RESUMEN
The bones of the mammalian skull respond plastically to changes in masticatory function. However, the extent to which muscle function affects the growth and development of the skull, whose regions have different maturity patterns, remains unclear. Using muscle dissection and 3D landmark-based geometric morphometrics we investigated the effect of changes in muscle function established either before or after weaning, on skull shape and muscle mass in adult mice. We compared temporalis and masseter mass and skull shape in mice with a congenital muscle dystrophy (mdx) and wild type (wt) mice fed on either a hard or a soft diet. We found that dystrophy and diet have distinct effects on the morphology of the skull and the masticatory muscles. Mdx mice show a flattened neurocranium with a more dorsally displaced foramen magnum and an anteriorly placed mandibular condyle compared with wt mice. Compared with hard diet mice, soft diet mice had lower masseter mass and a face with more gracile features as well as labially inclined incisors, suggesting reduced bite strength. Thus, while the early-maturing neurocranium and the posterior portion of the mandible are affected by the congenital dystrophy, the late-maturing face including the anterior part of the mandible responds to dietary differences irrespective of the mdx mutation. Our study confirms a hierarchical, tripartite organisation of the skull (comprising neurocranium, face and mandible) with a modular division based on development and function. Moreover, we provide further experimental evidence that masticatory loading is one of the main environmental stimuli that generate craniofacial variation.
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Dieta , Músculos Masticadores/anatomía & histología , Distrofias Musculares/complicaciones , Cráneo/anatomía & histología , Animales , Fuerza de la Mordida , Masculino , Masticación/fisiología , Ratones , Ratones Endogámicos mdxAsunto(s)
Técnicas de Apoyo para la Decisión , Aparatos Ortodóncicos Fijos , Adolescente , Humanos , PadresRESUMEN
Intestinal microcirculatory disturbances play an important role in the pathophysiology of sepsis. A neural anti-inflammatory pathway has been suggested as a potential target for therapy that may dampen systemic inflammation. The aim of this study is to investigate the effects of physostigmine, a cholinesterase inhibitor, on the intestinal microcirculation and vascular contractility in experimental endotoxemia. Endotoxemia was induced in Lewis rats by intravenous lipopolysaccharide (LPS) administration. Animals were treated with either physostigmine or saline (control) following LPS challenge. The intestinal microcirculation, including leukocyte-endothelial interaction, functional capillary density (FCD) and non-perfused capillary density (NCD), was examined by intravital microscopy (IVM) 2 hours after LPS administration. The impact of physostigmine on vascular contractility of rat aortic rings was examined by in vitro myography. Physostigmine significantly reduced the number of adhering leukocytes in intestinal submucosal venules (V1 venules: -61%, V3 venules: -36%) of LPS animals. FCD was significantly increased by physostigmine treatment (circular muscle layer: +180%, longitudinal muscle layer: +162%, mucosa: +149%). Low concentrations of physostigmine produced significant contraction of aortic ring preparations, whereas high concentrations produced relaxation. In conclusion, physostigmine treatment significantly improved the intestinal microcirculation in experimental endotoxemia by reducing leukocyte adhesion and increasing FCD.
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Inhibidores de la Colinesterasa/uso terapéutico , Endotoxemia/metabolismo , Microcirculación/efectos de los fármacos , Fisostigmina/uso terapéutico , Animales , Inhibidores de la Colinesterasa/administración & dosificación , Modelos Animales de Enfermedad , Endotoxemia/fisiopatología , Masculino , Fisostigmina/administración & dosificación , Ratas , Ratas Endogámicas Lew , SepsisRESUMEN
OBJECTIVE: To determine the lingual surface morphology of central and lateral upper incisors evaluating constant morphological regions for better adhesion of industrial prefabricated lingual brackets. MATERIAL AND METHODS: A total of 102 randomly selected patients at the end of the first phase of second dentition with intact central and lateral upper incisors participated in this study. After impression taking and cast model preparation, 3D laser scans of the lingual surface of the upper central and lateral incisors were taken (Laserscan 3D®, Willytec, Munich, Germany), digitalised, and transferred into CAD software to analyse the surface morphology by superimposition. For better comparison of morphological variations and determination of the most constant lingual regions, the surface was divided into five parts: incisal edge, mesial ridge, lateral ridge, cingulum, and medial sector. Statistical analysis was performed by the paired t-test. RESULTS: Statistically significant differences were found in all surfaces, with cingulum as the most inconstant region. The most constant region was the medial sector and the mesial ridge. CONCLUSION: As expected, the lingual surface underlies a high intra-individual variation complicating industrial prefabricated lingual brackets adhesion. However, the mesial ridge and the medial sector seem to be the most constant regions within intra-individual morphological variations.
