VOR gain by head impulse video-oculography differentiates acute vestibular neuritis from stroke

OBJECTIVE Vestibular neuritis is often mimicked by stroke (pseudoneuritis). Vestibular eye movements help discriminate the two conditions. We report vestibulo-ocular reflex (VOR) gain measures in neuritis and stroke presenting acute vestibular syndrome (AVS). METHODS Prospective cross-sectional study of AVS (acute continuous vertigo/dizziness lasting >24 h) at two academic centers. We measured horizontal head impulse test (HIT) VOR gains in 26 AVS patients using a video HIT device (ICS Impulse). All patients were assessed within 1 week of symptom onset. Diagnoses were confirmed by clinical examinations, brain magnetic resonance imaging with diffusion-weighted images, and follow-up. Brainstem and cerebellar strokes were classified by vascular territory-posterior inferior cerebellar artery (PICA) or anterior inferior cerebellar artery (AICA). RESULTS Diagnoses were vestibular neuritis (n = 16) and posterior fossa stroke (PICA, n = 7; AICA, n = 3). Mean HIT VOR gains (ipsilesional [standard error of the mean], contralesional [standard error of the mean]) were as follows: vestibular neuritis (0.52 [0.04], 0.87 [0.04]); PICA stroke (0.94 [0.04], 0.93 [0.04]); AICA stroke (0.84 [0.10], 0.74 [0.10]). VOR gains were asymmetric in neuritis (unilateral vestibulopathy) and symmetric in PICA stroke (bilaterally normal VOR), whereas gains in AICA stroke were heterogeneous (asymmetric, bilaterally low, or normal). In vestibular neuritis, borderline gains ranged from 0.62 to 0.73. Twenty patients (12 neuritis, six PICA strokes, two AICA strokes) had at least five interpretable HIT trials (for both ears), allowing an appropriate classification based on mean VOR gains per ear. Classifying AVS patients with bilateral VOR mean gains of 0.70 or more as suspected strokes yielded a total diagnostic accuracy of 90%, with stroke sensitivity of 88% and specificity of 92%. CONCLUSION Video HIT VOR gains differ between peripheral and central causes of AVS. PICA strokes were readily separated from neuritis using gain measures, but AICA strokes were at risk of being misclassified based on VOR gain alone.

Inflammation and Optic Nerve Regeneration

Neuroinflammation has long been studied for its connection to the development and progression of Multiple Sclerosis. In recent years, the field has expanded to look at the role of inflammatory processes in a wide range of neurological conditions and cognitive disorders including stroke, amyotrophic lateral sclerosis, and autism. Researchers have also started to note the beneficial impacts of neuroinflammation in certain diseases. Neuroinflammation: New Insights into Beneficial and Detrimental Functions provides a comprehensive view of both the detriments and benefits of neuroinflammation in human health. Neuroinflammation: New Insights into Beneficial and Detrimental Functions opens with two chapters that look at some fundamental aspects of neuroinflammation in humans and rodents. The remainder of the book is divided into two sections which examine both the detrimental and beneficial aspects of inflammation on the brain, spinal cord and peripheral nerves, on various disease states, and in normal aging. These sections provide a broad picture of the role neuroinflammation plays in the physiology and pathology of various neurological disorders. Providing cross-disciplinary coverage, Neuroinflammation: New Insights into Beneficial and Detrimental Functions will be an essential volume for neuroimmunologists, neurobiologists, neurologists, and others interested in the field.

Enhanced depth imaging optical coherence tomography of congenital cavitary optic disc anomaly (CODA).

