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During mammalian skeletal muscle development, muscle fibres form in a biphasic manner from the fusion of myoblasts. Primary fibres form first, which subsequently provide a surface for later secondary fibres to form on. The purpose of the present study was to successfully develop new and existing techniques and to employ them in order to study the commitment and behaviour of myoblasts during muscle development in mice. Following part 1; a general introduction into the development of skeletal muscle, the thesis is divided into two subsequent parts giving details of the investigations performed. In the main section (part 2) of this thesis, I investigated the commitment of myoblasts during the foetal development. It has been suggested, that separate populations of myoblasts are present, each committed to producing the different fibre types seen during development. The aim of this study was to see if different populations produced primary and secondary fibres, by seeing if clones of related cells were restricted to fusing with a single type of fibre. Following the injection of replication deficient retroviruses into the hindlimbs of Embryonic day (E)15 and El 7 foetal mice, cells became marked with the lac Z gene encoding for the enzyme [Special character omitted]-galactosidase. The infected cells, their descendants and the fibres they fused with could then be demonstrated histochemically. 83% of the clusters of marked fibres obtained following processing were found to contain both primary and secondary fibres as identified by electron microscopy. The clusters were assumed to be the result of the fusion of a single clone of cells. It was concluded that at these ages, a single population of cells contributes to primary and secondary fibres. Part 3 of the thesis describes a second, shorter study whereby the in vitro behaviour of El 7, El 9 and E21 myoblasts was investigated on artificial grooved substrata. Most cells on grooves with depths of 250nm-6um were found to align parallel with the direction of the grooves. Cells on the shallower grooves (40-140nm) either aligned parallel or perpendicular to the grooves. E21 cells however, orientated randomly on these groove sizes. It was generally concluded however, that myoblasts at the ages studied do align in grooves similar to those formed in vivo by adjacent primary and secondary fibres. It is suggested that grooves such as the ones mentioned may be a possible site for secondary myogenesis. The results of both my studies contribute to the current work being carried out on skeletal muscle development, and may also, in addition, provide useful information towards the development of myoblast transfer therapy, a possible treatment for Duchenne Muscular Dystrophy sufferers.

A Doença Periodontal (DP) tem sido indicada como um possível fator de risco para várias condições sistêmicas. Uma inflamação sistêmica de baixa intensidade originada a partir da DP tem sido a explicação para as associações observadas. A performance físicoatlética dos indivíduos e os mecanismos de desenvolvimento da Fadiga Muscular (FM) também têm sido estudados, inclusive tem se questionado se a condição de saúde bucal pode ser um fator de risco à redução da capacidade física dos indivíduos. O objetivo do presente estudo observacional foi verificar a associação entre DP e FM induzida pelo exercício em homens saudáveis. Foram avaliados 43 participantes, com idade entre 25 e 45 anos, oriundos da faculdade de odontologia e praticantes de atividades físicas. Exame periodontal completo e entrevista foram realizados no exame basal. Um questionário estruturado foi aplicado, medidas antropométricas, exames clínicos da condição periodontal e informações sobre a prática de atividade física por meio do International Physical Activity Questionnaire (IPAQ) foram obtidas. A seguir, os participantes foram submetidos a um protocolo de exercícios excêntricos para indução de FM e a Contração Isométrica Voluntária Máxima (CIVM) foi avaliada antes e imediatamente após a realização do protocolo A perda da capacidade de produção de força, calculada pela variação relativa da CIVM, foi o que caracterizou a FM e foi o desfecho deste estudo. Associações entre a condição periodontal e os parâmetros envolvidos na FM foram avaliados através de modelos de regressão linear múltipla com variância robusta, ajustando para índice de massa corporal, atividade física regular e fonte da amostra. Na totalidade da amostra, após o protocolo de FM, os participantes tiveram uma perda de 27,8% na capacidade de produção de força. Aqueles indivíduos com perda de inserção periodontal (PI) ≥4mm tiveram CIVM significativamente menor ao final do protocolo. Nos modelos de regressão linear multivariados, profundidade de sondagem (PS) (beta=- 10,32) e PI (beta=-3,53) médias estiveram associadas a uma redução significativamente maior na CIVM. Análises estratificadas para IPAQ (categorização de atividade física regular) encontraram associação entre parâmetros periodontais e CIVM somente entre os participantes com IPAQ baixo-médio, mostrando um possível efeito protetor da prática de atividade física sobre o efeito da DP na perda da capacidade de produção de força. Pode-se concluir, a partir dessa análise preliminar, que a doença periodontal pode vir a ser um indicador de risco para a FM. / Periodontal disease (PD) has been indicated as a possible risk factor for several systemic conditions. A low-intensity systemic inflammation originated from PD has been the explanation for the observed associations. The physical-athletic performance of individuals and the mechanisms of Muscle Fatigue (MF) development have also been studied, and there are doubts of whether the oral health condition may be a risk factor for the reduction in physical capacity and performance. The aim of this observational study was to evaluate the association between PD and exercise-induced MF in healthy men. The sample comprised 43 participants between 25-45 years of age sampled among patients from the Faculty of Dentistry of UFRGS and physically active subjects from different physical fitness centers of Porto Alegre. They were submitted to a protocol of eccentric exercises for induction of MF and the Maximum Voluntary Isometric Contraction (MVIC) was evaluated before and immediately after the fatigue protocol. The reduction of the strength production capacity was calculated by the relative variation of the MIVC, and this characterized MF in this study A structured questionnaire was applied, and anthropometric measurements, clinical examination of periodontal status and information about physical activity (through the IPAQ questionnaire) were performed. Associations between the periodontal condition and the parameters involved in MF were evaluated through multiple linear regression models adjusting for body mass index, physical activity and source of the sample. In the whole sample, participants had a loss of 27.8% in the capacity of force production after the MF protocol. Individuals with clinical attachment loss (CAL) ≥4 mm had significantly lower MVIC at the end of the protocol. In the multiple linear regression models, mean probing depth (beta = -10.32) and CAL (beta = -3.53) were associated with a significantly higher reduction in MVIC. Stratified analyzes for IPAQ found an association between periodontal parameters and MVIC only in participants with low-medium IPAQ, showing a possible protective effect of physical activity in the loss of strength production ability related to PD. It may be concluded from these preliminary findings that PD could be a risk indicator for MF.