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Imagenología Tridimensional/métodos , Incisivo/anatomía & histología , Odontometría/métodos , Lengua/anatomía & histología , Niño , Preescolar , Femenino , Humanos , Masculino , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
INTRODUCTION: Cannabinoid receptor 2 (CB2R) expression is upregulated during sepsis. However, there are conflicting results regarding the effects of CB2R modulation in the hyperinflammatory phase of the disease. The aim of this study was therefore to investigate the effects of CB2R manipulation on leukocyte activation within the intestinal microcirculation in two acute experimental sepsis models. METHODS: In the endotoxemia model we studied four groups of Lewis rats: controls, lipopolysaccharide (LPS), LPS + CB2R agonist HU308 (2.5 mg/kg), and LPS + CB2R antagonist AM630 (2.5 mg/kg). In the colon ascendens stent peritonitis (CASP)-induced sepsis model we also studied four groups: sham group, CASP and CASP + CB2R agonist (HU308, 2.5 or 10 mg/kg). Intravital microscopy was performed 2 hours following LPS/placebo administration or 16 hours following CASP/sham surgery to quantify intestinal leukocyte recruitment. Additionally, hemodynamic monitoring, histological examinations and measurements of inflammatory mediators were performed. RESULTS: HU308 administration significantly reduced intestinal leukocyte adhesion in both acute sepsis models. The systemic levels of inflammatory mediators were significantly reduced by 10 mg/kg HU308 treatment in CASP animals. CONCLUSION: CB2R activation reduces leukocyte activation and systemic release of inflammatory mediators in acute experimental sepsis. Drugs targeting the CB2R pathway may have therapeutic potential in sepsis.
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Mediadores de Inflamación/inmunología , Intestinos/inmunología , Leucocitos/inmunología , Receptores de Cannabinoides/inmunología , Sepsis/inmunología , Análisis de Varianza , Animales , Modelos Animales de Enfermedad , Endotoxemia/inmunología , Intestinos/citología , Masculino , Ratas , Ratas Endogámicas LewRESUMEN
The activity of cytoskeletal proteins like talin, vinculin and nestin increases in muscle that regenerates. Little is known about their role or at least their expression in the process of regeneration in masticatory muscles of mdx mice, a model of Duchenne muscular dystrophy. To determine a potential role of cytoskeletal proteins in the regeneration process of mdx masticatory muscles, we examined the expression of talin 1, talin 2, vinculin and nestin in 100-day-old control and mdx mice using quantitative RT-PCR, Western blot analyses and histochemistry. The protein expression of talin 1, talin 2, nestin and vinculin in mdx muscles remained unchanged as compared with normal mice. However, in mdx masseter it was found a relative increase of nestin compared to controls. The protein expression of talin 1 and vinculin tended to be increased in mdx tongue and talin 2 to diminish in mdx masseter and temporal muscle. In mdx mice, we found significantly lower percentage of transcripts coding for nestin, talin 1, talin 2 and vinculin in masseter (p < 0.05) and temporal muscle (p < 0.001). In contrast, the mRNA expression of nestin was found to be increased in mdx tongue. Activated satellite cells, myoblasts and immature regenerated muscle fibres in mdx masseter and temporal revealed positive staining for nestin. The findings of the presented work suggest dystrophin-lack-associated changes in the expression of cytoskeletal proteins in mdx masticatory muscles could be compensatory for dystrophin absence. The expression of nestin may serve as an indicator for the regeneration in the orofacial muscles.
