AFFERENT RELATIONS OF INFERIOR OLIVARY NUCLEUS: II. SITE OF RELAY FROM HIND LIMB AFFERENTS INTO DORSAL SPINO-OLIVARY TRACT IN CAT

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Abstract
On stimulating the dorso-lateral funiculus in the cat, electrical activity is evoked earlier in the contralateral olive when the spinal site of stimulation is high. The reverse is true when the stimulus is applied to the dorsal funiculus. Onset of olivary activity then is later when the stimulus is at the upper levels of the dorsal column and earliest when it is applied in the lumber cord. The relation between distance from the olive to the stimulating site and the latency of the olivary response is linear in both cases, but the slopes are reversed. Closest approximation of the response times occurs when both stimuli are applied in the levels L3-L5, indicating that the origin of the relayed dorsal spino-olivary pathway from hind limb afferents is confined close to the spinal entry of the latter. Minimal difference in olivary response time to the 2 modes of stimulation indicates that synaptic delay at this relay is about 1 msec. or less. The average conduction velocity in the spino-olivary pathway (63 m/sec; range 55-73 m/sec., 8 experiments) distinguishes the fibers of this pathway from the more rapidly conducting of the contiguous dorsal spino-cerebellar tract.