Increased c-fos expression in spinal neurons induced by electrical stimulation of the ureter in the rat

The spinal processing of afferent input from the ureter was examined using an immunocytochemical technique to detect the expression of c-fos, an immediate early gene. Proximal and distal sites in one ureter were electrically stimulated separately or together at intensities that elicited a pseudo-affective response (an increase in arterial pressure). Very few Fos + cells (range: 0.6–6.6 cells/half section were present in the L₁-L₂, L₅-S₂ spinal segments in sham operated control animals; however, following stimulation of the ureter, a significant increase in the numbers of Fos + cells was detected at spinal levels L₁-L₂ (mean 24.5–33.1 cells/half section) and L₆-S₁ (mean 17.4–33.0 cells/half section). In L₆-S₁,the numbers of Fos + cells were significantly greater ipsilateral (mean 25.2 cells/half section) vs. contralateral (12.3 cells/half section) to stimulation; whereas in L₁-L₂, the numbers were similar on both sides of the spinal cord. In L₁-L₂, a greater percentage of Fos + cells was present in superficial medial (MDH, 49.7%) and lateral dorsal hom (LDH, 40.8%); whereas in L₆-S₁, the cells were more numerous in sacral parasympathetic nucleus (SPN, 38.7%) and LDH (25.6%) regions. This distribution of Fos + cells varies in a number of respects from that noted in previous experiments after chemical irritation of the urinary bladder and urethra which activated neurons only in L₆-S₁ and primarily in the DCM and MDH. The results indicate that nociceptive afferent inputs from different areas of the urinary tract are processed in different regions of the spinal cord.