Nouchine Hadjikhani, Margarita Sanchez del Rio, Ona Wu, Denis Schwartz, Dick Bakker, Bruce Fischl, Kenneth K. Kwong, F. Michael Cutrer, Bruce R. Rosen, Roger B. H. Tootell, A. Gregory Sorensen, and Michael A. Moskowitz
Mechanisms of migraine aura revealed by functional MRI in human visual cortex
PNAS 98: 4687-4692; published online before print as 10.1073/pnas.071582498
"Cortical spreading depression (CSD) has been suggested to underlie migraine visual aura. However, it has been challenging to test this hypothesis in human cerebral cortex. Using high-field functional MRI with near-continuous recording during visual aura in three subjects, we observed blood oxygenation level-dependent (BOLD) signal changes that demonstrated at least eight characteristics of CSD, time-locked to percept/onset of the aura. Initially, a focal increase in BOLD signal (possibly reflecting vasodilation), developed within extrastriate cortex (area V3A). This BOLD change progressed contiguously and slowly (3.5 +/- 1.1 mm/min) over occipital cortex, congruent with the retinotopy of the visual percept. Following the same retinotopic progression, the BOLD signal then diminished (possibly reflecting vasoconstriction after the initial vasodilation), as did the BOLD response to visual activation. During periods with no visual stimulation, but while the subject was experiencing scintillations, BOLD signal followed the retinotopic progression of the visual percept. These data strongly suggest that an electrophysiological event such as CSD generates the aura in human visual cortex." [Full Text]

Lauritzen M.
Pathophysiology of the migraine aura. The spreading depression theory.
Brain. 1994 Feb;117 ( Pt 1):199-210.
"The characteristic form and development of sensory disturbances during migraine auras suggests that the underlying mechanism is a disturbance of the cerebral cortex, probably the cortical spreading depression (CSD) of Leao. The demonstration of unique changes of brain blood flow during attacks of migraine with aura, which have been replicated in animal experiments during CSD, constitutes another important line of support for the 'spreading depression' theory, which may be a key to an understanding of the migraine attack. Cortical spreading depression is a short-lasting depolarization wave that moves across the cortex at a rate of 3-5 mm/min. A brief phase of excitation heralds the reaction which is immediately followed by prolonged nerve cell depression synchronously with a dramatic failure of brain ion homeostasis, efflux of excitatory amino acids from nerve cells and enhanced energy metabolism. Recent experimental work has shown that CSD in the neocortex of a variety of species including man is dependent on activation of a single receptor, the N-methyl-D-aspartate receptor, one of the three subtypes of glutamate receptors. The combined experimental and clinical studies point to fruitful areas in which to look for migraine treatments of the future and provide a framework within which important aspects of the migraine attack can be modelled." [Abstract]

Gorji A, Scheller D, Straub H, Tegtmeier F, Kohling R, Hohling JM, Tuxhorn I, Ebner A, Wolf P, Werner Panneck H, Oppel F, Speckmann EJ.
Spreading depression in human neocortical slices.
Brain Res. 2001 Jul 6;906(1-2):74-83.
"Cortical spreading depression (CSD) occurrence has been suggested to be associated with seizures, migraine aura, head injury and brain ischemia-infarction. Only few studies identified CSD in human neocortical slices and no comprehensive study so far evaluated this phenomenon in human. Using the neocortical tissue excised for treatment of intractable epilepsy, we aimed to investigate CSD in human. CSD was induced by KCl injection and by modulating T-type Ca(2+) currents in incubated human neocortical tissues in an interphase mode. The DC-fluctuations were recorded by inserting microelectrodes into different cortical layers. Local injection of KCl triggered single CSD that propagated at 3.1+/-0.1 mm/min. Repetitive CSD also occurred spontaneously during long lasting application (5 h) of the T-type Ca(2+) channel blockers amiloride (50 microM) or NiCl(2) (10 microM) which was concomitant with a reversible extracellular potassium increase up to 50 mM. CSD could be blocked by the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovaleric acid in all cases. The results demonstrate that modulation of the Ca(2+) dynamics conditioned human neocortical slices and increased their susceptibility to generate CSD. Furthermore, these data indicate that glutamatergic pathway plays a role in CSD phenomenon in human." [Abstract]

