Cortical Spreading Depression (CSD) is characterized by a wave of neuronal and glial depolarization followed by depression of bioelectrical activity that slowly propagates through the cortex of many species, including humans. CSD is associated with brain disorders such as stroke, head trauma and migraine. Many earlier studies have provided compelling evidence that CSD is the underlying mechanism of aura in migraine; however, whether CSD can elicit headache associated with migraine is not fully understood. Cutaneous allodynia is highly prevalent in the peri-orbital area and extracephalic sites of migraine patients, suggesting that sensitization of primary afferents and central trigeminovascular neurons in these patients could be initiated by the underlying mechanism of aura.Unlike previous reports on the interaction between CSD and the trigeminal system, in which nociceptive behavior could not be measured since they employed anesthetized animals, we designed a model in which freely moving rats could be monitored for both CSD events and behavior responses due to pinprick plus KCl injection to the occipital cortex. We show that significant tactile hypersensitivity of the periorbital region of the face and hindpaws develop in a time-dependent manner following CSD. Enhanced expression of Fos protein and increased mRNA levels of the inflammatory cytokines IL-1beta and IL-6 are found within the trigeminal nucleus caudalis (TNC) two hours following cortical injection. We further show that systemic administration of anti-migraine drugs such as sumatriptan, naproxen and CGRP(8-37) (a CGRP antagonist) attenuate the generalized allodynia that ensue following cortical stimulation by KCl. Microinjection of bupivacaine in the ipsilateral trigeminal ganglion or in the rostral ventromedial medulla (RVM) prior to cortical pinprick plus KCl injection reversibly diminishes tactile hypersensitivity, suggesting that RVM pain-facilitating cells become activated by a trigeminal-RVM pathway following CSD. In addition we demonstrate that cortical pinprick plus KCl injection induced CSD events in 24/28 (85%) rats, among which 66% and 87% developed allodynia in the face and hindpaw, respectively.These studies suggest a potential association between CSD and development of hypersensitivity in rats, indicating that this model can be used to investigate the role of CSD-evoked migraine-related pain and to explore novel therapeutic strategies.

Migraine affects ~15% of the US population (nearly 40 million people), making it one of the most common neurological disorders; however currently available therapeutic options for migraine relief are often ineffective. Moreover, acute and prophylactic drugs are both commonly associated with contraindications and serious side effects, and routine use of acute treatments may result in medication overuse-headaches. Elevated levels of the neuropeptide calcitonin gene-related peptide (CGRP) are known to be a primary factor in migraine pathogenesis, although the mechanisms by which CGRP expression becomes errantly modulated are unclear. CGRP is a product of the trigeminal ganglion and can be released both peripherally onto the dura mater, leading to neurogenic inflammation, and centrally at the spinal trigeminal nucleus, leading to neuromodulation. A great deal of CGRP-relevant migraine research has focused on the trigeminovascular system, but whether the cerebral cortex may have a role in migraine pathophysiology been less well studied. A subset of migraineurs experience a premonitory aura, which often manifests as a disturbance in one visual hemifield. An aberration called cortical spreading depression (CSD) is the likely electrophysiological substrate of the migraine aura, but whether CSD and CGRP are functionally related is not known. CSD is characterized by an initial transient wave of neuronal and glial depolarization, followed by a prolonged period of quiescence that is largely refractory to subsequent stimulation. Converging evidence supports a facilitatory role for cortical spreading depression (CSD) in migraine with and without aura, and CSD propagation has been shown to be dependent on functional CGRP receptors. Moreover, reported effects of CSD overlap with those of CGRP-mediated neurogenic inflammation. The experiments described herein seek to test the hypothesis that induction of CSD in vivo will lead to increased CGRP expression in the rodent cerebral cortex. Preliminary data in rats suggests that 3M KCl-induced CSD can trigger increased CGRP expression in the ipsilateral cortex. Preliminary data in mice has been less conclusive. Presented here are the data obtained from mice and rats, as well as speculation on the cause(s) of the differences in CGRP expression between species and how these findings relate to human studies.

No description available.

The purpose of this study was to examine the effects of cortical spreading depression on neuronal activity in the rat motor (M1) cortex. It is known that cortical spreading depression causes widespread neuronal and glial activity in the cortex, but the degree to which it exerts its effects is unclear. Cortical spreading depression was induced in eight Sprague-Dawley male rats. After two hours, animals were euthanized and immunohistochemistry was performed on the brain to stain for the presence of c-Fos, an immediate early gene that is a well-known marker of neuronal activity. Sections were counterstained for Nissl substance to reveal two populations of cells: Nissl-stained neurons that were c-Fos positive, activated cells and Nissl-stained neurons that were c-Fos negative, non-activated cells. Three sections for each animal were examined and 20-30% of the total M1 cortex was analyzed. Cells were counted using systematic random sampling for each of the six cortical layers. Our results show that the cortical spreading depression did not produce an activation of all neurons. When layers were individually examined, there was a main effect of layer on neuronal activation. This confirmed previous findings that cortical spreading depression had the strongest effect on superficial layers of the cortex

