Effect of ageing on the cardiac activity of the small primate Microcebus murinus

Age is an important factor of comorbidity in the development of cardiovascular diseases. Regardless of lifestyle, aged people suffer from maximal heart rate (HR) and HR variability (HRV) decrease that could impair blood circulation, tissue oxygenation and consequently self-sufficiency. Given the increase of old people in modern societies it is important to study the effect of ageing on the heart to treat the related consequence on the body physiology. To study the effect of aging on HR dynamics it is important to use appropriate animal models that could replicate the cardiac physiology, but also the neural environment that modulates HR in aged patients. The small primate Microcebus murinus, also known as gray mouse lemur (ML), responds to these criteria. Indeed, differently from mice it spontaneously develops neurodegenerative diseases. In addition, although ML lies in between the size of mice and rats, it can live up to 12 years in captivity, generating about 3 billion heartbeats in a lifetime. Thus, ML generates as many heartbeats as humans in a lifetime and about three times more than mice. To study HR and HRV in ML, we used a mini Holter and we developed a jacket to record surface electrocardiograms (ECGs) in young (1–5 years) and aged (6–10 years) animals of both genders. These experiments showed HR decrease in correlation with age in male MLs, but not in females. To get insights on the sympathetic tone of ML, we measured the coefficient of variability of the interval between two heartbeats (CVRR). Under handling stress, we found higher CVRR in aged versus young ML males, indicative of lower sympathetic tone. Conversely, the index of short-term HRV, related to parasympathetic modulation (RMSSD), showed no difference in response to stress in young and aged MLs of both genders. Next, we measured the concentration of adrenaline and noradrenaline in the urines of ML of different age and both genders. Accordingly, with our measurements of HRV we found a tendency of decrease in the urine concentration of noradrenaline in aged versus young ML males. Our preliminary results suggest that age impairs the autonomic regulation of HR, but this effect is evident in aged ML males and not in females.