Observation of WWγ Production and Search for Hγ Production in Proton-Proton Collisions at sqrt[s]=13 TeV

The observation of WWγ production in proton-proton collisions at a center-of-mass energy of 13 TeV with an integrated luminosity of 138  fb^{-1} is presented. The observed (expected) significance is 5.6 (5.1) standard deviations. Events are selected by requiring exactly two leptons (one electron and one muon) of opposite charge, moderate missing transverse momentum, and a photon. The measured fiducial cross section for WWγ is 5.9±0.8(stat)±0.8(syst)±0.7(modeling)  fb, in agreement with the next-to-leading order quantum chromodynamics prediction. The analysis is extended with a search for the associated production of the Higgs boson and a photon, which is generated by a coupling of the Higgs boson to light quarks. The result is used to constrain the Higgs boson couplings to light quarks.

New Structures in the J/ψJ/ψ Mass Spectrum in Proton-Proton Collisions at sqrt[s]=13 TeV

A search is reported for near-threshold structures in the J/ψJ/ψ invariant mass spectrum produced in proton-proton collisions at sqrt[s]=13  TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135  fb^{-1}. Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of 6638_{-38}^{+43}(stat)_{-31}^{+16}(syst)  MeV. Another structure with even higher significance is found at a mass of 6847_{-28}^{+44}(stat)_{-20}^{+48}(syst)  MeV, which is consistent with the X(6900) resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of 7134_{-25}^{+48}(stat)_{-15}^{+41}(syst)  MeV. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference.

Search for Scalar Leptoquarks Produced via τ-Lepton-Quark Scattering in pp Collisions at sqrt[s]=13 TeV

The first search for scalar leptoquarks produced in τ-lepton-quark collisions is presented. It is based on a set of proton-proton collision data recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138  fb^{-1}. The reconstructed final state consists of a jet, significant missing transverse momentum, and a τ lepton reconstructed through its hadronic or leptonic decays. Limits are set on the product of the leptoquark production cross section and branching fraction and interpreted as exclusions in the plane of the leptoquark mass and the leptoquark-τ-quark coupling strength.

Search for Inelastic Dark Matter in Events with Two Displaced Muons and Missing Transverse Momentum in Proton-Proton Collisions at sqrt[s]=13 TeV

A search for dark matter in events with a displaced nonresonant muon pair and missing transverse momentum is presented. The analysis is performed using an integrated luminosity of 138  fb^{-1} of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV produced by the LHC in 2016-2018. No significant excess over the predicted backgrounds is observed. Upper limits are set on the product of the inelastic dark matter production cross section σ(pp→A^{'}→χ_{1}χ_{2}) and the decay branching fraction B(χ_{2}→χ_{1}μ^{+}μ^{-}), where A^{'} is a dark photon and χ_{1} and χ_{2} are states in the dark sector with near mass degeneracy. This is the first dedicated collider search for inelastic dark matter.

Observation of the Rare Decay of the η Meson to Four Muons

A search for the rare η→μ^{+}μ^{-}μ^{+}μ^{-} double-Dalitz decay is performed using a sample of proton-proton collisions, collected by the CMS experiment at the CERN LHC with high-rate muon triggers during 2017 and 2018 and corresponding to an integrated luminosity of 101  fb^{-1}. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the η→μ^{+}μ^{-} decay as normalization, the branching fraction B(η→μ^{+}μ^{-}μ^{+}μ^{-})=[5.0±0.8(stat)±0.7(syst)±0.7(B_{2μ})]×10^{-9} is measured, where the last term is the uncertainty in the normalization channel branching fraction. This work achieves an improved precision of over 5 orders of magnitude compared to previous results, leading to the first measurement of this branching fraction, which is found to agree with theoretical predictions.

Safety and efficacy of cerebral embolic protection devices in transcatheter aortic valve implantation: a meta-analysis

Funding Acknowledgements

Type of funding sources: None.

Background

Stroke during Transcatheter Aortic Valve implantation (TAVI) is not an uncommon complication with potential devastating consequences. With the extension of TAVI to the low-risk patient, stroke prevention takes on increasing importance. The use of cerebral embolic protection device (EPD) reveals conflicting data. This meta-analysis aims to evaluate the clinical efficacy and safety of EPDs.

