The Pattern of Sensitization Influences Exhaled and Nasal Nitric Oxide Levels in Young Adults.

Nitric oxide (NO) from upper (nasal NO, nNO) or lower airways (fractional exhaled NO, FeNO) is considered a surrogate marker for Th2-type inflammation, which is influenced by atopy. The aim of this study was to analyze nNO and FeNO in regard to qualitative and quantitative aspects of sensitization. We evaluated 244 non-smoking young adults. All of them were first-year students recruited for a longitudinal study. An inhalation allergy screening tool was used for atopy definition (specific immunoglobulin E (sIgE) to sx1 ≥ 0.35 kU/L), and also sIgE response to three inhalant perennial allergens, house dust mite (HDM, d1), cat (e1), and dog (e5), was determined in the non-pollen season. With respect to sx1, 100 subjects could be classified as atopic. Sensitization to one, two, or three perennial allergens could be demonstrated in 46, 10, and 16 students, respectively. The subjects with positive IgE response to sx1, but not sensitized to HDM, cat, and/or dog, had FeNO levels comparable to those of non-atopic subjects (13.5 vs. 13.0 ppb, respectively; p = 0.485). These levels were significantly lower compared to atopic subjects being sensitized to any perennial allergen (19.0 ppb; p = 0.0003). After grouping the atopic subjects for perennial sensitization patterns, significantly higher FeNO could be detected in subjects with poly-sensitization (n = 26; 26.0 ppb) compared to the mono-sensitized ones (n = 46; 18.0 ppb; p = 0.023). Regarding nNO, no differences could be observed. Applying a two-way ANOVA, we could reveal a significant correlation of specific HDM-IgE CAP-class with FeNO (p < 0.0001) and nNO levels (p = 0.007). Finally, a significant relationship was found between nNO and FeNO for the whole cohort (p < 0.0001). In summary, our findings support the argument that atopy and perennial sensitization should be considered for the interpretation of NO.

Muscular and neuromuscular control following soccer-specific exercise in male youth: Changes in injury risk mechanisms.

Poor neuromuscular control has been proposed as a risk factor for non-contact injuries, thus this study aimed to explore the effects of soccer-specific fatigue on leg muscle activation, reactive strength, leg stiffness, and functional hamstring/quadriceps ratio (H/QFUNC ) in elite male youth soccer players. Outcome measures were determined in 18 youth players (age 14.4 ± 0.5 years; stature 169.4 ± 9.9 cm; mass 59.3 ± 8.9 kg; maturity offset 0.86 ± 0.88 years) pre and post simulated soccer match play (SAFT90 ). There was no fatigue-related change in the H/QFUNC ; however, reactive strength and leg stiffness were both compromised (P < 0.001) after soccer-specific fatigue. Muscle activation was also locally compromised (P < 0.001) in the medial hamstring and quadriceps but not in the lateral muscles. Where statistically significant changes were observed, the effect sizes ranged from small to large (0.33-0.97). Compromised stiffness when fatigue is present suggests an increased yielding action, greater ground contact times, greater center of mass displacement, and less efficient movement when the limb comes into contact with the ground. This combined with a reduction in medial quadriceps muscle activation may reflect poor kinetic chain control at the hip and an increase in knee injury risk.

Training-induced changes in physical performance can be achieved without body mass reduction after eight week of strength and injury prevention oriented programme in volleyball female players.

The purpose of the study was to analyse the changes in muscle strength, power, and somatic parameters in elite volleyball players after a specific pre-season training programme aimed at improving jumping and strength performance and injury prevention. Twelve junior female volleyball players participated in an 8-week training programme. Anthropometric characteristics, isokinetic peak torque (PT) single-joint knee flexion (H) and extension (Q) at 60º/s and 180º/s, counter movement jump (CMJ), squat jump (SJ), and reactive strength index (RSI) were measured before and after intervention. Significant moderate effects were found in flexor concentric PT at 60º/s and at 180 º/s in the dominant leg (DL) (18.3±15.1%, likely; 17.8±11.2%, very likely) and in extensor concentric PT at 180º/s (7.4%±7.8%, very likely) in the DL. In the non-dominant leg (NL) significant moderate effects were found in flexor concentric PT at 60º/s and at 180º/s (13.7±11.3%, likely; 13.4±8.0%, very likely) and in extensor concentric PT at 180º/s (10.7±11.5%, very likely). Small to moderate changes were observed for H/QCONV in the DL at 60º/s and 180º/s (15.9±14.1%; 9.6±10.4%, both likely) and in the NL at 60º/s (moderate change, 9.6±11.8%, likely), and small to moderate decreases were detected for H/QFUNC at 180º/s, in both the DL and NL (-7.0±8.3%, likely; -9.5±10.0%, likely). Training-induced changes in jumping performance were trivial (for RSI) to small (for CMJ and SJ). The applied pre-season training programme induced a number of positive changes in physical performance and risk of injury, despite a lack of changes in body mass and composition.

