A hypothesized role for dysregulated bradykinin signaling in COVID-19 respiratory complications.

As of April 20, 2020, over time, the COVID-19 pandemic has resulted in 157 970 deaths out of 2 319 066 confirmed cases, at a Case Fatality Rate of ~6.8%. With the pandemic rapidly spreading, and health delivery systems being overwhelmed, it is imperative that safe and effective pharmacotherapeutic strategies are rapidly explored to improve survival. In this paper, we use established and emerging evidence to propose a testable hypothesis that, a vicious positive feedback loop of des-Arg(9)-bradykinin- and bradykinin-mediated inflammation â†’ injury â†’ inflammation, likely precipitates life threatening respiratory complications in COVID-19. Through our hypothesis, we make the prediction that the FDA-approved molecule, icatibant, might be able to interrupt this feedback loop and, thereby, improve the clinical outcomes. This hypothesis could lead to basic, translational, and clinical studies aimed at reducing COVID-19 morbidity and mortality.

The effects of concentric and eccentric training in murine models of dysferlin-associated muscular dystrophy.

INTRODUCTION: Dysferlin-deficient murine muscle sustains severe damage after repeated eccentric contractions. METHODS: With a robotic dynamometer, we studied the response of dysferlin-sufficient and dysferlin-deficient mice to 12 weeks of concentrically or eccentrically biased contractions. We also studied whether concentric contractions before or after eccentric contractions reduced muscle damage in dysferlin-deficient mice. RESULTS: After 12 weeks of concentric training, there was no net gain in contractile force in dysferlin-sufficient or dysferlin-deficient mice, whereas eccentric training produced a net gain in force in both mouse strains. However, eccentric training induced more muscle damage in dysferlin-deficient vs dysferlin-sufficient mice. Although concentric training produced minimal muscle damage in dysferlin-deficient mice, it still led to a prominent increase in centrally nucleated fibers. Previous exposure to concentric contractions conferred slight protection on dysferlin-deficient muscle against damage from subsequent injurious eccentric contractions. DISCUSSION: Concentric contractions may help dysferlin-deficient muscle derive the benefits of exercise without inducing damage.

Taking the Next Steps in Regenerative Rehabilitation: Establishment of a New Interdisciplinary Field.

The growing field of regenerative rehabilitation has great potential to improve clinical outcomes for individuals with disabilities. However, the science to elucidate the specific biological underpinnings of regenerative rehabilitation-based approaches is still in its infancy and critical questions regarding clinical translation and implementation still exist. In a recent roundtable discussion from International Consortium for Regenerative Rehabilitation stakeholders, key challenges to progress in the field were identified. The goal of this article is to summarize those discussions and to initiate a broader discussion among clinicians and scientists across the fields of regenerative medicine and rehabilitation science to ultimately progress regenerative rehabilitation from an emerging field to an established interdisciplinary one. Strategies and case studies from consortium institutions-including interdisciplinary research centers, formalized courses, degree programs, international symposia, and collaborative grants-are presented. We propose that these strategic directions have the potential to engage and train clinical practitioners and basic scientists, transform clinical practice, and, ultimately, optimize patient outcomes.

Myofiber damage precedes macrophage infiltration after in vivo injury in dysferlin-deficient A/J mouse skeletal muscle.

Mutations in the dysferlin gene (DYSF) lead to human muscular dystrophies known as dysferlinopathies. The dysferlin-deficient A/J mouse develops a mild myopathy after 6 months of age, and when younger models the subclinical phase of the human disease. We subjected the tibialis anterior muscle of 3- to 4-month-old A/J mice to in vivo large-strain injury (LSI) from lengthening contractions and studied the progression of torque loss, myofiber damage, and inflammation afterward. We report that myofiber damage in A/J mice occurs before inflammatory cell infiltration. Peak edema and inflammation, monitored by magnetic resonance imaging and by immunofluorescence labeling of neutrophils and macrophages, respectively, develop 24 to 72 hours after LSI, well after the appearance of damaged myofibers. Cytokine profiles 72 hours after injury are consistent with extensive macrophage infiltration. Dysferlin-sufficient A/WySnJ mice show much less myofiber damage and inflammation and lesser cytokine levels after LSI than do A/J mice. Partial suppression of macrophage infiltration by systemic administration of clodronate-incorporated liposomes fails to suppress LSI-induced damage or to accelerate torque recovery in A/J mice. The findings from our studies suggest that, although macrophage infiltration is prominent in dysferlin-deficient A/J muscle after LSI, it is the consequence and not the cause of progressive myofiber damage.

