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

Segmental synaptic responses in the obliquus externus abdominis (OEA) for stimulation of the dorsal cutaneous and cutaneous-muscle (CD) nerve and the ventral cutaneous and cutaneous-muscle (CV) nerve were investigated in 49 spinal cats and 28 cats under alpha-chloralose anesthesia (chloralose cats) with an intracellular recording method. The result that there was no monosynaptic PSP in OEA motoneurons for stimulation of the CD or CV nerves (containing the cutaneous-muscle nerve) indicates that the cutaneous muscle of the dorsal or ventral area does not connect monosynaptically to the OEA motoneuron. The OEA motoneurons in chloralose cats received few effects from descending pathways coming from the upper spinal cord and the brain. Almost all OEA neurons had polysynaptic EPSP responses for stimulation of the ipsilateral or contralateral CD or CV nerves at 5-10T stimulus intensity in spinal or chloralose cats, which indicates that the OEA muscle can contract bilaterally when strong impulses of superficial afferents from the left or right skin or cutaneous muscle enter in the spinal cord.