Spectroscopic confirmation of a galaxy at redshift z = 8.6.

Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host galaxies, cleared sightlines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day. Observations of the cosmic microwave background, and of galaxies and quasars at the highest redshifts, suggest that the Universe was reionized through a complex process that was completed about a billion years after the Big Bang, by redshift z ≈ 6. Detecting ionizing Lyman-α photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionization. Here we report the detection of Lyα photons emitted less than 600 million years after the Big Bang. UDFy-38135539 (ref. 5) is at a redshift of z = 8.5549 ± 0.0002, which is greater than those of the previously known most distant objects, at z = 8.2 (refs 6 and 7) and z = 6.96 (ref. 8). We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby.

Effects of Exposure to Welding Fume on Lung Function: Results from the German WELDOX Study.

The association between exposure to welding fume and chronic obstructive pulmonary disease (COPD) has been insufficiently clarified. In this study we assessed the influence of exposure to welding fume on lung function parameters. We investigated forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC, and expiratory flow rates in 219 welders. We measured current exposure to respirable particles and estimated a worker's lifetime exposure considering welding techniques, working conditions and protective measures at current and former workplaces. Multiple regression models were applied to estimate the influence of exposure to welding fume, age, and smoking on lung function. We additionally investigated the duration of working as a welder and the predominant welding technique. The findings were that age- and smoking-adjusted lung function parameters showed no decline with increasing duration, current exposure level, and lifetime exposure to welding fume. However, 15% of the welders had FEV1/FVC below the lower limit of normal, but we could not substantiate the presence of an association with the measures of exposure. Adverse effects of cigarette smoking were confirmed. In conclusion, the study did not support the notion of a possible detrimental effect of exposure to welding fume on lung function in welders.

Myeloid knockout of HIF-1 α does not markedly affect hemorrhage/resuscitation-induced inflammation and hepatic injury.

BACKGROUND: Hypoxia-inducible factor-1 α (HIF-1 α ) and NF- κ B play important roles in the inflammatory response after hemorrhagic shock and resuscitation (H/R). Here, the role of myeloid HIF-1 α in liver hypoxia, injury, and inflammation after H/R with special regard to NF- κ B activation was studied. METHODS: Mice with a conditional HIF-1 α knockout (KO) in myeloid cell-line and wild-type (WT) controls were hemorrhaged for 90 min (30 ± 2 mm Hg) and resuscitated. Controls underwent only surgical procedures. RESULTS: After six hours, H/R enhanced the expression of HIF-1 α -induced genes vascular endothelial growth factor (VEGF) and adrenomedullin (ADM). In KO mice, this was not observed. H/R-induced liver injury in HIF-1 α KO was comparable to WT. Elevated plasma interleukin-6 (IL-6) levels after H/R were not reduced by HIF-1 α KO. Local hepatic hypoxia was not significantly reduced in HIF-1 α KO compared to controls after H/R. H/R-induced NF- κB phosphorylation in liver did not significantly differ between WT and KO. CONCLUSIONS: Here, deleting HIF-1 α in myeloid cells and thereby in Kupffer cells was not protective after H/R. This data indicates that other factors, such as NF- κB, due to its upregulated phosphorylation in WT and KO mice, contrary to HIF-1 α, are rather key modulators of inflammation after H/R in our model.

Potential population growth and harmful effects on humans from bed bug populations exposed to different feeding regimes.

