Chemical sympathectomy of interscapular brown adipose tissue.

Adult non-cold adapted rats were injected with 6-hydroxydopamine (6-OHDA) or saline and their interscapular brown adipose tissue (BAT) was removed after appropriate periods of time. Fluorescence histochemistry of control BAT demonstrated the presence of an extensive network of varicose fibers among the adipocytes and at the blood vessels. This was confirmed by electron microscopy which also revealed large and small dense core vesicles sparsely distributed in axons and terminals indicating the presence of noradrenaline (NA). After 6-OHDA injection the fluorescence from varicosities was abolished both among the adipocytes and at the vessels. Thus, chemical sympathectomy was more effective than surgical- or immunosympathectomy, which spare the innervation of adipocytes. Parallelling the disappearance of fluorescence was a significant decrease of measurable NA. During recovery the extractable NA increased before the reappearance of fluorescent varicosities. This could be explained by transmitter accumulation in the nervetrunks within the tissue, which, in general, appeared unaffected by 6-OHDA. A large number of cells with a strong yellowish fluorescence distributed through the BAT was unaffected by 6-OHDA. There was no evidence for the presence of intrinsic ganglia.