Heteronymous H-reflex in temporal muscle motor units

An electric stimulation of the masseteric nerve elicits a heteronymous H-reflex in the temporal muscle. The characteristics of this reflex response were investigated by analysis of the firing probability changes of single motor units. Eleven healthy subjects participated in the experiments. The heteronymous H-reflex of the temporal muscle was electrically elicited by stimulation of the masseteric nerve at 120% of the intensity needed for the maximal masseteric M-wave. From 8 to 24 motor units were sampled from the temporal muscle of each subject. Peri-stimulus time histograms of motor unit recordings were built with a 0.5-ms bin width. The mean firing probability was calculated for the 20 ms preceding the stimulus. The firing probability was considered increased when it exceeded the mean by 3 standard deviations. Of 104 sampled motor units, 40 motor units showed a significant increase of the firing probability, which lasted 1 ms or less in 29 of them. In 12 out of 16 motor units, a significant increase of firing probability also persisted at a lower stimulation intensity (120% of the threshold needed to elicit a masseteric M wave). These data indicate that: (1) some temporal muscle motor units are modulated by afferents from the masseter muscle, (2) the heteronymous H-reflex has a monosynaptic component, and (3) there might be a more complex than just monosynaptic organization serving the heteronymous temporal H-reflex. For the latter conclusion regarding synaptic wiring, however, PSTH studies like the present one can offer only indirect evidence, and this question could be better studied in animals.     

Instrumentation and techniques for treating orthopedic infections in horses

Orthopedic infections-those involving bones, joints, tendon sheaths, or bursae-are some of the most difficult problems for equine surgeons to treat successfully. Sources of the infection are usually hematogenous, traumatic, or iatrogenic and knowledge of the most likely causative bacteria is very useful in selecting the most appropriate antimicrobial(s) to either prevent or treat these infections in horses. This article discusses the clinical findings, diagnosis, treatment, and prevention of orthopedic infections in horses. More recent treatment methods such as synovial drainage techniques (arthroscopy and arthrotomy), intrasynovial antimicrobials, regional perfusion of antimicrobials, and antimicrobial-impregnated polymethylmethacrylate (PMMA) beads or cylinders are also addressed.     

Pyogenic liver abscesses and acute schistosomiasis mansoni: report on 3 cases and experimental study

Three children with acute schistosomiasis mansoni developed pyogenic liver abscesses. The abscesses were diagnosed by ultrasonography and confirmed during laparotomy. Staphylococcus aureus were the sole bacteria isolated from the abscesses. An experimental study was carried out in mice to establish whether schistosomiasis is a predisposing cause for pyogenic liver abscesses. Seventeen mice (group 1) were infected with 40 Schistosoma mansoni cercariae (LE strain) and 60 d later inoculated intravenously with a strain of Staph. aureus, isolated from a patient with bacteraemia; 17 mice infected with Sch. mansoni (group 2), 19 infected with bacteria alone (group 3), and 18 uninfected mice (group 4), served as controls. Thirteen group 1 mice (77%) developed multiple liver abscesses while none was observed in the controls. These results indicate that acute schistosomiasis mansoni concurrent with Staph. aureus bacteraemia favours the colonization of the liver by bacteria and the development of pyogenic hepatic abscesses.     

Supplementation with canthaxanthin affects plasma and tissue distribution of alpha- and gamma-tocopherols in mice

The effects of oral doses of canthaxanthin on tissue distribution of alpha- and gamma-tocopherols were investigated in three experiments in male and female Balb/c mice. Mice were assigned to receive canthaxanthin [7 or 14 microg/(g body weight.d)] or placebo (olive oil) by gavage for different periods of time (0, 1, 2, 4 and 6 wk). A 2 wk-treatment with canthaxanthin resulted in incorporation of the carotenoid in all tissues analyzed, including liver, spleen, kidney, lung and heart. In liver, the maximum accumulation of the carotenoid was reached after 2 wk of dosing in female mice and after 6 wk in male mice. Canthaxanthin incorporation was accompanied by changes in alpha- and gamma-tocopherol concentrations in plasma and tissues. These included the following: 1) a significant increase (P < 0.001) in alpha-tocopherol concentration in spleen (21 and 27% in male and female mice, respectively) after 2 wk and in liver ( approximately 50% in both male and female mice) after 6 wk; 2) a significant decrease in gamma-tocopherol concentration in plasma (P < 0.05) and tissues (P < 0.001) after 2 wk of treatment. In female mice, this decrease was 55% in plasma, 43% in liver, 44% in kidney, 71% in lung and 70% in heart. In male mice, the decrease was observed only in plasma (30%), kidney (54%) and heart (46%). In liver, the decrease in gamma-tocopherol concentration was both dose- and time-dependent and significantly (P < 0.001) greater in female than in male mice. We conclude that dietary administration of canthaxanthin modifies tocopherol status in murine tissues.     

