Inhibition of dorsal spinocerebellar tract cells by interneurones in upper and lower lumbar segments in the cat.

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Abstract
The topographical distribution of interneurons mediating disynaptic inhibition of dorsal spinocerebellar tract (d.s.c.t) cells from group I muscle afferents in the cat was investigated using both physiological and morphological techniques. Lesions of either the dorsal funiculi or of the lateral and ventral funiculi were made between L4 and L5 segments in 2 groups of cats. IPSP [inhibitory postsynaptic potential] evoked from group I afferents were seen after both these lesions, showing that the IPSP were evoked by interneurons located more caudally as well as by interneurons in the same segments as Clarke''s column. Distribution of the caudally located interneuron in the lower lumbar segments was investigated after marking these interneurons with horseradish peroxidase retrogradely transported from Clarke''s column. The horseradish peroxidase was injected along L3-L4 segments of Clarke''s column in 2 cats with transected dorsal funiculi. The marked cells were found in L5, L6, L7 and S1 segments, with highest density in L6 and L7. They were seen in laminae V, VI and VII. A search was made for interneurons which could be antidromically invaded following stimuli applied in Clarke''s column and were monosynaptically excited by group I afferents. Such interneurons were found at locations corresponding to laminae V-VI of Rexed. The latencies of antidromic and orthodromic responses were within ranges allowing them to mediate disynaptic inhibition of DSCT cells.