No Evidence of Sensory Neuropathy in a Traditional Mouse Model of Idiopathic Parkinson's Disease.

Parkinson's disease (PD) is the second-most common neurodegenerative disorder worldwide and is diagnosed based on motor impairments. Non-motor symptoms are also well-recognised in this disorder, and peripheral neuropathy is a frequent but poorly appreciated non-motor sign. Studying how central and peripheral sensory systems are affected can contribute to the development of targeted therapies and deepen our understanding of the pathophysiology of PD. Although the cause of sporadic PD is unknown, chronic exposure to the pesticide rotenone in humans increases the risk of developing the disease. Here, we aimed to investigate whether peripheral neuropathy is present in a traditional model of PD. Mice receiving intrastriatal rotenone showed greatly reduced dopamine terminals in the striatum and a reduction in tyrosine hydroxylase-positive neurons in the Substantia nigra pars compacta and developed progressive motor impairments in hindlimb stepping and rotarod but no change in spontaneous activity. Interestingly, repeated testing using gold-standard protocols showed no change in gut motility, a well-known non-motor symptom of PD. Importantly, we did not observe any change in heat, cold, or touch sensitivity, again based upon repeated testing with well-validated protocols that were statistically well powered. Therefore, this traditional model fails to replicate PD, and our data again reiterate the importance of the periphery to the disorder.

The expression pattern of endometrial receptivity genes is desynchronized between endometrium and matched endometriomas.

RESEARCH QUESTION: Are paired samples of endometrium and ovarian endometriomas synchronous with each other throughout the menstrual cycle? DESIGN: The expression levels of 57 endometrial receptivity-associated genes were determined from matched endometrial and endometrioma samples (n=31) collected from women with endometriosis throughout the menstrual cycle. RESULTS: The expression profile of endometrial receptivity genes divided endometrial samples according to their menstrual cycle phase. Endometrioma samples grouped together irrespective of the menstrual cycle phase and formed a cluster distinct from endometrial samples. Pairwise comparison showed 21, 16, 33 and 23 differentially expressed genes (adjusted P < 0.001-0.05) between the lesions and endometria collected in the proliferative, early-secretory, mid-secretory and late-secretory menstrual cycle phases, respectively, confirming the distinct expression profiles of endometrium and endometrioma. CONCLUSIONS: No menstrual cycle synchronicity was found between matched eutopic and ectopic endometrium, suggesting that the concept of cycling endometrial tissue inside the endometrioma should be revised.

Expression of immune checkpoint PD-1 in non-small cell lung cancer is associated with tumor cell DNA-dependent protein kinase.

Immunotherapy using immune checkpoint inhibitors has demonstrated durable responses and has significantly improved survival in patients with non-small cell lung cancer (NSCLC). Moreover, immunotherapy is increasingly used in combination with cytotoxic treatments such as chemotherapy and radiotherapy. Although the combined treatments are more effective, the underling mechanisms that lead to higher antitumor activity are not fully understood. Therefore, the aim of the current retrospective study was to determine the relationship between expression of immune checkpoints [programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1)] and the enzyme DNA-dependent protein kinase (DNA-PK), which is part of a key pathway involved in the repair of cytotoxic cancer therapy induced damage. Surgically excised NSCLC tissues (n=121) were histologically examined for overall extent of inflammation (score 0-3). Expression levels of PD-1 (number of PD-1 positive cells), PD-L1 [tumor proportion score (TPS); %] and DNA-PK (proportion of DNA-PK positive tumor cells; %) were determined using immunohistochemistry. Expressions of these markers were compared in different clinicopathological subgroups and later used for nonparametric Spearman correlation analysis to determine associations. In patients with NSCLC, PD-1 was significantly expressed in males (P=0.030) and in patients with no or trivial inflammation scores (P=0.030). PD-L1 expression was also significantly higher in current smokers (P=0.025). Correlation analysis was based on the individual values of patients and revealed a significant association between one of the targets of immune checkpoint inhibitors and tumor cell DNA-PK. Tumors with higher numbers of PD-1 positive cells also demonstrated higher tumor cell DNA-PK expressions (P=0.027). The results demonstrated a significant positive correlation between the PD-1/PD-L1 axis and tumor cell DNA-PK expression in patients with NSCLC. Further studies are required to clarify the significance of this correlation and its effect on the efficacy of immunotherapy and cytotoxic cancer therapy combinations.

