Aging Differentially Affects the Loss of Neuronal Dendritic Spine, Neuroinflammation and Memory Impairment at Rats after Surgery

It is known that age is an important factor for postoperative cognitive dysfunction (POCD) and the patients with POCD suffer from the impairment of multiple brain regions and multiple brain functions. However currently animal studies of POCD mainly focus on hippocampus region, therefore in this study we performed partial hepatectomy in young adult and aged rats to test the questions (1) whether POCD in animals involves other brain areas besides hippocampus; (2) how age influences POCD of young adult and aged animals. We found that (1) in young adult rats, the memory was not significantly affected (P > 0.05) 1d, 3d and 7d after partial hepatectomy, but was significantly impaired (p < 0.001) in aged rats 1d and 3d post-surgery; (2) in young adult rats, the surgery did not significantly affect the densities of dendritic spines of neurons at CA1, dentate gyrus (DG) and cingulate cortex (P > 0.05, respectively) 1d and 3d post-surgery, but the spine densities at CA1 and DG of aged rats were significant reduced 1d and 3d post-surgery (p < 0.001, respectively), however this didn't happen at cingulate cortex (P > 0.05); (3) In young adult rats, surgery didn't affect the activation of microglia and levels of TNF-alpha and IL-1b at hippocampus (P < 0.05), but significantly activated microglia and increased levels of TNF-alpha and IL-1 beta at hippocampus of aged rats (P, 0.05). Our data suggest that (1) partial hepatectomy-induced POCD mainly involves hippocampus impairments, and (2) differential loss of neuronal dendritic spines and neuroinflammation at hippocampus are most likely the mechanism for the formation of POCD in aged rats.