Voltage-sensitive dye imaging of neuronal populations under hyperbaric conditions: preliminary results obtained using a new technique.

We used voltage-sensitive dye imaging to study the properties of transient large-scale neuronal populations under hyperbaric conditions using a newly-developed high-pressure optical cell. In our experiments we investigated propagation of neuronal voltage wave depolarization along the CA2-CA1 Schaffer collateral pathway in rat hippocampal slices. The voltage-sensitive dye responses were studied at pressures up to 20 atmospheres (atm) over a range in which changes in excitability and pressure-reversal of narcosis/anesthesia have been described to occur in animals. An electrode placed in the CA2 region was used to evoke a signal along the Schaffer collateral neuronal circuit toward CA1 using a paired pulse paradigm (PPF). Initial inspection of the data indicates that the signal amplitude of the excitation following the second PPF event is enhanced at high pressure. Data analysis using MatLab software revealed a range of conductance velocities between different layers within the Schaffer collateral and for sites at different distances from the stimulating electrode. The estimated value of the conductance velocity along the trajectory of maximum flow is in good agreement with previous determinations of axonal propagation along the Schaffer collateral.