Environmental enrichment reduces brain excitability in adult rats overnourished during lactation / Enriquecimento ambiental reduz excitabilidade cerebral em ratos adultos hipernutridos durante a lactação

ABSTRACT Objective: This study aimed to analyze whether exposure to environmental enrichment (EE) during the juvenile phase of life interferes with the electrical activity of the adult rat brain. In addition, the present research also investigated whether this putative effect on brain electrical activity could be affected by prior overnutrition during lactation. Electrophysiology was measured through cortical spreading depression (CSD), a phenomenon related to brain excitability. Methods: Wistar rats were suckled in litters of either nine or three pups, forming the nourished (N) or overnourished (ON) groups, respectively. At 36 days old, half of the animals from each nutritional condition were exposed to EE. The other half was kept in the standard environment (SE). At 90-120 days of life, each animal was anesthetized for CSD recordings. Results: Overnutrition during lactation caused increases (p < 0.05) in body and brain weights. The EE decelerated CSD propagation velocity regardless of nutritional state during lactation (p < 0.001). The CSD deceleration in the N-EE group was 23.8% and in the ON-EE group was 15% in comparison with the N-SE and ON-SE groups, respectively. Conclusion: Our data demonstrated that EE exposure in the juvenile phase of the rat's life reduced brain excitability, and this effect was observed even if animals were overnourished during lactation. An EE could be considered an adjuvant therapeutic resource to modulate brain excitability.

RESUMO Objetivo: Este estudo analisou se a exposição ao ambiente enriquecido durante a fase juvenil da vida interferiria na atividade elétrica do cérebro de ratos adultos. Além disso, a presente pesquisa também investigou se esse provável efeito na atividade elétrica cerebral poderia ser afetado pela hipernutrição durante a lactação. A eletrofisiologia foi medida através da depressão alastrante cortical, um fenômeno relacionado à excitabilidade cerebral. Métodos: Ratos Wistar foram amamentados em ninhadas de nove ou três filhotes, formando os grupos nutridos ou hipernutridos, respectivamente. Aos 36 dias, metade dos animais de cada condição nutricional foram expostos ao ambiente enriquecido. A outra metade foi mantida na condição de ambiente padrão. Aos 90-120 dias de vida, foram obtidos os registros da depressão alastrante cortical. Resultados: A hipernutrição durante a lactação causou incrementos (p < 0,05) nos pesos corporal e cerebral.O Ambiente Enriquecido desacelerou a velocidade de propagação da depressão alastrante cortical independentemente do estado nutricional durante a lactação (p < 0,001). A desaceleração da depressão alastrante cortical no grupo nutrido/ambiente enriquecido foi de 23,8% e no grupo hipernutrido/ambiente enriquecido foi de 15% em comparação com os grupos nutrido/ambiente padrão e hipernutrido/ambiente padrão, respectivamente. Conclusão: Nossos dados demonstram que a exposição ao ambiente enriquecido na fase juvenil da vida do rato reduz a excitabilidade cerebral, e esse efeito pode ser observado mesmo se os animais estiverem hipernutridos durante a lactação. O ambiente enriquecido pode ser considerado um recurso terapêutico adjuvante para modular a excitabilidade cerebral.

Antioxidant extract counteracts the effects of aging on cortical spreading depression and oxidative stress in the brain cortex

Abstract Purpose: To investigate the effects of Murici extract on the brain excitability-dependent phenomenon known as cortical spreading depression (CSD) and on brain oxidative stress. Methods: Adult and aged Wistar rats were supplemented with murici extract (150 mg/kg/day or 300 mg/kg/day) by gavage for fifteen days. Afterwards, the animals were submitted to a CSD electrophysiological recording and to brain oxidative stress evaluation. Results: Our results showed that aging decreased CSD propagation velocity, catalase activity and glutathione/oxidized glutathione ratio (GSH/GSSG) in the brain cortex of the rats, and increased malondialdehyde (MDA) concentrations and superoxide dismutase (SOD) activity. The highest dose (300 mg/kg/day) of murici extract accelerated CSD, whereas the lowest (150mg/kg/day) decelerated, in both adult and aged animals. In contrast, aged animals supplemented with murici extract in both doses presented low MDA levels and high GSG/GSSG ratio in comparison to the control-aged animals. Conclusion: Murici extract supplementation seems to revert detrimental effects in aged brains and could be considered as a strategy in the treatment of pathologies related to aging and cortical spreading depression.

