A distinct group of MNs in the sacral spinal cord termed ‘Onuf’s’ neurons, innervate the striated muscles of the external urethra, external anal sphincter via the pudental nerve, and the ischiocavernosus and bulbocavernosus muscles in males (Sato et al., 1978; Nagashima et al., 1979; Kuzuhara et al., 1980; Roppolo et al., 1985). These MNs are histologically similar to limb α-MNs (Mannen et al., 1977) and they are located anteromedial to the anterolateral nucleus and extend between the distal part of the S1 segment and the proximal part of S3.