Dans les synapses chimiques, des canaux calciques voltage-dépendants (VDCC) provoquent la fusion des vésicules synaptiques (SV) au niveau de la zone active. L’efficacité et la rapidité de la transmission synaptique dépendent de la distribution relative entre les VDCCs et les SVs prêtes à fusion. Cependant, les modalités d’interaction entre les VDCCs et les SVs ne sont pas connues. Afin de localiser les VDCCs à l’échelle nanométrique j’ai developpé une nouvelle approche chez Caenorhabditis elegans combinant le marquage in vivo des VDCCs, grâce à l’expression d’un épitope extracellulaire, et la microscopie électronique (EM). J’ai généré un transgene GFP::unc-36 qui code la seule sous-unité α2-δ qui s’associe à fois avec les sous-unités formant le pore α1 neuronal (UNC-2) et musculaire (EGL-19) chez C.elegans. J'ai ensuite utilisé des quantum dots conjugués avec l’anticorps anti-GFP, fluorescents et denses au électrons, pour localiser des VDCCs à haute résolution au niveau de la jonction neuromusculaire (NMJ) par EM. En parallèle, j'ai utilisé la technique de CALM (complementation activated light microscopy) pour étudier la dynamique des VDCC dans des vers vivants. Nos résultats montrent que les VDCCs diffusent à l’échelle de nanodomaines sur la membrane musculaire. De plus leur diffusion est modulée en réponse à la tension musculaire. La dystrophine participe au couplage électro-mécanique au niveau du sarcolemme en modulant la taille du domaine de confinement des VDCCs. Enfin, nous avons mis en evidence le rôle de RIM/UNC-10 dans la régulation de la mobilité latérale des VDCCs dans les neurones, probablement via son interaction avec les VDCCs et les SVs. / At chemical synapse voltage-dependent calcium channels (VDCC) trigger synaptic vesicles (SV) fusion at the active zone in response to depolarization stimuli. Intracellular Ca2+ influx forms a nanodomain around individual VDCC. Fast and efficient synaptic transmissions appear to be tightly coupled with the relative distribution between the VDCCs and SVs fusion sites. However, the connection between VDCCs and docked SVs at a few nanometer scales remain enigmatic. To localize VDCCs in nanometer resolution I developed a novel approach combining in vivo labeling of VDCCs via genetically-encoded extracellular epitope tags and electron microscopy (EM). I engineered a GFP/split-GFP tag fused at the extracellular N-terminal of UNC-36, the only C. elegans VDCC α2δ subunit associating with both neuronal (UNC-2) and muscular (EGL-19) VDCC pore-forming α1 subunit. I then used quantum dot (QD) conjugated antibodies as both fluorescent and electron dense probes to localize VDCCs at C. elegans neuromuscular junction (NMJ) by in vivo QD-antibodies labeling and EM. In parallel, I applied in vivo complementation activated light microscopy to study VDCC dynamics in live worms. I discovered that VDCCs diffuse within nanodomains at sarcomeric membrane and their nanoscale diffusion behavior is modulated in response to muscle tension. In addition, we found that dystrophin participates in electro-mechanical coupling at the sarcolemma by modulating the confinement size of VDCCs. Meanwhile, we discovered lateral mobility of N-type VDCC at NMJs, and that RIM/UNC-10 seems involved in regulation of VDCC dynamics via its interaction with VDCC and SVs.

This dissertation thesis concerns with Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries and it is divided into three main parts. Motivation for this dissertation thesis was in a study reviewing effect of material model upon resulting stresses in AAA. The effect was calculated in 70 patient-specific geometries of AAA, which exceeds the number of geometries in other scientific papers by one order. Within this study, two material models were used, i.e. real one and 100× stiffer, and obtained stresses were mutually compared. It was quantified that peak stress difference can be higher than 20 % in 10% of patients and therefore the real material model should be preferred over the artificial one although operation with this model is more demanding. The second part of this thesis deals with an identification of structural parameters (orientation and dispersion of collagen fibres) of porcine aortic tissue by using adjusted Fast Fourier Transform based algorithm. The extracted structural parameters were inserted into two-layer structure-motivated constitutive model Martufi-Gasser. This model was validated and its predictive capabilities were also tested with fine results. The most important information obtained from the digital image processing of ~9000 micrographs is existence of only one family of dispersed collagen fibres which breaks the current dogma present in many scientific papers about two families of collagen fibres. The third part concerns with a proposal of an automated phase-correlation based algorithm for obtaining collagen fibre direction from polarized light microscopy images. The proposed algorithm was verified and validated and it yields histograms of collagen fibre directions with overall number of measured points larger than it would be possible to get from any manual measurement. The limitation of the original proposed algorithm is in 90° period of polarized light intensity, thus the method results in angles in the range of 0°–90. Therefore the end of the thesis is dedicated resolving this problem and obtaining real angles in a span of 0°–180°. To this end, the microscope set-up was changed and the algorithm was adjusted accordingly. The original and the adjusted algorithms are collagen-specific, fast and an operator independent. Despite all the author´s effort put into collagen fibre waviness quantification directly from the histograms, the waviness has not been quantified yet in this way and it remains at the stage of research.

