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Resumo O conteúdo de dopamina nas estruturas cerebrais tem sido relacionado à excitabilidade neuronal e várias abordagens têm sido utilizadas para estudar este fenômeno durante o período de vulnerabilidade às crises. No presente trabalho, descrevemos os efeitos da depleção de dopamina após a administração de 6-hidroxidopamina (6-OHDA) na região pars compacta da substância negra de ratos submetidos ao modelo de epilepsia com pilocarpina. A susceptibilidade ao estado de mal epiléptico induzido pela pilocarpina, bem como a frequência de crises espontâneas e recorrentes durante o período crônico do modelo foi determinada. Sendo o hipocampo uma das principais estruturas afetadas no desenvolvimento desse modelo experimental de epilepsia, os níveis de dopamina nessa região foram determinados após a administração da droga. No primeiro experimento, 62% (15/24) dos ratos pré-tratados com 6-OHDA e 45% (11/24) daqueles que receberam ácido ascórbico como solução controle evoluíram para crises límbicas motoras e para o estado de mal epiléptico, após a administração de pilocarpina. A gravidade das crises durante o período agudo do modelo foi significativamente maior nos ratos epilépticos experimentais (56,52%) do que nos ratos controle (4,16%). No segundo experimento, não houve diferença significante entre os grupos quanto à frequência de crises na fase crônica do modelo. Nossos dados mostraram que a dopamina pode desempenhar um papel importante na gravidade das crises na fase aguda da pilo, o que parece ser exercido por sua ação inibitória da dopamina sobre a expressão motora das crises.

Abstract The dopamine content in cerebral structures has been related to neuronal excitability and several approaches have been used to study this phenomenon during seizure vulnerability period. In the present work, we describe the effects of dopamine depletion after the administration of 6-hidroxidopamine (6-OHDA) into the substantia nigra pars compacta of male rats submitted to the pilocarpine model of epilepsy. Susceptibility to pilocarpine-induced status epilepticus (SE), as well as spontaneous and recurrent seizures (SRSs) frequency during the chronic period of the model were determined. Since the hippocampus is one of main structures in the development of this experimental model of epilepsy, the dopamine levels in this region were also determined after drug administration. In the first experiment, 62% (15/24) of 6-OHDA pre-treated rats and 45% (11/24) of those receiving ascorbic acid as control solution progressed to motor limbic seizures evolving to SE, after the administration of pilocarpine. Severeness of seizures during the model´s the acute period, was significantly higher in epileptic experimental rats (56.52%), than in controls (4.16%). In the second experiment, the frequency of seizures in the model’s chronic phase did not significantly change between groups. Our data show that dopamine may play an important role on seizure severity in the pilo’s model acute period, which seems to be due to dopamine inhibitory action on motor expression of seizure.

https://doi.org/10.1590/1519-6984.248411

100 Anos da Cosmologia Relativística (1917–2017). Parte I: Das Origens à Descoberta da Expansão Universal (1929)
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Lima, J. A. S.

; Santos, R. C.

Revista Brasileira de Ensino de Física

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2018, Volume 40 N. 1 elocation e1313

Abstract: Pt En | Text: Pt En | PDF: Pt | PDF: En

Estamos vivenciando um período de extrema efervescência intelectual na área da cosmologia. Um volume enorme de dados observacionais em quantidade e qualidade sem precedência e um arcabouço teórico mais consistente, impeliram a cosmologia para uma era da precisão, transformando a disciplina em área de ponta da ciência contemporânea. Observações com Supernovas do tipo Ia (SNe Ia) mostraram que o Universo está expandindo aceleradamente, um fato sem explicação no modelo desacelerado tradicional. Identificar a causa dessa aceleração é hoje o problema mais fundamental da área. Tal como ocorreu no renascimento científico, a solução norteará os rumos da disciplina no futuro próximo e as possíveis respostas (se energia escura, alguma extensão da relatividade geral ou um mecanismo ainda desconhecido) deverão também alavancar o desenvolvimento da física. Nesse contexto, sem abdicar de uma abordagem pedagógica, apresentamos uma visão geral tanto dos principais resultados teóricos quanto das descobertas observacionais mais significativas da cosmologia nos últimos 100 anos. A saga da cosmologia moderna será apresentada numa trilogia. Neste artigo (Parte I), com base nos artigos de Einstein, de Sitter, Friedmann, Lemaître e Hubble, descreveremos o período decorrido entre as origens da cosmologia e a descoberta da expansão Universal (1929). Na Parte II veremos o período de 1930–1997, finalizando com o velho modelo padrão desacelerado. A Parte III será inteiramente dedicada ao modelo acelerado do Universo, o paradigma cósmico do século XXI.