Abstract not available

The goals of this research were to a) characterize the protein-function relationships of skeletal muscle single fibers from the mouse hindlimb b) examine mouse-strain related differences in myosin heavy chain composition (MHC) and single fiber contractile function, and c) quantify changes in fiber size and contractile function in response to 7 days of non-weight bearing. This research is significant because mechanistic approaches to understanding relationships between muscle protein expression, contractile function, and mechanical loading will likely benefit from a transition from the traditional laboratory rat to genetically modified mouse models. The methods used in this research feature an in vitro skinned-fiber preparation and single-fiber gel electrophoresis. Hindlimb muscles of mice were excised, and dissected into smaller bundles from which single muscle fibers were isolated. Single fibers were placed in skinning solution that permeabilized the fiber's membrane. The ends of skinned single muscle segments were attached to stainless steel troughs, which were connected to an isometric force transducer and a direct-current position motor. This system allowed the measurement of the fiber's cross-sectional area (CSA), peak isometric force (P���), and unloaded maximal shortening velocity (V���) during maximal Ca�����-activating. The identification of the fiber's MHC content was subsequently achieved by electrophoresis of a sample of each fiber segment. The results showed that the C57BL/6 mouse soleus muscle contains a MHC composition (20% type I) that is dramatically different than the ICR and CBA/J mouse strains (50% type I, respectively). Type I fibers from the C57BL/6 mouse had V��� that was 25% lower than type I fibers from ICR and CBA/J mice. Following 7 days of hindlimb suspension (HS) all strains experienced significant soleus muscle and single-fiber atrophy and decreases in the absolute and specific (force/fiber CSA) of type I and II fibers. However, type I fibers from C57BL/6 mice showed no change in V��� whereas type I fibers from ICR and CBA/J showed increased V���. In conclusion, this research demonstrates that unlike the rat and human models of non-weight bearing, mouse soleus type I and II fibers are equally affected by HS with respect to decreases in fiber CSA and force. However, type I fiber V��� was elevated only in mouse strains with solei containing at least 50% type I MHC. These findings challenge the current view that non-weight bearing affects slow fibers more than fast fibers, and suggests that changes in single fiber contractile function with HS may be influenced in part by the MHC distribution of the muscle. / Graduation date: 2003

Thesis (M.S.Ed.)--Baylor University, 2005. / Includes bibliographical references (p. 46-50).

No description available.