AIM To report the finding of extension of the 4th hyper-reflective band and retinal tissue into the optic disc in patients with cavitary optic disc anomalies (CODAs). METHODS In this observational study, 10 patients (18 eyes) with sporadic or autosomal dominant CODA were evaluated with enhanced depth imaging optical coherence tomography (EDI-OCT) and colour fundus images for the presence of 4th hyper-reflective band extension into the optic disc. RESULTS Of 10 CODA patients (18 eyes), five patients (8 eyes) showed a definite 4th hyper-reflective band (presumed retinal pigment epithelium (RPE)) extension into the optic disc. In these five patients (seven eyes), the inner retinal layers also extended with the 4th hyper-reflective band into the optic disc. Best corrected visual acuity ranged from 20/20 to 20/200. In three patients (four eyes), retinal splitting/schisis was present and in two patients (two eyes), the macula was involved. In all cases, the 4th hyper-reflective band extended far beyond the termination of the choroid into the optic disc. The RPE extension was found either temporally or nasally in areas of optic nerve head excavation, most often adjacent to peripapillary pigment. Compared with eyes without RPE extension, eyes with RPE extension were more myopic (mean dioptres -0.9±2.6 vs -8.8±5, p=0.043). CONCLUSIONS The RPE usually stops near the optic nerve border separated by a border tissue. With CODA, extension of this hyper-reflective band and retinal tissue into the disc is possible and best evaluable using EDI-OCT or analogous image modalities. Whether this is a finding specific for CODA, linked to specific gene loci or is also seen in patients with other optic disc abnormalities needs further evaluation.

Magneto-optic current sensor with Faraday mirror for linear birefringence compensation

Fiber optic sensors have some advantages in subjects related with electrical current and magnetic field measurement. In spite of the optical fiber utilization advantages we have to take into account undesirable effects, which are present in real non-ideal optical fibers. In telecommunication and sensor application fields the presence of inherent and induced birefringence is crucial. The presence of birefringence may cause an undesirable change in the polarization state. In order to compensate the linear birefringence a promising method has been chosen. This method employs orthogonal polarization conjugation in the back propagation direction of the light wave in the fiber. A study and a simulation of an experimental setup are realized with the advantage of a significant sensitivity improvement.

Application of active heat pulse method with fiber optic temperature sensing for estimation of wetting bulbs and water distribution in drip emitters.

Through the use of the Distributed Fiber Optic Temperature Measurement (DFOT) method, it is possible to measure the temperature in small intervals (on the order of centimeters) for long distances (on the order of kilometers) with a high temporal frequency and great accuracy. The heat pulse method consists of applying a known amount of heat to the soil and monitoring the temperature evolution, which is primarily dependent on the soil moisture content. The use of both methods, which is called the active heat pulse method with fiber optic temperature sensing (AHFO), allows accurate soil moisture content measurements. In order to experimentally study the wetting patterns, i.e. shape, size, and the water distribution, from a drip irrigation emitter, a soil column of 0.5 m of diameter and 0.6 m high was built. Inside the column, a fiber optic cable with a stainless steel sheath was placed forming three concentric helixes of diameters 0.2 m, 0.4 m and 0.6 m, leading to a 148 measurement point network. Before, during, and after the irrigation event, heat pulses were performed supplying electrical power of 20 W/m to the steel. The soil moisture content was measured with a capacitive sensor in one location at depths of 0.1 m, 0.2 m, 0.3 m and 0.4 m during the irrigation. It was also determined by the gravimetric method in several locations and depths before and right after the irrigation. The emitter bulb dimensions and shape evolution was satisfactorily measured during infiltration. Furthermore, some bulb's characteristics difficult to predict (e.g. preferential flow) were detected. The results point out that the AHFO is a useful tool to estimate the wetting pattern of drip irrigation emitters in soil columns and show a high potential for its use in the field.

Liquid-crystal electro-optic modulator based on electrohydrodynamic effects

A new method of light modulation is reported. This method is based on the electro-optical properties of nematic materials and on the use of a new wedge structure. The advantages of this structure are the possibility of modulating nonpolarized light and the improved signal-to-noise ratio. The highest modulating frequency obtained is 25 kHz.

