Some properties of spinal connections of the cat's dorsal column nuclei which do not involve the dorsal columns

Abstract

After total division of the dorsal columns at C4, both excitatory and inhibitory actions were produced in the gracile and in the cuneate nucleus, by electrical stimulation of the ipsilateral dorsolateral fascicle caudal to the section, and by mechanical stimulation of peripheral sstructures. Most observations were made in the rostral 5 mm of the nuclei. Stimulating the DLF produced direct responses of single fibres, and also postsynaptic responses in cells, in these nuclei. Postsynaptic responses were seen in 220 single units: 30% (out of 157 tested) were relay cells responding antidromically to stimulation in the contralateral upper brain stem, and some 40% of these cells were shown to have receptive fields, mostly sensitive cutaneous fields, on the appropriate ipsilateral limb. Some cells responding postsynaptically, for which there no evidence of lemniscal projection, responded only to noxious peripheral stimulation of one or more ipsilateral or contralateral paws, and it is suggested these may be inhibitory interneurones. Many cells in these nuclei could be inhibited by noxious peripheral stimulation from a wide and often bilateral field. Stimulating the ipsilateral DLF after dorsal column section inhibited the postsynaptic field potential (N-wave) in these nuclei, and it was shown by testing terminal excitability in dorsal column axons above the section that part at least of this inhibition was presynaptic. These results show that the dorsal column nuclei are associated in a complex way with sensory mechanisms in the dorsal part of the cord other than the dorsal columns,a fact which calls for re-evaluation of certain earlier experimental work.