ABNORMAL SPONTANEOUS ACTIVITY AND RESPONSES TO NOREPINEPHRINE IN DISSOCIATED DORSAL-ROOT GANGLION-CELLS AFTER CHRONIC NERVE CONSTRICTION

As a part of ongoing studies of the cellular mechanisms of sympathetic ally maintained pain, we investigated the effects of a peripheral nerv e injury on the responses of dissociated dorsal root ganglion (DRG) ce lls to norepinephrine (NE). Whole-cell patch-clamp recordings under cu rrent clamp were obtained from L4 and L5 DRG cells from adult rats in acute culture 11-25 days after a loose or tight ligation of the sciati c nerve. Only small to medium-sized cells from normal (uninjured) nerv es and from loosely ligated nerves were tested with NE. One of 15 cell s obtained from uninjured nerves responded to NE (500 mu M, the highes t dose, elicited a small depolarization without action potentials). In contrast, many cells from injured nerves responded to NE with a membr ane depolarization, accompanied in some cases by the generation of act ion potentials. Fifty-two percent responded to 500 mu M, while a signi ficantly lower percentage responded to the lower doses of 100 mu M (26 %) and 10 mu M (14%). Cells responsive to NE also responded to capsaic in. Spontaneous activity was observed in 14% and 21% of cells from loo sely and tightly ligated nerves, respectively, but none of the cells f rom uninjured nerves. We conclude that the abnormal electrogenesis and responsiveness to NE in certain nerve-injured primary sensory neurons are due at least in part to changes in the membrane properties of the soma.