Synchronization of the electrocorticogram by visceral and somatic bradykinin stimulation in anesthetized cats

The cortical response to visceral and somatic bradykinin stimulation was studied in cats under light to moderate pentobarbital anesthesia. Following the injection of bradykinin into arteries supplying visceral organs and somatic structures, a marked cortical synchronization was recorded. The bilateral, rhythmic discharge in the theta to alpha range was best seen on SI; occasionally the contralateral SI response was more prominent. The cortical synchronization and its distribution were the same for visceral and somatic stimulation. There was only minimal response desensitization to multiple injections of bradykinin in rapid succession. Following transection of the thoracolumbar spinal cord, synchronization failed to develop after hindlimb injections but continued to be seen after forelimb stimulation; similarly, partial denervation of a limb blocked the bradykinin response. No synchronization or desynchronization could be produced by epinephrine and nitroglycerine which caused phasic changes in systemic blood pressure equal to or greater than those seen with bradykinin. The results are discussed in terms of possible pathways and receptors. It is suggested that bradykinin acts primarily on free nerve endings common to visceral and deep somatic tissue with convergence of impulses occurring at spinal and higher levels. The preferential response of SI may reflect afferent activity generated by natural, painful stimulation of deep somatic and visceral organs. Normally, this component would be masked by the concomitant non-specific arousal response of the medial reticulo-thalamic system which was depressed by the anesthetic.