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 ce lls within the spinal cord that regulate micturition in male cats. The immediate early gene c-fos that encodes the Fos protein can be induce d 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, e lectrical stimulation of the pudendal nerve, a period of isometric mic turition (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 neuron s expressing Fos-like immunoreactivity (FLI) were visualized with immu nocytochemical methods. Stimulation with each protocol resulted in a s ubstantially larger number of neurons expressing FLI than in operated but unstimulated controls, which exhibited few Fos-positive neurons lo calized to the superficial dorsal horn. In animals undergoing isometri c micturition or stimulation of Barrington's nucleus, neurons exhibiti ng FLI were found bilaterally in the sacral (S1-S3) spinal cord and we re localized to the lateral portion of the superficial dorsal horn (la minae I and II), in the intermediolateral region (lateral laminae V-VI I), and around the central canal (lamina X and medial laminae V-VII). The intermediolateral region appeared to contain two populations of ce lls exhibiting FLI: a group of large multipolar cells and a group of s mall round cells. Few Fos-immunoreactive nuclei were observed in the m edial portion of the superficial dorsal horn, and FLI was not observed in ventral horn neurons. Electrical stimulation of the pudendal or pe lvic nerves resulted in fewer numbers of cells exhibiting FLI, with a less widespread spatial distribution. These results identify spinal ne urons that are active during the micturition cycle, and demonstrate th at a behaviorally relevant stimulus (isometric micturition) generated more widespread and greater intensity of Fos expression than repetitiv e electrical stimulation of the component peripheral nerves. (C) 1998 Elsevier Science B.V. All rights reserved.