Identification of the spinal neural network involved in coordination of micturition in the male cat.

In these studies, we used the expression of Fos protein to identify cells within the spinal cord that regulate micturition in male cats. The immediate early gene c-fos that encodes the Fos protein can be induced rapidly and transiently in neurons by increased electrical activity. Animals were anesthetized with alpha-chloralose, and received one of four stimulus protocols: electrical stimulation of the pelvic nerve, electrical stimulation of the pudendal nerve, a period of isometric micturition (induced by ligating the proximal urethra and infusing saline into the bladder), or electrical stimulation of Barrington's nucleus. After the period of stimulation, the animals were perfused and neurons expressing Fos-like immunoreactivity (FLI) were visualized with immunocytochemical methods. Stimulation with each protocol resulted in a substantially larger number of neurons expressing FLI than in operated but unstimulated controls, which exhibited few Fos-positive neurons localized to the superficial dorsal horn. In animals undergoing isometric micturition or stimulation of Barrington's nucleus, neurons exhibiting FLI were found bilaterally in the sacral (S1-S3) spinal cord and were localized to the lateral portion of the superficial dorsal horn (laminae I and II), in the intermediolateral region (lateral laminae V-VII), and around the central canal (lamina X and medial laminae V-VII). The intermediolateral region appeared to contain two populations of cells exhibiting FLI: a group of large multipolar cells and a group of small round cells. Few Fos-immunoreactive nuclei were observed in the medial portion of the superficial dorsal horn, and FLI was not observed in ventral horn neurons. Electrical stimulation of the pudendal or pelvic nerves resulted in fewer numbers of cells exhibiting FLI, with a less widespread spatial distribution. These results identify spinal neurons that are active during the micturition cycle, and demonstrate that a behaviorally relevant stimulus (isometric micturition) generated more widespread and greater intensity of Fos expression than repetitive electrical stimulation of the component peripheral nerves.