CNS origins of the sympathetic nervous system outflow to brown adipose tissue

Brown adipose tissue (BAT) plays a critical role in cold- and diet-induced thermogenesis. Although BAT is densely innervated by the sympathetic nervou s system (SNS), little is known about the central nervous system (CNS) orig ins of this innervation. The purpose of the present experiment was to deter mine the neuroanatomic chain of functionally connected neurons from the CNS to BAT. A transneuronal viral tract tracer, Bartha's K strain of the pseud orabies virus (PRV), was injected into the interscapular BAT of Siberian ha msters. The animals were killed 4 and 6 days postinjection, and the infecte d neurons were visualized by immunocytochemistry. PRV-infected neurons were found in the spinal cord, brain stem, midbrain, and forebrain. The intensi ty of labeled neurons in the forebrain varied from heavy infections in the medial preoptic area and paraventricular hypothalamic nucleus to few infect ions in the ventromedial hypothalamic nucleus, with moderate infections in the suprachiasmatic and lateral hypothalamic nuclei. These results define t he SNS outflow from the brain to BAT for the first time in any species.