Background: Delayed neuronal death, in areas distal from the infarct site, termed secondary neurodegeneration (SND), is linked with long-term functional deficits following stroke.  Increasing evidence demonstrates neuroinflammation as a potential driver of SND, although few studies have looked long-term post-stroke, which is essential in understanding the timeline of disease progression and identifying treatment targets. As such this study sought to investigate the spatiotemporal profile of neuroinflammation and functional changes long-term post-stroke.

Method: Male Sprague-Dawley rats (n=88; 12-weeks) underwent photothrombotic stroke or sham surgery. Motor outcomes (step test), anxiety (open field), and cognitive decline (Barnes maze) were assessed throughout the post-stroke period, with brain tissue and serum collected (n=30/stroke gp; n=14/sham gp) at 12- or 15-months post-stroke. Peripheral (serum) and neuroinflammation (thalamus, hippocampus) were analysed using a cytokine/chemokine multiplex (Millipore).

Results: Motor deficits were greater at 15-months post-stroke than 12-months post-stroke (p=0.0016), although higher levels of anxiety (p=0.001), and cognitive decline (p=0.03) were observed at 12-months. Within the thalamus and hippocampus, pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, IL-10, IFN-γ and MCP-1) were significantly decreased in stroke groups (p<0.05) compared to shams, but most pronounced in the 15-month group. Serum showed the opposite pattern, with pro-inflammatory cytokine levels elevated at 15-months post-stroke (p<0.05).

Conclusion: Given that we observed changes both beyond the understood timeline and in known regions of SND, our study suggests that disease progression continues >12-months. Indeed, suggesting that SND has a prolonged therapeutic window wherein treatments at these delayed time-points may be beneficial in improving patients’ quality of life.