Catecholaminergic innervation of interscapular brown adipose tissue in the naked mole-rat (Heterocephalus glaber)

Abstract

The thermogenic potential of the interscapular brown fat pad in the naked mole-rat Heterocephalus glaber, that exhibits poikilothermic thermal responses to changing temperatures is reported. Histological and ultrastructural study of the brown fat pad showed that it consists of layers of skeletal muscle interposed between the layers of brown adipose tissue with both unilocular and multilocular adipocytes. Large numbers of mitochondria were present between and around the lipid droplets of these cells. Glyoxylic acid condensation, used to demonstrate catecholaminergic nerves, was evident in low concentrations in the connective tissue between the brown adipocytes. A 3-dimensional computer-aided reconstruction of the fat pad showed the extent and ramification of nerves and blood vessels between the adipocytes. These findings show that although the naked mole-rat is regarded as an endothermic poikilotherm, it possesses anatomical features usually found in homeothermic mammals, which are essential for thermogenesis.