Methods

A comprehensive literature search for all studies till May 2022 reporting clinical safety and efficacy outcomes of the only EPD approved for use by the Food and Drug Administration (FDA) was performed. Study outcomes were divided based on time period - overall (up to 30 days and in-hospital) and short (≤7 days). Primary outcome was stroke - major and minor. Secondary outcomes included transient ischaemic attack (TIA), mortality, acute kidney injury (AKI), major vascular and bleeding complications.

Results

A total of 12 studies involving 288531 patients were analysed, which included 3 randomised controlled trials (RCTs), 7 propensity-matched and 2 cohort studies. Regarding overall outcomes, significant differences were noted for mortality (OR 0.59 [0.42-0.84], p=0.0036) and major stroke (OR 0.40 [0.18-0.91], p=0.028) (Fig 1). No significant differences were noted for all stroke (p=0.058), minor stroke (p=0.32), TIA (p=0.49), AKI (p=0.17), major vascular complications (p=0.40) and major bleeding complications (p=0.11). There was significant heterogeneity across the studies for mortality (p=0.032) and all stroke (p=0.009). In the subgroup analysis of studies reporting ≤7 days outcomes (n=5), EPDs showed significantly lower rates of all stroke (0.33 [95% CI 0.19-0.56], p=<0.0001), major stroke (0.19 [0.08-0.48], p=0.0004) and major bleeding complications (OR 0.29 [0.10-0.79], p=0.016), but no significant differences for mortality (p=0.67) and minor stroke (p=0.070). There was no significant heterogeneity across the studies (all p>0.05)

Conclusions

In this meta-analysis including non-randomised studies, the use of EPDs was associated with lower mortality and major stroke rates, although significant heterogeneity was noted for the studies reporting mortality. Further ongoing larger scale RCTs will further clarify these results.

Comparison of transcatheter, minimally invasive and conventional surgical aortic valve replacement: a systematic review and network meta-analysis

Funding Acknowledgements

Type of funding sources: None.

Background/Introduction

The landscape of aortic valve replacement (AVR) has evolved dramatically over the years, but long-term outcomes have yet to be comprehensively explored.

Purpose

To compare long-term mortality among three AVR techniques: transcatheter (TAVI), minimally invasive (MIAVR), and conventional surgical AVR (CAVR).

Methods

An electronic literature search was performed for randomized controlled trials (RCTs) comparing TAVI to CAVR, and RCTs or propensity score-matched (PSM) studies comparing MIAVR to CAVR or MIAVR to TAVI. Individual patient data for all-cause mortality was derived from graphical reconstruction of digitized Kaplan-Meier curves. Pairwise comparisons followed by network meta-analysis were conducted. Sensitivity analyses were performed in the TAVI arm for high risk and low/intermediate risk as well as transfemoral (TF-TAVI) patients.

Results

A total of 27 studies involving 16,554 patients were included. In the pairwise comparison of TAVI versus CAVR, TAVI showed superior mortality to CAVR until 39.5 months, beyond which there was no significant difference in longer term mortality. When restricted to TF-TAVI versus CAVR, consistent mortality benefit favoring TAVI was seen (shared-frailty hazard ratio [HR]=1.17, 95%CI=1.03-1.33, p=0.016). In the network meta-analysis involving majority PSM data, MIAVR was associated with significantly lower mortality than TAVI (HR=0.69, 95%CI=0.59-0.82) and CAVR (HR=0.68, 95%CI=0.58-0.80); this significant association was not seen when compared to TF-TAVI patients.

Conclusions

An initial short-medium term mortality benefit for TAVI over CAVR was noted but this benefit was attenuated over the longer term. In the subset of TF-TAVI patients, this long-term mortality benefit persisted, suggesting that non-TF techniques are associated with higher mortality. Amongst majority PSM data, MIAVR showed improved mortality compared to TAVI and CAVR but this was not seen in the TF-TAVI subset. This suggests that MIAVR may have a role in treating patients who are ineligible for TF-TAVI in experienced centers, and future RCTs are needed to conclusively validate this.

