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

UNLABELLED 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)-1β 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-1β and IL-6 and ionized calcium binding adaptor protein (Iba)-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-1β and IL-6 were observed when partial hepatectomy was performed in aged rats exposed to IS 24h later. The combination of IS and surgical trauma dramatically upregulated the levels of Iba-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.