Effects of host availability and feeding period on bed bugs, Cimex lectularius (L.) (Hemiptera: Cimicidae), were measured. Population growth and the potential harmful effect of bed bug populations on human hosts were modelled. Bloodmeal sizes were affected by both feeding length and frequency, with >2-fold difference between insects fed daily or weekly. Blood consumption increased >2-fold between bed bugs fed occasionally and often, and 1.5-fold between occasional and daily feeding. Bed bugs fed more often than once a week, potentially every 2-4 days. Egg production was associated with nutrition, being strongly correlated with blood consumption in the previous week. Bed bug populations can grow under different feeding regimes and are hard to control with <80% mortality. Bed bugs can survive and grow even in locations with a limited blood supply, where bed bug persistence may be important for the continual spread of populations. Persistence in non-traditional locations and a potential association with human pathogens increase the health risks of bed bugs. Potential blood loss as a result of a bed bug can have serious consequences because uncontrolled populations can reach harmful levels in 3-8 months. The reproduction potential of bed bug populations suggests serious consequences to human health and the need for efficacious control measures.

The rapid formation of a large rotating disk galaxy three billion years after the Big Bang.

Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks--the primary components of present-day galaxies--were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger.

New malignancies following cancer of the urinary bladder: analysis of German cancer registry data.

This analysis aimed at occurrence and distribution patterns of new malignancies following bladder cancer. Standardised incidence ratios (SIRs) were calculated for two German population-based cancer registries of North Rhine-Westphalia (NRW) and Saarland to access risks for subsequent primaries. An elevated risk for secondary cancer of any site but urothelium was observed in NRW men [SIR 1.35, 95% confidence interval (CI) 1.22-1.49]. The corresponding risk in Saarland was not significantly elevated (SIR 1.06, 95% CI 0.97-1.15). In data of both registries excess risks were observed for cancer of the respiratory tract (SIR 1.54, CI 1.23-1.89 in NRW men) and the prostate (SIR 1.91, 95% CI 1.61-2.24 in NRW; SIR 1.25, 95% CI 1.07-1.45 in Saarland). Common risk factors and incidental findings during follow-up care of bladder cancer patients might explain most of the observed patterns. In addition SIRs were throughout particular high for subsequent cancer of the renal pelvis and the ureter due to pathological characteristics of urothelial neoplasms.

[Skeletal tuberculosis of the distal radius during pregnancy]. / Ossäre Tuberkulose am distalen Radius in der Schwangerschaft.

We present a case of a pregnant woman (32nd gestational week) that suffered from a chronic non-healing wound at the distal radius. Skeletal tuberculosis was finally diagnosed and treated successfully with staged surgical therapy combined with appropriate medication. One year after surgical treatment, the outcome of the mother was excellent and the baby did not suffer from any disease related to operative procedures or pharmacotherapy. Operative treatment of skeletal tuberculosis (especially osteoarticular and vertebral tuberculosis) in combination with tuberculostatic therapy during pregnancy and lactation seem to be the appropriate treatment with minimal risk for the child and excellent outcome for the mother.

A case study of Megaselia scalaris (Diptera: Phoridae) causing ocular myiasis in a western hognose snake.

Late instar larvae of the scuttle fly, Megaselia scalaris Loew, were found near the right eye of a live captive-reared western hognose snake, Heterodon nasicus Baird and Girard. Dissection and removal of the snake's dorsal cranial bones revealed tissue degradation of the infected eye, the optic nerve, and the brain case; we suggest that these factors contributed to the death of this snake. This case study further demonstrates the opportunistic behavior of M. scalaris.

Control of Cimex lectularius using heat combined with dichlorvos resin strips.

Successful management of the bed bug, Cimex lectularius L. (Hemiptera: Cimicidae), is difficult because of its pesticide resistance, which can allow a reduction in population, but not elimination. We evaluated the effect of heat and/or air circulation on the efficacy of dichlorvos resin strips in the control of bed bugs. Treatments were performed in unoccupied dormitory rooms and consisted of dichlorvos resin strips containing 18.6% active ingredient, the same strips + fan, and strips + fan + heat. The mortality of recently fed bed bugs and weight loss of the dichlorvos strips were evaluated over 7 days. Dichlorvos resin strips killed bed bugs and eggs in just over 7 days. The addition of a fan or a fan + heat decreased time to 100% mortality to 3 days and 36 h, respectively. Eggs located in treated rooms did not hatch. Resin strips in the strips + fan treatment and the strips + fan + heat treatment volatilized 10 and 70 times, respectively, faster than strips in the strips-only treatment. The addition of heat in treatments with dichlorvos resin strips enhances the overall efficacy of the volatile insecticide and reduces the time required to eliminate live bed bugs and eggs.

