Abstract SFN 2000

Size and summation of synchronous and asynchronous population PSPs in rat neo-cortical neurons:
intracellular recording in vivo with dual intracortical microstimulation

D. Heck, J.F. Leger, E.A. Stern (2), A. Aertsen
Neurobiology and Biophysics,Inst. Biology III, Albert-Ludwigs-University, Freiburg, Germany
(2) Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA

We used intracellular recording in rat frontal cortex to quantify synaptic integration under the highly variable in vivo membrane potential conditions. We investigated the size and summation of population PSPs elicited by stimulation with one or two stimulating electrodes separated by varying distances.Recordings were performed under Urethane anaesthesia combined with Ketamine/Xylazine. Neurons in rat frontal cortex showed periods of intensive activity characterized by a depolarized and highly variable membrane potential, interspersed by quiescent hyperpolarized states. Population PSPs arriving in the depolarized state showed a clear reduction in amplitude and duration compared to those arriving in the quiescent state. This finding can be explained by a reduced membrane resistance due to intense synaptic input interacting with non-linear membrane conductances. Changes in membrane potential caused by the arrival of two synchronous or asynchronous population PSPs were measured for various time delays (0.2 to 100 ms) between both stimulating pulses and compared to the algebraic sum of the two individual population PSPs shifted in time relative to each other accordingly. We found that summation of population PSPs was linear within a specific range both in the quiescent and the depolarized state. These results indicate that the integrative properties of a neuron are strongly dependent on the network activity within a time scale of a few milliseconds.

Supported by: Fondation Fyssen and Deutsche Forschungsgemeinschaft (SFB 505)