Dysferlin stabilizes stress-induced Ca2+ signaling in the transverse tubule membrane.

Dysferlinopathies, most commonly limb girdle muscular dystrophy 2B and Miyoshi myopathy, are degenerative myopathies caused by mutations in the DYSF gene encoding the protein dysferlin. Studies of dysferlin have focused on its role in the repair of the sarcolemma of skeletal muscle, but dysferlin's association with calcium (Ca(2+)) signaling proteins in the transverse (t-) tubules suggests additional roles. Here, we reveal that dysferlin is enriched in the t-tubule membrane of mature skeletal muscle fibers. Following experimental membrane stress in vitro, dysferlin-deficient muscle fibers undergo extensive functional and structural disruption of the t-tubules that is ameliorated by reducing external [Ca(2+)] or blocking L-type Ca(2+) channels with diltiazem. Furthermore, we demonstrate that diltiazem treatment of dysferlin-deficient mice significantly reduces eccentric contraction-induced t-tubule damage, inflammation, and necrosis, which resulted in a concomitant increase in postinjury functional recovery. Our discovery of dysferlin as a t-tubule protein that stabilizes stress-induced Ca(2+) signaling offers a therapeutic avenue for limb girdle muscular dystrophy 2B and Miyoshi myopathy patients.

Improved immunoblotting methods provide critical insights into phenotypic differences between two murine dysferlinopathy models.

INTRODUCTION: We adopted a proteomics-based approach to gain insights into phenotypic differences between A/J and B10.SJL murine dysferlinopathy models. METHODS: We optimized immunoblotting of dysferlin by preparing homogenates of the tibialis anterior (TA) muscle under several different conditions. We compared TA muscles of control, A/J, and B10.SJL mice for levels of dysferlin; dysferlin's partners MG53, annexin-A2, and caveolin-3; and the endoplasmic reticulum (ER) stress marker CHOP. We performed immunoelectron microscopy on control rat TA muscle to determine the precise location of dysferlin. RESULTS: RIPA (radioimmunoprecipitation assay) buffer and sonication improves immunoblotting of dysferlin. The ER stress marker CHOP is elevated in A/J muscle. Dysferlin is localized mostly to membranes close to the Z-disk that have been reported to be part of the Golgi, ER, and sarcoplasmic reticulum (SR) networks. CONCLUSIONS: ER stress might underlie phenotypic differences between A/J and B10.SJL mice and play a role in human dysferlinopathies.

Extruded alginate tubes with myogenic potential.

