The vestibulospinal tract. Effects on alpha-motoneurones in the lumbosacral spinal cord in the cat.

Abstract

1. Effects evoked from the vestibulospinal tract in hindlimb motoneurones have been investigated with intracellular recording. Electrical stimulation of Deiters' nucleus was employed and for different effects the effective low threshold area in the brain stem was correlated with the region in which antidromic field potentials were evoked from the vestibulospinal tract. 2. The following effects from the vestibulospinal tract are described: a) Monosynaptic EPSPs are common in knee and ankle extensors, rare in hip and toe extensors and absent in flexor motoneurones. There was no marked difference in size of the monosynaptic EPSPs in motoneurones with short and long afterhyperpolarizations. b) Disynaptic IPSPs are common in flexor but also found in some hip extensor cells. c) Di(poly)synaptic EPSPs are common in extensor and in some pretibial flexor cells. 3. A comparison of the descending monosynaptic EPSP with the Ia EPSP showed that the former has a shorter rise time and duration. With repetitive stimulation the descending EPSPs sum more effectively than the Ia EPSPs. 4. The functional role of the pattern of synaptic action from the vestibulospinal tract is discussed also in relation to effects exerted on γ-motoneurones and interneuronal pathways.