13551398399831-171f83a418df200fec6f622f22b6fb3d.txt The Thesis describes new methods for automatic processing of image data in biology, physics and medicine. The developed methods reconstruct light microscopy images of growing microorganisms in intervals between observations, measure particles in atomic force microscopy images, and evaluate parameters of vocal fold vibrations in videokymographic images. All three problems have been hitherto solved primarily visually. The proposed methods allow automatic or computer-aided processing of the image data, and thus facilitate the evaluation process. Performance of the developed methods was tested on real images; the results were comparable with ground truth or results of visual evaluation. Application of the developed methods is not limited to the specific type of image data; the methods can be used in general for processing of images with similar characteristics. Page 1

Beurteilung von nativen und aufgetauten Spermatozoen fertiler und subfertiler Hengste mit Hilfe der Phasenkontrast- und Transmissionselektronenmikroskopie. Institut für Veterinär-Pathologie der Veterinärmedizinischen Fakultät, Universität Leipzig Reproduktionsmedizinische Einheit der Kliniken der Tierärztlichen Hochschule Hannover In dieser Arbeit wurde die Ultrastruktur von nativen und tiefgefrorenen Spermien mittels Phasenkontrast- und Transmissionselektronenmikroskopie (TEM) untersucht. Für die Beurteilung der Spermienmotilität und der Morphologie von in Formolzitrat fixierten Spermien standen jeweils drei Ejakulate von 50 Hannoveraner Hengsten des Niedersächsischen Landgestüts Celle zur Verfügung. Aus dieser Gruppe wurden drei fertile, drei subfertile Hengste und 6 Hengste mittlerer Fertilität ausgewählt, von denen sowohl die Nativ-Proben als auch eine Tiefgefrierprobe (TG-Probe) für die TEM im Institut für Veterinär-Pathologie der Universität Leipzig gemäß des Standardprotokolls des Institutes aufbereitet wurden. Die Spermien wurden gewaschen und das Seminalplasma der nativen Proben oder der Verdünner der TG-Proben abpipettiert und durch eine 5%-ige Glutaraldehydlösung in einem 0,1 M Kakodylatpuffer (pH 7,2) ersetzt. Die Fixierungslösung wurde anschließend entfernt und das Pellet gewaschen und danach mit Gelatine gemischt. Die spermienreichen Stellen wurden aus der Gelatine herausgeschnitten und in Glutaraldehyd aufbewahrt. Nach einer Nachfixierung in OsO4 und einer Entwässerung in Ethanollösungen erfolgte eine Einbettung in einer Eponmischung. Nach einer Polymerisation von 5 Tagen wurden die eingebetteten Eponblöckchen angetrimmt und die Semi- und Ultradünnschnitte angefertigt. Die Ultradünnschnitte wurden auf ein Kupfergrid gelegt, mit Uranylazetat und Bleizitrat kontrastiert und mit dem Transmissionselektronenmikroskop (Zeiss EM 900, Oberkochem) bei 80 kV analysiert. In den nativen Proben wurden insgesamt 360 Spermien pro Hengst beurteilt, in den TG-Proben 120 Spermien pro Hengst. Die Qualität der elektronenmikroskopischen Aufnahmen war sehr gut, doch die Plasmamembran zeigte fixierungsbedingte Artefakte. Nach dem Auftauen waren die Bilder heller und der Kontrast etwas geringer. Es gab eine Zunahme an Akrosomdefekten, akrosomreagierten Spermien und Beschädigungen der Plasmamembran, der Mitochondrien, sowie der Mantel- und Ringfasern. Durch die Membranbeschädigungen trat auch eine Verringerung der Anzahl proximaler und distaler Zytoplasmatropfen auf. Sowohl geschwollene Akrosome mit einer niedrigeren Dichte der akrosomalen Matrix als auch Mitochondrien mit einer zu hellen mitochondrialen Matrix waren typische Befunde in den TG-Proben. Die Studie der Ultrastruktur und die wahrgenommenen Defekte führten zur Erstellung eines Standardprotokolls für die transmissionselektronenmikroskopische Beurteilung von Hengstspermien. Die Beurteilung mittels TEM sollte aber nicht zu einer quantitativen, sondern zu einer qualitativen Aussage führen. Sie ermöglicht die Diagnose von Kern- (Kerndeformationen und Taschenbildung im Kern) und Akrosomabweichungen (deformierte Akrosome mit oder ohne Vakuolenbildung, abgehobene Akrosome und akrosomreagierte Spermien), Anomalien der Mitochondrien (Unterbrechung der Mitochondrienscheide, zu viele Mitochondrien, anormale Dichte der mitochondrialen Matrix), Defekten des Axonemas (Ordnung oder Anzahl der Mikrotubuli, Mantel- und Ringfasern) und der Anwesenheit immaturer Spermienvorstufen. Diese Methode eignet sich für die Diagnostik subfertiler