Activity-dependent Trafficking Of Hippocampal Kv7Channels And The Role Of Kv7Channels In Acute Stress-induced Memory Impairment

Part I Activity-dependent traffciking of Kv7channel in hippocampal neuronObjective:To study mechanism for activity-dependent regulation of Kv7channel in hippocampal neuron. Methods:Primary hippocampal neurons cultures were prepared from embryonic day18Sprague-Dawley rats, neurons (11-14DIV) were used in the experiments. Morris water maze (MWM) training was used to activate hippocampal cells in vivo. Western blotting, immunocytochemical staining and whole cell patch clamp recording were respectively used to study the drug effects on Kv7.2/Kv7.3protein expression, the distribution of Kv7.2/Kv7.3protein expression on cell and M-current. Results:In this study, we found that (1) glutamate induced-neuronal activity decreased surface expression of Kv7channels in cultured hippocampal neuron, the glutamate effects were recoverable,(2) glutamate acted through NMDARs and AMPARs,(3) the glutamate effects on Kv7channels required Ca2+influx,(4) glutamate-mediated activity-dependent decrease in Kv7channel surface expression was regulated by PKC pathway,(5) the reduction of Kv7channel surface expression contributed to long-term potentiation (LTP),(6) the reduction of Kv7channel surface expression occured following hippocampus-dependent behavioral learning training. Conclusion:Our results suggested that activation of glutamate receptors (NMDARs and AMPARs) and downstream PKC was involved in glutamate-induced activity-dependent downregulation of endogenous Kv7channel surface expression in hippocampal neurons, and this signal required Ca2+influx through L-type Ca2+channel, which might be an additional mechanism for regulation of intrinsic neuronal excitability and synaptic plasticity. Part Ⅱ The role of Kv7channels in acute stress-induced impairments of spatial memory retrieval and hippocampal LTP in ratsObjective:To test whether Kv7channels involve in acute stress-induced impairments of spatial memory retrieval and hippocampal LTP. Methods:Rats were placed on an elevated platform in the middle of a bright room for30min to evoke acute stress. The expression of Kv7subunits was analyzed at1,3and12h after stress by Western blotting. Spatial memory was examined by the Morris water maze (MWM) and the field excitatory postsynaptic potential (fEPSP) in the hippocampal CA1area was recorded in vivo. Results:In this paper, we found that acute stress transiently decreased the expression of Kv7.2and Kv7.3in the hippocampus; acute stress impaired the spatial memory retrieval and hippocampal LTP; the Kv7channel activator flupirtine (5mg/kg) and retigabine (8mg/kg) prevented the impairments, and the protective effects of flupirtine (5mg/kg) were blocked by XE-991(0.3mg/kg), a selective KCNQ channel blocker; acute stress decreased the phosphorylation of glycogen synthase kinase-3β (GSK-3β) at Ser9in the hippocampus; flupirtine (5mg/kg) and retigabine (8mg/kg) inhibited the reduction, and the effects of flupirtine (5mg/kg) were blocked by XE-991(0.3mg/kg); acute stress decreased the level of β-catenin in the hippocampus; flupirtine or inhibited the reduction, and the effects of flupirtine were blocked by XE-991. Conclusion:Our results suggested that Kv7channels might be a potential target for protecting both hippocampal synaptic plasticity and spatial memory retrieval from acute stress influences.