BACKGROUND: There are currently no proven methods to reverse muscle loss in humans, which is caused by trauma (e.g., volumetric muscle loss, VML), genetic neuromuscular diseases (e.g., muscular dystrophies, MDs), and accelerated senescence (e.g., sarcopenia). Since muscle tissue is capable of regeneration through muscle satellite cells (MuSCs), the implantation of autologous (or other) donor MuSCs and MuSC-derived myoblasts into host muscles can promote donor-cell-derived myogenesis. Direct injection or implantation of MuSCs or MuSC-derived myoblasts into host muscles only promotes minimal donor-cell-derived myogenesis, whereas implantation of MuSCs/myoblasts along with associated muscle tissue (muscle fibers, extracellular matrix, neurovascular pathways, etc.) gives better results. METHODS: We aim to leverage the benefits of constraining donor myogenic cells within a template that resembles muscle tissue. In this paper, we present a workflow for basic and translational studies aimed at promoting donor-cell-derived myogenesis to increase functional muscle mass in mice. Our workflow involves preparing a slurry of 10% sodium alginate mixed with myogenic cells in cell culture media, extruding the cell-containing slurry into 10% calcium lactate to form tubes, and implanting the cellularized alginate tubes into host muscle. RESULTS: Our data suggest that, the extruded alginate tubes can tolerate a peak stress of 1892 ± 527 mN, that the elastic range is at ~75-125% strain beyond initial length, and that the Young's modulus (stiffness) is 14.17 ± 1.68 %/mm2. Importantly, these mechanical properties render the alginate tubes suitable for a published technique known as minimally-invasive muscle embedding (MIME) that was developed by us to implant myogenic material into host muscle. MIME involves threading donor myogenic tissue into a needle track created within a host muscle. Cellularized alginate tubes implanted into the tibialis anterior muscle of previously euthanized mice had numerous hematoxylin-stained structures similar to nuclear staining, supporting the idea that our alginate tubes can support cell seeding. Alginate tubes that were seeded with MuSCs, incubated in MuSC/myoblast growth (i.e., proliferation) media for two days, incubated in myotube differentiation media for six days, and then minced and reseeded in new dishes, were able to promote in vitro myoblast outgrowth over several days. DISCUSSION: This pilot study is limited in its translational scope because it was performed in vitro and with previously euthanized mice. Additional studies are needed to confirm that cellularized alginate tubes can promote the de novo development of donor-cell-derived muscle fibers, which can contribute to contractile force production. CONCLUSION: Alginate tubes with MuSC/myoblasts can be generated by a simple extrusion method. The alginate tubes have sufficient mechanical strength to tolerate insertion into a host muscle, in a minimally-invasive manner, through a needle track. The cellularized alginate tubes demonstrate myogenic potential since they are capable of being maintained in culture conditions for several days, after which they can still facilitate myoblast outgrowth in a dish.

Protection against Severe Illness versus Immunity-Redefining Vaccine Effectiveness in the Aftermath of COVID-19.

Anti-SARS-CoV-2 vaccines have played a pivotal role in reducing the risk of developing severe illness from COVID-19, thus helping end the COVID-19 global public health emergency after more than three years. Intriguingly, as SARS-CoV-2 variants emerged, individuals who were fully vaccinated did get infected in high numbers, and viral loads in vaccinated individuals were as high as those in the unvaccinated. However, even with high viral loads, vaccinated individuals were significantly less likely to develop severe illness; this begs the question as to whether the main effect of anti-SARS-CoV-2 vaccines is to confer protection against severe illness or immunity against infection. The answer to this question is consequential, not only to the understanding of how anti-SARS-CoV-2 vaccines work, but also to public health efforts against existing and novel pathogens. In this review, we argue that immune system sensitization-desensitization rather than sterilizing immunity may explain vaccine-mediated protection against severe COVID-19 illness even when the SARS-CoV-2 viral load is high. Through the lessons learned from COVID-19, we make the case that in the disease's aftermath, public health agencies must revisit healthcare policies, including redefining the term "vaccine effectiveness."

Efficacy of Cochlear Implantation in Neurofibromatosis Type 2 Related Hearing Loss.

OBJECTIVE: To investigate the results of cochlear implantation in subjects with neurofibromatosis type 2 (NF2) and bilateral vestibular schwannomas (VS). STUDY DESIGN: Retrospective case series. SETTING: University-based tertiary referral center. SUBJECTS: Five subjects with NF2 and severe-to-profound sensorineural hearing loss. INTERVENTION: Cochlear implantation. MAIN OUTCOME MEASURE: Surgical outcomes and audiometric performance after cochlear implantation. RESULTS: Five subjects (3 female, 2 male) were included in the study. The mean age at the time of implantation was 54 years old (range 35-78 years). Follow-up after cochlear implantation averaged 38 months (range 21-106 months). In the 5 implanted ears, 2 had no prior treatment, 1 had undergone prior radiation therapy, 1 underwent prior microsurgical removal, and 1 underwent prior microsurgical removal with adjuvant radiation therapy. The mean ipsilateral VS dimensions at time of implantation were 14 mm × 7.2 mm × 6.1 mm (mediolateral × anteroposterior × craniocaudal). Following cochlear implant activation, all 5 subjects achieved sound awareness, open set speech recognition, and 4 continue to be daily users of the devices. CONCLUSION: Cochlear implantation is a viable hearing rehabilitation option for subjects with NF2 and severe-to-profound sensorineural hearing loss. All subjects reported benefit with their cochlear implant, including open set speech recognition, enhanced lip-reading skills and environmental awareness of sound. Four subjects continued to demonstrate improved open-set speech recognition at the time of their last evaluations.