Faria LC, Mody I
Protective Effect of Ifenprodil against Spreading Depression in the Mouse Entorhinal Cortex.
J Neurophysiol. 2004 Jun 16;
In the brain, spreading depression (SD) is characterized by a large extracellular DC shift, a massive failure of ion homeostasis and a transient cessation of neuronal function. Clinically, SD is believed to be involved in various neurological disorders including migraine and cerebrovascular diseases. The propagation of cortical SD requires the release of glutamate, and NMDA receptors play a crucial role in this process. Here, we have isolated the NMDA-receptor-mediated component of extracellularly recorded field EPSPs (fEPSPs) in layers 2-3 of the entorhinal cortex of murine brain slices. In the absence of GABAA and AMPA receptor mediated synaptic transmission, stimulation of layer 6 afferents every 15 - 90 s elicited spontaneous SD on average within 18.5 min after the start of the stimulation. In the presence of ifenprodil, an NR2B receptor subunit-selective NMDA receptor antagonist, the occurrence of SD was nearly abolished. Our results are consistent with an important role of NR2B subunits in triggering SD in the entorhinal cortex. [Abstract]

Benz B, Grima G, Do KQ
Glutamate-induced homocysteic acid release from astrocytes: possible implication in glia-neuron signaling.
Neuroscience. 2004;124(2):377-86.
Glial cells synthesise neuroactive substances and release them upon neurotransmitter receptor activation. Homocysteic acid (HCA), an endogenous agonist for glutamatergic N-methyl-D-aspartate (NMDA) receptors, is predominantly localised in glial cells. We have previously demonstrated the release of HCA from mouse astrocytes in culture following activation of beta-adrenergic receptors. Moreover, a release of HCA has also been observed in vivo upon physiological stimulation of sensory afferents in the thalamus. Here we report the glutamate-induced release of HCA from astrocytes. The effect of glutamate was mediated by the activation of ionotropic (NMDA and non-NMDA) as well as by metabotropic receptors. In addition, the release of HCA was Ca(2+)- and Na(+)-dependent, and its mechanism involved the activation of the Na+/Ca(2+)-exchanger. Furthermore, we provide evidence for the presence of functional NMDA receptors on astrocytes, which are coupled to an intracellular Ca2+ increase via stimulation of the Na+/Ca(2+)-exchanger. Our data thus favour a participation of glial cells in excitatory neurotransmission and corroborate the role of HCA as a "gliotransmitter." [Abstract]

Shi, Qi, Savage, Jason E., Hufeisen, Sandra J., Rauser, Laura, Grajkowska, Ewa, Ernsberger, Paul, Wroblewski, Jarda T., Nadeau, Joseph H., Roth, Bryan L.
L-Homocysteine Sulfinic Acid and Other Acidic Homocysteine Derivatives Are Potent and Selective Metabotropic Glutamate Receptor Agonists
J Pharmacol Exp Ther 2003 305: 131-142
"... because homocysteine is also involved in normal metabolic pathways of many biologically functional molecules, abnormalities in homocysteine metabolism may adversely affect many related and unrelated pathways which, in turn, cause diseases and disorders." [Full Text]

Görtz P, Hoinkes A, Fleischer W, Otto F, Schwahn B, Wendel U, Siebler M
Implications for hyperhomocysteinemia: not homocysteine but its oxidized forms strongly inhibit neuronal network activity.
J Neurol Sci. 2004 Mar 15;218(1-2):109-14.
Severe hyperhomocysteinemia (50-200 microM) often presents itself with acute neuronal dysfunction including seizures and psychosis. Its moderate form (15-50 microM) is associated with cognitive impairment and dementia. We investigated the neuropharmacological effects of homocysteine and its oxidized forms, homocysteinesulfinic acid (HCSA) and homocysteic acid (HCA), on neuronal network function utilizing dissociated cortical neurons from embryonic Wistar rats on microelectrode arrays. All substances inhibited dose-dependently and reversibly spontaneous neuronal network activity within seconds: L-HCSA and L-HCA blocked spontaneous spike rate (SSR) significantly at very low concentrations, with an IC50 of 1.9 and 1.3 microM, respectively; whereas the dose-response curve of D,L-homocysteine revealed an IC50 of 401 microM. These effects were antagonized by 2-amino-5-phosphonovaleric acid (APV) pointing to the NMDA receptor as mediator of this fast and reversible inhibition of network activity. We conclude that a neuronal dysfunction observed in hyperhomocysteinemia is likely due to HCSA and HCA since effective concentrations of homocysteine are not reached in patients. [Abstract]

