Suppression of noxious thermal evoked responses in thalamic central lateral nucleus by cortical spreading depression.

Several thalamic nuclei are associated with the processing of pain information and are influenced by cortical actions. This paper demonstrates a cortical influence upon the medial thalamic nuclei unit activity evoked by thermal noxious stimulation in rats. We studied the effects of cortical spreading depression (CSD) upon the responses of the centralis lateralis (CL) nucleus of the medial thalamus to noxious heat stimulation. Urethane was used as anaesthetic. Cells responding to noxious stimulation were localized in the dorsal portion of the CL. These cells responded like polymodal or nociceptive specific units in the spinal cord and exhibited their highest discharge frequency with noxious stimuli. When CSD is propagated and affects the medial frontal cortex it blocks the responses evoked in CL cells by noxious stimulation. Cortical cells located at this level also exhibited responses evoked by noxious stimulation. Our results suggest a cortical facilitatory control upon the noxious responses recorded in the CL cells.