Thyrotoxic periodic paralysis associated with Graves’ disease: a case series

Summary

Thyrotoxic periodic paralysis (TPP) is a rare condition characterised by acute onset hypokalaemia and paralysis which most commonly affects men of Asian descent between the ages of 20 and 40 years (1, 2). It has been reported in approximately 2% of patients with thyrotoxicosis in China and Japan (1, 2, 3). Hypokalaemia in TPP results from a massive intracellular shift of potassium induced by the thyroid hormone sensitisation of Na⁺/K⁺-ATPase (4). Treatment of TPP includes prevention of this shift by using beta-blockade, rapid potassium replacement and treatment of the underlying hyperthyroidism. We present two cases of TPP with differing outcomes. In the first case, a 33-year-old Filipino gentleman presented to our emergency department (ED) with a 3-month history of recurrent proximal lower limb weakness. Serum potassium was 2.2 mmol/L (3.3–5.1) and he was given i.v. potassium replacement. Thyroid function tests (TFTs) and thyroid antibodies were consistent with Graves thyrotoxicosis. He was discharged home on carbimazole and remains well controlled on long-term medical therapy. In the second case, a 22-year-old Malaysian gentleman presented to our ED with new-onset bilateral lower limb painless paralysis. Serum potassium was 1.9 mmol/L with TFTs demonstrating Graves thyrotoxicosis. He was treated with i.v. potassium replacement and discharged home on carbimazole and propranolol. He represented to the hospital on two further occasions with TPP and was advised to consider total thyroidectomy given his refractory Graves’ disease. These cases highlight the importance of prompt recognition of this rare life-threatening complication of Graves’ disease, especially in patients of Asian descent.

Learning points

Intra-articular injection of magnesium chloride attenuates osteoarthritis progression in rats

OBJECTIVE

To explore the effects of Mg²⁺ on the expression of osteoarthritic markers in human cartilage and synovium tissue explants. To investigate the therapeutic effect of intra-articular injection of Mg²⁺ in an established rat OA (Osteoarthritis) model of anterior cruciate ligament transection with partial medial meniscectomy (ACLT + PMM).

DESIGN

Human cartilage and synovium explants were collected from total knee replacement surgeries and incubated with MgCl₂ (20 mmol/L) in vitro. A rat OA model was established by ACLT + PMM surgery in 450-500 g male Sprague Dawley (SD) rats. To select the optimal dose, intra-articular injections of MgCl₂ (0.05, 0.5, 5 mol/L) were performed at 4 weeks after the surgery every 3 days for 2 weeks. The effect of optimized MgCl₂ was further determined by histology, immunohistochemistry, and quantitative real-time polymerase chain reaction.

RESULTS

The expressions of osteoarthritic markers in human cartilage and synovium explants were inhibited by Mg²⁺in vitro. Immunohistochemical analysis further suggested the inhibitory effects of Mg²⁺ on the expression of MMP-13 and IL-6 in the human tissue explants. Cartilage degeneration and synovitis in ACLT + PMM rats were significantly improved by intra-articular injections of Mg²⁺ (0.5 mol/L). Immunohistochemical analysis also showed the regulatory effects of Mg²⁺ on osteoarthritic markers in both cartilage and synovium in rats, consistent with in vitro results.

CONCLUSION

Intra-articular injections of Mg²⁺ at 0.5 mol/L attenuate the progression of OA in the ACLT + PMM rat model. Such effect was at least in part explained by the promotion of cartilage matrix synthesis and the suppression of synovial inflammation.

Attenuation of subchondral bone abnormal changes in osteoarthritis by inhibition of SDF-1 signaling

BACKGROUND

Current conservative treatments for osteoarthritis (OA) are largely symptoms control therapies. Further understanding on the pathological mechanisms of OA is crucial for new pharmacological intervention.

OBJECTIVE

In this study, we investigated the role of Stromal cell-derived factor-1(SDF-1) in regulating subchondral bone changes during the progression of OA.

