Hyperexcitability of hippocampal CA1 neurons after fluid percussion injury of the rat cerebral cortex.

Effects of fluid percussion injury (FPI) of the parietal cerebral cortex on the neuronal activity in the temporal region of the rat hippocampal CA1 area were investigated by using optical and extracellular recording techniques. Application of moderate impact (1.5-2.0 atm) to the parietal cerebral cortex enhanced the optical signal of the neuronal activity in the ipsilateral hippocampal CA1 area. The field potential evoked by the Schaffer collaterals had multiple population spikes in the ipsilateral hippocampal CA1 pyramidal cell layer. Bicuculline (15 microM) increased the amplitude and the number of population spikes of the field potential even after the brain injury. These results suggest that FPI produces hyperexcitability of hippocampal CA1 neurons, probably by increasing the activity of the Schaffer collaterals of hippocampal CA3 neurons.