[Proximal tibial fractures]. / Frakturen der proximalen Tibia.

Only 1-4% of all long bone fractures in children involve the proximal tibia. To evaluate these fractures appropriately, it is mandatory to differentiate between articular fractures and metaphyseal fractures. Articular fractures of the proximal physis are rare and include Salter Harris type III and IV injuries. The reconstruction of the articular surface is the fundamental goal of therapy. Injuries of the anterior crucial ligament which typically appear as an avulsion of the tibial spine and the avulsion fracture of the tibial tubercle apophysis can involve the articular surface. Dislocated fractures should be reduced and stabilized. Extraarticular fractures include Salter Harris type I and II fractures. Other types of metaphyseal fractures are the complete fracture, the compression fracture and the bending fracture of the proximal tibia. Care should be taken while treating bending fractures, especially a valgus deformity must be excluded. Due to unequal growth stimulation during remodelling, a progressive valgus deformity frequently develops. Small deformities in the sagittal plane can be compensated by spontaneous remodelling during further growth. Dislocated fractures should be reduced and stabilized by K-wires. The retention of bending fractures by a compression plate or external fixator for medial compression might be more beneficial.

[Concomitant injuries of distal radius fractures]. / Begleitverletzungen distaler Radiusfrakturen.

BACKGROUND: Following treatment of distal radius fractures poor functional results can still be found despite satisfactory radiological findings. This may be due to concomitant carpal lesions occurring together with these fractures. The aim of this prospective study was to analyze the clinical outcome depending on the type of fracture and concomitant carpal lesions. PATIENTS AND METHODS: A total of 66 patients with distal radius fractures treated over a 1-year period could be assessed. The functional results were compared with the uninjured contralateral side. The follow-up examination included patient history, physical and radiographic examination as well as the DASH (Disability of the arm, shoulder and hand) questionnaire and the modified Mayo wrist score. RESULTS: The average follow-up time was 12.7 months and the mean age of the examined patients was 53 years. The fracture classification according to AO (AO Working party for osteosynthesis questions) showed 32% type A, 10% type B and 58% type C fractures. In 55% a concomitant carpal lesion was found and 44% of the patients required surgical treatment. All fractures united without complications. In all cases X-rays showed no loss of reduction postoperatively. Overall grip strength and wrist motion was reduced to 81% compared to the uninjured side. Patients regained good function represented in a mean DASH score of 24.8 points and a Mayo score of 70.6 points. The number of complete intraarticular fractures (type C) was significantly higher in patients who needed surgical treatment for carpal lesions compared to the groups where concomitant carpal lesions did not require invasive treatment or those where no carpal lesions were found. However, due to the operative treatment a comparable functional result could be obtained in all groups independent of the injury severity. CONCLUSIONS: The results demonstrate, if a correct restoration and surgical stabilization technique is used, clinical outcome following fractures of the distal radius also depends on an optimized management of concomitant carpal lesions.

Unequal synthesis and differential degradation of alpha and beta spectrin during murine erythroid differentiation.