Distinct effects of contraction-induced injury in vivo on four different murine models of dysferlinopathy.

Mutations in the DYSF gene, encoding dysferlin, cause muscular dystrophies in man. We compared 4 dysferlinopathic mouse strains: SJL/J and B10.SJL-Dysf(im)/AwaJ (B10.SJL), and A/J and B6.A-Dysf(prmd)/GeneJ (B6.A/J). The former but not the latter two are overtly myopathic and weaker at 3 months of age. Following repetitive large-strain injury (LSI) caused by lengthening contractions, all except B6.A/J showed ~40% loss in contractile torque. Three days later, torque in SJL/J, B10.SJL and controls, but not A/J, recovered nearly completely. B6.A/J showed ~30% torque loss post-LSI and more variable recovery. Pre-injury, all dysferlinopathic strains had more centrally nucleated fibers (CNFs) and all but A/J showed more inflammation than controls. At D3, all dysferlinopathic strains showed increased necrosis and inflammation, but not more CNFs; controls were unchanged. Dystrophin-null DMD(mdx) mice showed more necrosis and inflammation than all dysferlin-nulls. Torque loss and inflammation on D3 across all strains were linearly related to necrosis. Our results suggest that (1) dysferlin is not required for functional recovery 3 days after LSI; (2) B6.A/J mice recover from LSI erratically; (3) SJL/J and B10.SJL muscles recover rapidly, perhaps due to ongoing myopathy; (4) although they recover function to different levels, all 4 dysferlinopathic strains show increased inflammation and necrosis 3 days after LSI.

Adult Onset Bilateral Cochlear Nerve Atrophy and Cochlear Implantation: A Case Report and Review of the Literature.

OBJECTIVE: To describe a case of idiopathic bilateral cochlear nerve atrophy acquired in adulthood. PATIENT: A 75-year-old male with acquired bilateral cochlear nerve atrophy. INTERVENTION(S): Unilateral cochlear implantation. MAIN OUTCOME AND RESULTS: Description of a patient with acquired bilateral cochlear nerve atrophy diagnosed at the age of 75. The patient had normal hearing and no communication deficits until the age of 66. At this point, the patient demonstrated a slight asymmetric hearing loss, which progressed to severe sensorineural hearing loss. Due to the resulting communication deficit, cochlear device implantation candidacy was pursued. Pre-operative magnetic resonance imaging (MRI) showed severe atrophy versus absence of the cochlear nerves bilaterally. After careful counseling regarding the expected communication outcomes given the MRI findings, the patient underwent left-sided cochlear implantation. The patient gained sound awareness, but no additional communication benefit compared to pre-operative baseline abilities. CONCLUSION: Cochlear nerve deficiency is a known finding in certain cases of congenital and acquired hearing loss, but no cases of idiopathic adult-onset bilateral nerve atrophy have been reported. Without MR imaging, the clinically significant finding would not have been identified. Thus, MRI is advantageous when compared with other imaging modalities in patients with progressive sensorineural hearing loss and enables improved patient counseling regarding expected auditory and communication outcomes.

How does moving public engagement with research online change audience diversity? Comparing inclusion indicators for 2019 & 2020 European Researchers' night events.

Taking place annually in more than 400 cities, European Researchers' Night is a pan- European synchronized event that aims to bring researchers closer to the public. In this paper audience profiles are compared from events in 2019 and 2020. In 2019, face-to-face events reached an estimated 1.6 million attendees, while in 2020, events shifted online due to the COVID-19 pandemic and reached an estimated 2.3 million attendees. Focusing on social inclusion metrics, survey data is analyzed across two national contexts (Ireland and Malta) in 2019 (n = 656) and 2020 (n = 506). The results from this exploratory, descriptive study shed light on how moving public engagement with research online shifted audience profiles. Based on prior research about the digital divide in access and use of online media, hypotheses were proposed that online European Researchers' Night events would attract audiences with higher educational attainment levels and greater self-reported, subjective economic well-being. While changes were observed from 2019 to 2020, results for each hypothesis show a mixed picture. The first hypothesis was upheld for the highest education levels but failed for the lowest levels suggesting that the pivot to online events simultaneously attracted participants with no formal education and those with postgraduate qualifications, while attracting less of those with undergraduate or lower levels of education. The second hypothesis was not upheld, with online European Researchers' Night events attracting audiences with slightly higher levels of economic well-being compared to face-to-face events. The findings of this study indicate that European Researchers' Night events present a clear opportunity to measure the effects of the digital divide in relation to public engagement with research across Europe.

