[Morphometric study of the lumbosacral plexus innervating the muscles of the rat pelvic floor].

Motoneurons of the pelvic muscles in the lumbo-sacral segment of the spinal cord have been extensively studied in different species. However, few informations occur in the literature about the individual morphology of each group of neurons and their connections. Thus, in the Rat we have studied the neuronal mapping of 5 pelvic muscles, bulbospongiosus, ischio-cavernosus, levator ani, sphincter ani, sphincter urethrae, using a retrograde tracer, the horseradish peroxidase (H.R.P.). Most of the muscles injected by H.R.P. receive their innervation from the motoneurons located in the homolateral side of the spinal cord. The motoneurons of sphincter ani (+/- 40) and those of the bulbo-spongiosus (+/- 50) have the same morphology. Their dendrites contact contralateral motoneurons. They are situated in the dorso-medial nucleus of the L5-L6 segments of the spinal cord. The motoneurons of the ischio-cavernosus (+/- 80) and those of sphincter urethrae (+/- 40) are situated in the dorsolateral nucleus of the L5-S1 segments of the spinal cord where they form two distinct groups. On the contrary, in the ventro-medial nucleus, the neurons are mixed. The dendrites in the dorso-lateral nucleus form an important longitudinal network. The motoneurons of the levator ani (+/- 50) are situated in the ventral nucleus of the L5-S1 segments. Our works demonstrate the significance of the dendritic networks: they could play a role in the synchronization and the activity of the pelvic muscles.(ABSTRACT TRUNCATED AT 250 WORDS)