Diagnostic significance of stromal changes in biopsies of prostate adenocarcinoma.

The diagnostic value of stromal changes in carcinomas, including prostate, is under debate; in terms of limited sample tissue of biopsy, in addition to glandular alterations, the stromal changes could have additional diagnostic value, but the results in clinical settings are controversial. The research aims to evaluate the potential of stromal changes as a supplementary tool to predict the presence of higher grade carcinomas in the prostate using Masson's trichrome and Fanconi anemia complementation group M (FANCM) antibody stainings. 385 biopsies and corresponding radical prostatectomy specimens were analyzed to evaluate the rates of the diversity of ISUP grades. Of 128 upgraded prostatectomy cases, 82 were diagnosed with ISUP Gleason Grade 1 (GG1) in a biopsy. All 82 cancerous samples were stained with Masson's trichrome and FACNM antibody and compared with 82 samples without cancer to see if there was a difference in stromal composition. Additionally, 50 GG1 samples without the upgrade were stained to demonstrate if stromal changes can predict less differentiated carcinomas in the prostate. In FANCM stained samples, the average percentage of positively staining stroma over the total in non-upgraded GG1 biopsies was 36 % (13-59 %, SD = 11); 34 % (9-58, SD = 13) in samples from the upgraded cancerous group, and 44 % (22-69, SD = 11) in samples without cancer. In Masson's trichrome stained samples, with collagen quantified, the percentage in non-upgraded GG1 biopsies was 41 % (20-78 %, SD = 11); 44 % (23-89, SD = 15) in samples from upgraded cancerous group and 37 % (15-57, SD = 9) in samples without cancer. In both FANCM and Masson's trichrome, no statistical significance was found between upgraded and non-upgraded groups (p = 0.84 and p = 0.5, respectively), although some upgrades from GG1 to GG4 showed extreme values. The statistical significance was found in cancerous vs. benign samples with both FANCM (p < 0.01) and Masson's trichrome (p = 0.012). The main limiting factor is a significant overlap in staining intensity between cancerous and cancer-free groups.

Pathadin - The essential set of tools to start with whole slide analysis.

Pathadin (https://gitlab.com/Digipathology/Pathadin) was designed as a WSI oriented open-source set of tools for beginners to experience the advantages of computer-assisted image analysis and cover essential features, frequently strenuous to access with the alternative programs. It is mainly oriented to work with histology slides but also includes a significant part of modern image formats. Introducing Pathadin, the manuscript aims to improve understanding of contemporary image analysis components, resolve technophobia and misbeliefs in the computational field, simplifying pathology research work, and shifting it into a quantitative paradigm. Despite being easy to use, Pathadin includes both basic and advanced analytical algorithms, as the application of machine learning. The functionality of Pathadin is demonstrated by AI-enhanced quantification of epithelial and stromal changes in prostate carcinoma, and their dependence on ISUP grade. The material included 5 radical prostatectomy samples for training and 83 (including 11 autopsies) samples for analysis. The analytical material was stained with Masson's trichrome and Ki67, as widely available and potentially prognostic markers. An integrated solution by HistomicsTK for Ki67 evaluation was used. A U-net model for separating glands and stroma was trained, simplifying the independent analysis of these components. During the process, the model successfully highlighted glands and stroma. Masson's trichrome stain demonstrated a gradual increase in collagen expression, being statistically significant between controls vs. G1, and G3 vs. G4. Although there was considerable overlap between adjacent groups, there was only a minor overlap in collagen amount between high- and low-grade carcinomas, affirming that with further research, stroma could be an additional diagnostic marker in prostate adenocarcinoma. Ki67 showed a statistically significant gradual increase in all groups except G1 vs. G2 and G4 vs. G5. Pathadin demonstrates that there is no need for significant resources to experience the advantages of modern computer-assisted analysis.

The decline of FANCM immunohistochemical expression in prostate cancer stroma correlates with the grade group.

