SELECTIVE CHANGES OF RECEPTIVE-FIELD PROPERTIES OF SPINAL NOCICEPTIVE NEURONS INDUCED BY NOXIOUS VISCERAL STIMULATION IN THE CAT

This study was designed to examine the central changes in the receptive field properties of dorsal horn neurones induced by a period of visceral noxious stimulation. The aim of this investigation was to establish whether noxious stimulation of the visceral input to the spinal cord could influence transmission of cutaneous information through dorsal horn neurones. Single-unit electrical activity was recorded in the lower thoracic spinal cord of anaesthetized cats from dorsal horn neurones with a somatic receptive field in the ipsilateral flank. Changes in the properties of these receptive fields induced by reversible spinalization (by means of a cold block 4 or 5 segments rostral to the recording electrodes) and by a conditioning noxious stimulation of the biliary system (3 successive distensions of the gall bladder for 30 sec at 65-80 mm Hg at 1-min intervals) were analysed. Nineteen neurones have been studied, 10 of which could be driven by stimulation of the gall bladder. All of these 10 cells showed increases in the size of their cutaneous receptive fields following conditioning noxious stimulation of the biliary system. The increases were large and lasted for at least 20 min. None of the 9 spinal cord neurones without an input from the gall bladder were affected by the conditioning visceral stimulus even though 7 showed changes in receptive field size when the animals were spinalised. These results show that noxious stimulation of viscera can evoke increases in the somatic receptive fields of spinal cord neurones but only of those neurones which are also driven by the visceral stimulus.