Dosage-Adjusted Resistance Training in Mice with a Reduced Risk of Muscle Damage.

Progressive resistance training (PRT), which involves performing muscle contractions against progressively greater external loads, can increase muscle mass and strength in healthy individuals and in patient populations. There is a need for precision rehabilitation tools to test the safety and effectiveness of PRT to maintain and/or restore muscle mass and strength in preclinical studies on small and large animal models. The PRT methodology and device described in this article can be used to perform dosage-adjusted resistance training (DART). The DART device can be used as a standalone dynamometer to objectively assess the concentric contractile torque generated by the ankle dorsiflexors in mice or can be added to a pre-existing isokinetic dynamometry system. The DART device can be fabricated with a standard 3D printer based on the instructions and open-source 3D print files provided in this work. The article also describes the workflow for a study to compare contraction-induced muscle damage caused by a single bout of DART to muscle damage caused by a comparable bout of isometric contractions (ISOM) in a mouse model of limb-girdle muscular dystrophy type 2B/R2 (BLAJ mice). The data from eight BLAJ mice (four animals for each condition) suggest that less than 10% of the tibialis anterior (TA) muscle was damaged from a single bout of DART or ISOM, with DART being less damaging than ISOM.

Physiological and histological changes in skeletal muscle following in vivo gene transfer by electroporation.

Electroporation (EP) is used to transfect skeletal muscle fibers in vivo, but its effects on the structure and function of skeletal muscle tissue have not yet been documented in detail. We studied the changes in contractile function and histology after EP and the influence of the individual steps involved to determine the mechanism of recovery, the extent of myofiber damage, and the efficiency of expression of a green fluorescent protein (GFP) transgene in the tibialis anterior (TA) muscle of adult male C57Bl/6J mice. Immediately after EP, contractile torque decreased by ∼80% from pre-EP levels. Within 3 h, torque recovered to ∼50% but stayed low until day 3. Functional recovery progressed slowly and was complete at day 28. In muscles that were depleted of satellite cells by X-irradiation, torque remained low after day 3, suggesting that myogenesis is necessary for complete recovery. In unirradiated muscle, myogenic activity after EP was confirmed by an increase in fibers with central nuclei or developmental myosin. Damage after EP was confirmed by the presence of necrotic myofibers infiltrated by CD68+ macrophages, which persisted in electroporated muscle for 42 days. Expression of GFP was detected at day 3 after EP and peaked on day 7, with ∼25% of fibers transfected. The number of fibers expressing green fluorescent protein (GFP), the distribution of GFP+ fibers, and the intensity of fluorescence in GFP+ fibers were highly variable. After intramuscular injection alone, or application of the electroporating current without injection, torque decreased by ∼20% and ∼70%, respectively, but secondary damage at D3 and later was minimal. We conclude that EP of murine TA muscles produces variable and modest levels of transgene expression, causes myofiber damage due to the interaction of intramuscular injection with the permeabilizing current, and that full recovery requires myogenesis.

Investigating diversity in European audiences for public engagement with research: Who attends European Researchers' Night in Ireland, the UK and Malta?

