Intracellular Recording from Cells in Clarke's Column.

Intracellular recording from the neurones of Clarke's column shows that the cells suffer much more from the impalement of the microelectrode, as evidenced by a rapid decline of the membrane potential. It has been possible to show that in general these aeurones resemble motoneurones in their electrical responses. With antidromic as well as with orthodromic activation the spike potential has two components. On analogy with the motoneurone it is inferred that the soma has a higher threshold than the initial segment and that on orthodromic activation the impulse is initiated in the initial segment. Excitatory and inhibitory synaptic actions evoke depolarizing and hyperpolarizing post-synaptic potentials respectively. Reversal of the inhibitory post-synaptic potential was found when micro-electrodes filled with a KCl solution were used for recording, suggesting that the ionic mechanism of its production is the same as in motoneurones. The onset of the inhibitory post-synaptic potential had a latency that was 0.8 msec longer than that of the monosynaptic excitatory post-synaptic potential. It is concluded that an interneurone is interpolated in the inhibitory pathway to the cells in Clarke's column, just as occurs with motoneurones.