Ascending pathways of skin and deep information projecting to the ventral posterior lateral nucleus of thalamus in the cat.

Abstract

In acupuncture, the typical sensation induced by insertion of a needle into the muscle that called “De Qi” is essential to induce acupuncture analgesia. The effect of acupuncture analgesia may depend on the deep afferents rather than to the cutaneous ones at the acupuncture point. The ascending pathways conveying these skin and deep afferents project to the ventral posterior lateral nucleus (VPL) of thalamus, one of the thalamic relay nuclei projected to the cerebral cortex, were examined by spinal cord lesion at the cervical level with observation of the responses evoked by electrical stimulation applied selectively to the skin and deep tissues.Neuronal discharges were recorded extracellularly from the VPL using the multimicroelectrode technique. After spontaneous neuronal activities were recorded, the receptive fields and characteristics were determined by applying some kinds of mechanical stimulation to the receptive field. The skin and deep structures were then selectively stimulated using a pair of stainless steel needles and insulated needles except for tips. Units were classified for skin units, deep units, and skin-deep units according to the responses to the electrical stimulation. Responses were elicited in some neurons following to both skin and deep stimuli. The latency of response elicited by electrical stimulation applied to the deep structure was slightly shorter than that of the skin structure. The recording sites for deep units were located more rostrally in the dorsal region of the VPL than that for the skin units.The afferents of some skin-deep neurons from both skin and deep structures were ascended through different pathways in the spinal cord. The skin and deep afferents were found to converge at the thalamic level.