[Morphometry of sacral neurons innervating the pelvic muscles. Experimental study].

Sacral motoneurons of the pelvic muscles have been extensively studied in the rat (1,2). Few informations occur in the literature on their specific morphology and their interconnection. In an experimental study we have differentiated the neuronal mapping of the: bulbo-spongiosus (B.S.M.), ischio-cavernosus (I.C.M.), levator ani (L.A.M.), sphincter ani (S.A.M.) and sphincter urethrae (S.U.M.) muscles. Each different or both sided pelvic muscle of 30 wistar rats have been injected by a solution of horse-radish-peroxidase. Using this H.R.P. technique, the mapping of the marked neurons and compared to the different muscles has been performed on horizontal and transversal spinal cord sections. A statistical study using the "T" test compares the maximal and minimal diameters and the surface of the neurons. 1. Most of the muscles injected in one side left or right receive their innervation from the neurons located in the homolateral side of the spinal cord. 2. The B.S.M. and the S.A.M. receive, in part, an innervation from the opposite side. 3. The neurons of the B.S.M. and of the S.A.M. are located in the D.M. group of L5 - L6 segment of the spinal cord. Their diameters are significantly different but not their surfaces (+/- 940 mu 2). 4. The neurons of the I.C.M. and of the S.U.M. located in the D.L. group have an equivalent diameter and surface. 5. The neurons of the L.A.M. have the largest diameter but an equivalent surface to the others. This work on a mammalian model brings further informations on the mapping of the sacral innervation of the pelvic muscles and offers a comparative reference for Man.