Prior stressor exposure delays the recovery of surgery-induced cognitive impairment and prolongs neuroinflammation in aged rats

Increasing evidence indicates that stress potentiates pro-inflammatory response to a subsequent peripheral immune challenge. The present study investigated if prior exposure to inescapable tailshock (IS) delayed the recovery of surgery-induced spatial learning and memory impairment and prolonged hippocampus interleukin (IL)-1 beta and IL-6 expression. Methods: A total of 192 aged rats were trained with Morris water-maze (MWM) for 6 consecutive days. A single session of inescapable tailshock was performed on day 6 after training. Then, the rats subjected to partial hepatectomy. Hippocampal-dependent spatial learning and memory were assessed on postoperative days 1, 3 and 7. The cytokines IL-1 beta and IL-6 and ionized calcium binding adaptor protein (lba)1 were measured at each time point. Cluster of differentiation 200 (CD200) was also measured to explore potential mechanisms of glial cell activation. Results: Exposure of IS alone failed to affect the latency to platform and increase hippocampal cytokine levels at each time point. However, IS alone significantly increased the expression levels of Iba-1. A prolonged latency and additional significant increase in hippocampal levels of IL-1 beta and IL-6 were observed when partial hepatectomy was performed in aged rats exposed to IS 24 h later. The combination of IS and surgical trauma dramatically upregulated the levels of lba-1 and significantly decreased the expression of CD200. Conclusion: IS alone failed to induce cognitive deficits and increase pro-inflammatory cytokines expression. However, IS delayed the recovery of surgery-induced spatial learning and memory impairment and prolonged pro-inflammatory response to the subsequent surgery challenge. (C) 2016 The Authors. Published by Elsevier B.V.