Ultrastructural study of muscle fibers and neuromuscular junctions in the opossum thyroarytenoid muscle

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.

Morphological evidence of neuromuscular junction reorganization in rat oblique abdominal muscles

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.

Estudo anatômico e morfométrico dos vasos que constituem o Polígono de Willis / Anatomical and morphometric study of the vessels that constituing the Circle of Willis

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.

Estudo das junçöes mioneurais de cobaia através das técnicas de esterase inespecífica e azul de metileno / Study of myoneural junctions of guinea-pig through non-specific esterase and methylene blue techniques

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.