Occipital headache can be a prominent feature of both migraine and non-migraineous headaches. One third of all migraines begin with tenderness of neck and shoulder muscles that gradually develop into a low-grade occipital headache. Sensations of cramp, tension, stiffness, tenderness or pain in neck and shoulder muscles that radiate to the back of the head are also common in tension-type headache, cervicogenic headache and Chiari malformation. One of the many speculations on the cause of occipital headache states that compression, irritation or inflammation of the C2 sensory root can be a trigger - a view supported by C2 nerve stimulation that evokes occipital pain and by documented relief of such headaches by C2 blockade. Given the above, it is surprising how little is known about the innervation of the dura overlying the cerebellum and occipital cortex, and even more so, how little is known about the functional properties of peripheral neurons that innervate the posterior fossa or the central neurons that process nociceptive information from this area. The broad objective of this proposal is to define the neural substrate of occipital headaches. Our working hypothesis is that occipital headaches involve activation of (a) meningeal nociceptors in the C2 DRG that innervate the dura overlying the cerebellum and (b) central neurons that process this information. This working hypothesis will be tested in one anatomical and two physiological studies. In the anatomical study, we will use a recombinant adeno-associated virus containing a green fluorescent protein reporter gene to infect C2 DRG cells and map the course of their axons and their distribution in the intracranial dura. In the physiological studies we will identify peripheral neurons in C2 DRG and central neurons in C1-3 dorsal horn whose receptive fields are located in the posterior dura overlying the cerebellum and spinomedullary junction, and determine whether their responses can be sensitized by stimulation of their dural and muscle receptive fields. Clinically, the proposed animal studies have the potential to shed new light on how occipital headaches that begin in pericranial tissues differ from occipital headaches that begin intracranially. Therapeutically, the findings may expand our understanding of C2/C3 manipulations commonly used in the treatment of migraine and non-migraine headaches; from assuming that it is mediated by reduction of nociceptive signals travelling along the occipital nerve to include reduction of nociceptive signals that originate in the posterior dura. Scientifically, the potential to identify novel triggers/causes of activation of nociceptors in the posterior dura (as compared to triggers of activation of nociceptors in the anterior dura) can lead to a deeper understanding of the neural basis of occipital headache and whether its origin differ from the origin of frontal/periorbital headache.
A large number of migraine and non-migraine headache patients experience pain in the back of the head (occipital headache). This grant proposal will test the hypothesis that pain signals originating in the posterior dura are transmitted through meningeal nociceptors whose cell bodies are located in C2 DRG to upper cervical dorsal horn neurons that process sensory/nociceptive signals from the occipital dura, skin and muscles of the neck.
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