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Proteínas de Filamentos Intermediarios/metabolismo , Músculos Masticadores/patología , Distrofia Muscular de Duchenne/metabolismo , Mioblastos/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Células Satélite del Músculo Esquelético/metabolismo , Animales , Células Cultivadas , Modelos Animales de Enfermedad , Distrofina/genética , Músculos Faciales/patología , Regulación del Desarrollo de la Expresión Génica/genética , Humanos , Proteínas de Filamentos Intermediarios/genética , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos mdx , Distrofia Muscular de Duchenne/genética , Mutación/genética , Mioblastos/patología , Proteínas del Tejido Nervioso/genética , Nestina , Regeneración , Células Satélite del Músculo Esquelético/patología , Talina/genética , Talina/metabolismo , Vinculina/genética , Vinculina/metabolismoRESUMEN
OBJECTIVE: The administration of glutamine (Gln), which is depleted in critical illness, is associated with an improvement of gut metabolism, structure, and function. The aim of the present study was to evaluate the effects of intravenous Gln and its galenic formulation, l-alanyl-l-glutamine dipeptide (AlaGln), on the intestinal microcirculation during experimental endotoxemia using intravital fluorescence microscopy. Gln or AlaGln administration was performed as pretreatment or post-treatment, respectively. To identify further the underlying mechanisms, amino acid levels were studied. METHODS: Sixty male Lewis rats were randomly divided into six groups (n = 10/group): control, LPS (lipopolysaccharide 5 mg/kg intravenously), Gln/LPS (LPS animals pretreated with Gln 0.75 g/kg Gln intravenously), AlaGln/LPS (LPS animals pretreated with AlaGln intravenously, 0.75 g/kg Gln content), LPS/Gln (LPS animals post-treated with Gln 0.75 g/kg intravenously), and LPS/AlaGln (LPS animals post-treated with AlaGln intravenously, 0.75 g/kg Gln content). Two hours after the endotoxin challenge, the microcirculation of the terminal ileum was studied using intravital fluorescence microscopy. Blood samples were drawn at the beginning, during, and the end of the experiment to determine the amino acid levels. RESULTS: The Gln and AlaGln pre- and post-treatment, respectively, prevented the LPS-induced decrease in the functional capillary density of the intestinal muscular and mucosal layers (P < 0.05). The number of adherent leukocytes in the submucosal venules was significantly attenuated after the Gln and AlaGln pre- and post-treatment (P < 0.05). CONCLUSION: The Gln and AlaGln administrations improved the intestinal microcirculation by increasing the functional capillary density of the intestinal wall and decreasing the submucosal leukocyte activation.
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Dipéptidos/farmacología , Endotoxemia/tratamiento farmacológico , Glutamina/farmacología , Microcirculación/efectos de los fármacos , Animales , Capilares/efectos de los fármacos , Adhesión Celular/efectos de los fármacos , Cromatografía Líquida de Alta Presión/métodos , Íleon/irrigación sanguínea , Íleon/efectos de los fármacos , Íleon/metabolismo , Leucocitos/efectos de los fármacos , Lipopolisacáridos/metabolismo , Masculino , Ratas , Ratas Endogámicas LewRESUMEN
The aim of this study was to investigate the effects of BONITmatrix(®) and OSSA NOVA on the expression of growth factors and osteogenic differentiation. For this purpose, the mRNA expression of VEGF, IGF1, IGF2, collagen-1, collagen-2 and MMP8 was analysed in surgically created defects on the crania of adult male rats. Cranial samples were collected after implantation of BONITmatrix(®) or OSSA NOVA scaffolds for 4 weeks and determinations of gene expression were performed by quantitative RT-PCR. Real-time RT-PCR analyses showed a significantly higher expression of IGF1 in both groups treated with BONITmatrix(®) and OSSA NOVA compared to untreated controls, whereas type I collagen mRNA expression only increased in BONITmatrix(®) treated rats compared to controls. No changes in transcript expression of IGF2, VEGF, collagen-2 and MMP8 were detectable between the analysed groups. In conclusion, BONITmatrix(®) and OSSA NOVA stimulate the expression of growth factor IGF1, but only the granular dosage form is able to stimulate osteoblast differentiation.
