Increased expression of spinal cord Fos protein induced by bladder stimulation after spinal cord injury

These studies examined Fos protein expression in spinal cord neurons synapt ically activated by stimulation of bladder afferent pathways after spinal c ord injury (SCI). In urethan-anesthetized Wistar rats after SCI for 6 wk, i ntravesical saline distension significantly (P less than or equal to 0.005) increased the number of Fos-immunoreactive (IR) cells in the rostrolumbar (L1, 38 cells/section; L2, 29 cells/section) and caudal lumbosacral (L6, 14 0 cells/section; S1, 110 cells/section) spinal cord compared with control a nimals, but Fos expression in the L5 segment was not altered. The distribut ion of Fos-IR cells was also altered in the lumbosacral spinal cord. Signif icantly greater numbers of Fos-IR cells were distributed in the dorsal comm issure and medial and lateral dorsal horn after intravesical distension in SCI animals. Large percentages of parasympathetic (75%) and sympathetic (85 %) preganglionic neurons also expressed Fos-IR after intravesical distensio n in SCI animals. These results demonstrate that bladder distension produce s increased numbers and an altered distribution pattern of Fos-IR cells aft er SCI. This pattern resembles that after noxious irritation of the bladder in control animals. Pretreatment with capsaicin significantly reduced the number of Fos-IR cells induced by bladder distension after SCI. These data suggest that SCI can reveal an altered Fos expression pattern in response t o a nonnoxious bladder stimulus that is partially mediated by capsaicin-sen sitive bladder afferents.