We are experiencing a period of extreme intellectual effervescence in the area of cosmology. A huge volume of observational data in unprecedented quantity and quality and a more consistent theoretical framework propelled cosmology to an era of precision, turning the discipline into a cutting-edge area of contemporary science. Observations with type Ia Supernovae (SNe Ia), showed that the expanding Universe is accelerating, an unexplained fact in the traditional decelerated model. Identifying the cause of this acceleration is the most fundamental problem in the area. As in the scientific renaissance, the solution will guide the course of the discipline in the near future and the possible answers (whether dark energy, some extension of general relativity or a still unknown mechanism) should also leverage the development of physics. In this context, without giving up a pedagogical approach, we present an overview of both the main theoretical results and the most significant observational discoveries of cosmology in the last 100 years. The saga of cosmology will be presented in a trilogy. In this article (Part I), based on the articles by Einstein, de Sitter, Friedmann, Lemaître and Hubble, we will describe the period between the origins of cosmology and the discovery of Universal expansion (1929). In Part II we will see the period from 1930 to 1997, closing with the old standard decelerated model. The Part III will be entirely devoted to the accelerated model of the universe, the cosmic paradigm of the XXI century.

https://doi.org/10.1590/1806-9126-rbef-2017-0196 5297 downloads

Can Lorentz transformations be determined by the null Michelson-Morley result?
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Lima, J. A. S.

; Sasse, Fernando D.

Revista Brasileira de Ensino de Física

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2017, Volume 39 N. 3 elocation e3304

Abstract: Pt En | Text: Pt En | PDF: Pt | PDF: En

O chamado princípio da relatividade é capaz de determinar uma transformação geral de coordenadas que difere da forma lorentziana padrão por um velocidade desconhecida que não pode, em princípio, ser identificada com a velocidade da luz. Com base em uma nova análise do experimento de Michelson-Morley, usando esta transformação estendida, mostramos que tal velocidade invariante é determinada analíticamente, sem qualquer referência às equações de Maxwell e questões conceituais relacionadas a procedimentos de sincronização, definição de tempo e causalidade. Tal resultado demonstra de uma maneira pedagógica que a constância da velocidade da luz não precisa ser suposta como um postulado básico da teoria da relatividade especial, uma vez que ela pode ser deduzida diretamente a partir de um experimento óptico em combinação com o princípio da relatividade. O método apresentado aqui resulta numa dedução das transformações de Lorentz que é simples e elucidativa, apropriada para um curso introdutório sobre teoria da relatividade especial.

The so-called principle of relativity is able to fix a general coordinate transformation which differs from the standard Lorentzian form only by an unknown speed which cannot in principle be identified with the light speed. Based on a reanalysis of the Michelson-Morley experiment using this extended transformation we show that such unknown speed is analytically determined regardless of the Maxwell equations and conceptual issues related to synchronization procedures, time and causality definitions. Such a result demonstrates in a pedagogical manner that the constancy of the speed of light does not need to be assumed as a basic postulate of the special relativity theory since it can be directly deduced from an optical experiment in combination with the principle of relativity. The approach presented here provides a simple and insightful derivation of the Lorentz transformations appropriated for an introductory special relativity theory course.

https://doi.org/10.1590/1806-9126-rbef-2016-0273 2508 downloads

A cross-check for H 0 from lyman-α forest and baryon. Acoustic oscillations
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Busti, V. C.

; Guimarães, R. N.

; Lima, J. A. S.

Revista mexicana de astronomía y astrofísica

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2016, Volume 52 N. 1 Pages 3 - 10

Abstract: En Es | Text: En Es | PDF: En | PDF: Es

Abstract: A new method is proposed to infer the Hubble constant Ho through the ob served mean transmitted flux from high-redshift quasars and the baryon acoustic oscillations (BAOs). A semi-analytical model for the cosmological-independent vol ume density distribution function was adopted; it allowed us to obtain constraints on the cosmological parameters once a moderate knowledge of the Inter Galactic Medium (IGM) parameters is assumed. Our analysis, based on two different sam ples of Lyman-α forest and the BAO measurement, restricts (h,Ω m) to the intervals 0.19 ≤ Ω m ≤ 0.23 and 0.53 ≤ h ≤ 0.82 (1σ). Although the constraints are weaker compared with other estimates, we point out that, with a bigger sample and a better knowledge of the IGM, this method could provide complementary results to measure the Hubble constant independently of the cosmic distance ladder.

