Convergence of afferents from superior sagittal sinus and tooth pulp on cells in the thalamus of the cat

Migraine headache pathophysiology

In both episodic and chronic migraine, headache is the most disabling symptom that requires medical care. The migraine headache is the most well-studied symptom of migraine pathophysiology. The trigeminal system and the central processing of sensory information transmitted by the trigeminal system are of considerable importance in the pathophysiology of migraine headache. Glutamate is the main neurotransmitter that drives activation of the ascending trigeminal and trigeminothalamic pathways. The neuropeptide, calcitonin gene-related peptide (CGRP) that is released by the trigeminal system, plays a crucial role in the neurobiology of headache. Peripheral and central sensitizations associated with trigeminal sensory processing are neurobiologic states that contribute to both the development of headache during a migraine attack and the maintenance of chronic migraine.

Migraine in people with epilepsy: a treatable and neglected co-morbidity

Migraine and epilepsy account for more than 40% of neurology outpatients and are leading causes of disability. They often co-exist and can be confused, because of shared clinical features. The borderlands and links between migraine and epilepsy have fascinated neurologists for centuries, and unresolved questions remain. Greater understanding of the relationship between migraine and epilepsy may give insight into shared mechanisms. It is already clear that treating co-existing migraine is an important therapeutic opportunity and may improve epilepsy.

Familial limb pain and migraine: 8-year follow-up of four generations

Background Migraine limb pain may be under-recognized in adults and children. There is little information about familial forms of this disorder. Objectives To describe the clinical and inheritance patterns of familial migraine limb pain over four generations and to review the evidence for limb pain as a manifestation of migraine. Methods Prospective clinical and pedigree analysis with an 8-year follow-up of 27 family members. Results Eight members of the family had benign recurrent limb pain associated with headache in a dominant inheritance pattern. Limb pain occurred before, during or after the headache, with probable or definite migraine with aura, migraine without aura and lower-half headache. The limb pain fulfilled the International Headache Society criteria for aura in six patients and also occurred without headache in three. Four members of the family had recurrent abdominal pain and/or motion sickness in childhood. Conclusions This is the first report of dominant familial limb pain temporally associated with migraine headache, starting in adulthood or starting in childhood and continuing into adulthood. A search for a genetic marker is indicated. Limb pain should be included as a childhood periodic syndrome linked to migraine and recognized as part of the migraine spectrum in adults.

Current Understanding on Pain Mechanism in Migraine and Cluster Headache

CONTEXT

Migraine and cluster headache are undoubtedly painful conditions. The respective pathogenesis of these two conditions is incompletely understood. In both cases, the treatments used have largely been empirical and have relied to a much lesser extent on our understanding of the mechanisms causing pain. We hereby review the pain mechanisms in migraine and cluster headache, two of the commonest primary headache disorders.

EVIDENCE ACQUISITION

A review of the English literature was conducted by searching PubMed for studies on pain mechanism in migraine and cluster headache. We entered [migraine] and [pain mechanism] in Pubmed and 488 articles were obtained. Articles were then included according to their relevance to the topic. Similarly, [cluster headache] and [pain mechanism] revealed 79 search results.

RESULTS

There is evidence that the trigeminovascular system and neurogenic inflammation play important roles, together with certain areas of the brain, leading to these conditions being termed 'neurovascular headaches'. Functional imaging findings suggest a possible role of the dorsolateral pons in generating migraine attacks while the role of the hypothalamus in cluster headache is more firmly established.

CONCLUSIONS

Migraine and cluster headache have complex pathophysiologies. The exact mechanism causing pain in both conditions is incompletely understood and more research needs to be undertaken in this area.

Migraine pathophysiology: anatomy of the trigeminovascular pathway and associated neurological symptoms, CSD, sensitization and modulation of pain

Scientific evidence support the notion that migraine pathophysiology involves inherited alteration of brain excitability, intracranial arterial dilatation, recurrent activation and sensitization of the trigeminovascular pathway, and consequential structural and functional changes in genetically susceptible individuals. Evidence of altered brain excitability emerged from clinical and preclinical investigation of sensory auras, ictal and interictal hypersensitivity to visual, auditory and olfactory stimulation, and reduced activation of descending inhibitory pain pathways. Data supporting the activation and sensitization of the trigeminovascular system include the progressive development of cephalic and whole-body cutaneous allodynia during a migraine attack. Also, structural and functional alterations include the presence of subcortical white mater lesions, thickening of cortical areas involved in processing sensory information, and cortical neuroplastic changes induced by cortical spreading depression. Here, we review recent anatomical data on the trigeminovascular pathway and its activation by cortical spreading depression, a novel understanding of the neural substrate of migraine-type photophobia, and modulation of the trigeminovascular pathway by the brainstem, hypothalamus and cortex.

Stimulation of dural vessels excites the SI somatosensory cortex of the cat via a relay in the thalamus

Aim

We carried out experiments in cats to determine the thalamo-cortical projection sites of trigeminovascular sensory neurons.

Methods

1) We stimulated the middle meningeal artery (MMA) with C-fibre intensity electrical shocks and made field potential recordings over the somatosensory cortical surface. 2) We then recorded neurons in the ventroposteromedial (VPM) nucleus of the thalamus in search of neurons which could be activated from the skin, MMA and superior sagittal sinus. 3) Finally, we attempted to antidromically activate the neurons found in stage 2 by stimulating the responsive cortical areas revealed in stage 1.

Results

VPM neurons received trigeminovascular input, input from the V1 facial skin and could also be activated by electrical stimulation of the somatosensory cortex. VPM neurons activated from the cortex responded with short and invariant latencies (6.7 ± 7.7 msec mean and SD). They could follow high rates of stimulation and sometimes showed collision with orthodromic action potentials.

