Response properties of trigeminal brain stem neurons with input from dura mater encephali in the rat

The responsiveness of trigeminal brain stem neurons to selective local mech anical and chemical stimulation of the cranial dura mater was examined in a preparation in the rat. The dura mater encephali was exposed and its surfa ce stimulated with electrical pulses through bipolar electrodes. Extracellu lar recordings were made from neurons in the subnucleus caudalis of the spi nal trigeminal nucleus. Single neurons driven by meningeal input were ident ified by their responses to electrical stimulation and to probing their rec eptive fields on the dura. Facial receptive fields were defined mechanicall y. Chemical stimuli (a combination of inflammatory mediators, bradykinin, p rostaglandin E-2, serotonin, capsaicin and acidic Tyrode's solution) were a pplied topically to the dura and by injection through a catheter into the s uperior sagittal sinus. All neurons with input from the parietal dura mater had convergent input from the facial skin, with preponderance of the perio rbital region. Proportions of units were activated by the combination of in flammatory mediators (55%), bradykinin (64.5%), acidic Tyrode's solution (6 4.1%) and capsaicin (78.6%). We conclude that, among the chemical mediators of inflammation, bradykinin and low pH are the most effective chemical stimuli in activating meningeal nociceptors. These stimuli may be important during meningeal inflammatory p rocesses that lead to the generation of headaches. (C) 1999 IBRO. Published by Elsevier Science Ltd.