Murine erythroleukemia (MEL) cells represent a valuable system to study the biogenesis of the cytoskeleton during erythroid differentiation. When attached to fibronectin-coated dishes MEL cells induce, upon addition of DMSO, a 7-d differentiation process during which they enucleate and reach the reticulocyte stage (Patel, V. P., and H. F. Lodish. 1987. J. Cell Biol. 105:3105-3118); they accumulate band 3, spectrin, and ankyrin in amounts equivalent to those found in mature red blood cells. To follow the biosynthesis of spectrin during differentiation, membranes and cytoskeletal proteins of cells metabolically labeled with [35S]methionine were solubilized by SDS and alpha and beta spectrins were recovered by specific immunoadsorption. In both uninduced and 3-d induced cells, the relative synthesis of alpha/beta spectrin is approximately 1:3. In uninduced MEL cells newly synthesized alpha and beta spectrins are degraded with a similar half-life of approximately 10 h. In contrast, in 3-d differentiated MEL cells newly made beta spectrin is much more unstable than alpha spectrin; the half-lives of alpha and beta spectrin chains are approximately 22 and 8 h, respectively. Thus, accumulation of equal amounts of alpha and beta spectrin is caused by unequal synthesis and unequal degradation. As judged by Northern blot analyses, the level of actin mRNA is relatively constant throughout the 7-d differentiation period. alpha and beta spectrin mRNAs are barely detectable in uninduced cells, increase during the first 4 d of induction, and remain constant thereafter. In contrast, band 3 mRNA is first detectable on day 4 of differentiation. Thus, most of the spectrin that accumulates in enucleating reticulocytes is synthesized during the last few days of erythropoiesis, concomitant with the onset of band 3 synthesis. To determine whether this was occurring in normal mouse erythropoiesis, we analyzed the rate of appearance of labeled membrane proteins in mature erythrocytes after a single injection of [35S]methionine. Our results show that most of the spectrin and band 3 in mature erythrocytes is synthesized during the last days of bone marrow erythropoiesis, and that, in the marrow, band 3 and protein 4.1 are synthesized at a somewhat later stage of development than are alpha and beta spectrin, ankyrin, and actin.

VIP21, a 21-kD membrane protein is an integral component of trans-Golgi-network-derived transport vesicles.

In simple epithelial cells, apical and basolateral proteins are sorted into separate vesicular carriers before delivery to the appropriate plasma membrane domains. To dissect the putative sorting machinery, we have solubilized Golgi-derived transport vesicles with the detergent CHAPS and shown that an apical marker, influenza haemagglutinin (HA), formed a large complex together with several integral membrane proteins. Remarkably, a similar set of CHAPS-insoluble proteins was found after solubilization of a total cellular membrane fraction. This allowed the cloning of a cDNA encoding one protein of this complex, VIP21 (Vesicular Integral-membrane Protein of 21 kD). The transiently expressed protein appeared on the Golgi-apparatus, the plasma membrane and vesicular structures. We propose that VIP21 is a component of the molecular machinery of vesicular transport.

[Quality of prehospital and early clinical care of pediatric trauma patients of school age compared to an adult cohort. A matched-pair analysis of 624 patients from the DGU trauma registry]. / Prä- und frühklinische Versorgungsqualität pädiatrischer Traumapatienten im Schulalter im Vergleich mit dem Erwachsenenkollektiv. Matched-Pair-Analyse an 624 Patienten aus dem Traumaregister der DGU.

Conflicting reports exist regarding the quality of prehospital treatment of pediatric trauma patients. The purpose of this investigation was to determine whether prehospital treatment and emergency management in pediatric trauma patients were similar to that in adult patients. All patients who had been prospectively documented in the registry of the German Trauma Society (DGU) between 2002 and 2005 were selected for this study. A total of 312 matched pairs of adult and pediatric patients suffering from identical injuries were defined and compared with respect to cause of trauma, diagnostic and therapeutic interventions, and outcome. Within the study group, 63% were male, and the average age was 10.5+/-2.7 (SD) years in the pediatric group and 33.9+/-9.3 years in the adult group. There was no significant difference regarding prehospital intubation, reanimation, fluid management, chest drainage, ground and air transport to the hospital, time to arrival or interval in the emergency room. In contrast, significant differences (p<0.05) were observed in terms of the cause of trauma and pre-existing diseases. Pediatric trauma patients were not triaged or treated differently from adult trauma patients in respect to key issues of prehospital and early clinical trauma management.

[Epidemiology of prostate cancer: recent results from the Epidemiological Cancer Register of the District of Münster (Germany)]. / Aktuelle Daten zur Epidemiologie des Prostatakarzinoms : Ergebnisse aus dem Regierungsbezirk Münster.