METHODS

Clinical samples of different stages of OA severity were analyzed by histology staining, micro-CT, enzyme-linked immunosorbent assay (ELISA) and western blotting, to compare SDF-1 level in subchondral bone. The effects of SDF-1 on human mesenchymal stem cells (MSCs) osteogenic differentiation were evaluated. In vivo assessment was performed in an anterior cruciate ligament transaction plus medial meniscus resection in the SD rats. The OA rats received continuous infusion of AMD3100 (SDF-1 receptor blocker) in osmotic mini-pump implanted subcutaneously for 6 weeks. These rats were then terminated and subjected to the same in vitro assessments as human OA samples.

RESULTS

SDF-1 level was significantly elevated in the subchondral bone of human OA samples. In the cell studies, the results showed SDF-1 plays an important role in osteogenic differentiation of MSCs. In the OA animal studies, there were less cartilage damage in the AMD3100-treated group; microCT results showed that the subchondral bone formation was significantly reduced and so did the number of positive Nestin or Osterix cells in the subchondral bone region.

CONCLUSIONS

Higher level of SDF-1 may induce the subchondral bone abnormal changes in OA and inhibition of SDF-1 signaling could be a potential therapeutic approach for OA.

Do-not-resuscitate decision: the attitudes of medical and non-medical students

OBJECTIVES

To study the attitudes of both medical and non-medical students towards the do-not-resuscitate (DNR) decision in a university in Hong Kong, and the factors affecting their attitudes.

METHODS

A questionnaire-based survey conducted in the campus of a university in Hong Kong. Preferences and priorities of participants on cardiopulmonary resuscitation in various situations and case scenarios, experience of death and dying, prior knowledge of DNR and basic demographic data were evaluated.

RESULTS

A total of 766 students participated in the study. There were statistically significant differences in their DNR decisions in various situations between medical and non-medical students, clinical and preclinical students, and between students who had previously experienced death and dying and those who had not. A prior knowledge of DNR significantly affected DNR decision, although 66.4% of non-medical students and 18.7% of medical students had never heard of DNR. 74% of participants from both medical and non-medical fields considered the patient's own wish as the most important factor that the healthcare team should consider when making DNR decisions. Family wishes might not be decisive on the choice of DNR.

CONCLUSIONS

Students in medical and non-medical fields held different views on DNR. A majority of participants considered the patient's own wish as most important in DNR decisions. Family wishes were considered less important than the patient's own wishes.

Electrocardiographical case. A young man with chest pain

A 31-year-old Chinese man presented with complaint of acute chest pain. 12-lead electrocardiogram (ECG) showed sinus rhythm, with widespread upward concave ST segment elevations. The ECG changes along with a history of acute chest pain in a young man with minimal coronary risk factors are suggestive of acute pericarditis. He subsequently developed a pericardial effusion. Diagnosis, treatment and complications of acute percarditis are discussed.

Age of seizure onset in adults with Down's syndrome

In a cohort of 68 adults (35 males and 33 females) with Down's syndrome aged 29-83 years, a history of seizures was found in 26.5%. The overall mean age of onset of seizures was 37 years, males (22 years) being significantly younger than females (51 years). The age of onset was bimodally distributed, with the first peak occurring in the first two decades, and a late-onset peak occurring in the fifth and sixth decades. A strong association between Alzheimer's disease and seizures was confirmed. Of those with a history of seizures, those aged over 45 years were significantly more likely to develop Alzheimer's disease than those younger than 45. It is suggested that late-onset epilepsy in Down's syndrome is associated with Alzheimer's disease, while early-onset epilepsy is associated with an absence of dementia.

Effects of general, special, and specific resistance training on throwing velocity in baseball: a brief review

Throwing velocity is a necessary requirement for success in baseball. All position players, including pitchers, may increase their defensive performance if their throwing velocity is improved. A review of the literature suggests that throwing velocity can be increased by resistance training and/or biomechanical improvement of the throwing motion. This paper reviews the 3 broad categories of resistance-training methods by which throwing velocity is increased. The results of research using general, special, and specific throwing resistance-training exercises are presented. The role and applications of these different exercises for baseball players of different ages are discussed.

