Galanin immunoreactivity in rat spinal lamina IX: emphasis on sexually dimorphic regions

Fibers and puncta that contained galanin-like immunoreactivity (GAL-LI) were distributed within lamina IX in a heterogeneous fashion. In cervical spinal segments, GAL-LI was almost absent except for the phrenic nucleus, which received the most robust GAL-LI innervation in lamina IX. In high and mid-thoracic segments, GAL-LI was found in moderate amounts, but the number of GAL-LI fibers gradually diminished in a caudal fashion, so that in low thoracic segments GAL-LI was sparse. Throughout all thoracic segments, GAL-LI fibers surrounded some clusters of motoneurons, while other groups of motoneurons were devoid of GAL-LI fibers. In lumbar segments, three sexually dimorphic nuclei received sparse to moderate amounts of GAL-LI, while GAL-LI in the remainder of lumbar lamina IX was very sparse. In sacral spinal segments, GAL-LI was very sparse. These data indicate that fibers and puncta that contain GAL-LI preferentially surround motoneurons that innervate muscles associated with the axial skeleton, while motoneurons that innervate appendicular or tail-associated skeletal muscles only have an occasional GAL-LI fiber associated with them.