Miyuki Yamamoto

Pathways for the vestibulo-ocular reflex excitation arising from semicircular canals of rabbits

SummaryIn anesthetized albino rabbits, ampullary branches of the vestibular nerve were stimulated electrically. Prominent and stable reflex contraction was induced in extra-ocular muscles by applying single current pulses of relatively long duration, 3–5 msec. Survey with a glass microelectrode revealed that, during application of relatively wide pulses to a canal, primary vestibular fibers discharged impulses repetitively at a rate as high as 300–1400/sec and that after being transmitted across second-order vestibular neurons these impulses built up summated EPSPs in oculomotor neurons, large enough to trigger off motoneuronal discharges. From each semicircular canal, prominent reflex contraction was evoked selectively in two muscles; from the anterior canal in the ipsilateral superior rectus and contralateral inferior oblique; from the horizontal canal in the ipsilateral medial rectus and contralateral lateral rectus; and from the posterior canal in the ipsilateral superior oblique and contralateral inferior rectus. Acute lesion experiments indicated that signals for this excitation reached IIIrd and IVth nuclei via three different pathways; from the anterior canal through the ipsilateral brachium conjunctivum, from the horizontal canal through the ipsilateral fasciculus longitudinalis medialis and from the posterior canal through the contralateral fasciculus longitudinalis medialis.

Topographical representation in rabbit cerebellar flocculus for various afferent inputs from the brainstem investigated by means of retrograde axonal transport of horseradish peroxidase

A small amount of horseradish peroxidase (HRP) was injected into several small areas of the flocculus and adjacent ventral paraflocculus of albino rabbits. Labeled cells were surveyed through the inferior olive, vestibular nuclear complex, nucleus reticularis tegmenti pontis, pontine nucleus and abducens nucleus. Distribution of labeled neurons in these structures varied depending on the location of injection sites, indicating the existence of a fine topographical organization for afferent inputs in the flocculus and adjacent ventral paraflocculus.

Vestibular nucleus neurons relaying excitation from the anterior canal to the oculomotor nucleus

A morphological approach was undertaken to determine which vestibular nucleus neurons relay excitation from the anterior canal to the IIIrd nucleus. In anesthetized rabbits HRP was iontophoresed into the IIIrd nucleus and cells filled with HRP reaction product (positive cells) searched for within the vestibular nuclear complex. By lesioning the MLF or brachium conjunctivum immediately after iontophoresis it was demonstrated that positive cells in the dorsum of the superior vestibular nucleus are backfilled via their axons which ascend in the brachium conjunctivum. By contrast positive cells in the center of the superior nucleus are backfilled via their axons in the MLF. In electrophysiological experiments in the presence of a severed MLF the anterior canal was selectively stimulated for orthodromic, and the 3rd nucleus stimulated for antidromic, activation of vestibular nucleus neurons. Recording extracellularly with glass microelectrodes filled with fast green FCF the only cells both ortho- and antidromically activated were localized to the dorsum of the superior vestibular nucleus. It is concluded that cells dorsally located in the superior nucleus relay the disynaptic excitatory vestibulo-ocular reflex from the anterior canal to the contralateral 3rd nucleus via their axons which ascend in the brachium conjunctivum.

Differential localization of rabbit's flocculus Purkinje cells projecting to the medial and superior vestibular nuclei, investigated by means of the horseradish peroxidase retrograde axonal transport

The retrograde axonal transport of horseradish peroxidase (HRP) was used to study distribution of those Purkinje cells in the flocculus which project to the medial and superior vestibular nuclei of albino rabbits. HRP was injected electrophoretically into those nuclei and after survival for 24-48 h the flocculus was examined microscopically. It was found that Purkinje cells projecting to the medial nucleus were located relatively rostrally, while those projecting to the superior nucleus lay relatively caudally. These two groups of Purkinje cells, however, were distributed in such a way as to yield an interdigitated striped pattern over the surface of the flocculus.

Localization of rabbit's flocculus purkinje cells projecting to the cerebellar lateral nucleus and the nucleus prepositus hypoglossi investigated by means of the horseradish peroxidase retrograde axonal transport

Abstract HRP was injected electrophoretically into the cerebellar lateral nucleus (CLN), the nucleus prepositus hypoglossi (PH), the descending vestibular nucleus (DV) and the caudal portion of the medial vestibular nucleus (MV) of the rabbit. After survival for 36–48 h the cerebellum was examined microscopically. It was found that Purkinje cells projecting to the CLN are densely distributed in the caudal part of the flocculus, while those to the PH cluster in a folium which forms a border zone between the flocculus and the ventral paraflocculus. No specific projection area to the DV and the caudal portion of the MV was found. Only a relatively small number of labelled Purkinje cells were found to be dispersed over the flocculus after HRP injection to them.

Theoretical basis for multielement analysis by coherent forward scattering atomic spectroscopy

Abstract A theoretical basis for multielement analysis by coherent forward scattering atomic spectroscopy is discussed. Forward scattering spectra are calculated for various atomic transitions in the Faraday and Voigt configurations. It is shown that the multielement capability of forward scattering stems from spectral response to continuum radiation. Comparison is made with the Zeeman atomic absorption method. An experimental result with a xenon arc lamp is also given.