Prostate adenocarcinoma (PCa) stromal markers have recently gained attention as complementary diagnostic tools. The DNA reparation complex protein FANCM has been shown to express in the normal prostate stroma and FANCM gene alterations to be associated with PCa susceptibility; this has led to the hypothesis that an insufficient level of FANCM expression may provide additional information for the evaluation of PCa. The study cohort comprised 60 radical prostatectomy specimens. The controls involved 11 autopsies (CTRL) and non-cancerous tissue (NCT) areas from the prostatectomy specimen. The samples were stained with the FANCM antibody. The quantification of the stromal staining index (SSI) was made using ImageJ and QuPath. Overall, 655 regions of interest (ROI) were analyzed. FANCM expression appeared equally intense and stroma specific in both CTRL and NCT, indicating the absence of underlying baseline alterations. Within the age span of the cohort 47-89 years, no significant effect of the age of the patients on the FANCM expression was seen. FANCM demonstrated Gleason grade (G) dependent decline in PCa, being statistically significant in controls versus G1 and G2 versus G3. In other adjacent International Society of Urological Pathology (ISUP) groups, it remained insignificant, still being meaningful between high and low-grade cancers.

Bi-allelic Recessive Loss-of-Function Variants in FANCM Cause Non-obstructive Azoospermia.

Infertility affects around 7% of men worldwide. Idiopathic non-obstructive azoospermia (NOA) is defined as the absence of spermatozoa in the ejaculate due to failed spermatogenesis. There is a high probability that NOA is caused by rare genetic defects. In this study, whole-exome sequencing (WES) was applied to two Estonian brothers diagnosed with NOA and Sertoli cell-only syndrome (SCOS). Compound heterozygous loss-of-function (LoF) variants in FANCM (Fanconi anemia complementation group M) were detected as the most likely cause for their condition. A rare maternally inherited frameshift variant p.Gln498Thrfs∗7 (rs761250416) and a previously undescribed splicing variant (c.4387-10A>G) derived from the father introduce a premature STOP codon leading to a truncated protein. FANCM exhibits enhanced testicular expression. In control subjects, immunohistochemical staining localized FANCM to the Sertoli and spermatogenic cells of seminiferous tubules with increasing intensity through germ cell development. This is consistent with its role in maintaining genomic stability in meiosis and mitosis. In the individual with SCOS carrying bi-allelic FANCM LoF variants, none or only faint expression was detected in the Sertoli cells. As further evidence, we detected two additional NOA-affected case subjects with independent FANCM homozygous nonsense variants, one from Estonia (p.Gln1701∗; rs147021911) and another from Portugal (p.Arg1931∗; rs144567652). The study convincingly demonstrates that bi-allelic recessive LoF variants in FANCM cause azoospermia. FANCM pathogenic variants have also been linked with doubled risk of familial breast and ovarian cancer, providing an example mechanism for the association between infertility and cancer risk, supported by published data on Fancm mutant mouse models.

Impact of Blood Vessel Quantity and Vascular Expression of CD133 and ICAM-1 on Survival of Glioblastoma Patients.

Glioblastoma (GB) is the most angiogenic tumor. Nevertheless, antiangiogenic therapy has not shown significant clinical efficacy. The aim of this study was to assess blood vessel characteristics on survival of GB patients. Surgically excised GB tissues were histologically examined for overall proportion of glomeruloid microvascular proliferation (MP) and the total number of blood vessels. Also, immunohistochemical vascular staining intensities of CD133 and ICAM-1 were determined. Vessel parameters were correlated with patients' overall survival. The survival time depended on the number of blood vessels (p = 0.03) but not on the proportion of MP. Median survival times for patients with low (

The alterations in the extracellular matrix composition guide the repair of damaged liver tissue.

While the cellular mechanisms of liver regeneration have been thoroughly studied, the role of extracellular matrix (ECM) in liver regeneration is still poorly understood. We utilized a proteomics-based approach to identify the shifts in ECM composition after CCl4 or DDC treatment and studied their effect on the proliferation of liver cells by combining biophysical and cell culture methods. We identified notable alterations in the ECM structural components (eg collagens I, IV, V, fibronectin, elastin) as well as in non-structural proteins (eg olfactomedin-4, thrombospondin-4, armadillo repeat-containing x-linked protein 2 (Armcx2)). Comparable alterations in ECM composition were seen in damaged human livers. The increase in collagen content and decrease in elastic fibers resulted in rearrangement and increased stiffness of damaged liver ECM. Interestingly, the alterations in ECM components were nonhomogenous and differed between periportal and pericentral areas and thus our experiments demonstrated the differential ability of selected ECM components to regulate the proliferation of hepatocytes and biliary cells. We define for the first time the alterations in the ECM composition of livers recovering from damage and present functional evidence for a coordinated ECM remodelling that ensures an efficient restoration of liver tissue.

