Spinal cord localization of the motoneurons innervating the sacrococcygeus dorsi lateralis muscle and their noradrenergic nerve terminals in rats.

We examined in the present study the spinal cord localization of motoneurons innervating the caudal portion of the sacrococcygeus dorsi lateralis (SCDL) muscle and their noradrenergic nerve terminals in Sprague-Dawley rats, using horseradish peroxidase (HRP) and dopamine-beta-hydroxylase (DBH) double-labeling techniques. Retrogradely HRP-labeled motoneurons innervating the caudal part of the SCDL muscle were located ipsilaterally in the ventromedial aspect of the ventral horn (lamina IX) in spinal segments of S2-S4. These cells were polygonal in shape, with an average soma diameter of 37.0 +/- 1.1 microns (mean +/- S.E.M., n = 95) and amounted to 33.6 +/- 5.7 (n = 7) in the horizontal plane. Of note was the presence of abundant DBH-positive nerve terminals arborizing on the soma and dendrites of HRP-labeled motoneurons. These results provided anatomical evidence to further support our previous findings that the coerulospinal noradrenergic neurotransmission is involved in the mediation of fentanyl-induced muscular rigidity.