Projection from excitatory C3-C4 propriospinal neurones to spinocerebellar and spinoreticular neurones in the C6-Th1 segments of the cat.

Extra- and intracellular recording was made from neurones in laminae VII and VIII of the C6-Th1 segments, which were disynaptically excited from the contralateral pyramid, nucleus ruber and monosynaptically from the ipsilateral lateral reticular nucleus. The results suggest collateral excitation from the C3-C4 propriospinal neurones which are excited monosynaptically from the former two inputs and antidromically from the latter nucleus. The cells were antidromically activated from the ipsilateral nucleus fastigus, and from the ipsilateral or contralateral reticular formation. Some of the spinocerebellar and spinoreticular neurones were also antidromatically activated from Th13. It is suggested that spinocerebellar, spinoreticular and bifurcating spinocerebellar and spinoreticular neurones receive collateral input from the same excitatory C3-C4 propriospinal neurones which project to motoneurones and/or Ia inhibitory interneurones.