Quantification of effects of global ischemia on dynamics of ventricular fibrillation in isolated rabbit heart

BACKGROUND: Ventricular fibrillation (VF) leads to global ischemia of the heart. After 1 to 2 minutes of onset, the VF rate decreases and appears more organized. The objectives of this study were to determine the effects of no-flow global ischemia on nonlinear wave dynamics and establish the mechanism of ischemia-induced slowing of the VF rate. METHODS AND RESULTS: Activation patterns of VF in the Langendorff-perfused rabbit heart were studied with the use of 2 protocols: (1) 15 minutes of no-flow global ischemia followed by reperfusion (n=7) and (2) decreased excitability induced by perfusion with 5 micromol/L of tetrodotoxin (TTX) followed by washout (n=3). Video imaging ( approximately 7500 pixels per frame; 240 frames per second) with a voltage-sensitive dye, ECG, and signal processing (fast Fourier transform) were used for analysis. The dominant frequency of VF decreased from 13.5+/-1.3 during control to 9.3+/-1.4 Hz at 5 minutes of global ischemia (P<0.02). The dominant frequency decreased from 13.9+/-1.1 during control to 7.0+/-0.3 Hz at 2 minutes of TTX infusion (P<0.001). The rotation period of rotors on the epicardial surface (n=27) strongly correlated with the inverse dominant frequency of the corresponding episode of VF (R2=0. 93). The core area, measured for 27 transiently appearing rotors, was 5.3+/-0.7 mm2 during control. A remarkable increase in core area was observed both during global ischemia (13.6+/-1.7 mm2; P<0.001) and TTX perfusion (16.8+/-3.6 mm2; P<0.001). Density of wave fronts decreased during both global ischemia (P<0.002) and TTX perfusion (P<0.002) compared with control. CONCLUSIONS: This study suggests that rotating spiral waves are most likely the underlying mechanism of VF and contribute to its frequency content. Ischemia-induced decrease in the VF rate results from an increase in the rotation period of spiral waves that occurs secondary to an increase in their core area. Remarkably, similar findings in the TTX protocol suggest that reduced excitability during ischemia is an important underlying mechanism for the changes seen.     

The role of polymorphonuclear leukocytes in the resistance to cutaneous Leishmaniasis

The massive infiltration by polymorphonuclear leukocytes (PMN) soon after skin infection with Leishmania major suggests that PMN could participate in reducing parasite load and controlling the spreading of leishmanial infection. Yet, direct evidence for the participation of PMN in host defense against L. major was lacking. We investigated L. major infection in susceptible and resistant mice treated with the monoclonal (mAb) antibody RB6-8C5 that depletes the population of mature neutrophils and eosinophils. Both BALB/c and C57BL/6 mice depleted of PMN show accelerated parasite spreading and more severe footpad swelling than similarly infected untreated mice. In addition, significant higher parasite numbers were found in the lesion draining lymph nodes from PMN-depleted C57BL/6 mice. Histopathological analysis of the paw confirmed neutrophils containing ingested parasites as the dominant cell type in the infiltrate of the first days after infection and the nearly absolute neutrophil depletion in mAb-treated mice. Our data show the importance of PMN in early control of parasite load and parasitism spreading in cutaneous leishmaniasis.     

Subspecific differentiation of Burkholderia cepacia isolates in cystic fibrosis

While ceramide has emerged as a potent signal transducer, inconsistencies in the kinetics of ceramide generation, or its absence, in response to stimuli have led to confusion and skepticism as to its potential role in apoptosis or proliferation. Here we show that in U937 and HL60 myeloid leukemia cells and in normal skin fibroblasts, cell-permeant ceramides can trigger neutral sphingomyelinase activation, sphingomyelin hydrolysis, and endogenous ceramide generation regardless of Bcl2 overexpression. These observations identify neutral sphingomyelinase as a novel target for ceramide and show that this positive feedback mechanism is responsible for signal propagation, as exemplified by mitogen-activated protein kinase activation in daunorubicin-treated cells. This study provides insight into a fundamental process of cell biology. Indeed, such a sustained ceramide-mediated signal throughout the apoptotic process would ensure self-destruction, perhaps by overriding evolutionary conserved primal cell survival mechanisms.     

The Hephaestus Smart Wheelchair system

The Hephaestus Smart Wheelchair System is envisioned as a series of components that clinicians and wheelchair manufacturers will be able to attach to standard power wheelchairs to convert them into "smart wheelchairs." A prototype of the system has been developed and mounted on an Everest and Jennings Lancer2000 wheelchair. The prototype bases its navigation assistance behavior on the behavior developed for the NavChair Assistive Wheelchair Navigation System, but the underlying hardware and software are being designed to facilitate commercialization. This paper describes our design goals for the Hephaestus system and discusses the current status of the system prototype as well as plans for future work.     

Stability of N-Acetylglutamine and Glutamine in Aqueous Solution and in a Liquid Nutritional Product by an Improved HPLC Method

ABSTRACT: Stability of N-acetylglutamine (NAQ) in aqueous solutions from pH 2.0 to 8.0 and at 100 °C and in a liquid nutritional product was compared to glutamine using an improved HPLC method that allowed quantitation of degradation products. NAQ was stable for 6 mo at pH > 4.0 at about 20 °C. N-acetylglutamic acid, the major degradation, was found in samples stored for ≥ 2 wk. At pH 4.0 and higher, it remained at < 1% through 6 mo. At pH 2.0 and 3.0, N-(2,6-dioxo-3-piperidinyl) acetamide was also detected. Pyroglutamic acid formed at pH ≤ 3.0. No degradation of NAQ was observed in a liquid nutritional product (pH = 6.5) after 3 mo.