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Materiales Biocompatibles , Sustitutos de Huesos , Fosfatos de Calcio/farmacología , Colágeno Tipo I/biosíntesis , Factor I del Crecimiento Similar a la Insulina/biosíntesis , ARN Mensajero/biosíntesis , Dióxido de Silicio/farmacología , Regulación hacia Arriba/efectos de los fármacos , Animales , Diferenciación Celular/efectos de los fármacos , Cadena alfa 1 del Colágeno Tipo I , Colágeno Tipo II/biosíntesis , Factor II del Crecimiento Similar a la Insulina/biosíntesis , Factor II del Crecimiento Similar a la Insulina/genética , Masculino , Metaloproteinasa 8 de la Matriz/biosíntesis , Osteoblastos/efectos de los fármacos , Osteogénesis/efectos de los fármacos , Prótesis e Implantes , ARN Mensajero/genética , Ratas , Reacción en Cadena en Tiempo Real de la Polimerasa , Andamios del Tejido , Factor A de Crecimiento Endotelial Vascular/biosíntesisRESUMEN
UNLABELLED: Adaptive remodelling of the mandibular condyle in response to mandibular advancement is the mechanism exploited by orthodontic forward displacement devices. OBJECTIVE: This work investigated the expression of collagens, matrix metalloproteinases and vascular endothelial growth factor during this process. DESIGN: Twenty juvenile pigs were randomly divided into two experimental groups, where the treatment group was fitted with mandibular advancement splints, and the control group was not. Changes in the mRNA content of condylar cartilage tissue was then were measured by real-time PCR using specific primers after 4weeks of treatment. RESULTS: The temporal pattern of the expression of Col1 and MMP13 during condylar adaptation coincided with that during natural condylar growth. The amount of the expression of Col10 during condylar adaptation was significantly lower (p<0.05), whereas the expression of Col2, MMP8 and VEGF was significantly higher compared to natural growth (p<0.05). CONCLUSIONS: It is suggested that condylar adaptation in growing pigs triggered by mandibular forward positioning results not only from passive adaptation of cartilage, but also involves growth affected processes. Our results showed that mechanical strain produced by mandibular advancement induced remodelling and revascularization in the posteriocranial mandibular condyle. These results are mostly consistent with former published histological and histomorphometrical analyses.
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Remodelación Ósea , Cartílago/metabolismo , Avance Mandibular , Cóndilo Mandibular/metabolismo , Adaptación Fisiológica , Animales , Cartílago/anatomía & histología , Femenino , Expresión Génica , Cóndilo Mandibular/anatomía & histología , Metaloproteinasas de la Matriz/metabolismo , ARN Mensajero/metabolismo , Distribución Aleatoria , Reacción en Cadena en Tiempo Real de la Polimerasa , Estrés Mecánico , Porcinos , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
Over the past decade, coinciding with the appearance of a number of new ultrasonic surgical devices, there has been a marked increase in interest in the use of ultrasound in oral surgery and implantology as alternative osteotomy method. The aim of this study was the comparison of the effect of osteotomies performed using ultrasonic surgery (Piezosurgery(®)), sonic surgery SONICflex(®) and the conventional bur method on the heat generation within the bone underneath the osteotomy and light-microscopy observations of the bone at different cutting positions in porcine mandibular segments. It was found that the average heat generated by SONICflex(®) sonic device was close to that by conventional rotary bur (1.54-2.29°C), whereas Piezosurgery(®) showed a high generated heat up to 18.17°C. Histological investigations of the bone matrix adjacent to the defect radius showed intact osteocytes with all three instruments and similar wide damage diameter at the bottom region. SONICflex(®) showed smooth cutting surfaces with minimal damage in the upper defect zone. Finally, presented results showed that sonic surgery performed with SONICflex(®) is an alternative osteotomy method and can be used as an alternative to the conventional bur method.
