c-Fos expression in the spinal cord of female rats with artificial ureteric calculosis

Rats with an artificial stone in the left ureter display spontaneous pain behavior (ureteral 'crises') and referred hyperalgesia/contraction in the ipsilateral oblique musculature. To evaluate neuronal activation in both sensitive and motor pathways in this model, c-Fos expression was studied in the spinal cord of calculosis rats vs. sham controls. Fos-labeled cells were never observed in sham controls. In stone rats, they were found in the T10-L2 segments, throughout the dorsal horn, significantly more on the left than the right side (P < 0.002). Fos-labeled cells were also found in lamina IX, containing motoneurons; at the T11-T12 level, these were significantly more on the left than the right side (P < 0.03). Nociceptive input from the ureter thus activates not only sensory but also efferent neurons in the spinal cord, suggesting the triggering of reflex arcs by the visceral focus.