Legislative funding of athletic training positions in public secondary schools

In 1991, approximately 21 000 student athletes were actively participating in organized athletics in Hawaii's 61 (38 public and 23 private) secondary schools. Of the 61 schools, only 5 (all private) employed full-time, NATABOC-certified athletic trainers (ATCs) to facilitate the sports health care of their respective student athletes. In an attempt to convince the state legislature that providing funding to hire ATCs was a primary health and safety issue in the state, a community-based educational platform was established and a twofold needs-assessment study was implemented statewide. The educational platform was aimed at parents, coaches, athletic directors, and school administrators. The needs-assessment studies consisted of a 30-question survey on the current practices of sports health care and a year-long injury surveillance survey within the 38 public secondary schools. There were significant differences between the public and private schools with respect to the practice of sports health care. The public school student athletes demonstrated a normative incidence of injury rate. These findings definitively quantified and qualified the need to hire ATCs in the public secondary schools. In July of 1993, the State of Hawaii funded a 2-year athletic training pilot program for approximately $1.2 million, following an extensive lobbying effort and media campaign.

Pre-participation examination: a new form for Hawaii

A recent study examining the adequacy of the existing pre-participation physical examination (PPE) form in the State of Hawaii suggested that the form be modified and expanded. The standards for a comprehensive PPE indicate that the screening should include an extensive medical history, assessment of height, weight, blood pressure, pulses, vision, cardiopulmonary (heart, and lungs), maturation, skin, abdominal, genitalia, and musculoskeletal function. Pursuant to the recommendation of this recent study and the accepted standards of the American Academy of Family Physicians, American Academy of Pediatrics, American Medical Society for Sports Medicine, American Orthopedic Society for Sports Medicine, and the American Osteopathic Academy of Sports Medicine, the PPE form utilized by the Hawaii High School Athletic Association has been drastically modified. The new form includes an expanded medical history, a maturational assessment (Tanner Stage), a complete musculoskeletal examination, and a participation clearance and recommendation.

Adequacy of a pre-participation examination form: a study of Hawaii physicians

Many states currently require a medical screening prior to participation in organized sports. The purpose of this study was to examine the adequacy of the existing pre-participation examination form in Hawaii. One hundred forty-eight physicians who perform school health/pre-participation physical examinations were surveyed. The results indirectly suggest that these physicians agreed that the form should be modified and improved (p, .001).

Prevention of hepatitis B virus in athletic training

Hepatitis B virus (HBV) infection is highly communicable and is the leading cause of acute and chronic liver disease worldwide. In recognition that 10,000 to 15,000 health care workers are becoming infected with HBV annually, the Occupational Health and Safety Administration has instituted strict regulations and guidelines concerning the handling of blood-borne pathogens. Due to the exposure to blood-borne pathogens and potentially infectious materials, athletic training is an allied health care profession that has an increased risk of exposure to HBV. Therefore, it is essential that athletic trainers employ extensive preventive strategies to decrease the exposure to this health-and life-threatening infection.

Multi-adjustable post-operative orthosis for congenital muscular torticollis

A multi-adjustable torticollis orthosis is described for the post-operative bracing of patients after surgical correction of congenital muscular torticollis. The orthosis can be put on in the early post-operative period and the head and neck position can be maintained in the corrected, and later over-corrected position by the built-in multi-adjustable joint-mechanism. The details of the manufacturing are described. Twenty-five patients (13 girls and 12 boys) from age 1 to 22 with congenital muscular torticollis were fitted with the orthosis post-operatively for an average duration of 10 weeks. Satisfactory compliance with the orthosis was found in 23 cases. Complications were minimal (3 cases) and were related to scalp irritation which improved after minor adjustments of the halo.

Sleep apnoea syndrome--a study of 5 cases

Sleep apnoea syndrome (SAS) is common in the West but its prevalence is uncertain in Southeast Asia. Five Chinese patients seen in a Sleep Assessment Unit in Hong Kong are presented to illustrate the spectrum of clinical features and treatment methods involved in obstructive and central sleep apnoea. The first patient is a 45-year old woman with severe obstructive SAS and cardiopulmonary complications who improved significantly after tracheostomy. The second patient is a 43-year old man who improved with weight reduction and protriptyline. The third is a 42-year old man whose SAS did not improve with uvulopalatopharyngoplasty but with continuous positive airway pressure (CPAP). The fourth is a 12-year old girl with obstructive SAS who improved significantly after tonsillectomy. The last patient is a 52-year old man with central SAS who improved with CPAP.

