Effect of dorsal-column stimulation on gelatinosa and marginal neurons of cat spinal cord.

Single neuronal units with physiological characteristics of superficial dorsal-horn neurons were recorded extracellularly in laminae 1, 2, and 3 of cat spinal cord. When focal electrical stimulation was applied to the ipsilateral dorsal column, most of the units were excited transsynaptically at various latencies consistent with an effect mediated by large myelinated axons. Units recorded in laminae 2 and 3 had earlier latencies of activation than units in lamina 1. Units with cutaneous receptive fields only for noxious stimuli were activated at significantly longer latencies than units responsive to innocuous stimuli. The time course of these effects was consistent with the concept that many cells in laminae 1 to 3 receive direct excitatory synaptic input from collaterals of dorsal-column fibers, and some lamina 1 cells receive excitatory synaptic input from lamina 2 neurons. Previous reports have emphasized the inhibitory action of dorsal-column stimulation on nociceptive responses of cells in laminae 4 and 5 of the dorsal-horn, particularly those of the spinocervical tract in cats and the spinothalamic tract in primates. The present study suggests that some of this inhibition might be sustained by a network of interneurons in or near the substantia gelatinosa and marginal layer. The therapeutic efficiency of dorsal-column stimulation for pain relief in humans may depend in part on the activation of neurons in the superficial layers of the dorsal horn.