Our series of rat experiments have shown that locomotor activity, arousal level, body and brown adipose tissue temperatures, heart rate and arterial pressure increase episodically in an integrated manner approximately every 100 min (ultradian manner).Although it has been proposed that the integrated ultradian pattern is a fundamental biological rhythm across species, there are no reports of the integrated ultradian pattern in species other than rats. The aim of the present study was to establish a mice model using simultaneous recording of locomotor activity, eating behaviour, body temperature, heart rate and arousal in order to determine whether their behaviour and physiology are organised in an ultradian manner in normal (wild type) mice. We also incorporated the same recording in prepro-orexin knockout mice to reveal the role of orexin in the brain mechanisms underlying ultradian patterning. The orexin system is one of the key conductors required for coordinating autonomic functions and behaviours, and thus may contribute to ultradian patterning. In wild type mice, locomotor activity, arousal level, body temperature and heart rate increased episodically every 93±18 min (n=8) during 24 hours. Eating was integrated into the ultradian pattern, commencing 23±4 min (n=8) after the onset of an EEG ultradian episode. The integrated ultradian pattern in wild type mice is very similar to that observed in rats. In prepro-orexin knockout mice, the ultradian episodic changes in locomotor activity, EEG arousal indices and body temperature were significantly attenuated, but the ultradian patterning was preserved. Our findings support the view that the ultradian pattern is common across species. The present results also suggest that orexin contributes to driving ultradian episodic changes, however, this neuropeptide is not essential for the generation of the ultradian pattern.
Keywordsultradian, orexin knockout mice, body temperature, arousal level, hypothalamus 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4
IntroductionCircadian variation in behavioural and physiological parameters is well established.What is not so well recognized is the integrated fashion in which each parameter varies within each phase of the day/night cycle as the animal alternates between inactive and active states (Richter, 1927, Honma and Hiroshige, 1978, Shimada and Marsh, 1979, Livnat et al., 1984, Stupfel et al., 1985, Alfoldi et al., 1990, Holstein-Rathlou et al., 1995. It is proposed that, in addition to circadian patterning, ultradian (<24 hour) alternation between active interaction with the external environment and rest is a fundamental part of animal life (Aschoff and Gerkema, 1985, Ootsuka et al., 2011, Blessing et al., 2012, 2013, Blessing and Ootsuka, 2016. The ultradian pattern, also referred to as the basic-rest activity ...