Sleep apnoea presenting as severe hypertension and silent occipital haemorrhage

A 39-year old Chinese man presented with an acute onset of severe headache, accelerated hypertension and subsequently an unexpected extensive right occipital haemorrhage. These were found to be related to a sleep apnoea syndrome which had been unrecognized for many years despite its typical symptoms of loud snoring and excessive daytime sleepiness. Weight reduction led to significant clinical but not polysomnographic improvement of the sleep apnoea syndrome.

Postnatal muscle fibre histochemistry in the rat

Histochemical techniques were used to study the postnatal muscle fibre differentiation patterns in the plantaris and soleus muscles of male Sprague-Dawley rats. Nine groups of animals (n = 6/group) were killed at 1, 6, 11, 16, 21, 26, 31, 36, and 140 days of age. Serial transverse sections of the two muscles were stained with H & E, NADH-D, and myofibrillar ATPase with acid (pH 4.35) or alkali (pH 10.4) preincubation. In each of the age groups, all available fibres across the muscle sections were classified. Obtained data show that fibre types are basically undifferentiated at birth in both muscles. In the plantaris muscle there are about 99% type IIA and less than 1% type I fibres at 6 days of age. Type IIB fibres can be identified at 11 days of age. There are increases in the percentages of type I fibres (from 0.7% to 3.5%) and type IIB fibres (from 1.1% to 6.5%) between 6 and 11 days and between 16 and 21 days respectively. By 36 days of age the relative numbers of type IIA, IIB, and type I fibres in the plantaris are approximately 80%, 14%, and 6%, respectively. A gradual change in fibre-type composition continues until it becomes 47% for type IIA, 43% for type IIB, and 10% for type I at 140 days of age. In the soleus muscle there are approximately 73% type IIA and 26% type I fibres at both 6 and 11 days of age. However, type IIA fibres decrease to 44% and type I fibres increase to 56% at 16 days of age. This rapid shift in fibre composition continues up to 31 days of age when the distribution becomes 25% for type IIA and 74% for type I fibres. Thereafter, the differentiation rate is much slower. At 140 days of age, there are 17% type IIA and 83% type I fibres in the soleus muscle. The results of this study show that the fibre populations in the plantaris and soleus muscles of the rat undergo a postnatal differentiation process. In both muscles the adult fibre population is established by 140 days of age. Although relatively rapid increases of type I and type IIB fibres occur in the plantaris during the second and third weeks of life, differentiation in that muscle appears to be an essentially continuous process. There is a notable shift in the fibre composition of the soleus muscle during the second postnatal week. Differences between the patterns of differentiation in the two muscles are apparent.

Postnatal muscle fibre histochemistry in the rat

Histochemical techniques were used to study the postnatal muscle fibre differentiation patterns in the plantaris and soleus muscles of male Sprague-Dawley rats. Nine groups of animals (n = 6/group) were killed at 1, 6, 11, 16, 21, 26, 31, 36, and 140 days of age. Serial transverse sections of the two muscles were stained with H & E, NADH-D, and myofibrillar ATPase with acid (pH 4·35) or alkali (pH 10·4) preincubation. In each of the age groups, all available fibres across the muscle sections were classified. Obtained data show that fibre types are basically undifferentiated at birth in both muscles.

In the plantaris muscle there are about 99% type IIA and less than 1% type I fibres at 6 days of age. Type IIB fibres can be identified at 11 days of age. There are increases in the percentages of type I fibres (from 0·7% to 3·5%) and type IIB fibres (from 1·1% to 6·5%) between 6 and 11 days and between 16 and 21 days respectively. By 36 days of age the relative numbers of type IIA, IIB, and type I fibres in the plantaris are approximately 80%, 14%, and 6%, respectively. A gradual change in fibre-type composition continues until it becomes 47% for type IIA, 43% for type IIB, and 10% for type I at 140 days of age.

