Central distribution of efferent and afferent components of the pudendal nerve in macaque monkeys

Abstract

Central distribution of efferent and afferent components of the pudendal nerve was studied by the horseradish peroxidase (HRP) method in 13 macaque monkeys, i.e., in nine Japanese monkeys (Macaca fuscata), two rhesus monkeys (Macaca mulatta), and two crab-eating monkeys (Macaca fascicularis). The enzyme was applied to the central cut end of the pudendal nerve; then the monkeys were allowed to survive for 36 to 72 hr. Retrogradely labeled neuronal cell bodies of pudendal motoneurons constituted a slender longitudinal cell column in the ventral horn. The cell column extended from high or middle S1 to high or middle S2 in eight monkeys, from middle or low L7 to high S2 in four monkeys, and from high L7 to middle S1 in a monkey. The cell column appeared to correspond to Onuf's X nucleus in man. No sex difference was recognized in the position of the cell column. The average number of HRP-labeled pudendal motoneurons was larger in male than in female adult Japanese monkeys, whereas no sex difference was found in the average soma diameter of the pudendal motoneurons. Transganglionically labeled axons entered into the spinal cord through the S1 and S2 dorsal roots in 12 monkeys and through the L7 and S1 dorsal roots in one monkey. Labeled axons were distributed ipsilaterally in laminae I–VI and X of the spinal cord at the same and adjacent levels of entry of HRP-labeled dorsal root fibers (from L7 to S3 in 12 monkeys and from L6 to S3 in one monkey). At the levels of entry, some of the labeled dorsal root fibers crossed the midline of the cord through the dorsal commissural gray to distribute contralaterally in the medial portions of lamine I–VI, especially laminae III–V, of the dorsal horn. Although the craniocaudal extent of HRP-labeled afferent fibers varied somewhat among 13 monkeys examined, no HRP-labeled axons were observed in the gray matter of the spinal cord segments cranial to L6 and caudal to S3. In a Japanese monkey with a postoperative survival time of 72 hr, two clusters of labeled axons were observed ipsilaterally in the medial portions of the gracile nucleus.