RESUMO

Although the myotendinous junction (MTJ) of skeletal striated muscle is well known, more detailed studies regarding the structure of the cardiac MTJ are scarce. The objective of the present study was to investigate the morphological characteristics of the MTJ in hearts of healthy and hypertensive (SHR) female rats using histological, ultrastructural and three-dimensional (SEM) methods, as well as to evaluate the expression of vinculin by immunofluorescence. In the two groups, light microscopy showed branching tendinous cords and collagen bundles penetrating the apex of the finger-like projections of the papillary muscle. SEM analysis revealed an enlarged apex of the papillary muscle in SHR which was not observed in healthy animals. The loss of force transmission appears to be compensated by the amplified connection between the papillary muscle and valvular collagen. A large number of intercalated disks close to the fiber apex, small amounts of an amorphous intercellular substance and numerous vesicles were observed in SHR. In these animals, the expression of vinculin was more marked showing a regular distribution and a pattern of transverse striations along the sarcolemma. The presence of this protein in transverse bands suggests that vinculin surrounds myofibrils in the region of the Z band. Vinculin staining was also more marked in the region of the tendinous cord-papillary muscle junctions of SHR compared to control animals. Vinculin was quantified by electrophoresis and higher amounts of this protein were observed in SHR compared to control animals.

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RESUMO

Some muscle groups of mammals, such as the laryngeal muscle, present tonic muscle fibers among fast twitch muscle fibers. The latter are supplied by single en plaque neuromuscular junctions (NMJs) and the former by multiple NMJs. The aim of the present study was to characterize the muscle fiber types and their NMJs in the thyroarytenoid (TA) muscle of the opossum. Five adult opossums (Didelphis albiventris) were anesthetized and perfused with Karnovsky solution. The TA muscles of the right side were processed for TEM. The contralateral TA muscles were submitted to connective tissue digestion with HCl before scanning electron microscopy processing. Based on myofibril morphology, the number and arrangement of mitochondria, sarcoplasmic reticulum and T tubule profiles and Z-line width, three fast twitch muscle fiber types were identified. Tonic fibers characterized by small and compact myofibrils were also found. Although tonic muscle fibers were present, only single NMJs were observed. In these NMJs the axon terminals occupy the synaptic clefts, which have variable depths. The sarcolemmal folds were not homogeneously arranged along the NMJ cleft. The Schwann cell bodies and their cytoplasmic projections were covering the axon terminals. Scanning electron microscopy analysis revealed empty synaptic clefts with irregular distribution of junctional folds. At some NMJs, the axon terminals were not removed and were present, filling up the synaptic cleft. The presence of only the en plaque NMJ type is discussed in view of the functions performed by the opossum TA muscle. Moreover, we demonstrate the similarity in NMJ distribution between the opossum TA muscle and those of rats and humans, with the opossum thus representing another useful experimental animal model for studies regarding intrinsic laryngeal muscles.

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The motor endplates are dynamic structures that present a high degree of plasticity which does not stop with the cessation of development, but lasts throughout life. The present study describes the ultrastructural aspects that characterize this junction renewal process in the oblique abdominal muscles of aged rats (18-24 months). About 50% of the motor endplates studied presented reorganization characteristics such as shallow primary clefts without an axonal terminal, free junctional folds, axon terminals with few synaptic vesicles and presenting pleomorphic structures, large junctional folds containing collagen, and cytoplasmic projections of Schwann cells penetrating the primary synaptic cleft. These aspects are similar to those previously described in adult rats during retraction and degeneration of the axon terminal. Although less frequent, further evidence included the presence of small nerve terminals rich in vesicles, covered by a common Schwann cell and associated with closely packed junctional folds. This last characteristic was associated with nerve sprouting and occupation of the synaptic cleft with new nerve endings. The results of this study are discussed in view of the pertinent literature and we conclude that the plasticity phenomenon of the motor endplate is present throughout life and is more frequent and intense in old animals.

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A avaliaçao do calibre médio das artérias formadoras do Polígono de Willis, a porcentagem de anormalidades no diâmetro dessas artérias, segundo critérios estabelecidos na literatura, e o estudo das correlaçoes entre diferentes parâmetros, como fluxo potencial, volume, peso e algumas dimensoes do encéfalo foram analisadas em 50 indivíduos brasileiros, adultos, de ambos os sexos. A possível compensaçao anastomótica relativa a alteraçao de calíbre também foi avaliada. Foram observadas 11 anormalidades (2,2 por cento) em 9 encéfalos, com maior incidência na a artéria cerebral posterior (7 casos). Em 3 polígonos nao foi constatada a artéria comunicante anterior e em 1 caso a artéria cerebral anterior direita originava-se da artéria cerebral anterior esquerda. As artérias comunicantes exibiram maior coeficiente de variaçao demonstrando sua importância na manutençao do fluxo cerebral. O peso encefálico foi, em média, de 1075g e os diâmetros transversais frontal e parietal foram de 1O,7cm e 12,5cm respectivamente, em média. Foi observada correlaçao inversa significativa entre os diâmetros das artérias comunicante posterior direita e artéria cerebral posterior direita. Esta correlaçao nao foi demonstrada no antímero esquerdo. Nao foram observadas correlaçoes significativas entre artérias basilar e comunicantes posteriores e entre fluxo potencial e volume ou peso encefálicos. As artérias carótidas internas e cerebrais anteriores, basilar e cerebrais posteriores, comunicante anterior e cerebrais anteriores, cerebrais posteriores e carótidas homolaterais demonstraram correlaçoes diretas de calibre.

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As junçoes mioneurais e o calibre das fibras musculares de músculos da parede abdominal de cobaia foram medidas após serem corados com esterase inespecífica e Azul de Metileno. Demonstrou-se que existe correlaçao direta entre diâmetro da fibra muscular e dimensao da sua junçao mioneural. Nao existe, entretanto, correspondência precisa entre os valores obtidos nos dois métodos utilizados. Este último aspecto deixa claro que, embora importante para o estudo da morfologia das junçoes mioneurais, o método para demonstraçao da esterase inespecífica nao se presta para estudos morfométricos ou onde se objetiva estudar os axonios pré-terminais, já que ele provoca acentuada retraçao do tecido e nao marca os axonios.

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