Cortical spreading depression in migraine-time to reconsider? / Depressão alastrante cortical na enxaqueca – hora de reconsiderar?

New evidence concerning the pathophysiology of migraine has come from the results of therapeutic transcranial magnetic stimulation (tTMS). The instantaneous responses to single pulses applied during the aura or headache phase, together with a number of other observations, make it unlikely that cortical spreading depression is involved in migraine. tTMS is considered to act by abolishing abnormal impulse activity in cortical pyramidal neurons and a suggestion is made as to how this activity could arise.

Novas evidências referentes à fisiopatologia da enxaqueca são o resultado de estimulação magnética transcraniana terapêutica (tTMS). As respostas imediatas a pulsos simples aplicados durante as fases de aura ou de cefaleia, em associação a diversas outras observações, tornam improvável a ideia de que a depressão alastrante esteja envolvida na enxaqueca. Considera-se que tTMS tenha sua ação abolindo atividade anormal de impulsos em neurônios corticais piramidais, sugerindo que esta atividade tenha um papel desencadeante.

Aristides Leão: a birth centennial homage with comments on his spreading depression / Aristides Leão: homenagem ao centenário de nascimento com comentários sobre sua depressão alastrante

The year of 2014 is the birth centenary of Aristides Azevedo Pacheco Leão (1914-1993), and also marks seventy years of the publication of his discovery of the novel electrophysiological phenomenon, named by him “spreading depression” (SD), soon designated “Leão’s wave” or “Leão’s spreading depression”. This was a remarkable scientific milestone, and the author must be celebrated for this achievement, as the studies he triggered proceeded worldwide, with new concepts, as spreading depolarization, until the present days. Robust experimental and clinical evidence emerged to suggest that these and related electrophysiological phenomena are involved in the mechanisms of migraine aura, acute cerebrovascular diseases, traumatic brain injury, transient global amnesia, epileptic seizures, and their pathophysiological characteristics come to offer new therapeutic perspectives. He was a remarkable and complex personality, and the authors remit the readers to a paper where his personal life is contemplated.

O ano de 2014 é o centenário de nascimento de Aristides Azevedo Pacheco Leão (1914-1993), e também assinala setenta anos da publicação de sua descoberta, que ele denominou “depressão alastrante” (DA), logo designada “onda de Leão” ou “depressão alastrante de Leão”. Foi um notável marco científico e o autor deve ser celebrado por esse feito, considerando que estudos que desencadeou continuaram no mundo todo, com novos conceitos, como a despolarização alastrante, até os dias atuais. Evidência experimental e clínica robusta emergiram sugerindo que esses fenômenos eletofisiológicos e outros relacionados encontram-se envolvidos nos mecanismos da aura da enxaqueca, doenças cerebrovasculares agudas, lesão cerebral traumática, amnésia global transitória, crises epiléticas, sendo que suas características fisiopatológicas vêm oferecer novas perspectivas terapêuticas. Foi uma personalidade complexa e notável, e os autores remetem os leitores para um artigo no qual sua vida pessoal é contemplada.

