Spinal cord injury‐induced expression of TrkA, TrkB, phosphorylated CREB, and c‐Jun in rat lumbosacral dorsal root ganglia

Abstract

Previous studies have demonstrated increased expression and phosphorylation of tyrosine kinase receptor (TrkA, TrkB) in lumbosacral DRG after chronic (6 weeks) spinal cord (T8-T10) injury. This study examined the effects of acute SCI (48 hours, 2 weeks) on TrkA and TrkB expression and phosphorylation, and CREB and c-Jun expression in DRG. A significant increase in the number of TrkA- (1.5–3-fold; P ≤ 0.05), TrkB- (1.3–2.0-fold; P ≤ 0.05), and phosphorylated Trk (pTrk)-immunoreactive (1.5–3-fold; P ≤ 0.05) cells was observed in the L1, L6, and S1 DRG 48 hours, 2, or 6 weeks after SCI. A significant increase in the number of phosphorylated (p-) CREB-immunoreactive cells was observed in the L1, L2, L6, and S1 DRG 48 hours, 2, or 6 weeks after SCI. The largest changes in p-CREB-immunoreactivity were in L1 and L2 DRG (10-fold; P ≤ 0.01) at 48 hours after SCI; however, changes were modest in bladder afferent neurons. After SCI, the overall number of c-Jun-immunoreactive cells in L1, L2, and S1 DRG was dramatically increased (3–10-fold; P ≤ 0.01); however, only a low percentage of bladder afferent cells expressed c-Jun-IR before or after SCI. In summary, these results suggest that TrkA or TrkB may be involved in reorganization of micturition pathways after SCI. However, CREB or c-Jun may not be downstream transcription factors in Trk-mediated signaling cascades in micturition reflex pathways after SCI but may play a role in other, nonbladder SCI-induced changes. J. Comp. Neurol. 482:142–154, 2005.