient temperatures (Ta) accelerates appearance of the winter phenotype in Siberian hamsters transferred from long to short day lengths. Because melatonin transduces the effects of day length on the neuroendocrine axis, the authors assessed whether low Ta promotes the transition to winterlike traits by accelerating the onset of increased(More)
The role of the intergeniculate leaflet of the thalamus (IGL) in photoperiod responsiveness was examined in a laboratory-selected line of photoperiod nonresponsive (NR) Siberian hamsters. NR hamsters fail to exhibit typical winter-type responses (i.e., gonadal regression and development of winter-type pelage) when exposed to short day lengths (e.g., 10 h of(More)
Groups from three different breeding lines of Siberian hamsters (UNS = general colony animals, PNRa = selected for photoperiod nonresponsiveness as adults, PNRj = selected for photoperiod nonresponsiveness as juveniles) were exposed to short days at weaning and again as adults (Experiment 1) or only as adults (Experiment 2). The proportion of photoperiod(More)
The oxidative modification of low density lipoprotein (LDL) may provide a crucial link between plasma LDL and the atherosclerotic lesion. The studies presented herein define time-dependent modifications of LDL constituents caused by CuSO4-catalyzed oxidation. Measurement of the cholesterol content of oxidized LDL by the cholesterol esterase-oxidase assay(More)
The effects of Se and I supplementation on growth rate and on thyroid and somatotropic function were examined for heifer calves from two herds fed pasture. Supplementation of calves with intraruminal Se pellets increased the basal plasma concentration of 3,5,3'-triiodothyronine and reduced the basal plasma concentration of thyroxine for both herds. For one(More)
In studies of photoperiodism, animals typically are transferred abruptly from a long (e.g., 16 h light per day [16L]) to a short (8L) photoperiod, and circadian oscillators that regulate pineal melatonin secretion are presumed to reentrain rapidly to the new photocycle. Among rats and Siberian hamsters, however, reentrainment rates vary depending on whether(More)
Siberian hamsters (Phodopus sungorus) exhibit seasonal cycles of reproduction driven by changes in day length. Day length is encoded endogenously by the duration of nocturnal melatonin (Mel) secretion from the pineal gland. Short-duration Mel signals stimulate reproduction and long-duration signals inhibit reproduction. The mechanism by which Mel signals(More)
The mid-winter development of refractoriness to melatonin (Mel) triggers recrudescence of the atrophied reproductive apparatus of rodents. As a consequence, over-wintering animals become reproductively competent just before the onset of spring conditions favorable for breeding. The neural target tissues that cease to respond to winter Mel signals have not(More)
Seasonally breeding animals use a combination of photic (i.e. day length) and nonphotic (e.g. food availability, temperature) cues to regulate their reproduction. How these environmental cues are integrated is not understood. To assess the potential role of two candidate neuropeptides, kisspeptin and RFamide-related peptide-3 (RFRP), we monitored regional(More)