The electrophysiological study of axonal branching of the C6-C7 neurones of the cat's spinal cord projecting to the lateral reticular nucleus and the cerebellum.

Ascending projections of the cervical spinal cord neurones to the lateral reticular nucleus (LRN) and the restiform body (RB) were electrophysiologically investigated in alpha-chloralose anaesthetized cats. The main purpose of the study was to demonstrate whether the some of C6/C7 segments neurones gave off collateral branches that reached both the LRN and RB. Antidromic action potentials were recorded from 50 neurones located in laminae IVVIII of the grey matter of C6/C7 segments following stimulation of the LRN and RB with tungsten electrodes. Analysis of the antidromic responses allowed to distinguish three populations of neurones according to their projection patterns, 41% cells ascended exclusively to either one of the two structures investigated (26% to LRN and 15% to RB), while in the remaining cases (59%) collateral projections ascended to both LRN and RB. The axonal conduction velocities were comprised in the range of 14-90 m/s and no differences were found when compared mean values for particular groups of neurones. In conclusion, the results obtained indicate that in a great number of C6/C7 neurones both spinoreticular and spinocerebellar projections are present. It is likely that afferent input from forelimbs may be directly of indirectly transmitted to the cerebellum through the same neurones.