Brimonidine tartrate effect on retinal spreading depression depends on Müller cells / O efeito do tartarato de brimonidina sobre a depressão alastrante retiniana depende das células de Müller

Objective: Demonstrate the Brimonidine effect over Retinal Spreading Depression (SD). Brimonidine is an alpha-2–adrenergic receptor agonist, used in the management of glaucoma. Alpha2-agonists have been shown to be neuroprotective in various experimental models, however the molecular and cellular targets leading to these actions are still poorly defined. The SD of neuronal electric activity is a wave of cellular massive sustained depolarization that damages the nervous tissue. Local trauma, pressure, ischemic injuries and other chemical agents as high extracellular potassium concentration or glutamate, can trigger SD, leading to exaggerated focal electrical followed by an electrical silence. Methods: Using chicken retina as model, we performed alpha2-receptor detection by Western Blotting and Immunohistochemistry. After that we obtained electrical signals of SD by microelectrodes on retina in the absence or presence of Brimonidine. For in vivo visualization we observed retina with optical coherence tomography on normal state, with SD passing, and with SD + Brimonidine. Results: Our data demonstrated that: (1) alpha2-adrenergic receptors are present in Müller cells, (2) the treatment with Brimonidine decreases the SD‘s velocity as well as the voltage of SD waves and (3) OCT revealed that SD creates a hyper reflectance at inner plexiform layer, but on retinal treatment with brimonidine, SD was not visualized. Conclusions: Our study about brimonidine possible pathways of neuroprotection we observed it reduces SD (a neuronal damage wave), identified a new cellular target – the Müller cells, as well as, firstly demonstrated SD on OCT, showing that the inner plexiform layer is the main optically affected layer on SD. .

Objetivo: Demonstrar o efeito do Tartarato de Brimonidina, um alfa2-agonista usado no manejo do glaucoma, sobre a depressão alastrante (DA) retiniana. Esses agonistas têm demonstrado ser neuroprotetores em vários modelos experimentais, contudo seus alvos celulares e moleculares continuam indefinidos. A DA da atividade elétrica neuronal é uma onda de despolarização celular massiva e sustentada que leva ao dano no tecido nervoso. Trauma local, pressão, isquemia e outros agentes químicos como o aumento do potássio extracelular e o glutamato podem disparar a DA, levando a uma atividade elétrica exagerada seguida de silêncio elétrico. Métodos: Usando a retina de pinto como modelo, realizamos a detecção do alfa2-receptor por Western Blotting e ensaio Imunohistoquímico. Após isso, obtivemos os sinais elétricos da DA através de microeletrodos inseridos na retina durante sua passagem na presença ou ausência de Brimonidina. Para visualização do tecido utilizamos o tomógrafo de coerência optica (OCT), analisando como é a retina no seu estado de repouso, durante a passagem da DA, e a DA + brimonidina. Resultados: Nossos dados demonstraram que: (1) os receptores alfa adrenérgicos presentes na retina são do subtipo-2A e estão localizados nas células de Müller; (2) o tratamento com Brimonidina diminui a velocidade e a voltagem da onda de DA; (3) A OCT demonstrou que a DA retiniana possui um sinal óptico de maior reflectância na camada plexiforme interna, fato não observado quando foi associada à Brimonidina. Conclusão: A Brimonidina foi capaz de reduzir a DA (uma onda de lesão neuronal) e identificamos um novo possível alvo celular – a célula de Müller e demonstramos pela primeira vez uma OCT da DA, visualizando a camada plexiforme interna como a mais afetada opticamente pelo fenômeno. .

Wave onset in central gray matter - its intrinsic optical signal and phase transitions in extracellular polymers

The brain is an excitable media in which excitation waves propagate at several scales of time and space. ''One-dimensional'' action potentials (millisecond scale) along the axon membrane, and spreading depression waves (seconds to minutes) at the three dimensions of the gray matter neuropil (complex of interacting membranes) are examples of excitation waves. In the retina, excitation waves have a prominent intrinsic optical signal (IOS). This optical signal is created by light scatter and has different components at the red and blue end of the spectrum. We could observe the wave onset in the retina, and measure the optical changes at the critical transition from quiescence to propagating wave. The results demonstrated the presence of fluctuations preceding propagation and suggested a phase transition. We have interpreted these results based on an extrapolation from Tasaki's experiments with action potentials and volume phase transitions of polymers. Thus, the scatter of red light appeared to be a volume phase transition in the extracellular matrix that was caused by the interactions between the cellular membrane cell coat and the extracellular sugar and protein complexes. If this hypothesis were correct, then forcing extracellular current flow should create a similar signal in another tissue, provided that this tissue was also transparent to light and with a similarly narrow extracellular space. This control tissue exists and it is the crystalline lens. We performed the experiments and confirmed the optical changes. Phase transitions in the extracellular polymers could be an important part of the long-range correlations found during wave propagation in central nervous tissue

