Integration in descending motor pathways controlling the forelimb in the cat. 1. Pyramidal effects on motoneurones.

Stimulation of the contralateral pyramid and intracellular recording from forelimb motoneurones was used to investigate corticimotoneuronal pathways in the cat. A train of pyramidal volleys evokes short-latency EPSPS in flexor motoneurones and in many extensor motoneurones. The latency for the onset after the effective pyramidal volley-usually the third - strongly indicates a disynaptic linkage. These disynaptic EPSPs were common in triceps motoneurones to fast heads but rare in those to slow heads. Pyramidal IPSPs with a slightly longer latency, suggesting a trisynaptic linkage, were found in both flexor and extensor motoneurones. They were common in motoneurones to slow heads of triceps. Disynaptic pyramidal IPSPs were found only occasionally. In addition pyramidal volleys may evoke late large EPSPs and/or IPSPs in any combination with the short-latency PSPs.