Reversal potential for Ia excitatory post synaptic potentials in spinal motoneurones of cats

A technique permitting the introduction of two separate microelectrodes into spinal motoneurones of cats has been used to study the effect of injections of large depolarizing currents on membrane properties and on synaptic potentials. By using one electrode for passage of current, and the other for recording, continuous measurement of membrane potentials was possible. The Ia excitatory postsynaptic potential has been reversed in twelve motoneurones, and the reversal level in most of-these has been measured at between 0 and +10mV. During continuous injection of strong depolarizing currents, large variations in membrane potential and input resistance, sometimes of a repetitive nature, were observed.The results indicate that the characteristics of the Ia excitatory postsynaptic potential are explainable by a chemically mediated increase in ionic conductance, a concept which has been challenged by other recent studies in which reversal of these potentials could not be obtained.