Afferent signals from leptin sensors in the white adipose tissue of the epididymis, and their reflex effect in the rat.

Afferent nerve signals were recorded from a peripheral cut end of the small nerve bundle innervating the white adipose tissue (WAT) of the epididymis in the anesthetized rat. An injection of leptin (2 ng, 0.2 ml) into the white adipose tissue facilitated the afferent activity. The response was dose dependent and the least effective dose was 100 pg (0.1 ml). An injection of 2 ng (0.2 ml) leptin into the one side of the WAT resulted in a reflex activation of efferent activity of the sympathetic nerve innervating the WAT of the bilateral epididymis. The observations suggest the existence of leptin sensors in WAT which send afferent signals from the WAT to the central nervous system and evoke a reflex activation of sympathetic outflow to the WAT which may accelerate lipolysis. This WAT to WAT reflex can explain a part of the effect of leptin on metabolic function of the fatty tissue such as the reduction of body weight and increase in energy expenditure as a negative feed-back reflex response.