Resumen: Se propone un nuevo método para inferir el valor de la constante de Hubble. Ho, mediante el flujo medio observado de cuásares de alto corrimiento al rojo y las oscilaciones acústicas de los bariones (BAOs). Se adopta un modelo semianalítico para la distribución de densidad volumétrica independiente de la cosmología que nos permite obtener límites para los parámetros cosmológicos una vez que se cuenta con una aceptable estimación de los parámetros del medio intergaláctico (IGM). Basado en dos muestras diferentes del bosque de Lyman-α y en la medición de las BAOs, nuestro análisis restringe (h,Ω m) a los intervalos 0.19 ≤ Ω m ≤ 0.23 y 0.53 ≤ h ≤ 0.82. Si bien estos límites son menos estrictos que los que se obtienen por otros métodos, señalamos que con muestras más numerosas y con un mejor conocimiento del IGM nuestro método podría aportar resultados complementarios para la determinación de la constante de Hubble, independientemente de la escala cósmica de distancias.

605 downloads

Energetic status of crossbreed dairy cows during transition period in two different seasons
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Moreira, T. F.

; Facury Filho, E. J.

; Meneses, R. M.

; Mendonça, F. L. M.

; Lima, J. A. M.

; Carvalho, A. U.

Arquivo Brasileiro de Medicina Veterinária e Zootecnia

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oct 2015, Volume 67 N. 5 Pages 1327 - 1334

Abstract: Pt En | Text: Pt En | PDF: Pt | PDF: En

RESUMOForam utilizadas 31 vacas leiteiras mestiças para comparar o perfil energético em duas estações, verão e inverno. Amostras de sangue foram colhidas semanalmente durante o pré-parto, no dia do parto e nos dias dois, cinco, 10, 15, 21 e 30 do pós-parto. Todos os metabólitos analisados foram influenciados pelo estádio fisiológico. As concentrações de glicose foram maiores no inverno, enquanto as concentrações de triglicérides e lactato desidrogenase (LDH) foram maiores no verão. As concentrações de colesterol, AST e GGT mostraram um padrão de comportamento diferente entre o verão e o inverno. Ácidos graxos não esterificados (NEFA) e beta-hidroxibutirato (BHB) não foram influenciados pela estação do ano. As vacas que pariram durante o inverno tinham um escore de condição corporal (ECC) maior e perderam mais ECC até o parto. No verão, 32,26% e, no inverno, 29,03% dos animais apresentaram concentrações de NEFA acima do recomendado no pré-parto; 22,58% dos animais no verão e 19,35% no inverno tiveram cetose subclínica em algum momento do período de transição, tornando-os mais suscetíveis a outras doenças.

ABSTRACTWe used 31 crossbreed dairy cows to compare the energetic profile in summer and winter. Blood samples were taken weekly prepartum, at calving and on days 2, 5, 10, 15, 21 and 30 postpartum. All metabolic indicators analyzed were influenced by the physiological status. The glucose concentrations were higher during winter while the triglyceride concentrations and lactate dehydrogenase (LDH) were higher in the summer. The season influenced the concentrations of cholesterol, AST and GGT, showing a different pattern between summer and winter. Non-esterified fatty acids (NEFA) and beta-hidroxibutirate (BHB) were not influenced by the season. Cows that calved during winter had a greater body condition score (BCS) and lost more BCS until calving. During summer, 32.26% of the animals and 29.03% during winter had NEFA concentrations above the optimum level and 22.58% of the animals in summer and 19.35% in the winter had subclinical ketosis at some point during the transition period, making then more susceptible to diseases.

https://doi.org/10.1590/1678-4162-8287 1939 downloads

Hamilton-Jacobi approach for power-law potentials
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Santos, R. C.

; Santos, J.

; Lima, J. A. S.

Brazilian Journal of Physics

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dec 2006, Volume 36 N. 4a Pages 1257 - 1261

Abstract: En | Text: En | PDF: En

The classical and relativistic Hamilton-Jacobi approach is applied to the one-dimensional homogeneous potential, V(q) = alphaq n, where alpha and n are continuously varying parameters. In the non-relativistic case, the exact analytical solution is determined in terms of alpha, n and the total energy E. It is also shown that the non-linear equation of motion can be linearized by constructing a hypergeometric differential equation for the inverse problem t(q). A variable transformation reducing the general problem to that one of a particle subjected to a linear force is also established. For any value of n, it leads to a simple harmonic oscillator if E > 0, an "anti-oscillator" if E < 0, or a free particle if E = 0. However, such a reduction is not possible in the relativistic case. For a bounded relativistic motion, the first order correction to the period is determined for any value of n. For n >> 1, it is found that the correction is just twice that one deduced for the simple harmonic oscillator (n = 2), and does not depend on the specific value of n.

