Influence of inflammation or disconnection from peripheral target tissue on the capsaicin sensitivity of rat dorsal root ganglion sensory neurones.

Dorsal root ganglion (DRG) sensory neurones from adult rats are known to lose their capsaicin sensitivity in vitro if they are cultured without nerve growth factor (NGF). Here we show similar results following peripheral nerve transection in vivo, which deprives DRG sensory neurones of target-derived NGF. By measuring capsaicin-stimulated 45Ca uptake into DRG neurones which had been briefly cultured, capsaicin sensitivity was shown to decrease in neurones whose axons had been previously severed in vivo. Conversely, during experimental inflammation of the rat paw, there is an increase in the supply of NGF to neurones innervating the inflamed area. In this case, however, no significant increase in capsaicin sensitivity could be demonstrated in briefly cultured neurones which had previously innervated an inflamed limb. This suggests that expression of capsaicin sensitivity in DRG is maximal at levels of NGF found in normal animals.