Molecular mechanisms and the role of the protein kinase pathway in rat spatial memory impairment following isoflurane anesthesia

BACKGROUND: Animal experiments have demonstrated that isoflurane exposure alone induces learning and memory deficits for weeks or months. However, the molecular mechanisms of learning and memory remain poorly understood. Hippocampal expression of calcium/phospholipid- dependent protein kinase (PKC) and cAMP-dependent protein kinase (PKA) in rats have been shown to be associated with memory processing. OBJECTIVE: To investigate changes in rat spatial memory and hippocampal CA1 neuronal kinase system following isoflurane anesthesia, and to explore the correlation between molecular changes in cerebral neurons and behavioral manifestations following anesthesia. DESIGN, TIME AND SETTING: A randomized, controlled, animal study. All experiments were performed at the Department of Anesthesia, Beijing Chaoyang Hospital, Capital Medical University from November 2007 to December 2008. MATERIALS: A total of 72 male, 3 month-old (young group), Sprague Dawley rats, and 36 male, 20 month-old (aged group), Sprague-Dawley rats were used in the study. Isoflurane was purchased from Baxter, USA. METHODS: Young and aged rats were randomly assigned to control, training (no anesthesia, Morris water maze training), and isoflurane (1.2% isoflurane, Morris water maze training) groups. The isoflurane group was further subdivided into four groups, which were exposed to anesthesia for 2 or 4 hours, and were subjected to Morris water maze training at 2 days or 2 weeks post- anesthesia. Finally, each aged group comprised 6 rats, and the young group comprised 12 rats. MAIN OUTCOME MEASURES: Spatial learning and memory were observed during Morris water maze training. Hippocampal CA1 PKA and PKC expression and activity were detected by immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). RESULTS: A 4-hour isoflurane exposure induced spatial memory deficits in all rats for 2 days to 2 weeks. In particular, aged rats exhibited more severe spatial memory deficits. Immunohistochemistry and ELISA results showed a significant increase in PKC and PKA expression and activity in the hippocampus CA1 subfield following Morris water maze training (P < 0.05). Moreover, isoflurane anesthesia inhibited PKC and PKA expression and activity, and this inhibition increased with increasing exposure duration and increasing age. CONCLUSION: Results suggested that increased isoflurane exposure and age could extensively inhibit the hippocampal CA1 kinase system. Inhibition of protein kinases could play an important role in the cognitive decline following anesthesia.