Heated fiber optic distributed temperature sensing for measuring soil volumetric heat capacity and water content: A dual probe heat-pulse approach

The first feasibility study of using dual-probe heated fiber optics with distributed temperature sensing to measure soil volumetric heat capacity and soil water content is presented. Although results using different combinations of cables demonstrate feasibility, further work is needed to gain accuracy, including a model to account for the finite dimension and the thermal influence of the probes. Implementation of the dual-probe heat-pulse (DPHP) approach for measurement of volumetric heat capacity (C) and water content (θ) with distributed temperature sensing heated fiber optic (FO) systems presents an unprecedented opportunity for environmental monitoring (e.g., simultaneous measurement at thousands of points). We applied uniform heat pulses along a FO cable and monitored the thermal response at adjacent cables. We tested the DPHP method in the laboratory using multiple FO cables at a range of spacings. The amplitude and phase shift in the heat signal with distance was found to be a function of the soil volumetric heat capacity. Estimations of C at a range of moisture contents (θ = 0.09– 0.34 m3 m−3) suggest the feasibility of measurement via responsiveness to the changes in θ, although we observed error with decreasing soil water contents (up to 26% at θ = 0.09 m3 m−3). Optimization will require further models to account for the finite radius and thermal influence of the FO cables. Although the results indicate that the method shows great promise, further study is needed to quantify the effects of soil type, cable spacing, and jacket configurations on accuracy.

Mapping variability of soil water content and flux across 1¿1000 m scales using the actively heated fiber optic method

The Actively Heated Fiber Optic (AHFO) method is shown to be capable of measuring soil water content several times per hour at 0.25 m spacing along cables of multiple kilometers in length. AHFO is based on distributed temperature sensing (DTS) observation of the heating and cooling of a buried fiber-optic cable resulting from an electrical impulse of energy delivered from the steel cable jacket. The results presented were collected from 750 m of cable buried in three 240 m colocated transects at 30, 60, and 90 cm depths in an agricultural field under center pivot irrigation. The calibration curve relating soil water content to the thermal response of the soil to a heat pulse of 10 W m−1 for 1 min duration was developed in the lab. This calibration was found applicable to the 30 and 60 cm depth cables, while the 90 cm depth cable illustrated the challenges presented by soil heterogeneity for this technique. This method was used to map with high resolution the variability of soil water content and fluxes induced by the nonuniformity of water application at the surface.

Glutamate receptor-mediated toxicity in optic nerve oligodendrocytes

In cultured oligodendrocytes isolated from perinatal rat optic nerves, we have analyzed the expression of ionotropic glutamate receptor subunits as well as the effect of the activation of these receptors on oligodendrocyte viability. Reverse transcription–PCR, in combination with immunocytochemistry, demonstrated that most oligodendrocytes differentiated in vitro express the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluR3 and GluR4 and the kainate receptor subunits GluR6, GluR7, KA1 and KA2. Acute and chronic exposure to kainate caused extensive oligodendrocyte death in culture. This effect was partially prevented by the AMPA receptor antagonist GYKI 52466 and was completely abolished by the non-N-methyl-d-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), suggesting that both AMPA and kainate receptors mediate the observed kainate toxicity. Furthermore, chronic application of kainate to optic nerves in vivo resulted in massive oligodendrocyte death which, as in vitro, could be prevented by coinfusion of the toxin with CNQX. These findings suggest that excessive activation of the ionotropic glutamate receptors expressed by oligodendrocytes may act as a negative regulator of the size of this cell population.

The visual response of retinal ganglion cells is not altered by optic nerve transection in transgenic mice overexpressing Bcl-2

Attempts to rescue retinal ganglion cells from retrograde degeneration have had limited success, and the residual function of surviving neurons is not known. Recently, it has been found that axotomized retinal ganglion cells die by apoptotic mechanisms. We have used adult transgenic mice overexpressing the Bcl-2 protein, a powerful inhibitor of apoptosis, as a model for preventing injury-induced cell death in vivo. Several months after axotomy, the majority of retinal ganglion cells survived and exhibited normal visual responses. In control wild-type mice, the vast majority of axotomized retinal ganglion cells degenerated, and the physiological responses were abolished. These results suggest that strategies aimed at increasing Bcl-2 expression, or mimicking its function, might effectively counteract trauma-induced cell death in the central nervous system. Neuronal survival is a necessary condition in the challenge for promoting regeneration and eventually restoring neuronal function.

