The lateral reticular nucleus in the cat. V. Does collateral activation from the dorsal spinocerebellar tract occur?

1. The assertion made by Burton, Bloedel and Gregory (1971) that neurones in the mLRN (major portion of lateral reticular nucleus comprising its parvi- and magnocellular parts) receive collateral excitation from the dorsal spinocerebellar tract (DSCT) has been tested. The activation of mLRN neurones on stimulation of limb nerves was studied in preparations with the spinal cord interrupted at C3 sparing only the dorsal part of the ipsilateral lateral funiculus (iDLF preparations), only the ipsilateral ventral quadrant (iVQ preparations), or only the ipsilateral lateral and ventral funiculi (iLFVF preparations). 2. In iDLF preparations (with the DSCT intact) stimulation of limb nerves evoked responses in only occasional mLRN neurones. These responses could be attributed to activation from some dorsally located fibres belonging to the bilateral ventral flexor reflex tract (bVFRT) and to activation from a previously unknown path activated after a long latency from ipsilateral forelimb and hindlimb afferents. 3. In iLFVF preparations (with the DSCT intact) and iVQ preparations (with the DSCT interrupted) most mLRN neurones responsed to limb nerve stimulation. The responses in two preparations were similar and could be attributed largely or exclusively to activation from the bVFRT. 4 It is concluded that the DSCT does not activate any major group of mLRN neurones.