Hengste mit normalen Spermienparametern bei der routinemäßige Spermienbeurteilung und kann sowohl in nativen als auch in TG-Proben angewendet werden. Im Vergleich zur Phasenkontrastmikroskopie waren die elektronenmikroskopischen Bilder wegen ihrer stärkeren Vergrößerung und der Darstellung innerer Spermienstrukturen viel aussagekräftiger. Für die Beurteilung von Halsansatzdefekten, abweichende Geißelformen und Mehrfachmißbildungen ist die Phasenkontrastmikroskopie die am besten geeignete Methode. / Evaluation of fresh and frozen-thawed semen samples of fertile and subfertile stallions by light microscopy and transmission electron microscopy. Institut of Pathology of the Faculty of Veterinary Medicine, University of Leipzig Reproduktionsmedizinische Einheit der Kliniken der Tierärztlichen Hochschule Hannover In this study the ultrastructure of fresh and frozen-thawed semen samples of 50 stallions from the National Stud of Lower Saxony (Celle, Germany) were evaluated by light microscopy and transmission electron microscopy (TEM). Three ejaculates of each stallion were available for the motility analysis and the morphological analysis by lightmicroscopy after fixation in formol citrate. Based on the fertility data, the ejaculates of 12 stallions (3 fertile stallions, 3 subfertile stallions and 6 stallions of average fertility) were selected for the morphological analysis by TEM. The native samples and one frozen-thawed sample from these stallions were prepared for the TEM at the Institute of Pathology of the Faculty of Veterinary Medicine, Uni-versity of Leipzig. The sperm cells were washed and the seminal plasma from the native samples and the diluents of the frozen-thawed samples were replaced by a 5%-glutaraldehyde solution in a 0,1 M cacodylate buffer pH 7,2. The fixative was removed, the pellet was washed again and mixed with gelatin. The sperm rich fraction in the gelatin mass was excised and stored in glutaraldehyde. A second fixation in OsO4 was followed by a dehydratation in ethanol and a polymerization phase in epon. After 5 days of polymerization the starred samples were used for semi- and ultratight cuts. The latter were placed on a copper grid, contrasted with uranyl acetate and lead citrate and analyzed with the transmission electron micro-scope (EM 900) by 80 kV. In the fresh samples, 360 sperm cells were examined per stallion, whereas in the frozen-thawed samples only 120 sperm cells per stallion were evaluated. The microscopic pictures were of a high quality. However, the sperm plasma membrane showed some fixation artifacts. In the thawed samples a lower contrast was noticed than in the fresh samples. The sperm cells in the frozen-thawed samples showed an increase in acrosome defects, acrosome reactions, damage of the cell plasma membrane, mitochondria, fibrous sheet and outer dense fibers. The latter defect was associated with a decrease in proximal and distal cytoplasmatic droplets. Swollen acrosomes with a lower matrix density and a bright mitochondrial matrix were typically present in the cryopreserved samples. The ultrastructural defects in these samples, examined by TEM, have led to the development of a standard evaluation protocol with the most common sperm defects in stallion semen. TEM is an expensive and time consuming technique, which cannot be used to obtain quantitative results, but is considered as an accurate method for the qualitative examination of semen samples in cases of unexplained subfertility. TEM can especially be recommended for the diagnosis of nuclear (nuclear malformations and pouches) and acrosomal defects (acrosome deformations, acrosome vacuoles, detached acrosomes and acrosome reactions), mitochondrial (mitochondrial sheet defects, mitochondrial proliferation, decrease in mitochondrial matrix density) and axonema malformations (anormal position or quantity of microtubules and fibrous sheet or outer dense fibers defects) and the detection of immature sperm cells in ejaculates. The results of this study state that TEM can be useful for the evaluation of both fresh and frozen-thawed semen samples. Compared to the light microscopic evaluation of stallion sperm, the TEM images give more precise information because of their higher magnification rate and the ability to reveal internal sperm structures. However, light microscopy remains the best method to detect sperm neck defects, deformed tailes and sperm cells with multiple heads or tails.

