Changes in galanin immunoreactivity in rat lumbosacral spinal cord and dorsal root ganglia after spinal cord injury

Abstract

Alterations in the expression of the neuropeptide galanin were examined in micturition reflex pathways 6 weeks after complete spinal cord transection (T8). In control animals, galanin expression was present in specific regions of the gray matter in the rostral lumbar and caudal lumbosacral spinal cord, including: (1) the dorsal commissure; (2) the superficial dorsal horn; (3) the regions of the intermediolateral cell column (L1-L2) and the sacral parasympathetic nucleus (L6-S1); and (4) the lateral collateral pathway in lumbosacral spinal segments. Densitometry analysis demonstrated significant increases (P < or = 0.001) in galanin immunoreactivity (IR) in these regions of the S1 spinal cord after spinal cord injury (SCI). Changes in galanin-IR were not observed at the L4-L6 segments except for an increase in galanin-IR in the dorsal commissure in the L4 segment. In contrast, decreases in galanin-IR were observed in the L1 segment. The number of galanin-IR cells increased (P < or = 0.001) in the L1 and S1 dorsal root ganglia (DRG) after SCI. In all DRG examined (L1, L2, L6, and S1), the percentage of bladder afferent cells expressing galanin-IR significantly increased (4-19-fold) after chronic SCI. In contrast, galanin expression in nerve fibers in the urinary bladder detrusor and urothelium was decreased or eliminated after SCI. Expression of the neurotrophic factors nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) was altered in the spinal cord after SCI. A significant increase in BDNF expression was present in spinal cord segments after SCI. In contrast, NGF expression was only increased in the spinal segments adjacent and rostral to the transection site (T7-T8), whereas spinal segments (T13-L1; L6-S1), distal to the transection site exhibited decreased NGF expression. Changes in galanin expression in micturition pathways after SCI may be mediated by changing neurotrophic factor expression, particularly BDNF. These changes may contribute to urinary bladder dysfunction after SCI.