In the soleus muscle there are approximately 73% type IIA and 26% type I fibres at both 6 and 11 days of age. However, type IIA fibres decrease to 44% and type I fibres increase to 56% at 16 days of age. This rapid shift in fibre composition continues up to 31 days of age when the distribution becomes 25% for type IIA and 74% for type I fibres. Thereafter, the differentiation rate is much slower. At 140 days of age, there are 17% type IIA and 83% type I fibres in the soleus muscle.

The results of this study show that the fibre populations in the plantaris and soleus muscles of the rat undergo a postnatal differentiation process. In both muscles the adult fibre population is established by 140 days of age. Although relatively rapid increases of type I and type IIB fibres occur in the plantaris during the second and third weeks of life, differentiation in that muscle appears to be an essentially continuous process. There is a notable shift in the fibre composition of the soleus muscle during the second postnatal week. Differences between the patterns of differentiation in the two muscles are apparent.

Skeletal muscle fiber splitting with weight-lifting exercise in rats

Adult male albino rats were assigned randomly to control (CON) and weight-lifting (WL) groups. The WL rats were subjected to a progressive weight-lifting program against high resistance for 8 weeks. During the last 2 weeks, each WL rat lifted a load equal to 130% of its body weight. The mean weight of the adductor longus muscle was significantly increased in the WL group ( p < 0.05). This increased muscle weight was shown to be due to an increase in the number of fibers per unit cross-sectional area ( p < 0.05), and the mean sizes of both fast-twitch oxidative glycolytic and slow-twitch oxidative fibers were significantly smaller in the WL rats than in the CON rats (p < 0.05). Light and electron microscopic examination showed that five out of eight WL rats exhibited longitudinally split muscle fibers, while only one CON rat had a few centrally placed nuclei. The splitting process appeared as either a "pinching-off" of a small segment from the parent fiber or an invagination of the sarcolemma deep into the muscle fiber in a plane parallel to the sarcomeres. There were preliminary indications that this work-induced fiber-splitting process may be a physiological adaptation of muscle to the stress of exercise.

Enhancement of reflex vagal bradycardia following intracerebroventricular administration of methysergide in cats

Metehysergide in total doses of 100, 200 and 400 micrograms injected into the fourth cerebral ventricle of cats potentiated the reflex bradycardic responses which were evoked by i.v. pressor doses of norepinephrine. Methysergide (400 micrograms) injected i.v., or intracerebroventricularly in vagotomized cats did not affect the reflex bradycardia. These results suggest that the enhancement of reflex vagal activation is due to an action of methysergide in the central nervous system. Intracerebroventricular methysergide significantly reduced the resting arterial pressure and heart rate, while i.v. administration caused only significant bradycardia. Carotid occlusion responses were depressed following both i.v. and intracerebroventricular methysergide. The magnitude of reductions in arterial pressure and heart rate following the injection of methysergide into the fourth cerebral ventricle were the same in vagotomized cats and in intact vagus preparations. It is suggested that depression of cardiovascular function is due to a central action of methysergide and is mediated by reduction in sympathetic outflow.

Effects of swimming on dystrophic Syrian hamster heart

Morphological and histopathological heart changes were determined for sixteen dystrophic Syrian hamsters (B10 14.6 strain) and sixteen normal hamsters. Eight animals were randomly assigned to each of the following groups: dystrophic swim (DYS-SWM), dystrophic sedentary (DSY-SED), normal swim (NOR-SWM), and normal sedentary (NOR-SED). The daily swimming program consisted of an initial 30-minute swim which was gradually extended to 60 minutes by the end of eight weeks. Weights up to 3% body weight were attached during swimming to increase the work load. Sedentary animals received no experimental treatment. Four animals in each group were sacrificed at 4 and 8 weeks after the initiation of treatments. In comparison with the two groups of sedentary animals, the NOR-SWM group had a greater heart weight/body weight ratio at both 4 and 8 weeks (P less than .05), while the DYS-SWM group had an increased ratio only at 8 weeks (P less than .05). Subjective histopathological evaluation of heart lesions showed that the DYS-SED group had many large areas of inflammatory reaction with infrequent diffuse areas of calcification. In contrast, the DYS-SWM group had fewer and smaller areas of inflammatory reaction with moderate amounts of calcification.