Spreading depression is facilitated in adult rats previously submitted to short episodes of malnutrition during the lactation period

Lactating rat dams were submitted to short episodes (1,2 or 3 weeks) of nutritional restriction by receiving the "regional basic diet" (RBD), with 8 percent protein) of low-income human population of Northeast Brazil. Their pups were then studied regarding the developmental effects on body and brain weights. When the rats reached adulthood, cortical susceptibility to the phenomenon of spreading depression (SD) was evaluated by performing electrophysiological recordings on the surface of the cerebral cortex. SD was elicited at 20-min intervals by applying 2 percent KCL for 1 min to a site on the frontal cortex and its occurrence was monitored at 2 sites in the parietal region by recording the electrocorticogram and the slow potential change of SD. When compared to control rats fed a commercial diet with 23 percent protein, early malnourished rats showed deficits in body and brain weights (10 percent to 60 percent and 3 percent to 15 percent, respectively), as well as increases in velocity of SD propagation (10 percent to 20 percent). these effects were directly related to the duration of maternal dietary restriction, with pups malnourished for 2 ou 3 weeks presenting more intense weight and SD changes than those malnourished for 1 week. The effects of 1-week restrictions on SD were less evident in the pups malnourished during the second week of lactation and were more evident in pups receiving the RBD during the third week. The results indicate that short episodes of early malnutrition during the suckling period can affect body and brain development, as well as the cortical susceptibility to SD during adulthood. The data also suggest that the third week of lactation is the period during which the brain is most sensitive to malnutrition, concerning the effects on SD.

Effect of aging on cortical spreading depression

The effects of aging on spreading depression (SD) were investigated in the Mongolian gerbil (G; age range 1.5 to 58 months; N = 35) and in the albino rat (R; 2.5 to 24 months; N = 100). Two strains of rats were studied: Wistar (W; N = 35) and Sprague-Dawley (SDAW; N = 65). SDAW rats were divided into two groups: one group was fed a commercial lab chow diet (CD) containing 22 per cent protein (N = 47), and the other was fed a 22 per cent casein diet (CAS; N = 18). SD was elicited on the frontal cortical surface by 1-min application of 2 per cent KCl and its appearance was recorded (ECoG and DC potential) at two points in the parieto-occipital area of the same hemisphere. SD propagation velocity was measured on the basis of the time spent for an SD "wave" to cross the distance between the two recording points. Within the age range studied, older animals displayed significantly lower SD velocities than the younger ones, independent of the species, strain or diet (velocity ranges, in mm/min: G, 2.22-5.99; W, 2.47-4.12; SDAW-CD, 2.32-4.42 and SDAW-CAS, 2.65-4.14). The correlation coefficients between age and SD velocity were: G, -0.78; W, -0.45; SDAW-CD, -0.68 and SDAW-CAS, -0.72 (P<0.05 in all cases). As a rule, at each time point the gerbils presented higher SD velocities than the rats of the same age. In another set of experiments, in order to test the role of free radicals in SD, 7 gerbils (14-51 months old) and 13 W rats (3-24 months old) were fed a 22 per cent casein diet free of the antioxidant vitamins C and E for 4-6 weeks before the experiments. No correlation was found between age and SD propagation in these animals fed a diet free of vitamins C and E, although gerbils displayed higher SD velocities than age-matched rats (velocities: G, 3.70-5.34; R, 3.25-4.44 mm/min; correlation coefficients: G, -0.39; W, -0.29; P>0.05). These data indicate that gerbils have higher SD susceptibility than rats of the same age, and that this susceptibility decreases with aging in both species. The lack of correlation between age and SD velocity in the animals fed a diet free of antioxidant vitamins suggests a possible role of free radicals in cortical SD, in accordance with evidence from other laboratories obtained in the isolated retina.

