Non-shivering thermogenesis activation and maintenance in the aging gray mouse lemur (Microcebus murinus)

The cold-induced enhancement of non-shivering thermogenesis (NST), involving brown-adipose tissue (BAT) metabolism, could participate to impair energy balance in the aged gray mouse lemur (Microcebus murinus). We first investigated the age-related modulations of cold-stimulated BAT cell morphology and contents. Then, NST was pharmacologically stimulated to assess whether aging impaired NST activation in the mouse lemur. In reference conditions, the ability to activate NST was preserved during aging in the mouse lemur as BAT morphology and UCP-1 presence did not differ between adult and aged mouse lemurs. Also, the pharmacological activation of NST revealed similar increased levels of O(2) consumption in adult and aged animals, confirming that no age effect could be evidenced on NST activation at 25 degrees C. However, preliminary histological data revealed a lack of lipid resources in one aged individual during cold exposure. Surprisingly, the pharmacological activation of NST revealed an impaired evacuation of the excess body heat in aged animals, associated with increased energy expenditure. Thus, aging seems to be related to decreased capacities in the maintenance of NST rather than in its activation. Energy mobilization could be impaired in the aging mouse lemur but remains to be demonstrated.