Aktivierung trigeminaler Hirnstammneurone durch chemische Stimulation der Dura mater encephali

Migraine: where and how does the pain originate?

Migraine is a complex neurological disease with a genetic background. Headache is the most prominent and clinically important symptom of migraine but its origin is still enigmatic. Numerous clinical, histochemical, electrophysiological, molecular and genetical approaches form a puzzle of findings that slowly takes shape. The generation of primary headaches like migraine pain seems to be the consequence of multiple pathophysiological changes in meningeal tissues, the trigeminal ganglion, trigeminal brainstem nuclei and descending inhibitory systems, based on specific characteristics of the trigeminovascular system. This contribution reviews the current discussion of where and how the migraine pain may originate and outlines the experimental work to answer these questions.

Convergence of meningeal and facial afferents onto trigeminal brainstem neurons: an electrophysiological study in rat and man

Headache is often accompanied by referred pain in the face. This phenomenon is probably due to a convergence of afferent inputs from the meninges and the face onto central trigeminal neurons within the medullary dorsal horn (MDH). The possible existence and extent of this convergence was examined in rat and man. MDH neurons activated by stimulation of the parietal meninges were tested for convergent tactile and noxious mechanical input from all three facial branches of the trigeminal nerve. All 21 units with meningeal input could also be activated by facial stimuli. Brush stimuli applied to the supraorbital nerve area activated 86%, to the infraorbital nerve area 29%, and to the mental nerve area none of the units. Pinch stimuli applied to the supraorbital nerve area activated 95%, to the infraorbital nerve area 86%, and to the mental nerve area 52% of the units. The results suggest convergence of meningeal and facial inputs concentrated on the supraorbital nerve in rat. In man convergence was examined by probing neuronal excitability of MDH applying the blink reflex (BR) during Valsalva maneuver which probably increases intracranial pressure. The BR evoked by supraorbital nerve stimulation remained unchanged, while the BR evoked by mental nerve stimulation was significantly facilitated. This facilitation may be due to convergence of meningeal and facial inputs onto trigeminal neurons in man.

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 mechanical and chemical stimulation of the cranial dura mater was examined in a preparation in the rat. The dura mater encephali was exposed and its surface stimulated with electrical pulses through bipolar electrodes. Extracellular recordings were made from neurons in the subnucleus caudalis of the spinal trigeminal nucleus. Single neurons driven by meningeal input were identified by their responses to electrical stimulation and to probing their receptive fields on the dura. Facial receptive fields were defined mechanically. Chemical stimuli (a combination of inflammatory mediators, bradykinin, prostaglandin E2, serotonin, capsaicin and acidic Tyrode's solution) were applied topically to the dura and by injection through a catheter into the superior sagittal sinus. All neurons with input from the parietal dura mater had convergent input from the facial skin, with preponderance of the periorbital region. Proportions of units were activated by the combination of inflammatory mediators (55%), bradykinin (64.5%), acidic Tyrode's solution (64.1%) 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 processes that lead to the generation of headaches.