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Huesos/anatomía & histología , Electrocirugia/instrumentación , Procedimientos Quirúrgicos Orales/instrumentación , Osteotomía/métodos , Procedimientos Quirúrgicos Ultrasónicos/instrumentación , Animales , Médula Ósea/fisiología , Electrocirugia/métodos , Diseño de Equipo , Calor , Procedimientos Quirúrgicos Orales/métodos , Osteotomía/instrumentación , Piezocirugía , Porcinos , Temperatura , Procedimientos Quirúrgicos Ultrasónicos/métodosRESUMEN
BACKGROUND: Orofacial muscles in mdx mice, a model of Duchenne muscular dystrophy (DMD), undergo muscle necrosis followed by muscle regeneration. The activity of myogenic regulatory factors (MRF) in muscles that regenerate may reveal specific changes. Little is known about the role of MRF, particularly their expression after muscle necrosis in the orofacial muscles of mdx mice and in DMD. Patients suffering from DMD present characteristic malocclusions in association with orofacial dysfunctions. Investigating the role of MRFs in mdx masticatory muscles may help to develop preventive and therapeutic strategies for DMD. MATERIAL AND METHODS: Using Western Blot analysis, we examined the protein expression of MRFs (myogenin and MyoD1) in masticatory muscles such as masseter, temporal, and tongue muscle and one hindlimb muscle, the soleus of control and mdx mice (n = 6-7). The mean optical density (MOD) of proteins was measured for quantification. RESULTS: Myogenin and MyoD1 were detected in mdx and control mice. The amount of myogenin in masseter (MOD, mean ± standard error of the mean (SEM), control vs. mdx: 3.08 ± 0.67 vs. 1.83 ± 0.33), tongue (MOD control vs. mdx: 1.53 ± 0.22 vs. 1.41 ± 0.14), temporal (MOD control vs. mdx: 1.23 ± 0.16 vs. 1.43 ± 0.35), and soleus muscles (MOD, control vs. mdx: 1.95 ± 0.26 vs. 2.31 ± 0.42) did not differ between the mouse strains. MyoD1 amounts in mdx, similar to that of myogenin, remained unchanged when compared to control mice (MOD control vs. mdx: masseter 0.75 ± 0.09 vs. 0.86 ± 0.13; tongue 1.55 ± 0.25 vs. 1.41 ± 0.28; temporal 0.71 ± 0.10 vs. 0.73 ± 0.11; soleus 1.09 ± 0.26 vs. 1.03 ± 0.24). CONCLUSION: The results indicate that protein expression of MyoD1 and myogenin in mdx mice does not differ from controls, suggesting a secondary role of MyoD1 and myogenin in the regeneration stage of mdx orofacial muscles.
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Músculos Masticadores/fisiopatología , Distrofia Muscular de Duchenne/fisiopatología , Proteína MioD/metabolismo , Miogenina/metabolismo , Regeneración/fisiología , Animales , Femenino , Masculino , Ratones , Ratones Endogámicos mdx , Regulación hacia ArribaRESUMEN
Duchenne muscular dystrophy (DMD) and murine X-linked muscular dystrophy (mdx), its murine model, are characterized by muscle damage and muscle weakness associated with inflammation and new vessel formation. Caveolins, dystrophin-associated proteins, are involved in the pathogenesis of DMD, because increased numbers of caveolae are found in DMD and mdx hindlimb muscles. Caveolae influence angiogenesis due to their content of vascular endothelial growth factor (VEGF) receptors. Orofacial muscles in mdx mice undergo muscle necrosis followed by muscle regeneration. To ascertain the role of caveolins and VEGF in the pathogenesis of dystrophic masticatory muscles, we examined the expression of caveolin-1 (cav-1), caveolin-3 (cav-3) and VEGF in control and mdx mice. In mdx masticatory muscles, no changes in transcript and protein levels of VEGF were found, whereas cav-1 and cav-3 expression was increased. Using immunohistochemistry, a strong sarcolemmal staining of caveolin-3 in regenerated muscle fibers was found. Furthermore, immunohistochemistry with the caveolin-1 antibody showed an increase in the amount of blood vessels in areas with regenerating muscle fibers. Dystrophic masticatory muscles showed changes comparable to those of hindlimb muscles in the expression of cav-1 and cav-3. The angiogenesis seems to be unaffected in the jaw muscles of mdx mice. We speculate that the increased caveolin expression could cause extensive and efficient muscle regeneration.