European Researchers' Night is an annual pan-European synchronized event devoted to public engagement with research. It was first held in 2005 and now occurs in over 400 cities across Europe, with the aim of bringing researchers closer to the general public. To investigate social inclusion in these events, we conducted survey research across three national contexts (Ireland, Malta and the UK) and events in seven cities between 2016 and 2019 (n = 1590). The results from this exploratory descriptive study confirmed one hypothesis, namely that event attendees had substantially higher levels of university qualification than the national publics. This is in line with wider patterns of unequal participation in public engagement with research activities based on socio-economic status. However, we also found mixed evidence on the prevalence of ethnic minority representation among event attendees compared to the general population, thus failing to uphold the second hypothesis that predicted an over-representation of white majority participants. This second finding diverges from existing research findings about ethnic diversity amongst science communication audiences, raising the possibility that some public engagement events are over-performing on this dimension of social inclusion. Overall, the findings demonstrate that European Researchers' Night has potential for addressing the critical goal of enhancing the diversity of audiences for public engagement with research, even as it falls short on the key metric of socio-economic diversity.

Women's Lives Matter-The Critical Need for Women to Prioritize Optimal Physical Activity to Reduce COVID-19 Illness Risk and Severity.

Physical activity (PA) is beneficial for the health and wellness of individuals and societies. During an infectious disease pandemic, such as the one caused by COVID-19, social distancing, quarantines, and lockdowns are used to reduce community spread of the disease. Unfortunately, such nonpharmacological interventions or physical risk mitigation measures also make it challenging to engage in PA. Reduced PA could then trigger physiological changes that affect both mental and physical health. In this regard, women are more likely to experience physical and psychological distress. PA is a safe and effective nonpharmacological modality that can help prevent and manage several mental and physical health problems when performed correctly. PA might even confer benefits that are directly related to decreasing COVID-19 morbidity and mortality in women. In this review, we summarize why optimal PA must be a priority for women during the COVID-19 pandemic. We then discuss chronic COVID-19 illness and its impact on women, which further underscores the need for worldwide preventive health strategies that include PA. Finally, we discuss the importance of vaccination against COVID-19 for women, as part of prioritizing preventive healthcare and an active lifestyle.

Systematic Comparison of Trial Exclusion Criteria for Pupillometry Data Analysis in Individuals With Single-Sided Deafness and Normal Hearing.

The measurement of pupil dilation has become a common way to assess listening effort. Pupillometry data are subject to artifacts, requiring highly contaminated data to be discarded from analysis. It is unknown how trial exclusion criteria impact experimental results. The present study examined the effect of a common exclusion criterion, percentage of blinks, on speech intelligibility and pupil dilation measures in 9 participants with single-sided deafness (SSD) and 20 participants with normal hearing. Participants listened to and repeated sentences in quiet or with speech maskers. Pupillometry trials were processed using three levels of blink exclusion criteria: 15%, 30%, and 45%. These percentages reflect a threshold for missing data points in a trial, where trials that exceed the threshold are excluded from analysis. Results indicated that pupil dilation was significantly greater and intelligibility was significantly lower in the masker compared with the quiet condition for both groups. Across-group comparisons revealed that speech intelligibility in the SSD group decreased significantly more than the normal hearing group from quiet to masker conditions, but the change in pupil dilation was similar for both groups. There was no effect of blink criteria on speech intelligibility or pupil dilation results for either group. However, the total percentage of blinks in the masker condition was significantly greater than in the quiet condition for the SSD group, which is consistent with previous studies that have found a relationship between blinking and task difficulty. This association should be carefully considered in future experiments using pupillometry to gauge listening effort.

µ-Crystallin in Mouse Skeletal Muscle Promotes a Shift from Glycolytic toward Oxidative Metabolism.

µ-Crystallin, encoded by the CRYM gene, binds the thyroid hormones, T3 and T4. Because T3 and T4 are potent regulators of metabolism and gene expression, and CRYM levels in human skeletal muscle can vary widely, we investigated the effects of overexpression of Crym. We generated transgenic mice, Crym tg, that expressed Crym protein specifically in skeletal muscle at levels 2.6-147.5 fold higher than in controls. Muscular functions, Ca2+ transients, contractile force, fatigue, running on treadmills or wheels, were not significantly altered, although T3 levels in tibialis anterior (TA) muscle were elevated ~190-fold and serum T4 was decreased 1.2-fold. Serum T3 and thyroid stimulating hormone (TSH) levels were unaffected. Crym transgenic mice studied in metabolic chambers showed a significant decrease in the respiratory exchange ratio (RER) corresponding to a 13.7% increase in fat utilization as an energy source compared to controls. Female but not male Crym tg mice gained weight more rapidly than controls when fed high fat or high simple carbohydrate diets. Although labeling for myosin heavy chains showed no fiber type differences in TA or soleus muscles, application of machine learning algorithms revealed small but significant morphological differences between Crym tg and control soleus fibers. RNA-seq and gene ontology enrichment analysis showed a significant shift towards genes associated with slower muscle function and its metabolic correlate, ß-oxidation. Protein expression showed a similar shift, though with little overlap. Our study shows that µ-crystallin plays an important role in determining substrate utilization in mammalian muscle and that high levels of µ-crystallin are associated with a shift toward greater fat metabolism.

