The effects of unilateral surgical
denervation on brown adipose tissue (BAT) composition were evaluated to assess the importance of the sympathetic innervation in the maintenance of a high concentration of the
uncoupling protein thermogenin in cold-acclimated (CA) mice and to assess whether suppression of neural activity could account for BAT
atrophy observed during fasting or when CA mice are returned to a thermoneutral environment (33 degrees C).
Denervation-induced BAT
atrophy was characterized by
protein and
thermogenin losses in absence of changes in the tissue cellularity (
DNA content). There was a marked reduction in the concentration of
thermogenin in mitochondria isolated from denervated BAT, but the concentration of the
adenine nucleotide translocator was unchanged. Fasting or exposure of CA mice to 33 degrees C induced a rapid and extensive loss of tissue
protein from both innervated and denervated BAT. In CA mice exposed to 33 degrees C, there was also reduction in tissue cellularity and loss of
thermogenin from BAT mitochondria. Since surgical
denervation suppressed BAT
hyperplasia and the increase in the mitochondrial concentration of
thermogenin observed during cold exposure, these results indicate that an intact innervation is required for both synthesis and maintenance of a high mitochondrial content of
thermogenin in CA mice. In addition, the lesser changes in tissue composition caused by
denervation compared with those caused by fasting or exposure of CA mice to 33 degrees C question the importance of the suppression of neural activity as the exclusive cause of rapid BAT
atrophy in mice.