Impact of tumor infiltrating CD63 positive cells on survival in patients with glioblastoma multiforme.

BACKGROUND: Glioblastoma multiforme (GBM) is the most aggressive type of brain cancer in adults. It is suggested that tumour microenvironment might influence treatment outcome. The aim of the study was to evaluate the impact of tumor infiltrating CD63 positive (CD63+) inflammatory and immune cells on treatment response and survival of GBM patients. METHODS: Forty patients were operated and received postoperative radiotherapy (±chemotherapy for recurrent disease). In surgically excised GBM tissues, the number of CD63+ cells per microscopic field was determined and correlated with patient's survival. RESULTS: Immunohistochemical parameters were examined by two independent researchers whose results were in good accordance (R=0.8, P<0.001). Median survival time of the study group was 10.0 months (95% CI 9.0-11.0). However, the survival time clearly depended on the number of CD63+ cells in GBM tissue (log rank test, P=0.003). Median survival times for patients with low (

VEGFR-2 Expression in Glioblastoma Multiforme Depends on Inflammatory Tumor Microenvironment.

Glioblastoma multiforme (GBM) is one of the most angiogenic tumors. However, antiangiogenic therapy has not shown significant clinical efficacy. The aim of our study was to evaluate the impact of inflammatory tumor microenvironment on the expression of vascular endothelial growth factor receptor 2 (VEGFR-2). Surgically excised primary GBM tissues were histologically examined for overall extent of inflammation (score 1-3). After immunohistochemistry, the tissue expression of ICAM-1 (optical density), the number of VEGFR-2 positive (VEGFR-2+) blood vessels (per microscopic field), and the endothelial staining intensity of VEGFR-2 (score 0-3) were determined. In GBM, the extent of inflammation was 1.9 ± 0.7 (group mean ± SD). Mean optical density of inflammatory mediator ICAM-1 was 57.0 ± 27.1 (pixel values). The number of VEGFR-2+ blood vessels and endothelial VEGFR-2 staining intensity were 6.2 ± 2.4 and 1.2 ± 0.8, respectively. A positive association was found between endothelial VEGFR-2 staining intensity and the extent of inflammation (p = 0.005). Moreover, VEGFR-2 staining intensity correlated with the expression level of ICAM-1 (p = 0.026). The expression of VEGFR-2, one of the main targets of antiangiogenic therapy, depends on GBM microenvironment. Higher endothelial VEGFR-2 levels were seen in the presence of more pronounced inflammation. Target dependence on inflammatory tumor microenvironment has to be taken into consideration when treatment approaches that block VEGFR-2 signaling are designed.

Impact of CD133 positive stem cell proportion on survival in patients with glioblastoma multiforme.

BACKGROUND: The aim of the study was to assess the impact of CD133-positive (CD133+) cancer stem cell proportions on treatment results of glioblastoma multiforme (GBM) patients. PATIENTS AND METHODS: Patients with GBM (n = 42) received postoperative radiotherapy (± chemotherapy). Surgically excised GBM tissue sections were immunohistochemically examined for CD133 expression. The proportions of CD133+ GBM cells were determined (%). The proportion of CD133+ GBM stem cells was established by 2 independent researchers whose results were in good accordance (R = 0.8, p < 0.01). Additionally, CD133 expression levels were correlated with patients overall survival. RESULTS: The proportion of CD133+ cells varied between patients, being from 0.5% to 82%. Mean and median proportions of CD133+ cells of the entire study group were 33% ± 24% (mean ± SD) and 28%, respectively. Clinical data do not support the association between higher proportion of stem cells and the aggressiveness of GBM. Median survival time of the study group was 10.0 months (95% CI 9.0-11.0). The survival time clearly depended on the proportion of CD133+ cells (log rank test, p = 0.02). Median survival times for patients with low (< median) and high (≥ median) proportion of CD133+ cells were 9.0 months (95% CI 7.6-10.5) and 12.0 months (95% CI 9.3-14.7), respectively. In multivariate analysis, the proportion of CD133+ cells emerged as a significant independent predictor for longer overall survival (HR 2.0, 95% CI 1.0-3.8, p = 0.04). CONCLUSIONS: In patients with higher stem cell proportion, significantly longer survival times after postoperative radiotherapy were achieved. Underlying reasons and possible higher sensitivity of GBM stem cells to fractionated radio-therapy should be clarified in further studies.