Lea RA, Ovcaric M, Sundholm J, MacMillan J, Griffiths LR
The methylenetetrahydrofolate reductase gene variant C677T influences susceptibility to migraine with aura.
BMC Med. 2004 Feb 12;2(1):3.
BACKGROUND: The C677T variant in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with increased levels of circulating homocysteine and is a mild risk factor for vascular disease. Migraine, with and without aura (MA and MO), is a prevalent and complex neurovascular disorder that may also be affected by genetically influenced hyperhomocysteinaemia. To determine whether the C677T variant in the MTHFR gene is associated with migraine susceptibility we utilised unrelated and family-based case-control study designs. METHODS: A total of 652 Caucasian migraine cases were investigated in this study. The MTHFR C677T variant was genotyped in 270 unrelated migraine cases and 270 controls as well as 382 affected subjects from 92 multiplex pedigrees. RESULTS: In the unrelated case-control sample we observed an over-representation of the 677T allele in migraine patients compared to controls, specifically for the MA subtype (40% vs. 33%) (chi2 = 5.70, P = 0.017). The Armitage test for trend indicated a significant dosage effect of the risk allele (T) for MA (chi2 = 5.72, P = 0.017). This linear trend was also present in the independent family-based sample (chi2 = 4.25, Padjusted = 0.039). Overall, our results indicate that the T/T genotype confers a modest, yet significant, increase in risk for the MA subtype (odds ratio: 2.0 - 2.5). No increased risk for the MO subtype was observed (P > 0.05). CONCLUSIONS: In Caucasians, the C677T variant in the MTHFR gene influences susceptibility to MA, but not MO. Investigation into the enzyme activity of MTHFR and the role of homocysteine in the pathophysiology of migraine is warranted. [Abstract]

Oterino A, Valle N, Bravo Y, Muńoz P, Sánchez-Velasco P, Ruiz-Alegría C, Castillo J, Leyva-Cobián F, Vadillo A, Pascual J
MTHFR T677 homozygosis influences the presence of aura in migraineurs.
Cephalalgia. 2004 Jun;24(6):491-4.
It has been suggested that folate metabolism could be involved in migraine pathogenesis. We analysed the 5',10'-methylenetetrahydrofolate reductase (MTHFR) genotypic distribution in a large migraine sample. We genotyped 230 migraine patients (152 migraine without aura (MO) and 78 migraine with aura (MA)) and 204 nonheadache controls. The incidence of TT homozygosis for migraine in general (12%), MO (9%) and MA (18%) did not significantly differ from that found in healthy controls (13%). Differences were significant when the frequency of TT homozygosis between MA and MO (P = 0.03, OR = 2.34, 95% CI = 1.04-5.26) was compared. There was a tendency for a higher frequency of the MTHFR T allele in the MA group (42%) as compared to MO (29%) and controls (36%). These differences were significant only in the case of MA vs. MO (P = 0.006, OR = 1.75, 95% CI = 1.15-2.65). These results could indicate that the MTHFR C677T polymorphism, causing mild hyperhomocystinaemia, might be a genetic risk factor for experiencing aura among migraineurs. Overall, however, there was no association between migraine and the C677T MTHFR polymorphism. [Abstract]