Temporal distribution of the ganglion cell volleys in the normal rat optic nerve

We describe experiments on behaving rats with electrodes implanted on the cornea, in the optic chiasm, and on the visual cortex; in addition, two red light-emitting diodes (LED) are permanently attached to the skull over the left eye. Recordings timelocked to the LED flashes reveal both the local events at each electrode site and the orderly transfer of visual information from retina to cortex. The major finding is that every stimulus, regardless of its luminance, duration, or the state of retinal light adaptation, elicits an optic nerve volley with a latency of about 10 ms and a duration of about 300 ms. This phenomenon has not been reported previously, so far as we are aware. We conclude that the retina, which originates from the forebrain of the developing embryo, behaves like a typical brain structure: it translates, within a few hundred milliseconds, the chemical information in each pattern of bleached photoreceptors into a corresponding pattern of ganglion cell neuronal information that leaves via the optic nerve. The attributes of each rat ganglion cell appear to include whether the retinal neuropile calls on it to leave after a stimulus and, if so when, within a 300-ms poststimulus epoch. The resulting retinal analysis of the scene, on arrival at the cortical level, is presumed to participate importantly in the creation of visual perceptual experiences.

Antibodies against the T61 antigen inhibit neuronal migration in the chick optic tectum.

Cell migration in the central nervous system depends, in part, on receptors and extracellular matrix molecules that likewise support axonal outgrowth. We have investigated the influence of T61, a monoclonal antibody that has been shown to inhibit growth cone motility in vitro, on neuronal migration in the developing optic tectum. Intraventricular injections of antibody-producing hybridoma cells or ascites fluid were used to determine the action of this antibody in an in vivo environment. To document alterations in tectal layer formation, a combination of cell-nuclei staining and axonal immunolabeling methods was employed. In the presence of T61 antibody, cells normally destined for superficial layers accumulated in the ventricular zone instead, leading to a reduction of the cell-dense layer in the tectal plate. Experiments with 5-bromo-2'-deoxyuridine labeling followed by antibody staining confirmed that the nonmigrating cells remaining in the ventricular zone were postmitotic and had differentiated. The structure of radial glial cells, as judged by staining with a glia-specific antibody and the fluorescent tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), remained intact in these embryos. Our findings suggest that the T61 epitope is involved in a mechanism underlying axonal extension and neuronal migration, possibly by influencing the motility of the leading process.

Isolation of cDNA clones encoding RICH: a protein induced during goldfish optic nerve regeneration with homology to mammalian 2',3'-cyclic-nucleotide 3'-phosphodiesterases.

Using data derived from peptide sequencing of p68/70, a protein doublet induced during optic nerve regeneration in goldfish, we have isolated cDNAs that encode RICH (regeneration-induced CNPase homolog) from a goldfish regenerating retina cDNA library. The predicted RICH protein comprises 411 amino acids, possesses a pI of 4.48, and shows significant homology to the mammalian myelin marker enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase; EC 3.1.4.37). The mRNA encoding RICH was demonstrated, by both Northern blot analysis and RNase protection assays, to be induced as much as 8-fold in regenerating goldfish retinas at 20 days after nerve crush. Analysis of total RNA samples from various tissues showed a broad distribution of RICH mRNA, with the highest levels observed in gravid ovary. The data obtained strongly suggest that RICH is identical or very similar to p68/70. The molecular cloning of RICH provides the means for a more detailed analysis of its function in nerve regeneration. Additionally, the homology of RICH and CNPase suggests that further investigation may provide additional insight into the role of these proteins in the nervous system.