Relationship between neovascularization and degenerative changes in herniated lumbar intervertebral discs.

PURPOSE: Lumbar disc degeneration may be associated with intensity of neovascularization in disc herniations. Our study was designed to evaluate how much the severity of histodegeneration is related to the development of neovascularization and to the level of pleiotrophin in the herniated lumbar discs. METHODS: Surgically excised lumbar disc specimens were obtained from 29 patients with noncontained (i.e., extruding through the posterior longitudinal ligament) and 21 patients with contained disc herniations. The histodegeneration scores and levels of neovascularization were estimated according to semiquantitative analysis in lumbar disc and endplate samples. Immunohistochemical staining were performed to identify the newly formed blood vessels and to detect the presence of pleiotrophin in the specimens. RESULTS: Higher levels of disc and endplate neovascularity were registered in noncontained herniations. The level of neovascularization was significantly related to the score of histodegeneration in the herniated disc tissues but not in the endplate specimens. Both contained and noncontained herniations had the highest values of histodegeneration in conjunction with the highest level of neovascularization but the relations between neovascularity and degenerative changes remained to be significant only in the group of noncontained herniations. Registration or frequency of pleiotrophin positive cells did not correlate significantly with histodegeneration or level of neovascularization in the disc samples. CONCLUSION: Severe histodegeneration of the lumbar disc herniations is associated with enhanced neovascularization and potentially also spontaneous regression of the herniated tissue.

Mid-gestational gene expression profile in placenta and link to pregnancy complications.

Despite the importance of placenta in mediating rapid physiological changes in pregnancy, data on temporal dynamics of placental gene expression are limited. We completed the first transcriptome profiling of human placental gene expression dynamics (GeneChips, Affymetrix®; ~47,000 transcripts) from early to mid-gestation (n = 10; gestational weeks 5-18) and report 154 genes with significant transcriptional changes (ANOVA, FDR P<0.1). TaqMan RT-qPCR analysis (n = 43; gestational weeks 5-41) confirmed a significant (ANOVA and t-test, FDR P<0.05) mid-gestational peak of placental gene expression for BMP5, CCNG2, CDH11, FST, GATM, GPR183, ITGBL1, PLAGL1, SLC16A10 and STC1, followed by sharp decrease in mRNA levels at term (t-test, FDR P<0.05). We hypothesized that normal course of late pregnancy may be affected when genes characteristic to mid-gestation placenta remain highly expressed until term, and analyzed their expression in term placentas from normal and complicated pregnancies [preeclampsia (PE), n = 12; gestational diabetes mellitus (GDM), n = 12; small- and large-for-gestational-age newborns (SGA, LGA), n = 12+12]. STC1 (stanniocalcin 1) exhibited increased mRNA levels in all studied complications, with the most significant effect in PE- and SGA-groups (t-test, FDR P<0.05). In post-partum maternal plasma, the highest STC1 hormone levels (ELISA, n = 129) were found in women who had developed PE and delivered a SGA newborn (median 731 vs 418 pg/ml in controls; ANCOVA, P = 0.00048). Significantly higher expression (t-test, FDR P<0.05) of CCNG2 and LYPD6 accompanied with enhanced immunostaining of the protein was detected in placental sections of PE and GDM cases (n = 15). Our study demonstrates the importance of temporal dynamics of placental transcriptional regulation across three trimesters of gestation. Interestingly, many genes with high expression in mid-gestation placenta have also been implicated in adult complex disease, promoting the discussion on the role of placenta in developmental programming. The discovery of elevated maternal plasma STC1 in pregnancy complications warrants further investigations of its potential as a biomarker.

Clinical and pathological findings of fatal 2009-2010 pandemic influenza A (H1N1) infection in Estonia.