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The main objective of this thesis was to create an educational website aimed at soil arthropods. It can be used primarily by teachers of biology and ecology, lecturers of extracurricular science education or by the students who are interested in this issue. This photographic atlas of soil arthropods consists of my own micro images obtained by the use of light and scanning electron microscope. The micro images are accompanied by text to each group of soil arthropods, which is divided into sections containing information about the systematic classification, anatomy and morphology, biology and importance, eventually representatives of the group. The atlas is accompanied by other materials usable in the classroom, such as didactic test, didactic game and proposals for group work, worksheet, field and laboratory work or educational presentations focused on soil arthropods. These materials can be downloaded from the website, along with the entire atlas of soil arthropods. The atlas is available on the following address: https://sites.google.com/site/pudniclenovci/. The review of the literature deals with the importance of arthropods in the soil and their mutual interactions. Then I describe the methods of study of arthropods (sampling, sample preparation for light and scanning electron microscopy and...

Measurements on coccolith abundance and mass can be used as a signal of primary productivity and pelagic calcification in response to environmental change. The Leeuwin Current (LC) is known to transport warm and low-salinity waters from the Indo-Pacific Warm Pool (IPWP) southwards along the coast of West Australia. Along with the onset of continental aridity during late Neogene, increased strength of the LC may have played a role in reef expansion on the Northwest Shelf. In this study the morphological variation in size and mass of reticulofenestrid coccoliths was assessed in material from IODP Site U1461 in the eastern Indian Ocean spanning the past 500 ka. Both the absolute abundance of all reticulofenstrid coccoliths (Emiliania huxleyi, Reticulofenestra spp., Gephyrocapsa spp. and Pseudoemiliania spp.) was determined, as well as the relative abundance of large versus small coccoliths. Coccolith size and mass were measured quantitatively under circularly polarized light. The data was compared to variations in sea surface temperatures (SST) of the LC, and to continental aridity of Australia. SST fluctuations could influence coccolithophore productivity by affecting their metabolic rate, whereas continental aridity may influence the influx of terrestrial matter by wind. The investigated interval is dominated by small species of Gephyrocapsa. Peak values of absolute abundance and mass were observed during Marine Isotope Stage (MIS) 11, an interglacial period of extended warmth and humidity. These results coupled with high densities of aragonite needles in the same samples indicate the sediments were diluted by material overflowing from the adjacent shallow- water carbonate platform, analogous to the whiting events observed in the modern-day Bahamas. A decrease in abundance of Gephyrocapsa caribbeanica at 240 ka can be linked to the timing of their last common occurrence (LCO), within MIS 7. The subsequent shift to Gephyrocapsa oceanica as the dominant large species may indicate an ecological replacement of G. caribbeanica, or signify warm and low-salinity waters. / Mätningar av abundans och massa hos coccoliter kan användas som en signal för primärproduktion och pelagisk förkalkning som resultat av miljöförändringar. Leeuwin Current (LC) är känd för att transportera varmt vatten och vatten med låg salthalt från Indo-Pacific Warm Pool (IPWP) söderut längs kusten i västra Australien. Tillsammans med början av kontinental torka under sen Neogen kan ökad styrka hos LC ha spelat en roll i expansionen av rev på nordvästsockeln. I denna studie bedömdes den morfologiska variationen i storlek och massa hos coccoliter i material från IODP plats U1461 i östra Indiska oceanen från de senaste 500 000 åren. Både den absoluta abundansen av alla reticulofenstridcoccoliter (Emiliania huxleyi, Reticulofenestra spp., Gephyrocapsa spp. och Pseudoemiliania spp.) bestämdes, liksom den relativa