Background

We have discovered a neuronal pathway that contributes to a physiological increase in energy expenditure and thermogenesis in skeletal muscle when rats are exposed to a predator odor (PO) from ferrets. Brown adipose tissue (BAT) is a regulator of energy expenditure and a major site of SNS-mediated non-shivering thermogenesis; however, it comprises less of the total body composition than skeletal muscle. Skeletal muscle makes up 40% of total body composition and has a greater capacity for increasing energy expenditure and affecting overall energy balance. We predict that PO-induced skeletal muscle thermogenesis can occur independently of BAT.

Methods

Male (n=8) and female (n=8) Sprague-Dawley rats underwent surgical excision of interscapular BAT (n=4/sex) or sham surgery (n=4/sex), and transponders were implanted in the left and right gastrocnemius muscles. Single-housed rats were habituated to experimental conditions prior to PO and control exposure. PO and control towels (1.5”x2”) were placed in home cages, and PO-induced thermogenesis was measured for 120 minutes after exposure. Activity thermogenesis following PO exposure was measured using a treadmill walking protocol, and calorimetry was used to measure differences in energy expenditure (EE).

Results

PO exposure induced skeletal muscle thermogenesis similarly in animals with and without interscapular BAT, and there was no significant difference in activity thermogenesis. Similarly, PO exposure did not significantly affect the PO-associated increase in energy expenditure (EE).

Conclusions

The excision of interscapular BAT, the largest depot in rats, did not impede PO-induced skeletal muscle thermogenesis or EE. These results do not support the idea that BAT makes a meaningful contribution to PO-induced thermogenesis or EE.