Crossed and uncrossed segmental synaptic effects on rectus abdominis motoneurons from cutaneous and cutaneous-muscle nerve in spinal cats and alpha-chloralose-anesthetized cats.

Segmental synaptic responses evoked by stimulation of the dorsal cutaneous and cutaneous-muscle (CD) nerve or the ventral cutaneous and cutaneous-muscle (CV) nerve were investigated with intracellular recording from rectus abdominis (RA) motoneurons in 49 spinal cats and 28 alpha-chloralose-anesthetized cats. No monosynaptic and few disynaptic connections existed in the circuit from the ipsilateral or contralateral CD or CV nerves to RA motoneurons in spinal cats. Polysynaptic EPSP responses equal to or over trisynaptic connections were dominant. In alpha-chloralose-anesthetized cats, RA motoneurons exhibited significantly more polysynaptic EPSP responses at lower stimulus intensities (1.5T and 2T) of ipsilateral CV nerve stimulation than at those of contralateral CV nerve stimulation. The result that there was no monosynaptic or disynaptic PSP in RA motoneurons produced by low-intensity stimulation of the ipsilateral CD or CV nerve containing the cutaneous-muscle nerves indicated that Ia afferents from the cutaneous-muscle did not connect mono- or di-synaptically to the RA motoneuron. RA motoneurons exhibited more polysynaptic IPSP responses in alpha-chloralose-anesthetized cats than in spinal cats. Segmental pathways from the CD or CV nerves to RA motoneurons might receive inhibitory descending inputs from the upper spinal cord or the brain, in contrast to those from the same nerves to obliquus externus abdominis motoneurons previously reported.