Kara I, Sazci A, Ergul E, Kaya G, Kilic G
Association of the C677T and A1298C polymorphisms in the 5,10 methylenetetrahydrofolate reductase gene in patients with migraine risk.
Brain Res Mol Brain Res. 2003 Mar 17;111(1-2):84-90.
Although controversial, diminished activity of 5,10 methylenetetrahydrofolate reductase (MTHFR), a regulatory enzyme of homocysteine metabolism, may predispose to migraine in Turkish people. In a case-control study, we determined the prevalence of two common MTHFR polymorphisms,C677T and A1298C, in 102 migraine patients (23 migraine with aura, 70 migraine without aura and nine with tension-type headache) and compared it to that of 136 healthy controls. The frequencies of the T allele of MTHFR677 and the C allele of MTHFR1298 were significantly higher in the total migraine population (33.82%, 33.82%) than in controls (25.38% and 24.26%), respectively.The genotypes T677T and C1298C were the only genotypes significantly associated with migraine (OR=5.702; 95% CI=1.184-27.457; P=0.015) and (OR=8.933; 95% CI=1.953-40.869; P=0.001), respectively). Individuals with migraine with aura with C1298C and C677C/C1298C genotypes were even more profoundly associated with migraine risk than others (OR=14.105; 95% CI=2.417-82.320; P=0.0001) and (OR=10.050; 95% CI=1.580-63.907; P=0.003), respectively. However individuals with migraine without aura with T677T and C1298C genotypes showed the same susceptibility (OR=7.444; 95% CI=1.503-36.863); P=0.005). Patients with C1298C and C677C/C1298C genotypes may also predispose to tension-type headache (OR=8.375; 95% CI=0.685-102.458); P=0.049). [Abstract]

Kowa H, Yasui K, Takeshima T, Urakami K, Sakai F, Nakashima K
The homozygous C677T mutation in the methylenetetrahydrofolate reductase gene is a genetic risk factor for migraine.
Am J Med Genet. 2000 Dec 4;96(6):762-4.
Increased homocysteine levels are associated with various pathological conditions in humans, including stroke and cardiovascular disorders. Homocysteine acts as an excitatory amino acid in vivo and may influence the threshold of migraine headache. Frosst et al. [1995] reported an association between the homozygous C677T mutation in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene and serum homocysteine levels. This study was designed to determine the prevalence of the MTHFR mutation in Japanese patients with migraine and tension-type headache (TH). Seventy-four patients with migraine headaches (22 with aura and 52 without aura), 47 with THs, and 261 normal controls were recruited. Genotyping of MTHFR C677T polymorphism was performed by polymerase chain reaction-restriction fragment length polymorphism. We detected that the incidence of the homozygous transition (T/T) in migraine sufferers (20.3%) was significantly higher than that in controls (9.6%). Moreover, the frequency of the T/T genotype in individuals with migraine headaches with aura was remarkably high (40.9%). The MTHFR T allele was more frequent in the migraine group than in the control group. Our results support the conclusion that the MTHFR gene, causing mild hyperhomocysteinemia may be a genetic risk factor for migraine. [Abstract]

Santhosh-Kumar CR, Hassell KL, Deutsch JC, Kolhouse JF.
Are neuropsychiatric manifestations of folate, cobalamin and pyridoxine deficiency mediated through imbalances in excitatory sulfur amino acids?
Med Hypotheses. 1994 Oct;43(4):239-44.
Folate, cobalamin and pyridoxine deficiency are associated with psychiatric or neurological symptomatology. Disturbances in sulfur amino acid metabolism leading to accumulation of homocysteine occurs in all three conditions as the metabolism of homocysteine depends on enzymes requiring these vitamins as cofactors. Oxidation products of homocysteine (homocysteine sulfinic acid and homocysteic acid) and cysteine (cysteine sulfinic acid and cysteic acid) are excitatory sulfur amino acids and may act as excitatory neurotransmitters, whereas taurine and hypotaurine (decarboxylation products of cysteic acid and cysteine sulfinic acid) may act as inhibitory transmitters. Homocysteic acid and cysteine sulfinic acid have been considered as endogenous ligands for the N-methyl-D-aspartate (NMDA) type of glutamate receptors. The profile of these sulfur amino acid neurotransmitters could be altered in a similar fashion in states of decreased availability of folate, cobalamin or pyridoxine. It is proposed that the mechanism of neuropsychiatric manifestations in all three conditions result from a combination of two insults to homocysteine catabolism in the brain. [Abstract]