A simple handling technique for mammalian oocytes and embryos during preparation for transmission electron microscopy

Due to their small size, mammalian oocytes and embryos pose unique problems during preparation for transmission electron microscopy. This paper outlines a method which combines protein embedding with centrifugation to locate the specimens on the face of a Beem capsule mould. This method facilitates both the processing of oocytes with minimal loss and rapid location of the specimens within the block for simultaneous sectioning, staining and examination.     

Effects of anxiety arousal and mental stress on the vestibulo-ocular reflex

Although the subjective reports of patients suggest that anxiety may aggravate vertigo and imbalance, there has been little research into how anxiety might directly affect balance system functioning. We conducted two studies to examine the effect of anxiety and arousal on the vestibulo-ocular reflex (VOR). In the first study, pre-lest fear ratings were obtained from 20 normal subjects and 36 anxious subjects immediately prior to rotation and caloric testing. Fear ratings were significantly correlated with the maximum slow-phase velocity (SPV) of nystagmus induced by caloric testing. In the second study, we assessed the VOR response to rotation of 36 normal subjects under 3 task conditions: a) minimal alerting (counting backwards during rotation), b) physical arousal (induced by exertion prior to rotation); c) mental arousal (induced by performance of stressful mental tasks during rotation). Both the physical and mental tasks induced a significant increase in heart rate compared with the alerting condition. The maximum SPV of the nystagmus induced by rotation was significantly greater during performance of the mental task than in the other two conditions. These combined results indicate that anxiety may influence the gain of the VOR.     

Modulation of postural tremors at the wrist by supramaximal electrical median nerve shocks in essential tremor, Parkinson's disease and normal subjects mimicking tremor

The response of postural wrist tremors to supramaximal median nerve stimulation was examined in patients with hereditary essential tremor (n = 10) and Parkinson's disease (n = 9), and in normal subjects mimicking wrist tremor (n = 8). The average frequency of on-going tremor was the same in all three groups. Supramaximal peripheral nerve shocks inhibited and then synchronised the rhythmic electromyographic (EMG) activity of all types of tremor. The duration of inhibition ranged from 90 to 210ms, varying inversely with the frequency of on-going tremor. There was no significant difference in mean duration of inhibition or in the timing of the first peak after stimulation on the average rectified EMG records between the three groups. The degree to which supramaximal peripheral nerve shocks could modulate the timing of rhythmic EMG bursts in the forearm flexor muscles was also quantified by deriving a resetting index. No significant difference in mean resetting index of the three groups was found. These results suggest that such studies cannot be used to differentiate between the common causes of postural wrist tremors.     

Time-dependent optical spectroscopy and imaging for biomedicalapplications

The application of optical spectroscopy and imaging in living tissue is complicated by multiple scattering of light. In spectroscopy, this scattering causes uncertainty in the pathlength traveled by photons in the tissue, while images suffer reduced resolution and contrast. Picosecond light sources and fast detectors have made it possible to address these problems by direct measurement of the photon time-of-flight. Diffusion models of light propagation can be used to relate the measured distribution of photon transit times to the scattering and absorption coefficients of the tissue. The advantages of absolute absorption measurement are demonstrated for two problems: determination of hemoglobin oxygenation in tissue and in vivo measurement of the uptake of an exogenous chromosphere such as photosensitizer. Optical imaging may also be improved by the elimination of multiply scattered photons or by selective detection of photons arriving from a given region of the tissue. The potential advantages of these techniques are discussed and illustrated with experimental data     

Reaction of hexamethylphosphorous triamide with cotton cellulose

The reactivity of hexamethylphosphorus triamide, (P[N? (CH₃)₂]₃) (HPT), with cotton cellulose was examined under various conditions. HPT was found to react readily with the cellulose to produce a cellulose phosphite and/or phosphate ester having approximately one acidic hydrogen atom per phosphorus atom. The reaction of HPT with cotton cellulose was efficiently catalyzed by dimethylamine hydrochloride (1%). The phosphorus content imparted by the catalyzed reaction on cotton fabrics was approximately twice that imparted by the uncatalyzed reaction. Flame resistance of the treated fabrics ranged from fair to excellent. The treated fabrics also exhibited ion exchange properties and some crosslinking.     

Serotonin and serotonin receptors in the central auditory system

Single channel currents were activated by GABA (0.5 to 5 microM) in cell-attached and inside-out patches from cells in the dentate gyrus of rat hippocampal slices. The currents reversed at the chloride equilibrium potential and were blocked by bicuculline (100 microM). Several different kinds of channel were seen: high conductance and low conductance, rectifying and "nonrectifying." Channels had multiple conductance states. The open probability (Po) of channels was greater at depolarized than at hyperpolarized potentials and the relationship between Po and potential could be fitted with a Boltzmann equation with equivalent valency (z) of 1. The combination of outward rectification and potential-dependent open probability gave very little chloride current at hyperpolarized potentials but steeply increasing current with depolarization, useful properties for a tonic inhibitory mechanism.     

Fluorescent heterogeneities in turbid media: limits for detection, characterization, and comparison with absorption

The fundamental limits for detection and characterization of fluorescent (phosphorescent) inhomogeneities embedded in tissuelike highly scattering turbid media are investigated. The absorption and fluorescence contrast introduced by exogenous fluorophores are also compared. Both analyses are based on practical signal-to-noise ratio considerations. For an object with fivefold fluorophore concentration and lifetime contrast with respect to the background tissue, we find the smallest detectable fluorescent object at 3-cm depth in tissuelike turbid media to be ~0.25 cm in radius, whereas the smallest characterizable object size is ~0.75 cm in radius, given a model with 1% amplitude and 0.5 degrees phase noise. We also find that, for fluorescence extinction coefficients epsilon 相似文献   

Fluorescent diffuse photon density waves in homogeneous and heterogeneous turbid media: analytic solutions and applications

We present analytic solutions for fluorescent diffuse photon density waves originating from fluorophores distributed in thick turbid media. Solutions are derived for a homogeneous turbid medium containing a uniform distribution of fluorophores and for a system that is homogeneous except for the presence of a single spherical inhomogeneity Generally the inhomogeneity has fluorophore concentration, and lifetime and optical properties that differ from those of the background. The analytic solutions are verified by numerical calculations and are used to determine the fluorophore lifetime and concentration changes required for the accurate detection of inhomogeneities in biologically relevant systems. The relative sensitivities of absorption and fluorescence methods are compared.