Descending pathways from the medial longitudinal fasciculus and lateral vestibular nucleus to tail motoneurons in the decerebrate cat.

Responses of motoneurons supplying two tail muscles (m. extensor caudae lateralis [ECL] and m. flexor caudae longus [FCL]) to stimulation of the medial longitudinal fasciculus (MLF) and lateral vestibular nucleus (LVN) were studied using intracellular recording in the decerebrate cat. Stimulation of the MLF and the LVN produced mainly excitatory postsynaptic potentials (EPSPs) or mixed PSPs (EPSP/IPSPs), but inhibitory postsynaptic potentials (IPSPs) were also observed in a few motoneurons. The segmental latencies of early PSPs produced by MLF or LVN stimulation were distributed over a wide range, and PSPs with a segmental latency of mono- or disynaptic origin were observed in ECL and FCL motoneurons. The spatial facilitation technique indicated convergence of the descending pathways from MLF and LVN on a common interneuron.