SENSORY NERVES AFFECT THE RECRUITMENT AND DIFFERENTIATION OF RAT PERIOVARIAN BROWN ADIPOCYTES DURING COLD-ACCLIMATION

Rat periovarian adipose tissue contains a low number of uncoupling pro tein-expressing brown adipocytes scattered into lobules of white fat. Their increase following cold acclimation is matched by a major increa se in noradrenergic and neuropeptide Y-, substance P- and calcitonin g ene-related peptide-containing nerves. To ascertain whether periovaria n fat is provided with sensory nerves, and whether any relationship ex ists between such nerves tin particular the calcitonin gene-related pe ptide-containing fibers found in cold-acclimated rats in close associa tion with brown adipocytes) and brown fat recruitment, the effects of capsaicin desensitization on neuropeptide-containing nerves and brown adipocyte density were studied in the periovarian tissue of rats kept at 20 degrees C and on a group acclimated to 4 degrees C for 14 days. In both groups, systemic capsaicin administration considerably reduced the expression of substance P and calcitonin gene-related peptide in vascular-nerve bundles and parenchyma. In cold-acclimated rats, the in crease in brown adipocyte density was significantly checked by capsaic in administration (21.11 versus 7.96 brown adipocytes/mm(2), P<0.05). Finally, ultrastructural investigation showed the occurrence of brown adipocyte precursors filled with aggregates of glycogen and poorly dif ferentiated multilocular adipocytes in capsaicin-treated cold-acclimat ed rats. These data suggest that periovarian adipose tissue is indeed provided with sensory neuropeptide-containing nerves and that they pla y a role in the recruitment and differentiation of brown adipocytes.