A Comprehensive Analysis of Voluntary Wheel Running Effects on Neural Control of the Heart Rate in Rats

Aerobic exercise training is aimed to prevent and correctvarious cardiovascular disorders. To study its effects, variousrodent models are currently in use, among which the rat model ofvoluntary wheel running is of particular interest, as its patternof motor activity is close to natural rat locomotion, while beingnon-stressful. This work was aimed at a comprehensive investigationof wheel running effects on the neural control of heart rate (HR)in rats. The animals, aged 6 weeks, were divided into two groups: training(TR, free access to wheels, n =11) and sedentary control (CON, n =12). After a 6-week training, ECG was recorded in freely movingrats using skin electrodes in three modes: at rest, after autonomicblockade of cardiotropic influences, and during 4-min air-jet stress.Autonomic neural influences were analyzed by administering the β₁-adrenoceptorblocker atenolol (2 mg/kg) and the peripheral M-cholinoceptor antagonistmethylatropine (1 mg/kg), as well as by analyzing HR variability viaspectral and wavelet analyses. At rest, the TR group showed a decreasein the baseline HR level vs. CON group. Аtenolol decreased HR equallyin two groups, but methylatropine elicited a more significant increasein HR in the TR vs. CON group. After atenolol and methylatropineco-administration, HR levels in two groups were similar. TR ratsshowed an increased contribution of high-frequency (0.75–3 Hz) oscillationsto the total RR interval power spectrum. During emotional (air-jet) stress,the TR group demonstrated a more pronounced increase in HR vs. CONgroup. In addition, stressed TR rats exhibited a decrease in theamplitude of HR high-frequency oscillations, which was absent inthe CON group. Thus, voluntary wheel running in rats is accompaniedby an increase in parasympathetic influences on the heart, as manifestedin an increase both in respiratory sinus arrhythmia and in vagaleffects on the resting HR level (increased tachycardia). Moderateresting bradycardia promotes a more pronounced increase in HR underemotional stress conditions due to suppression of parasympatheticcardiac influences.