Dendritic spikes in normal spinal motoneurons of cats

A spike of about 2 ms in duration and 3-8 mV in amplitude (D-spike) was produced by peripheral nerve (biceps semitendinosus, tibial and sciatic nerves) and dorsal root (L7 and S1) stimulation in normal spinal motoneurons of cats in a decerebrate, non-anesthetized state. The strength of the hyperpolarizing current to abolish the D-spike was always greater than that to abolish the IS-spike. The D-spike triggered the IS-spike at a level more depolarized than that at which the M-spike triggered the IS-spike. An inhibitory postsynaptic potential, which inhibited the IS-spike, could not inhibit the D-spike. Two different D-spikes, as distinguished by a difference in threshold, could occur in the same motoneuron. These results suggested that the D-spike was dendritic in origin.