The studies in this thesis research were conducted to investigate if sensitivity to induced cortical spread depression (CSD) or the consequence of a CSD event is affected by sumatriptan induced latent sensitization. Previous studies in our lab showed persistent exposure of sumatripan to rats produced a latent state of sensitization. Using persistent sumatripan exposed rats as a model for medication overuse headache, behavior, electrical stimulation threshold to provoke a CSD event and the immunoreactivity of c-Fos in the trigeminal nucleus caudalis (TNC) were characterized. Current results showed no statistical difference of electrically induced CSD thresholds in anesthetized rats measured at day 20 in sumatripan exposed rats compared with saline treated rats. Topiramate (80 mg/kg, i.p.) used clinically for prophylaxis of migraine headache significantly increased CSD threshold in both saline and sumatriptan infused rats. CSD events appear to be associated with trigeminal vascular system activation in TNC because c-Fos expression significantly enhanced in rats with electrically stimulated CSD events. As compared to saline treated rats, sumatriptan-exposed rats demonstrated a significantly higher number of c-Fos positive cells following the electrically stimulated CSD event. Under environmental stress (bright light), sumatripan exposed rats demonstrated decreased response thresholds to periorbital and hindpaw tactile stimuli (i.e., allodynia) and enhanced c-Fos expression in TNC. A single dose of topiramate (80 mg/kg, i.p.) reversed environmental stress induced allodynia and c-Fos over-activity. Taken together, these results suggest that latent sensitization induced by persistent sumatripan exposure seems not correlated to the threshold of electrically stimulated CSD in current model. However, CSD enhanced the responses of trigeminal system in rats with sumatriptan-induced latent sensitization. The protective effects of topiramate shown in this model may be related to blocking the initiation of CSD events resulting from environmental stimulation as well as inhibiting the consequences of CSD events in primary afferents. These findings correlate with clinical observations of protective effects of topiramate for migraine prophylaxis.

O que se desejou apresentar neste trabalho é se a aplicação da medida de complexidade LMC no estudo do fenômeno da depressão alastrante mostra-se eficiente na perspectiva de contribuir para uma melhor compreensão do fenômeno. Para isso, usou-se como modelo experimental a retina de pintinho in vitro. Na tentativa de obter informações sobre estados de equilíbrio entre a ordem e desordem, propõe-se as análises dos registros de dois dos concomitantes do fenômeno: a alteração lenta do potencial extracelular e do sinal intrínseco óptico. Para isso, avaliou-se o efeito de manipulações fármaco-química sobre esses dois concomitantes do fenômeno e através de análises comparativas entre as ondas de controle e as ondas obtidas em presença das diversas substâncias foram discutidas a aplicabilidade do método proposto, mostrando que a medida de complexidade trouxe novas informações sobre a depressão alastrante contribuindo para um entendimento melhor do fenômeno. / What we wanted to present in this work is the application of the LMC measure of complexity in the study of the phenomenon of spreading depression proves efficient in order to contribute to a better understanding of the phenomenon. For this, we used as an experimental model of the chick retina in vitro. In an attempt to obtain information about equilibrium states between order and disorder, it is proposed that the analysis of the records of two of the concomitant phenomena: a slowly changing the extracellular potential and intrinsic optical signal. For this, we evaluated the effect of pharmaco-chemical manipulations on these two concomitant phenomenon and by comparative analyzes of the control waves and the waves obtained in the presence of various substances discussed the applicability of the proposed method, the measure complexity brought new information on the spreading depression to a better understanding of the phenomenon.

Spreading depression (SD) is an interesting and important phenomenon due to its role in mammalian pathologies such as migraine, seizures, and stroke. Until recently investigations of the mechanisms involved in SD have mostly utilized mammalian cortical tissue, however in my thesis I demonstrated that SD-like events occur in the CNS of an invertebrate model, Locusta migratoria. Locusts enter comas in response to stress during which neural and muscular systems shut down until the stress is removed, and this is believed to be an adaptive strategy to survive extreme environmental conditions. Using the ventilatory central pattern generator (vCPG) as a model circuit I was able to show that stress-induced arrest of vCPG function is associated with SD-like events in the locust metathoracic ganglion (MTG) that closely resemble cortical SD (CSD) in many respects, including mechanism of induction, extracellular potassium ion ([K+]o) changes, and propagation in areas equivalent to mammalian grey matter. SD-like events in the locust were characterized as abrupt [K+]o increases associated with electrical activity silence in the locust CNS that propagate to other areas within the MTG. In this thesis I described the generation of comas by several cellular stressors (hyperthermia, metabolic stressors, Na+/K+-ATPase inhibition, and KCl) and the associated SD-like events in the locust, provide a description of the similarities to CSD, and show how they can be manipulated both by stress preconditioning and pharmacologically. I showed that hyperthermic vCPG arrest can be preconditioned by prior heat shock (HS) treatment and induced-thermotolerance was associated with an increased rate of [K+]o clearance associated with vCPG recovery that was not linked to changes in ATP levels or total Na+/K+-ATPase activity. I also provided evidence for the involvement of the stress-sensor AMP-activated protein kinase (AMPK) in stress-induced comas in the locust. AMPK activation was linked to a switch in motor pattern behavior following recovery from anoxia-induced vCPG arrest and exacerbated repetitive SD-like events induced by ouabain (Na+/K+-ATPase inhibitor). I suggested that locust SD-like events are adaptive by conserving energy and preventing cellular damage, and I provided a model for the mechanism of SD onset and recovery in the locust nervous system. / Thesis (Ph.D, Biology) -- Queen's University, 2010-08-05 16:08:19.905

