Aged C57BL/6J mice respond to cold with increased sympathetic nervous activity in interscapular brown adipose tissue

Aged, male C57BL/6J mice produce less heat than adults during cold, which may lead to a reduced ability to maintain core temperature, but the underlying mechanisms of the decreased heat production in aged mice are still unclear. We measured sympathetic nervous activity (SNA) to interscapular brown adipose tissue (IBAT) in aged mice and compared this activity with that of adults. Mice were anesthetized by urethane and isoflurane, and SNA was recorded from one of the fine nerves to IBAT. The animal's body caudal to the pelvic area was covered with a plastic bag containing iced-water to decrease colonic temperature 7 degrees C below control over 20 minutes. SNA to IBAT (IBAT-SNA) increased during cold in both groups, but aged mice had higher IBAT-SNA before and during cold. These findings indicate that neither the ability of aged mice to detect cold nor their ability to generate sympathetic outflow to BAT is deficient.