Responses of spinocervical tract neurones to noxious stimulation of the skin.

Abstract

Activity of single spinocervical tract neurons was recorded in the lumbar spinal cord of chloralose anesthetized or decerebrated cats. Reversible spinalization was produced by cold block at L3. Sensitivity of these neurons to noxious stimulation was studied by heating their cutaneous receptive fields above 40-45.degree. C. Most of the units were located in lamina IV of the dorsal horn and had their receptive fields in the ipsilateral foot. All but 1 of the studied neurons were excited by moving hairs or by gentle mechanical stimulation of the skin. Of the units 84% were affected by noxious stimuli and 3 kinds of response were obtained: 61% were excited (E-cells) by noxious heat; 19% were inhibited (I-cells); and 19% gave a mixed response reversing from excitatory to inhibitory (EI-cells). E-cells had axons with a wider range of conduction velocities than the rest and received the strongest descending inhibition from supraspinal structures. The recording sites of EI-cells were located in the medial 1/3 of the dorsal horn, whereas E- and I-cells were distributed over the full width of the dorsal horn. The possible role of the spinocervical tract in nociception is discussed.