Alterations in spinal cord Fos protein expression induced by bladder stimulation following cystitis.

These studies examined Fos protein expression in spinal cord neurons synaptically activated by stimulation of bladder afferent pathways after cyclophosphamide (CYP)-induced bladder inflammation. In urethan-anesthetized Wistar rats with cystitis, intravesical saline distension significantly (P </= 0.0005) increased the number of Fos-immunoreactive (IR) cells observed in the rostral lumbar (L1, 35 cells/section; L2, 27 cells/section) and caudal lumbosacral (L6, 120 cells/section; S1, 96 cells/section) spinal cord compared with control animals, but Fos protein expression in the L5 segment was not altered. The topographical distribution of Fos-IR cells was also altered in the lumbosacral spinal cord. The majority of Fos-IR cells were distributed in the dorsal commissure (45%), with smaller percentages in the sacral parasympathetic nucleus (25%), medial dorsal horn (20%), and lateral dorsal horn (10%). These results demonstrate that urinary bladder distension produces increased numbers and an altered distribution pattern of Fos-IR cells after cystitis. This altered distribution pattern resembles that following noxious irritation of the bladder in control animals. Pretreatment with capsaicin significantly reduced the number of Fos-IR cells induced by bladder distension after cystitis. These data suggest that chronic cystitis can reveal a nociceptive Fos expression pattern in the spinal cord in response to a non-noxious bladder stimulus that is partially mediated by capasaicin-sensitive bladder afferents.