Association of Heart Rate with N-terminal Pro-b-type Natriuretic Peptide in Septic Patients: A Prospective Observational Cohort Study

ABSTRACT Background: Excessive sympathetic stress has multiple adverse effects during critical illness including sepsis. Recent studies showed that heart rate control had a significant effect on reducing mortality in septic shock patients. Furthermore, elevated N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels in septic patients were reportedly associated with adverse outcome. However, no study has evaluated the relationship between hemodynamic profiles of septic patients and the circulating cardiac biomarker. Our objective was to determine whether hemodynamic profiles, specifically tachycardia and new-onset atrial fibrillation (AF), were associated with NT-proBNP elevation in septic patients. Methods: We consecutively enrolled patients admitted to our intensive care unit (ICU). NT-proBNP levels, heart rate, and rhythm at ICU admission were measured, and all clinical and laboratory data were prospectively collected. Tachycardia was defined as a heart rate of above 100 bpm. Results: Ninety-five patients out of 267 patients (35.6%) were diagnosed as sepsis. Of these septic patients, 47 presented with tachycardia and 6 developed new-onset AF. Multivariate Cox regression analysis revealed that tachycardia was an independent predictor of 28-day overall survival in septic patients (hazard ratio, 4.22; 95% confidence interval, 1.10–27.72; P < 0.05), but not in nonseptic patients. Multivariate linear regression analysis demonstrated that the presence of tachycardia was an independent determinant of NT-proBNP elevation (P < 0.05) in septic patients, but not in nonseptic patients. Conclusions: Tachycardia was significantly and independently associated with NT-proBNP elevation and lower survival rate in septic patients, although no association was observed in nonseptic patients. Increased NT-proBNP in sepsis with tachycardia might predict poor outcomes in ICU.

Inhibitory interaction between the vestibulo-ocular reflexes arising from semicircular canals of rabbits.

SummaryIn anesthetized albino rabbits, electric pulse stimulation was applied to ampullary branches of the vestibular nerve. Reflex discharges evoked from a canal in an extraocular muscle were depressed very effectively by conditioning stimulation at a certain other canal. The present systematic survey revealed that this reflex depression occurred specifically in 3 combinations of conditioning and testing canals; 1. anterior and posterior canals of the same side; 2. anterior and posterior canals of the opposite sides; and 3. horizontal canals of the two sides. Occurrence of postsynaptic inhibition in oculomotor neurons, on the other hand, was indicated by appearance of slow muscle potentials in extraocular muscles. It was confirmed that this motoneuronal inhibition did not contribute to the reflex depression in the above combination (1). Even in combinations (2) and (3), the accompanying motoneuronal inhibition was eliminated by adjusting intensities of canal stimuli or by severing its pathway in the medulla, or it was discriminated from the reflex depression by their different latencies and time courses. Hence, it was concluded that the reflex depression was attributable, at least largely, to non-motoneuronal inhibition, presumably postsynaptic inhibition at relay neurons for vestibulo-ocular reflexes. Slow muscle potentials evoked from a canal were also used as testing responses, but their depression could not be detected after conditioning at other canals.

Organ System Network Disruption in Nonsurvivors of Critically Ill Patients

Objectives:As interactions of each organ system have been conceptually known to play an important role during life-threatening conditions, we quantitatively evaluated the organ system interactions in critically ill patients and examined the difference in the organ system network structure between the survivors and the nonsurvivors. Design:Prospective observational study. Settings:An ICU of a university hospital. Patients:Two hundred and eighty-two patients who were admitted to the ICU. Interventions:Blood samples were obtained at ICU admission. Measurements and Main Results:We analyzed the associations among nine representative laboratory variables of each organ system using network analysis. We compared the network structure of the variables in the 40 nonsurvivors with that in the 40 survivors. Their baseline characteristics, including the degree of organ dysfunction, were matched using propensity score matching method. Network structure was quantitatively evaluated using edge (significant correlation among variables evaluated by the p value), weight (connective strength of edge evaluated by coefficient), and cluster (group with tight connection evaluated by edge betweenness). The number of edges among the nine variables was significantly fewer for the nonsurvivors than for the severity-matched survivors (3 vs 12; p = 0.035). The mean weight of edges was significantly smaller for the nonsurvivors (0.055 vs 0.119; p = 0.007). The nine laboratory variables for the nonsurvivors were divided into a significantly larger number of clusters (7 vs 2; p = 0.001). Statistical conclusions were preserved with Bonferroni multiple comparison procedure. These findings were consistently observed in comparison of the 40 nonsurvivors with all the survivors. Conclusions:This study, as a preliminary proof-of-concept, quantitatively demonstrated a more disrupted network structure of organ systems in the nonsurvivors compared with that in the survivors. These observations suggest the necessity of assessment for organ system interactions to evaluate critically ill patients.

Mortality prediction by acute kidney injury biomarkers in comparison with serum creatinine

Abstract Objectives: To investigate the performance of acute kidney injury (AKI) biomarkers for mortality prediction. Materials and methods: Cutoff values of urinary L-type fatty acid-binding protein (L-FABP) and N-acetyl-β-d-glucosaminidase (NAG) for AKI diagnosis in ICU were determined in the derivation cohort. The performance of these AKI biomarkers for mortality prediction was evaluated in the validation cohort with stratification of serum-creatinine based AKI diagnosis. Results: Mortality in the AKI patients diagnosed by serum creatinine was increased remarkably when urinary L-FABP and NAG were positive. Conclusions: These AKI biomarkers can specifically detect high-risk patients among creatinine-base diagnosed AKI.