Cognitive dysfunction has been reported in patients with
spinal cord injury (SCI), but it has been questioned whether such changes may reflect concurrent
head injury, and the issue has not been addressed mechanistically or in a well-controlled experimental model. Our recent rodent studies examining SCI-induced
hyperesthesia revealed neuroinflammatory changes not only in supratentorial
pain-regulatory sites, but also in other brain regions, suggesting that additional brain functions may be impacted following SCI. Here we examined effects of isolated thoracic SCI in rats on cognition,
brain inflammation, and neurodegeneration. We show for the first time that SCI causes widespread microglial activation in the brain, with increased expression of markers for activated microglia/macrophages, including translocator
protein and
chemokine ligand 21 (C-C motif). Stereological analysis demonstrated significant neuronal loss in the cortex, thalamus, and hippocampus. SCI caused chronic impairment in spatial, retention, contextual, and fear-related emotional memory-evidenced by poor performance in the Morris water maze, novel objective recognition, and passive avoidance tests. Based on our prior work implicating cell cycle activation (CCA) in chronic
neuroinflammation after SCI or
traumatic brain injury, we evaluated whether CCA contributed to the observed changes. Increased expression of cell cycle-related genes and
proteins was found in hippocampus and cortex after SCI. Posttraumatic
brain inflammation, neuronal loss, and cognitive changes were attenuated by systemic post-injury administration of a selective
cyclin-dependent kinase inhibitor. These studies demonstrate that chronic brain neurodegeneration occurs after isolated SCI, likely related to sustained microglial activation mediated by cell cycle activation.