2532 downloads

Galaxy luminosity function: a new analytic expression
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Alcaniz, J. S.

; Lima, J. A. S.

Brazilian Journal of Physics

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jun 2004, Volume 34 N. 2a Pages 455 - 458

Abstract: En | Text: En | PDF: En

We propose a new analytic approximation for the luminosity function of galaxies. The suggested expression behaves like the Schechter function at the faint end (f ~ La) but departs considerably at the bright end (L >> L*). We argue here that such a behavior may provide a better fit for the current observational data than does the Schechter function. Its practical interest is stressed by considering roughly the data set provided by the Stromlo-APM redshift survey. Implications on the estimates of the matter density parameter from mass-to-light ratio are also briefly discussed.

1341 downloads

Alternative dark energy models: an overview
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Lima, J. A. S.

Brazilian Journal of Physics

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mar 2004, Volume 34 N. 1a Pages 194 - 200

Abstract: En | Text: En | PDF: En

A large number of recent observational data strongly suggest that we live in a flat, accelerating Universe composed of ~ 1/3 of matter (baryonic + dark) and ~ 2/3 of an exotic component with large negative pressure, usually named Dark Energy or Quintessence. The basic set of experiments includes: observations from SNe Ia, CMB anisotropies, large scale structure, X-ray data from galaxy clusters, age estimates of globular clusters and old high redshift galaxies (OHRG's). It is now widely believed that such results provide the remaining piece of information connecting the inflationary flatness prediction (W T = 1) with astronomical observations. From a theoretical viewpoint, they have also stimulated the current interest for more general models containing an extra component describing this unknown dark energy, and simultaneously accounting for the present accelerating stage of the Universe. In this review we present a simplified picture of the main results and discuss briefly some difficulties underlying the emerging dark energy paradigm.

3269 downloads

Cosmological implications of old galaxies at high redshifts
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Lima, J. A. S.

; Alcaniz, J. S.

Brazilian Journal of Physics

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dec 2001, Volume 31 N. 4 Pages 583 - 586

Abstract: En | Text: En | PDF: En

Old high-z galaxies are important tools for understanding the structure formation problem and may become the key to determine the ultimate fate of the Universe. In this paper, the inferred ages of the three oldest galaxies at high redshifts reported in the literature are used to constrain the first epoch of galaxy formation and to reanalyse the high-z time scale crisis. The lower limits on the formation redshift z f depends on the quantity of cold dark matter in the Universe. In particular, if omegam > or = 0.37 these galaxies are not formed in FRW cosmologies with no dark energy. This result is in line with the Supernovae type Ia measurements which suggest that the bulk of energy in the Universe is repulsive and appears like an unknown form of dark energy component. In a complementar analysis, unlike recent claims favoring the end of the age problem, it is shown that the Einstein-de Sitter model is excluded at high-z by 3sigma.

1134 downloads

10.

Bounds on the conical defect parameter from solar system tests
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Freire, Wilson H. C.

; Bezerra, V. B.

; Lima, J. A. S.

Brazilian Journal of Physics

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jun 2000, Volume 30 N. 2 Pages 398 - 402

Abstract: En | Text: En | PDF: En

We analyse the planetary perihelion precession and the deffection of light in the Schwarzschild field modified by a conical defect. By using observational results from solar system tests of general relativity, we obtain limits on the conical defect parameter <img src="http:/img/fbpe/bjp/v30n2/ses.gif">. For the physical case of a cosmic string the quoted limits are one and three orders weaker than the cosmological bounds.

1308 downloads

11.

On the classical energy equipartition theorem
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Lima, J. A. S.

; Plastino, A. R.

Brazilian Journal of Physics

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mar 2000, Volume 30 N. 1 Pages 176 - 180

Abstract: En | Text: En | PDF: En

A general proof of the energy equipartition theorem is given. Our derivation holds for any distribution function depending on the phase space variables only through the Hamiltonian of the system. This approach generalizes the standard theorem in two main directions. On the one hand, it considers the contribution to the total mean energy of homogeneous functions having a more general type than the ones usually discussed in the literature. On the other hand, our proof does not rely on the assumption of a Boltzmann-Gibbs exponential distribution.

6020 downloads

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