abundansen av stora jämfört med små coccoliter. Storlek och massa av coccoliter mättes kvantitativt under cirkulärt polariserat ljus. Uppgifterna jämfördes med variationer i havsytans temperatur (SST) hos LC, och med kontinental torrhet i Australien. SST-fluktuationer kan påverka produktiviteten hos coccolitoforider genom att påverka deras metabolism, medan kontinental torrhet kan påverka inflödet av markmaterial med vind. Det undersökta intervallet domineras av små arter av Gephyrocapsa. Toppvärden av absolut abundans och massa observerades under marinisotopsteget (MIS) 11, en interglacial period med förlängd värme och fuktighet. Dessa resultat kombinerat med hög densitet av aragonitnålar i samma prover indikerar att sedimenten späddes ut med material som svämmade över från den intilliggande grunda karbonatplattformen, vilket är jämförligt med de vitningshändelser som har observerats i dagens Bahamas. En minskning i abundans av Gephyrocapsa caribbeanica vid 240 ka kan kopplas till tidpunkten för deras senaste gemensamma förekomst (LCO) inom MIS 7. Den efterföljande övergången till Gephyrocapsa oceanica som den dominerande stora arten kan indikera en ekologisk ersättning av G. caribbeanica, eller indikera varmt vatten med låg salthalt.

As bromélias são valorizadas por suas características ornamentais, sendo o gênero Vriesea representativo neste setor. O aprimoramento de métodos de propagação in vitro destas plantas é altamente necessário a fim de suprir as necessidades do mercado, e evitar o extrativismo ilegal. Nesse contexto, o presente trabalho objetivou aprimorar o protocolo de propagação in vitro de espécies do gênero Vriesea, bem como aumentar o conhecimento global das espécies em estudo. Para tanto, sementes das espécies V. carinata, V. friburgensis, V. paraibica e V. simplex foram submetidas a processos de assepsia e introduzidas in vitro sob três temperaturas: 22 °C, 27 °C e 32 °C. Paralelamente, sementes das mesmas espécies foram semeadas em bandejas e mantidas em casa de vegetação. Através da microscopia eletrônica de varredura e ótica foi realizada a descrição morfo-anatômica do desenvolvimento pós-seminal das plântulas das mesmas espécies. Além disso, procurou-se adequar o meio de cultura às necessidades das mesmas espécies e de V. hieroglyphica, sendo testadas 3 doses de nitrogênio e 3 doses de magnésio. Também procurou-se avaliar a taxa de sobrevivência durante o processo de aclimatização de plântulas das espécies de Vriesea mencionadas (com exceção de V. hieroglyphica). Objetivou-se comparar características anatômicas e morfológicas de folhas das referidas espécies cultivadas in vitro e em casa de vegetação. Por fim, com o objetivo de estabelecer um protocolo de micropropagação para as espécies Vriesea carinata, V. paraibica, V. phillipo-coburgii; V. simplex e Aechmea nudicaulis, foram introduzidos in vitro explantes somáticos, após testes de assepsia. A partir dos experimentos citados foi verificado que a temperatura exerce uma forte influência nas taxas de germinação e mortalidade das sementes de Vrieseas in vitro, sendo que a temperatura de 32°C proporcionou as maiores taxas de mortalidade, mostrando-se prejudicial ao sucesso reprodutivo. A germinação em casa de vegetação apresentou altas taxas de mortalidade e taxas de germinação mais baixas do que in vitro. A descrição morfo-anatômica do desenvolvimento pós-seminal permitiu a caracterização de cinco estágios de desenvolvimento. Com relação ao experimento de nutrição mineral, foi evidenciado que as doses de nitrogênio e magnésio testadas acarretaram em menor acúmulo de cálcio e de potássio nas plantas, sendo que esse fato resultou em menor acúmulo de massa fresca. O experimento de aclimatização ficou inviabilizado devido ao ataque às plântulas por praga Fungus Gnats. Com a análise morfo-anatômica das folhas de plantas cultivadas in vitro e em casa de vegetação foi possível observar a presença de estruturas típicas de Bromeliaceae nas plantas cultivadas em ambas as condições: estômatos, tricomas escamiformes, mesofilo com epiderme unisseriada, parênquima aqüífero, feixes colaterais fechados e canais de aeração. Com relação à introdução in vitro a partir de explantes somáticos, pode-se afirmar que o uso de cefotaxima apresentou uma boa eficiência no