EFFECTS OF SPINAL-CORD INJURY ON NEUROFILAMENT IMMUNOREACTIVITY AND CAPSAICIN SENSITIVITY IN RAT DORSAL-ROOT GANGLION NEURONS INNERVATING THE URINARY-BLADDER

The effect of chronic spinal cord transection on neurofilament immunor eactivity and capsaicin sensitivity of L6 and S1 dorsal root ganglion neurons innervating the urinary bladder was examined using an antibody (RT97) against 200,000 mol. wt subunit of neurofilament protein and a cobalt uptake assay, respectively. Bladder afferent neurons labelled by axonal transport of a fluorescent dye (Fast Blue) injected into the bladder wall were identified in sections of intact dorsal root gangli a and among dissociated neurons in short-term culture. Approximately t wo thirds of bladder afferent neurons from spinal intact rats were neu rofilament-poor (i.e. C-fibre neurons). These neurons were on average 37% smaller in cross-sectional area than neurofilament-rich neurons (A delta-fibre neurons). In spinal intact rats, 78% of neurofilament-poo r dissociated bladder afferent neurons were sensitive to capsaicin, wh ile only 6.2% of neurofilament-rich neurons were capsaicin-sensitive. Dissociated bladder afferent neurons from spinal transected animals ha d larger diameters (34.2 +/- 1.1 mu m) than those from spinal intact a nimals (29.2 +/- 1.2 mu m). In tissue sections from dorsal root gangli a, the mean cross-sectional area of bladder afferent neuron profiles i n spinal transected animals was also lar er by approximately 35% than in spinal intact animals. Immunoreactivity to neurofilament protein wh ich occurred in 32% of bladder afferent neurons in spinal intact anima ls was detected in a larger percentage (56% to 62%) of neurons from sp inal transected animals. Conversely, the population of capsaicin-sensi tive dissociated neurons was reduced from 55% in spinal intact rats to 38% in spinal transected rats. These results indicate that spinal cor d injury induces functional and morphological plasticity in C-fibre vi sceral afferent neurons innervating the urinary bladder. (C) 1997 IBRO . Published by Elsevier Science Ltd.