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Caveolina 1/metabolismo , Caveolina 3/metabolismo , Músculos Masticadores/metabolismo , Factor A de Crecimiento Endotelial Vascular/metabolismo , Animales , Caveolina 1/genética , Caveolina 3/genética , Femenino , Regulación de la Expresión Génica , Inmunohistoquímica , Músculos Masticadores/patología , Ratones , Ratones Endogámicos mdx , Transporte de Proteínas , ARN Mensajero/genética , ARN Mensajero/metabolismo , Factor A de Crecimiento Endotelial Vascular/genéticaAsunto(s)
Métodos de Anclaje en Ortodoncia/métodos , Técnicas de Movimiento Dental/métodos , Fenómenos Biomecánicos , Fricción , Humanos , Maloclusión Clase I de Angle/terapia , Maloclusión Clase II de Angle/terapia , Diseño de Aparato Ortodóncico , Soportes Ortodóncicos , Cierre del Espacio Ortodóncico/instrumentación , Alambres para OrtodonciaRESUMEN
The activities of myogenic regulatory factors (MRF) and muscle growth factors increase in muscle that is undergoing regeneration, and may correspond to some specific changes. Little is known about the role of MRFs in masticatory muscles in mdx mice (the model of Duchenne muscular dystrophy) and particularly about their mRNA expression during the process of muscle regeneration. Using Taqman RT-PCR, we examined the mRNA expression of the MRFs myogenin and MyoD1 (myogenic differentiation 1), and of the muscle growth factors myostatin, IGF1 (insulin-like growth factor) and MGF (mechano-growth factor) in the masseter, temporal and tongue masticatory muscles of mdx mice (n = 6 to 10 per group). The myogenin mRNA expression in the mdx masseter and temporal muscle was found to have increased (P < 0.05), whereas the myostatin mRNA expressions in the mdx masseter (P < 0.005) and tongue (P < 0.05) were found to have diminished compared to those for the controls. The IGF and MGF mRNA amounts in the mdx mice remained unchanged. Inside the mdx animal group, gender-related differences in the mRNA expressions were also found. A higher mRNA expression of myogenin and MyoD1 in the mdx massterer and temporal muscles was found in females in comparison to males, and the level of myostatin was higher in the masseter and tongue muscle (P < 0.001 for all comparisons). Similar gender-related differences were also found within the control groups. This study reveals the intermuscular differences in the mRNA expression pattern of myogenin and myostatin in mdx mice. The existence of these differences implies that dystrophinopathy affects the skeletal muscles differentially. The finding of gender-related differences in the mRNA expression of the examined factors may indicate the importance of hormonal influences on muscle regeneration.
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Factor I del Crecimiento Similar a la Insulina/metabolismo , Músculo Esquelético/metabolismo , Distrofia Muscular Animal/metabolismo , Proteína MioD/metabolismo , Miogenina/metabolismo , Animales , Modelos Animales de Enfermedad , Distrofina/deficiencia , Distrofina/genética , Distrofina/metabolismo , Femenino , Factor I del Crecimiento Similar a la Insulina/genética , Masculino , Ratones , Ratones Endogámicos mdx , Distrofia Muscular Animal/patología , Proteína MioD/genética , Miogenina/genética , Miostatina/genética , Miostatina/metabolismo , Factores SexualesRESUMEN
The dystrophin-deficient mouse (mdx) is a homologue animal model of Duchenne muscular dystrophy (DMD) and is characterized by slowly progressive muscle weakness accompanied by changes in myosin heavy chain (MyHC) composition. It is likely that the masticatory muscles undergo similar changes. The aim of this study was to examine the masticatory muscles (masseter, temporal, tongue, and soleus) of 100-day-old mdx and control mice (n = 8-10), and the fibre type distribution (by immunohistochemistry) as well as the expression of the corresponding MyHC messenger RNA (mRNA) (protein and mRNA expression, using Western blot or quantitative real-time polymerase chain reaction (RT-PCR)). Immunohistochemistry and western blot analysis revealed that the masticatory muscles in the control and mdx mice consisted mainly of type 2 fibres, whereas soleus muscle consisted of both type 1 and 2 fibres. In the masseter muscle, the mRNA in mdx mice was not different from that found in the controls. However, the mRNA content of the MyHC-2b isoform in mdx mice was lower in comparison with the controls in the temporal muscle [11.9 versus 36.9 per cent; P < 0.01; mean ± standard error of the mean (SEM), Student's unpaired t-test], as well as in the tongue muscle (65.7 versus 73.8 per cent; P < 0.05). Similarly, the content of MyHC-2x isoforms in mdx tongue muscle was lower than in the controls (25.9 versus 30.8 per cent; P < 0.05). The observed down-regulation of the MyHC-2x and MyHC-2b mRNA in the masticatory muscles of mdx mice may lead to changed fibre type composition. The different MyHC gene expression in mdx mice masticatory muscles may be seen as an adaptive mechanism to muscular dystrophy.