BACKGROUND: Prostate cancer is characterized by worldwide increasing incidence rates, improved survival, and decreasing mortality. We investigated the current situation in the Epidemiological Cancer Register of the District of Münster, Germany (which has approximately 1.25 million male inhabitants). MATERIALS AND METHODS: We calculated the incidence and mortality rates, stage distribution, and relative survival rates for prostate cancer between the years 2002 and 2004. RESULTS: The age-standardized incidence rate was 115/100,000 men per year, and the median age at diagnosis was 70 years. The tumour stage was T1/T2 in 69.6% of cases. The estimated relative survival after 5 years was 83.5% (95% confidence interval 81.4-85.4) and after 10 years was 73.3% (69.5-77.0). Survival was barely affected when the tumour was limited to the prostate (UICC I-II), whereas survival rates were markedly reduced when the tumour had spread or had infiltrated adjacent structures (UICC IV; relative 10-year survival rate 22.1%). CONCLUSIONS: The majority of patients with prostate cancer now have a favourable prognosis. Increased incidence rates must be interpreted in the context of widespread use of prostate-specific antigen testing.

Expression of p21(Wafl/Cip1), p57(Kip2) and HER2/neu in patients with gallbladder cancer.

BACKGROUND: To improve the prognosis of gallbladder cancer (GC) patients, a better understanding of the mechanisms of tumor development and progression is essential. The deregulation of cell cycle control is a critical step in the development of cancer. The purpose of this study was to investigate the expression of p21(Wafl/Cip1), p57(Kip2) and HER2/neu in an unselected GC patient population and to assess the association of these markers with p27(Kip1) expression, p53 gene mutation status and clinical parameters of the patients. PATIENTS AND METHODS: Formalin-fixed paraffin-embedded tissues from 55 operated GC patients were used to determine the expression of p21(Wafl/Cip1), p57(Kip2) and HER2/neu with immunohistochemistry. RESULTS: Expression of p21(Wafl/Cip1) was observed in 28%, of p57(Kip2) in 19% and of HER2/neu in 13% of the patients. Absence of p57(Kip2) expression was significantly associated with T3/T4 stage (p = 0.01), positive lymph nodes (p = 0.02) and advanced UICC stages (p = 0.05). HER2/neu expression significantly correlated with advanced T stages (p = 0.02). In the total patient population, p21(Wafl/Cip1), p57(Kip2) and HER2/neu had no impact on survival of the patients. Among patients with a mutated p53 gene, those without p21(Wafl/Cip1) expression had a prolonged survival compared to patients with p21(Wafl/Cip1) expression (p = 0.004). Moreover, in p27(Kip1)-positive patients, those without p21(Wafl/Cip1) expression had a longer survival than those with p21(Wafl/Cip1) expression (p = 0.003). CONCLUSION: In the subgroup of patients with a mutated p53 gene or in p27(Kip1)-positive patients, absence of p21(Wafl/Cip1) expression may be associated with longer survival of GC patients. Therefore, further analyses of this protein in larger patient populations are warranted.

The histochemical profile of the rat extensor digitorum longus muscle differentiates after birth and dedifferentiates in senescence.

Age dependent motor unit dedifferentiation is a key component of impaired muscle function in advanced age. Here, we tested the hypothesis that rat muscle histochemical profile during the lifespan of an individual has an age-specific pattern since comprehensive longitudinal studies of muscle differentiation after birth and dedifferentiation in advanced age are scarce. Our results show that extensor digitorum longus muscle (EDL) is comprised only of two fiber types after birth, type slow-oxidative (SO) and type SDH-intermediate (SDH-INT), the latter being indicative for the presence of polyneuronal innervation. In contrast to the constantly growing cross-sectional area of the muscle fibers, a dramatic decrease in SDH-INT proportion occurs between day 14 and 21 after birth resulting in a complete loss of fiber type SDH-INT at the age of 90 days (p<0.05). At the age of 270 days, the fiber type composition of rat EDL dedifferentiates as shown by the reappearance of the SDH-INT type with a further increase at the age of 540 days (p<0.05). These changes in histochemical fiber type spectra are brought about by fiber type conversion within the fast twich fibers. The findings of the present study provide further evidence that fiber type conversion is a basic mechanism leading to motor unit differentiation and dedifferentiation during ontogenesis. Fiber type conversion shows a distinct time specific pattern and is also characteristic for motor unit regeneration after peripheral nerve repair. Factors that influence fiber type conversion and thereby motor unit organization may provide a future therapeutic option to enhance the regenerative capacity of motor units.