Conclusions

We conclude that somatosensory (SI) cortical stimulation excites trigeminovascular VPM neurons antidromically. In consequence, these VPM neurons project to the somatosensory cortex. These findings may help to explain the ability of migraineurs with headache in the trigeminal distribution to localise their pain to a particular region in this distribution.

Cortical projections of functionally identified thalamic trigeminovascular neurons: implications for migraine headache and its associated symptoms

This study identifies massive axonal arbors of trigeminovascular (dura-sensitive) thalamic neurons in multiple cortical areas and proposes a novel framework for conceptualizing migraine headache and its associated symptoms. Individual dura-sensitive neurons identified and characterized electrophysiologically in first-order and higher-order relay thalamic nuclei were juxtacellularly filled with an anterograde tracer that labeled their cell bodies and processes. First-order neurons located in the ventral posteromedial nucleus projected mainly to trigeminal areas of primary (S1) as well as secondary (S2) somatosensory and insular cortices. Higher-order neurons located in the posterior (Po), lateral posterior (LP), and lateral dorsal (LD) nuclei projected to trigeminal and extra-trigeminal areas of S1 and S2, as well as parietal association, retrosplenial, auditory, ectorhinal, motor, and visual cortices. Axonal arbors spread at various densities across most layers of the different cortical areas. Such parallel network of thalamocortical projections may play different roles in the transmission of nociceptive signals from the meninges to the cortex. The findings that individual dura-sensitive Po, LP, and LD neurons project to many functionally distinct and anatomically remote cortical areas extend current thinking on projection patterns of high-order thalamic neurons and position them to relay nociceptive information directly rather than indirectly from one cortical area to another. Such extensive input to diverse cortical areas that are involved in regulation of affect, motor function, visual and auditory perception, spatial orientation, memory retrieval, and olfaction may explain some of the common disturbances in neurological functions during migraine.

Thalamic sensitization transforms localized pain into widespread allodynia

OBJECTIVE

Focal somatic pain can evolve into widespread hypersensitivity to nonpainful and painful skin stimuli (allodynia and hyperalgesia, respectively). We hypothesized that transformation of headache into whole-body allodynia/hyperalgesia during a migraine attack is mediated by sensitization of thalamic neurons that process converging sensory impulses from the cranial meninges and extracephalic skin.

METHODS

Extracephalic allodynia was assessed using single unit recording of thalamic trigeminovascular neurons in rats and contrast analysis of blood oxygenation level-dependent (BOLD) signals registered in functional magnetic resonance imaging (fMRI) scans of patients exhibiting extracephalic allodynia.

RESULTS

Sensory neurons in the rat posterior thalamus that were activated and sensitized by chemical stimulation of the cranial dura exhibited long-lasting hyperexcitability to innocuous (brush, pressure) and noxious (pinch, heat) stimulation of the paws. Innocuous, extracephalic skin stimuli that did not produce neuronal firing at baseline (eg, brush) became as effective as noxious stimuli (eg, pinch) in eliciting large bouts of neuronal firing after sensitization was established. In migraine patients, fMRI assessment of BOLD signals showed that brush and heat stimulation at the skin of the dorsum of the hand produced larger BOLD responses in the posterior thalamus of subjects undergoing a migraine attack with extracephalic allodynia than the corresponding responses registered when the same patients were free of migraine and allodynia.

INTERPRETATION

We propose that the spreading of multimodal allodynia and hyperalgesia beyond the locus of migraine headache is mediated by sensitized thalamic neurons that process nociceptive information from the cranial meninges together with sensory information from the skin of the scalp, face, body, and limbs.

Effects of conditioning stimulation of the central amygdaloid nucleus on tooth pulp-driven neurons in the cat somatosensory cortex (SI)

To study the limbic control of nociception, we examined the effect of conditioning stimulation of the central amygdaloid nucleus (ACE) on tooth pulp-driven (TPD) neurons in the first somatosensory cortex (SI). Cats were anesthetized with N(2)O-O(2) (2:1) and 0.5% halothane, and immobilized with tubocurarine chloride. The tooth pulp test stimulus was applied by a single rectangular pulse (0.5 ms in duration and 3-5 times the threshold intensity for the jaw-opening reflex). Conditioning stimuli to the ACE consisted of trains of 33 pulses (300 microA) delivered at 330 Hz at intervals of 8-10 s. In 35 out of 61 of the slow (S)-type TPD neurons with latencies of more than 20 ms, conditioning stimulation in the ACE, especially in the medial division, markedly reduced the firing response to the pulpal stimulation. The inhibition of the firing rate in the S-type neurons was 74% of the control. In these S-type neurons, the neurons that were inhibited had significantly longer latencies compared to the non-inhibited neurons (45.0 +/- 17.6 ms, n = 32 vs. 34.8 +/- 10.5 ms, n = 26). In contrast, the ACE conditioning stimulation affected only one out of 18 fast-type TPD neurons with latencies of less than 20 ms. In addition, ACE stimulation had no effect on the spontaneous discharges of either S-type or F-type neurons. The ACE inhibitory effect on S-type neurons was not diminished by naloxone administration (1 mg/kg, I.V. ), while the blockade of histamine H(1)-receptor by diphenhydramine hydrochloride (0.5 mg/kg, I.V.) partially reversed the inhibitory effect. These results suggest that the ACE inhibits ascending nociceptive information to the SI and that this inhibition is mediated in part by histamine (H(1)) receptors. It seems likely that the antinociceptive effect is a neurophysiological basis for stress-induced analgesia (SIA).