Extensive mononuclear infiltration and myogenesis characterize recovery of dysferlin-null skeletal muscle from contraction-induced injuries.

We studied the response of dysferlin-null and control skeletal muscle to large- and small-strain injuries to the ankle dorsiflexors in mice. We measured contractile torque and counted fibers retaining 10-kDa fluorescein dextran, necrotic fibers, macrophages, and fibers with central nuclei and expressing developmental myosin heavy chain to assess contractile function, membrane resealing, necrosis, inflammation, and myogenesis. We also studied recovery after blunting myogenesis with X-irradiation. We report that dysferlin-null myofibers retain 10-kDa dextran for 3 days after large-strain injury but are lost thereafter, following necrosis and inflammation. Recovery of dysferlin-null muscle requires myogenesis, which delays the return of contractile function compared with controls, which recover from large-strain injury by repairing damaged myofibers without significant inflammation, necrosis, or myogenesis. Recovery of control and dysferlin-null muscles from small-strain injury involved inflammation and necrosis followed by myogenesis, all of which were more pronounced in the dysferlin-null muscles, which recovered more slowly. Both control and dysferlin-null muscles also retained 10-kDa dextran for 3 days after small-strain injury. We conclude that dysferlin-null myofibers can survive contraction-induced injury for at least 3 days but are subsequently eliminated by necrosis and inflammation. Myogenesis to replace lost fibers does not appear to be significantly compromised in dysferlin-null mice.

Hearing loss alters serotonergic modulation of intrinsic excitability in auditory cortex.

Sensorineural hearing loss during early childhood alters auditory cortical evoked potentials in humans and profoundly changes auditory processing in hearing-impaired animals. Multiple mechanisms underlie the early postnatal establishment of cortical circuits, but one important set of developmental mechanisms relies on the neuromodulator serotonin (5-hydroxytryptamine [5-HT]). On the other hand, early sensory activity may also regulate the establishment of adultlike 5-HT receptor expression and function. We examined the role of 5-HT in auditory cortex by first investigating how 5-HT neurotransmission and 5-HT(2) receptors influence the intrinsic excitability of layer II/III pyramidal neurons in brain slices of primary auditory cortex (A1). A brief application of 5-HT (50 µM) transiently and reversibly decreased firing rates, input resistance, and spike rate adaptation in normal postnatal day 12 (P12) to P21 rats. Compared with sham-operated animals, cochlear ablation increased excitability at P12-P21, but all the effects of 5-HT, except for the decrease in adaptation, were eliminated in both sham-operated and cochlear-ablated rats. At P30-P35, cochlear ablation did not increase intrinsic excitability compared with shams, but it did prevent a pronounced decrease in excitability that appeared 10 min after 5-HT application. We also tested whether the effects on excitability were mediated by 5-HT(2) receptors. In the presence of the 5-HT(2)-receptor antagonist, ketanserin, 5-HT significantly decreased excitability compared with 5-HT or ketanserin alone in both sham-operated and cochlear-ablated P12-P21 rats. However, at P30-P35, ketanserin had no effect in sham-operated and only a modest effect cochlear-ablated animals. The 5-HT(2)-specific agonist 5-methoxy-N,N-dimethyltryptamine also had no effect at P12-P21. These results suggest that 5-HT likely regulates pyramidal cell excitability via multiple receptor subtypes with opposing effects. These data also show that early sensorineural hearing loss affects the ability of 5-HT receptor activation to modulate A1 pyramidal cell excitability.