RESPONSES OF T2-4 SPINAL-CORD NEURONS TO IRRITATION OF THE LOWER AIRWAYS IN THE RAT

The aim of the study was to investigate the information processing in the thoracic spinal cord (T2-4) after chemical irritation of the lower airways. Experiments were performed in pentobarbital sodium-anestheti zed and pancuronium-paralyzed male Sprague-Dawley rats. Balloon disten sion of the esophagus was used as the search stimulus. Ammonia and smo ke were applied by means of a tracheal cannula; they produced excitato ry, inhibitory, and biphasic responses in a concentration-related mann er (ammonia 39/39; smoke 23/39). Inhaled irritant-responsive neurons e xhibited a number of similarities that have been described for neurons responding to stimulation of other thoracic viscera. These similariti es relate to the distribution of neurons in the deeper laminae of the thoracic spinal cord, the relatively small number of neurons receiving input from the lower airways, the extensive convergent input from the skin and other thoracic viscera, and the pattern of responses. In add ition, both stimulus-induced responses and spontaneous activity are su bject to modulation from supraspinal sites. On the basis of responses to inhaled irritants after either spinal cord or vagus nerve block/tra nsection, these T2-4 spinal neurons are likely to receive spinal affer ent input that is modulated by vagal-brain stem input.