Gradual reappearance of post-hibernation circadian rhythmicity correlates with numbers of vasopressin-containing neurons in the suprachiasmatic nuclei of European ground squirrels

Abstract

Gradual reappearance of post-hibernation circadian rhythmicity correlates with numbers of vasopressin-containing neurons in the suprachiasmatic nuclei of European ground squirrels Hut, R.A; van der Zee, E.A; Jansen, K; Gerkema, M.P.; Daan, S. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract European ground squirrels (Spermophilus citellus) in outside enclosures show suppressed circadian rhythmicity in body temperature patterns during the ®rst days of euthermia after hibernation. This may re¯ect either gradual reappearance of circadian rhythmicity following suppressed functioning of the circadian system during hibernation, or it may re¯ect transient days during re-entrainment of the circadian system which, during hibernation, has drifted out of phase with the environmental light-dark cycle. Here we report that animals kept under continuous dim light conditions also showed absence of circadian rhythmicity in activity and body temperature in the ®rst 5±15 days after hibernation. After post-hibernation arrhythmicity, spontaneous circadian rhythms re-appeared gradually and increased daily body temperature range. Numbers of argininevasopressin immunoreactive neurons in the suprachiasmatic nuclei correlated positively with individual circadian rhythmicity and increased gradually over time after hibernation. Furthermore, circadian rhythmicity was enhanced rather than suppressed after exposure to a light-dark cycle but not after a single 1-h light pulse (1,700 lux). The results support the view that the functioning of the circadian system in the European ground squirrel is suppressed during hibernation at low temperatures and that it requires several days of euthermia to resume its summer function.Keywords Hibernation á Post-hibernation arrhythmicity á Circadian system á SCN á AVP Abbreviations AVP arginine-vasopressin á AVPir AVPimmunoreactive á ct circadian time á LD light-dark á PAF paraformaldehyde á PB phosphate buer á PBS phosphate-buered saline á SCN suprachiasmatic nuclei á SON supraoptic nuclei

Daily Torpor and Sleep in a Non-human Primate, the Gray Mouse Lemur (Microcebus murinus)

“…One possible interpretation of these results is that torpor tends to change delta waves, reflecting changes in neuronal activity (Vyazovskiy et al, 2009). Several studies showed that during hibernation, different brain areas have reduced neuronal connectivity (Popov and Bocharova, 1992; Hut et al, 2002). Indeed, in hibernating species, synaptic changes were associated with cyclic changes in the density of synaptic vesicles and proteins mediating the rapid rebuilding of dendritic spines and synapses during arousal (von der Ohe et al, 2007; Arendt and Bullmann, 2013).…”

Entraining to the polar day: circadian rhythms in arctic ground squirrels

“…In vasopressin-deficient Battleboro rats, circadian rhythms are dominated by a foodentrainable oscillator (Murphy et al, 1998), but whether this is relevant for AGS, where food is available throughout the day, is unclear. Irrespective of the function of low vasopressin in AGS, this pattern does not appear to be a general feature of ground squirrels as Hut et al (2002) report high numbers of vasopressin-expressing neurons in the SCN of European ground squirrels once circadian T b rhythms became re-established upon completion of hibernation.…”

Seasonal and post-trauma remodeling in cone-dominant ground squirrel retina

“…This has been interpreted as the cessation of circadian function for about half of every year of the animal’s life. A study of European GSs revealed disrupted circadian patterns of activity and T body that lasted up to 2 weeks after the animals had resumed euthermia (Hut et al, 2002), suggesting that GS circadian clock function is re-entrained by zeitgebers upon emergence from hibernation. With respect to the retina, one wonders if photoreceptor disc shedding might also be dysregulated in the first days aboveground in spring, an idea which to our knowledge has not been examined.…”