Biphasic effects of gap junctional uncoupling agents on the propagation of retinal spreading depression

The spreading depression wave of Leäo (SD) propagates in the nervous tissue at 3-10 mm/min and is a accompanied by an increase of intracellular Ca²+ concentration and a decrease in the extracellular milieu. Recently the spread of Ca²+ waves with propagating velocities of the same order of magnitude has been detected in cultures of nerve cells. It has been suggested that these waves, which can be blocked by gap junctional agents, are related to SD. The present experiments describe some effects of heptanol and octanol (10µM to 10mM), well-known uncoupling agents of gap junctions, on the slow voltage changes and the velocity of propagation of Leäo's phenomenon in isolated chick retina: 1) a 50 to 700 µM concentration of these alcohols in the superfusate solutions increased the velocity, whereas high concentration (1 to 10 mM) decreased and subsequently halted the spread; 2) the recovery period of the slow voltage changes of SD was shorter in the presence of alcohol and its amplitude was larger during faster SD waves. These effects were observed in the retina during successive individual waves as well as in the course of circling SD. All of these effects were reversible, without any sign of damage to the retina. In the concentration range of 50 µM, methanol, ethanol, butanol and cyclo-hexanol had no effect on retinal SD. These data suggest the involvement of gap junctions in Leäo's wave. This involvement is complex and its functional effects together with other factors that influence the velocity of propagation of SD sre being investigated

Effect of d-fenfluramine on cortical spreading depression in rats

We investigated the effect of a single ip injection of ed-fenfluramine (d-fen; 5-10 mg/kg), a serotinin reuptake blocker, on cortical spreading depression (SD) in 17 male Wistar rats (300-360 g body weight). SD was elicited at the right frontal cortex by 1-min application of 2 percent KCl at 20-min intervals. SD propagation was monitored (electrocorticogram and DC-recording) at 2 points on the right parietal surface for 3 h. After a "baseline" recording period (1 h), d-fen was injected and the recording session was continued for 2 h. When compared to the predrug SD velocities (t = 0 min) the values measured after d-fen decreased significantly at t = 20 min (3.44 + or - 0.63 vs 2.66 + or - 0.51 mm/min; N = 17, P<0.001), at t = 40 min (3.32 + or - 0.58 vs 2.53 + or - 0.52 mm/min; N = 14, P<0.001), att=60 min (3.68 + or - 0.63 vs 2.92 + or - 0.72 mm/min; N = 11, P<0.001) and at t = 80 min (3.57 + or - 0.61 vs 3.03 + or - 0.83 mm/min; N = 12, P<0.05) but not at t = 100 min (3.47 + or - 0.72 vs 3.31 + or - 0.88 mm/min; N = 12) nor at t = 120 min (3.44 + or - 0.67 vs 3.37 + or - 0.76 mm/min; N = 11). Furthermore, in 19 of 48 KCl stimulations (40 percent) performed ...

Spreading depression: a neurohumoral reaction

1. The main characteristics of spreading depression are a decrease of spontaneous electrical activity, slow negative potential changes, transmembrane ion translocations, and an increase in tissue lactate. This is a general phenomenon in the central nervous system. 2. Retinal spreading depression, a very useful model for this phenomenon, has been extensively studied in terms of its optical, electrical and mechanical components. Ionic changes in the extracellular microenvironment have also been assessed and chemical substances liberated from tissue have been detected. 3. The velocity of propagation has been measured and some physical and chemical factors underlying the spread of the electrophysiological depression have been identified. Hypotheses about the nature of the reaction are discussed.