Enhanced excitability of dissociated primary sensory neurons after chronic compression of the dorsal root ganglion in the rat

A chronic compression of the dorsal root ganglion (CCD) produces ipsilateral cutaneous hyperalgesia and allodynia in rats. Intracellular electrophysiological recordings from formerly compressed neurons in the intact dorsal root ganglion (DRG) reveal lower than normal current thresholds (CTs) and abnormal spontaneous activity (SA) (Zhang JM, Song XJ, LaMotte RH. Enhanced excitability of sensory neurons in rats with cutaneous hyperalgesia produced by chronic compression of the dorsal root ganglion. J Neurophysiol 1999;82:3359-66). To determine if the neuronal hyperexcitability is intrinsic to the soma, L4 and L5 DRG neurons from rats that had prior CCD surgery or those that did not (controls) were dissociated, and intracellular recordings obtained 3-8 It (acute) or 24-30 h (1d) after culture. The CTs of large(>45 mum diameter) and medium- (30similar to45 mum) sized neurons from control rats after acute or Id culture were similar to those formerly recorded from the intact DRG and significantly lower for CCD than for control rats. However, the CTs of small- (less than or equal to 30 mum) sized neurons from control rats were significantly lower in acute or 1d culture groups than they were in the intact DRG and not significantly different from those of dissociated small neurons front CCD rats. The overall incidence of SA was higher for CCD than for control neurons after 1d culture (10.3 vs. 1.8%) and similar to that obtained in the intact DRG. We conclude that the CCD-induced hyperexcitability of medium- and large-sized neurons remains after dissociation and is intrinsic to the soma. For small-sized neurons, the effects of CCD observed in the intact DRG are less apparent after dissociation possibly due to the hyperexcitability produced by the dissociation process itself. (C) 2004 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.