Proceedings of The Physiological Society

Sleep Sleep and Circadian Rhythms (London, UK) (2018) Proc Physiol Soc 42, C04

Poster Communications

Heart rate dynamics during NREM sleep in rats under cold environment

O. Shylo1, V. Lomako1, G. Babiychuk1

1. Cryophysiology, Institute for Problems of Cryobiology and Cryomedicine of the National Academy of Sciences of Ukraine, Kharkiv, Ukraine, Kharkiv, Ukraine.

Autonomic activation caused by contact to low temperature environment may increase the number of activation phenomena on sleep EEG, sleep fragmentation and sleep onset latency, as well as depress sleep at all. It should be note that the episodes of autonomic activation are clearly seen in NREMS even at thermoneutral zone and characterized by the pseudo-rhythmic appearance of arousal phenomena in EEG. To what extend the cold influences the vegetative background of such phenomena is still poorly understood. The research aimed to study the long-term heart rate (HR) variations as a marker of autonomic activity changes in NREM after periodic cold exposures in rats. The experiments were performed in 7-8-month male white breedless rats males (m=250-300 g, n=14). Heart rate (HR) and EEG were recorded and processed using a Poly-Spectrum-8 ECG system and Neuron-Spectrum-2 EEG system (Neurosoft). Under general anaesthesia (i/p, thiopental sodium-oxybutyrate sodium mixture, 30 and 100 mg/kg) 4 electrodes for HR registration were secured under the skin in the paws' areas, tunnelled subcutaneously, fixed to the skull (together with 2 EEG electrodes) by dental acrylic and connected to the registration systems via electric swivel (Moog). Animals were exposed to cold over two days to +10°C or -12°C in the light period for 15 min hourly, for a total of nine exposures per day. Sleep stages were scored following the standard criteria on 4-second epochs. Continuous (45 min) HR registration after every cold exposure was performed. To minimize a transition effect, after each cold exposure the corresponding 46 s' interval during NREMS toward the end of the registration period were chosen for the analysis. Artefact-free, visually corrected R-R intervals data were imported into Kubios 2.2 software (Kubios Oy). Data were means±SD, compared by ANOVA. Every cold exposure awaked the animals and different time was needed for them to enter sleep and achieve the stable HR level in NERMS again. However, RR temporary dynamics in NREMS consisted of rather stable episodes (40-200 s) interrupted by short (10-20 s) activation-deactivation periods. The mean distance between acceleration-deceleration episodes in control NREMS was 86.78±35.47, n=6, but decreased in NREMS both after +10°C (37.69±21.88, n=9, p=0.0001) and -12°C (77.37±38.16 s, n=6, p=0.0003). The mean HR increased significantly during NREMS after -12°C (from 336.3±9.7 at control to 352.3±29.2, n=6, p=0.05) and had a positive tendency after +10°C (347.2±27.5 ms, n=9, p=0.07). According to LF/HF ratio calculations the slight shift in sympatho-vagal balance was shown from 0.40± 0.19, n=6, at control, to 0.55± 0.36, n=6, p=0.06 and 0.53± 0.24, n=9, p=0.02, after -12°C and +10°C, correspondently. Thus, the studied periodic cold effects slightly change the sympatho-vagal balance and probably influence brain arousability as well as recuperative value of sleep.

Where applicable, experiments conform with Society ethical requirements