RECORDINGS FROM BRAIN STENT NEURONS RESPONDING TO CHEMICAL-STIMULATION OF THE SUBARACHNOID SPACE

The subarachnoid space at the base of the skull was perfused continuou sly with artificial cerebrospinal fluid in anesthetized rats. A combin ation of inflammatory mediators consisting of histamine, bradykinin, s erotonin, and prostaglandin E2 (10(-5) M) at pH of 6.1 was introduced into the flow for defined periods to stimulate meningeal primary affer ents. Secondary neurons in the caudal nucleus of the trigeminal brain stem were searched by electrical stimulation of the cornea. Of the uni ts receiving oligosynaptic input from the cornea, 44% were excited by stimulation of the meninges with inflammatory mediators. Most of these units had small receptive fields including cornea and the periorbital region, and their responsiveness was restricted to stimuli of noxiuos intensity. Three types of responses to stimulation of the meninges wi th algogenic agents were encountered: responses that did not outlast t he stimulus period, responses outlasting the stimulus period for sever al minutes, and oscillating response patterns containing periods of en hanced and suppressed activity. The response pattern of a unit was rep roducible, however, upon repetitive stimulation at 20-min intervals. t he response magnitude showed tachyphylaxis upon stimulus repetition. T he preparation presented mimics pathophysiolocial slates normally acco mpanied by headache, e.g.. subarachnoidal bleeding. Responsiveness of neurons in the caudal nucleus of the trigeminal brain stem to inflamma tory mediators may play a role in the generation and maintenance of he adache. e.g., migraine.