SYMPATHETIC OUTFLOW TO INTERSCAPULAR BROWN ADIPOSE-TISSUE IN COLD-ACCLIMATED MICE

C57BL/6J male mice were subjected to a cold acclimation procedure whic h consisted of three consecutive cold stress tests: 3-h partial restra int at 6 degrees C at 2-wk intervals. During the week following the la st cold stress test, each animal previously subjected to the cold accl imation procedure, and an additional group of naive mice (animals that never had been exposed to an environment below room temperature) were anesthetized with urethane, paralyzed with vecuronium bromide, artifi cially ventilated, and subjected to cold stimulation for approximately 16 min. Electrical impulse activity from one of the fine sympathetic nerves entering the interscapular brown adipose tissue was recorded be fore and during cold stimulation, until body temperature dropped 8 deg rees C below control level. Sympathetic outflow increased significantl y during cold stimulation in all mice. Animals that did not achieve co ld acclimation in three repeated cold stress tests (they demonstrated less cold tolerance in the last test) had lower sympathetic nervous ou tflow to brown adipose tissue at room temperature and during cold stim ulation than mice that had achieved cold acclimation. In fact, sympath etic nervous outflow to brown adipose tissue in mice that had failed t o show cold acclimation was similar to that of naive mice. These findi ngs indicate that the sympathetic nervous system plays a primary role in cold acclimation.