Effects of spino-bulbo-spinal reflex volleys on extensor motoneurons of hindlimb in cats.

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Abstract
Recent workers have investigated a spino-bulbo-spinal (SBS) reflex system which depends upon relay through the buibar retlcular formation and recurrent projection to spinal flexor motoneurons in decerebrated cats and also dogs, monkeys and man. However, no SBS reflex response was observed in extensor motor nerves. In this experiment, any covert excitability changes of extensor motoneurons elicited by the SBS reflex have been investigated on 32 cats under conditions of chloralose anesthesia or decerebration. After a single shock to a cutaneous nerve, late inhibition of the extensor motoneurons was observed. The mechanism of this late inhibition was analyzed by means of recording of spinal cord potentials, dorsal root potentials, dorsal root reflexes, segmental spinal reflexes and the intracellular potentials of extensor motoneurons. The late inhibition on the extensor motoneurons appears to be related to the descending volleys of the SBS reflex, and to be mainly due to presynaptic Inhibition at the spinal segment.

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