The aim of this study was to analyze all deaths from A (H1N1) in Estonia during the 2009-2010 epidemic to find out the reasons of high mortality and optimize management strategies for future influenza epidemics. MATERIAL AND METHODS. A retrospective review of medical records, autopsy reports, and reassessment of autopsy slides of all fatal cases of proven A (H1N1) influenza in Estonia from October 2009 to May 2010 was carried out. RESULTS. There were a total of 21 proven fatal cases (median age, 57 years); the population mortality rate of 1.56 per 100 000 inhabitants was one of the highest in the world. Altogether, 18 of the 21 patients had known risk factors for influenza, and 3 patients were previously healthy children. Three decedents had received antiviral treatment, and none had been immunized. There were 19 decedents autopsied, with viral pneumonia (58%) being the most frequent pathological finding; 40% had evidence of bacterial superinfection. In 4 cases, influenza was not clinically suspected and was diagnosed postmortem. Influenza was the primary cause of death in 15 decedents, while in 9 cases, comorbidities played a significant role in fatal outcome. In the remaining 4 cases, another illness was considered the primary cause of death with influenza as an accompanying factor. CONCLUSIONS. High autopsy rate and liberal postmortem PCR testing enables the detection of additional A (H1N1) influenza cases, yet it might lead to overestimation of the population mortality rates, especially in a small population with low number of events. Increased vaccine coverage, vigilant diagnosing including wide PCR testing, and early more liberal use of antiviral medications during the influenza A (H1N1) epidemic may hold the potential of lowering population mortality.

Association of the chaperone alphaB-crystallin with titin in heart muscle.

alphaB-crystallin, a major component of the vertebrate lens, is a chaperone belonging to the family of small heat shock proteins. These proteins form oligomers that bind to partially unfolded substrates and prevent denaturation. alphaB-crystallin in cardiac muscle binds to myofibrils under conditions of ischemia, and previous work has shown that the protein binds to titin in the I-band of cardiac fibers (Golenhofen, N., Arbeiter, A., Koob, R., and Drenckhahn, D. (2002) J. Mol. Cell. Cardiol. 34, 309-319). This part of titin extends as muscles are stretched and is made up of immunoglobulin-like modules and two extensible regions (N2B and PEVK) that have no well defined secondary structure. We have followed the position of alphaB-crystallin in stretched cardiac fibers relative to a known part of the titin sequence. alphaB-crystallin bound to a discrete region of the I-band that moved away from the Z-disc as sarcomeres were extended. In the physiological range of sarcomere lengths, alphaB-crystallin bound in the position of the N2B region of titin, but not to PEVK. In overstretched myofibrils, it was also in the Ig region between N2B and the Z-disc. Binding between alphaB-crystallin and N2B was confirmed using recombinant titin fragments. The Ig domains in an eight-domain fragment were stabilized by alphaB-crystallin; atomic force microscopy showed that higher stretching forces were needed to unfold the domains in the presence of the chaperone. Reversible association with alphaB-crystallin would protect I-band titin from stress liable to cause domain unfolding until conditions are favorable for refolding to the native state.

Titin-based contribution to shortening velocity of rabbit skeletal myofibrils.

The shortening velocity of skeletal muscle fibres is determined principally by actomyosin cross-bridges. However, these contractile elements are in parallel with elastic elements, whose main structural basis is thought to be the titin filaments. If titin is stretched, it may contribute to sarcomere shortening simply because it can recoil 'passively'. The titin-based contribution to shortening velocity (V(p)) was quantified in single rabbit psoas myofibrils. Non-activated specimens were rapidly released from different initial sarcomere lengths (SLs) by various step amplitudes sufficient to buckle the myofibrils; V(p) was calculated from the release amplitude and the time to slack reuptake. V(p) increased progressively (upper limit of detection, approximately 60 microm s(-1) sarcomere(-1)) between 2.0 and 3.0 microm SL, albeit more steeply than passive tension. At very low passive tension levels already (< 1-2 mN mm(-2)), V(p) could greatly exceed the unloaded shortening velocity measured in fully Ca(2+)-activated skinned rabbit psoas fibres. Degradation of titin in relaxed myofibrils by low doses of trypsin (5 min) drastically decreased V(p). In intact myofibrils, average V(p) was faster, the smaller the release step applied. Also, V(p) was much higher at 30 degrees C than at 15 degrees C (Q(10): 2.0, 3.04 or 6.15, for release steps of 150, 250 or 450 nm sarcomere(-1), respectively). Viscous forces opposing the shortening are likely to be involved in determining these effects. The results support the idea that the contractile system imposes a braking force onto the passive recoil of elastic structures. However, elastic recoil may aid active shortening during phases of high elastic energy utilization, i.e. immediately after the onset of contraction under low or zero load or during prolonged shortening from greater physiological SLs.