Functional organization of connexions to the ventral spinocerebellar tract

Abstract

1. The functional organization of synaptic connexions to the ventral spinocerebellar tract (VSCT) has been investigated with intracellular recording from 89 spinal border cells (SBCs). 2. EPSPs from primary afferents. Monosynaptic group I EPSPs were evoked in 62 SBCs, in 50 of them from Ia afferents. Ia EPSPs were from knee extensors in 34 cells and knee flexors in 14 cells. No monosynaptic EPSP was evoked by stimulation of peripheral nerves in 27 SBCs. Dorsal column stimulation was tested in 15 of these cells; the absence of monosynaptic EPSPs in 14 of them proves the existence of VSCT cells without monosynaptic connexions from group I afferents. Polysynaptic EPSPs were woked in some cells from Ib afferents, high threshold muscle and cutaneous afferents. 3. IPSPs from primary afferents. Disynaptic IPSPs were evoked from Ia or Ib afferents in many cells. Ib IPSPs were common in SBCs without monosynaptic group I EPSPs. SBCs with Ia EPSPs received Ia or Ib IPSPs mainly from knee muscles. Convergence of Ia EPSPs and IPSPs from the same nerve was observed in 10 cells. Polysynaptic IPSPs were commonly evoked from Ib afferents and invariably evoked from high threshold muscle and skin afferents. 4. Stimulation of the ipsilateral dorsal and/or ventral quadrant of the spinal cord evoked monosynaptic EPSPs and/or IPSPs in many SBCs. 5. The results show that the synaptic input to the VSCT is much more complex than hitherto believed. It is pointed out that all investigated afferent systems, peripheral or descending, which evoke excitation also give inhibition.