Calcitonin gene-related peptide and somatostatin immunoreactivities in the rat lumbar spinal cord: sexually dimorphic aspects

The immunohistochemical distribution of calcitonin gene-related peptide and somatostatin in rat lumbar spinal laminae VII-X was investigated using the peroxidase-antiperoxidase technique. Within L1,2 laminae VII and X, calcitonin gene-related peptide and somatostatin fibers demarcate the location of preganglionic sympathetic neurons in a similar fashion in either sex but somatostatin is distributed in a sexually dimorphic manner in the lumbosacral (L5-S2) spinal cord with the male rat containing more somatostatin fibers and neurons than females. Within the ventral horn (lamina IX), calcitonin gene-related peptide has a sexually dimorphic distribution. Calcitonin gene-related peptide varicose fibers are found within the sexually dimorphic male cremaster nucleus but are virtually absent in the female cremaster nucleus. Calcitonin gene-related peptide varicose fibers are nearly absent in the remainder of the male and female lamina IX: this area includes the other two known sexually dimorphic spinal motonuclei: the dorsomedial and dorsolateral nuclei. Virtually all motoneurons in the lumbosacral spinal cord which are not sexually dimorphic contain calcitonin gene-related peptide. However, calcitonin gene-related peptide containing motoneurons have a heterogeneous distribution within sexually dimorphic nuclei. Calcitonin gene-related peptide containing motoneurons within the male and female cremaster nucleus are extremely rare. Some motoneurons within the male and female dorsomedial and dorsolateral nuclei contain calcitonin gene-related peptide with the female dorsomedial and dorsolateral nuclei containing a greater percentage of calcitonin gene-related peptide-containing motoneurons (c. 50%) than males (c. 20%). Somatostatin fibers are preferentially located in sexually dimorphic nuclei of either sex and are distributed in a sexually dimorphic manner within these nuclei with males containing a greater amount of somatostatin fibers than females. The amount of somatostatin immunoreactivity is most dense in the medial aspect of the dorsolateral nucleus, dense in the dorsomedial nucleus, moderate in the cremaster nucleus, and sparse in the lateral portion of the dorsolateral nucleus. In addition, a small column of motoneurons, between the dorsomedial and dorsolateral nuclei at the L5 level, is outlined by somatostatin fibers in females but is absent in males. Somatostatin containing motoneurons were not observed within the lumbar sexually dimorphic nuclei of either sex.