Regional topography of spinal cord neurons innervating pelvic floor muscles and bladder neck in the dog: a study by combined horseradish peroxidase histochemistry and autoradiography.

To identify the spinal origin of the innervation of the bladder neck and pelvic floor muscles retrograde axonal transport of horseradish peroxidase and tritiated horseradish peroxidase was used in a technique combining histochemistry and autoradiography. This technique proved to be suitable for differential labeling of spinal cord neurons innervating two different targets, thus extension as well as overlap of different nuclei could be judged. The parasympathetic outflow was concentrated in the intermediolateral and intermediomedial gray matter of S2, the somatic innervation was derived mostly from Onuf's motor nucleus in S1 and S2. Onuf's nucleus proved to be the main somatic motonucleus for pelvic floor muscles; there was no evidence of an autonomic share. The innervation of the striated urethral sphincter also originated in this nucleus; there was no basic difference when it was compared to the innervation of other pelvic floor muscles.