Intracellular recording from cells in Clarke's column.

Summary. 1 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. 2 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. 3 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.