Extrasomatic spikes recorded from cat motoneurons. Possible dendritic spikes.

Extrasomatic (ES-) spikes were recorded in motoneurons in cats anesthetized with pentobarbital sodium and immobilized with d-tubocurarine. ES-spikes, 40-79 mV in amplitude, were distinguished from intrasomatic spikes by their differences in responses to a train of 8 pulses at 500 Hz given to the L 7 or S 1 ventral root. In 23 motoneurons 3-6 different spikes could be recorded from the same site in the same cell in response to the ventral root stimulation. It was not possible to explain these multiple spikes as axon spikes or IS-(initial segment) spikes because too many spikes were observed at the same site. Accordingly, it was suggested that they were dendritic in origin.