combate à contaminação bacteriana em cultura de ápices caulinares. A escolha de ápice vegetativo de brotos laterais como explantes iniciais para a cultura das referidas espécies in vitro é uma boa opção. A otimização da propagação destas espécies in vitro poderá diminuir a pressão extrativista que estas vêm sofrendo e, ao mesmo tempo, abastecer o mercado ornamental / Bromeliads are valued for their ornamental characteristics and the genus Vriesea is representative in this sector. The improvement of in vitro propagation of these plants is highly necessary in order to meet market needs, and, at the same time, to prevent illegal extraction of this plants from their natural habitat. In this context, this study aimed to improve the protocol for in vitro propagation of species of Vriesea and increase the global knowledge of these by morpho-anatomical characterization of the development of the seedling and leaf. Seeds of V. carinata, V. friburgensis, V.paraiba and V. simplex were submitted to aseptic procedures and introduced in vitro under three temperatures: 22 ° C, 27 ° C and 32 ° C. Additionaly, seeds of these species were sown in trays and maintained in a greenhouse. The post-seminal development was described by light and scanning electron microscopy. In addition, the adjustment of the culture medium for these four species and V. hieroglyphica was tested, by testing three doses of nitrogen combined with three doses of magnesium. The acclimatization efficiency of these Vriesea species, except for V. hieroglyphica, after a prior culture in the presence and absence of IBA was done, in three commercial substrates to verify IBA effect in rooting and seedling survival. This study also aimed to compare anatomical and morphological characteristics of leaves of the species cultivated in vitro and in the greenhouse. Finally, in order to establish a micropropagation protocol for the species Vriesea carinata, V. paraiba, V. phillipo-coburgii; V. simplex and Aechmea nudicaulis, somatic explants were introduced in vitro after sterilization tests. From all the experiments cited it was observed that the temperature strongly influences germination and mortality rates of Vriesea germinating seeds in vitro. The temperature of 32 ° C provided the highest mortality rates, being harmful to the reproductive success of this species. The germination in the greenhouse showed higher mortality and lower germination rates than in vitro germination. The morpho-anatomical description of the post-seminal development allowed for the characterization of five stages of development. With regard to the mineral nutrition experiment, the doses of nitrogen and magnesium tested resulted in less accumulation of calcium and potassium in plants, resulting in less accumulation of fresh weight. The acclimatization experiment was lost by the attack of Fungus gnats. With the morpho-anatomical analysis of leaves of plants grown in vitro and in the greenhouse it was possible to observe the presence of typical structures of Bromeliaceae such as stomata, scales, mesophyll with uniseriate epidermis, water storage tissue, collateral vascular bundles and air channels. Finally, the use of cefotaxime proved efficient against bacterial contamination in in vitro establishment of shoot apex explants in vitro. The choice of shoot apices from lateral buds as initial explants for in vitro establishment of those species was a good alternative. Optimization of in vitro propagation of bromeliad species can reduce their extractivism pressure and, at the same time, supply the ornamental plant market

A laserterapia tem sido muito utilizada como tratamento alternativo em pacientes com dores crônicas relacionadas às disfunções temporomandibulares. Isso se deve aos efeitos: analgésico, antiinflamatório, miorrelaxante, de redução da fadiga durante as contrações tetânicas, aumento da força de mordida e diminuição da dor orofacial. Embora sejam observados resultados clínicos, ainda não é bem compreendido o seu efeito em nível celular. Assim, este estudo tem como objetivo analisar os efeitos das diferentes densidades (doses) de irradiação do laser de baixa intensidade (LLLI), em nível celular, sobre o músculo masseter de ratos Wistar. Os animais foram alocados aleatoriamente em 6 grupos (n=10), receberam 10 irradiações do laser (GaAlAs,780nm, 5mW e spot 0,04cm²) sobre o músculo masseter esquerdo variando a densidade de energia (I. 0; II. 0,5; III. 1,0; IV. 2,5; V. 5,0 e VI. 20 J/cm²). Após as 10 irradiações os músculos masseteres foram obtidos dos animais sob anestesia para análises: 1. Histoenzimológicas para atividade da nicotinamida adenina dinucleotídeo diaforase(NADH), succinato desidrogenase (SDH) e adenosina trifosfatase (ATPase), 2. Microscopia de luz (HE), 3. Microscopia eletrônica de transmissão e 4. Imunohistoquímica para fator de crescimento do endotélio vascular (VEGF) e o receptor 2 para VEGF (VEGFR-2). A atividade do NADH nos grupos IV, V e VI (30±1,26; 33,47±2,15; 31,67±1,77 - fibras intermediárias) apresentou um aumento significativo (p>0,05) no metabolismo oxidativo em relação aos demais grupos. Na atividade do SDH, o aumento foi discreto, com aumento significativo (p>0,05), apenas no grupo V (32,2±1,61 fibras intermediárias), com o padrão de aumento metabólico muito parecido nas reações de NADH e SDH. A atividade da ATPase não revelou diferenças entre os grupos tanto em meio ácido como no alcalino. A microscopia de luz revelou fibras musculares arredondadas e núcleos periféricos achatados, os quais tornaram mais arredondados com as densidades maiores de energia. Ultraestruturalmente as irradiações com as maiores densidades de energia revelaram mitocôndrias de tamanhos e formas variadas e cisternas do retículo sarcoplasmático dilatadas entre as miofibrilas. As análises qualitativas mostraram um padrão de aumento a expressão do VEGF e VEGFR-2 proporcionais à densidade de energia do laser usada. Conclui-se que o laser com densidades maiores foi capaz de aumentar o metabolismo oxidativo, sem alterar a capacidade contrátil, aumentar o volume do núcleo, modificar a ultraestrutura das fibras musculares e as expressões do VEGF e VEGFR-2. / The laser therapy has been widely used as an alternative treatment in patients with chronic pain related to temporomandibular disorders. This is due to the effects: analgesic, anti inflammatory, muscle relaxant, reducing fatigue during tetanic contractions, increased bite strength and decrease in orofacial pain. Although clinical results are observed, is not well understood its effect on the cellular level. This study aims to analyze the effects of different densities (doses) irradiation of low level laser therapy (LLLI) on cellular level, on the masseter muscle of rats. The animals were randomly assigned to 6 groups (n=10), received 10 laser irradiation (GaAlAs, 780nm, 5mW spot and 0.04 cm²) on the left masseter muscle by varying the energy density (I. 0; II. 0.5; III. 1.0; IV. 2.5; V. 5.0 and VI. 20 J/cm²). After 10 irradiations the masseter muscles were obtained from animals under anesthesia for analysis: 1. Histoenzimologic for nicotinamide adenine dinucleotide (NADH), succinate dehydrogenase (SDH) and adenosine triphosphatase (ATPase), 2. Light microscopy (HE), 3. Transmission electron microscopy and 4. Immunohistochemistry for vascular endothelial growth factor (VEGF) and receptor 2 for VEGF (VEGFR-2). The activity of NADH in groups IV, V and VI (30±1,26; 33,47±2,15; 31,67±1,77 - intermediate fiber) increased significantly (p> 0.05) in oxidative metabolism in relation to other groups. The activity of SDH showed a slight increase, only the group V (32,2±1,61 intermediate fiber) increased significantly (p> 0.05), but the pattern of metabolic increase was very similar in both reactions. The ATPase activity showed no differences between groups nor in acid or alkaline. The qualitative analysis showed a pattern of increased expression of VEGF and VEGFR-2 directly proportional to the energy density of laser. Light microscopy showed rounded muscle fibers and peripheral flattened nuclei, which become more rounded with the highest energy densities. Ultrastructurally the irradiation with higher energy densities showed mitochondria of different sizes and shapes and dilated cisterns of sarcoplasmic reticulum between the myofibrils. It is concluded that higher densities of laser was able to increase the oxidative metabolism without altering the contractile capacity, increasing nuclei volume, modify ultrastructure of muscle fibers and the expressions of VEGF and VEGFR-2.