O que se desejou apresentar neste trabalho é se a aplicação da medida de complexidade LMC no estudo do fenômeno da depressão alastrante mostra-se eficiente na perspectiva de contribuir para uma melhor compreensão do fenômeno. Para isso, usou-se como modelo experimental a retina de pintinho in vitro. Na tentativa de obter informações sobre estados de equilíbrio entre a ordem e desordem, propõe-se as análises dos registros de dois dos concomitantes do fenômeno: a alteração lenta do potencial extracelular e do sinal intrínseco óptico. Para isso, avaliou-se o efeito de manipulações fármaco-química sobre esses dois concomitantes do fenômeno e através de análises comparativas entre as ondas de controle e as ondas obtidas em presença das diversas substâncias foram discutidas a aplicabilidade do método proposto, mostrando que a medida de complexidade trouxe novas informações sobre a depressão alastrante contribuindo para um entendimento melhor do fenômeno. / What we wanted to present in this work is the application of the LMC measure of complexity in the study of the phenomenon of spreading depression proves efficient in order to contribute to a better understanding of the phenomenon. For this, we used as an experimental model of the chick retina in vitro. In an attempt to obtain information about equilibrium states between order and disorder, it is proposed that the analysis of the records of two of the concomitant phenomena: a slowly changing the extracellular potential and intrinsic optical signal. For this, we evaluated the effect of pharmaco-chemical manipulations on these two concomitant phenomenon and by comparative analyzes of the control waves and the waves obtained in the presence of various substances discussed the applicability of the proposed method, the measure complexity brought new information on the spreading depression to a better understanding of the phenomenon.

Migraine is a debilitating neurological disorder, which affects over 10% of the general population. In addition to headache, migraine includes a host of associated symptoms, such as nausea and hypersensitivity to light, noise, and touch. While great strides have been made in migraine treatment in recent decades, the basic biological and pathophysiological mechanisms underlying migraine are still not well understood. Pain signals travel via a polysynaptic pathway from the periphery to the cortex, where conscious perception of pain occurs. This multi-neuron pathway produces a message that can be modified at any step of its transit. One peptide that may modify this pathway is calcitonin gene-related peptide (CGRP). CGRP is a potent vasodilator and neuromodulator, and mounting evidence suggests CGRP may play a causative role in migraine. CGRP levels are increased during migraine, but can be reduced upon successful treatment with drugs in the triptan class. Importantly, injection of CGRP into migraine patients can elicit a delayed, migraine-like headache. Finally, CGRP receptor antagonists are clinically effective in providing relief to migraine patients. In addition to CGRP, the CGRP gene (CALCA) expresses another peptide that may also be relevant to migraine. Procalcitonin (proCT) is a recognized biomarker for sepsis, but emerging evidence suggests it may have actions similar to CGRP in migraine. First, proCT has biological activity at the CGRP receptor. Second, proCT is reported to be increased during migraine. We hypothesized that regulation of CGRP and proCT may be altered in migraineurs, and that migraineurs may also be sensitized to the effects of these peptides. To study the role of these peptides in migraine pathways, a number of methods have been employed. Studies exploring regulation of gene expression were performed in cultured trigeminal ganglia, as well as primary cultures of trigeminal and cortical glia. These studies show that the Calca gene can be regulated by a number of stimuli, including hypoxia and reactive oxygen species. These insults have the ability to induce CALCA gene and peptide expression to varying degrees on different cell types. In addition to in vitro experiments on Calca gene regulation, the in vivo effects of CGRP on mouse behavior were also investigated. Animals were genetically sensitized to CGRP via overexpression of the rate-limiting CGRP receptor subunit. In these animals, injection of CGRP is sufficient to induce light aversion, which is used to model photophobia. Physiological and biochemical triggers of migraine were tested using this behavioral paradigm. While stress and mast cell degranulation are sufficient to induce light aversion, the role of CGRP in these events remains unclear, as both CGRP sensitized and control animals displayed a light aversion phenotype. Together, these studies show the dynamic regulation of the Calca gene in migraine pathways as well as highlight some of the challenges of modeling a complex disease in an animal model.

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