PARTIAL PERIPHERAL-NERVE INJURY LEADS TO ACTIVATION OF ASTROGLIA AND MICROGLIA WHICH PARALLELS THE DEVELOPMENT OF ALLODYNIC BEHAVIOR

Three different cell markers were studied in rats to note changes in t he immunoreactivity (IR) in the lumbar spinal cord 1 to 84 days follow ing partial sciatic nerve ligation (PSNL). Alteration in average IR we re studied for complement receptor C3bi (OX42; microglia), major histo compatibility complex II (OX6; microglia), and glia fibrillary acidic protein (GFAP; astroglia). Thirty-four female rats underwent ligation of approximately 1/2 of the sciatic nerve (PSNL). This injury resulted in the development of mechanical allodynia, which was quantitated by the measurement of foot withdrawal threshold to the application of Von Frey filaments. Ipsilateral increase in IR of OX42 and GFAP was obser ved to occur within 2 days, maximized by day 14, and did not return to contralateral spinal gray matter IR levels by day 84 (time period of study). Increases in OX42 IR and GFAP IR were observed within the spin al segments innervated by the sciatic nerve. GFAP IR was not expressed in all lumbar segments. OX42 staining with the upper portion of the d orsal horn was found to localize within the areas of deafferentation d emonstrated by loss of thiamine monophosphatase activity within the su bstantia gelatinosa. OX6 IR was only seen in a few cells within the ip silateral gray matter, indicating that microglia did not become phagoc ytic. Both GFAP IR and OX42 IR were found to linearly correlate with a llodynic behavior with OX42 IR being more statistically significant. C orrelation of OX42 LR in only the upper portion of the dorsal horn (no t including the neck) resulted in an even a greater level of significa nce. These findings demonstrate that microglia and astroglia are activ ated following PSNL and that their increase in IR correlates with the development of allodynic behavior. (C) 1998 Wiley-Liss, Inc.