Corneal D.C. recordings of slow ocular potential changes such as the ERG c-wave and the light peak in clinical work

A set-up for D.C. recordings of slow ocular potentials such as the c-wave of the electroretinogram (ERG) as well as the fast oscillation (FO), the light peak (LP) and the dark trough (DT) in both clinical and experimental work is described. It includes matched calomel half-cells connected by saline-agar bridges to a corneal contact lens on the eye and a reference chamber on the forehead, a low-drift differential-input D.C. amplifier, an A/D converter, a computer, a thermoprinter, a flexible disc memory, a plotter, and a device for light stimulation controlled by the computer.Examples of the usefulness of the set-up in clinical work are shown in the form of D.C. c-wave ERGs of normal subjects as well as of patients with vitelliform macular degeneration, choriocapillaris atrophy, and retinitis pigmentosa. The direct corneal recording of the FO and LP is demonstrated as well. The different origins of the standing potential (SP) of the eye, the ERG c-wave, the FO and the LP are reviewed briefly.     

A slim needle-shaped multiwire microelectrode for intracerebral recording

The construction of a needle-shaped multiwire microelectrode is described. It can be made with simple mechanical tools. The presented electrode assembly consists of 12 insulated nichrome wires (core diameter 25 μm) which are embedded in epoxylite resin. The straight-cut wire tips are aligned lengthwise and have a relative spacing of 150 μm. Outer dimensions vary from 100 × 180 μm at the level of the 1st electrode channel, to 100 × 100 μm at the level of the 12th channel at the tip. The configuration of this electrode was determined by its application: the laminar analysis of evoked potentials in the cortex of the rat. However, the number of channels, the diameter of the (nichrome) wire which determines the surface area of these channels, and the channel spacing can be easily adjusted during construction to meet other experimental requirements, such as the recording of single-unit activity. The electrode which is composed of biocompatible materials is suited for the study of field potentials and multiple-unit activity, in both acute and chronic experiments, and can be used repeatedly. To demonstrate the performance of the electrode assembly, a depth profile of field potentials is presented, accompanied by the corresponding current source density distribution. The potentials were recorded in the somatosensory cortex of the rat following stimulation of the median nerve under ketamine anesthesia.     

MEG Characterization of Spontaneous Alpha Rhythm in the Human Brain

The present piece of research studied the spontaneous alpha rhythm of the human brain by combining the use of a whole-cortex neuromagnetometer and Magnetic Resonance Imaging. Single trials of spontaneous brain activity were recorded from ten human subjects asked to rest, with their eyes either closed or open, in relaxed wakefulness. MEG measurements were conducted over a period of one and a half years. The replicability of the results was confirmed for eight subjects out of ten. For three subjects, the alpha rhythm did not show any reductions due to the opening of the eyes. Both field map pattern and location of the estimated source were persistently stationary during each of the bursts of oscillations of the alpha rhythm. Dipoles were concentrated in clusters, indicating the existence of several spatially distributed sources. The calcarine fissure, the parieto-occipital sulcus and the surrounding occipital and parieto-occipital areas were identified as cortical sites of the brain where the alpha rhythm may originate. For four subjects, the majority of the sources were located near or in the calcarine fissure, while for five subjects, they were located near or in the parieto-occipital sulcus and for the remaining subject they were equally divided between the two generation sites.     

Ensemble noise and current relaxation analysis of K+ current in single isolated salivary acinar cells from rat

The K⁺ channel in rat parotid gland acinar cells were investigated by ensemble current noise analysis in single isolated cells employing the giga-seal whole cell current recording mode. Sets of 20–40 identical de- and hyperpolarization voltage steps were applied and the resultant current records were processed by computer to obtain the mean and the variance of the current. The time-course of the mean current could be fitted by the sum of two exponentials, suggesting a 3-state model. The simplest plausible hypothesis is a model with one open and two closed states. Assuming this model, the relationship between the variance (₂) and the mean current (I) could be fitted by the function ₂/I=i–I/N. The estimated single channeli/V-relations were similar to those taken from single channel current recordings, and the size of the population of channels per cell (N) was 76±26 (n=12). The validity of the model was tested by a successful simulation of the time-course of the variance.     

Electrical properties of metallic electrodes

The series equivalent resistance R and capacitance C of metal/saline electrode/electrolyte interfaces were measured as a function of frequency (100 Hz–20k Hz) and current density (0·25 to 1000 A m⁻²) for eight typical electrode metals. For each of the metals tested, R decreased and C increased as the current density was increased above a critical value (with the exception of silver and MP35N at frequencies above 1 kHz for which R increased and C decreased slightly). With the exception of copper, the current density linearity limit (for 10 per cent decrease in R or 10 per cent increase in C) increased with increasing frequency and, in most cases, the current density linearity limit for 10 per cent increase in C was slightly less than that for 10 per cent decrease in R. Among the metals tested, copper and aluminium had the lowest current carrying capability and rhodium had the highest current-carrying capability. The current carrying capabilities of 316 SS, platinum, silver and MP35N, were intermediate and similar. With increasing current density, an increase in the electrode/electrolyte capacitance was the most sensitive indicator of the current-carrying linearity limit.     

Providing Interdisciplinary Geriatric Team Care: What Does It Really Take?

We concur with Speer and Schneider's arguments (2003 ; this issue) that more psychologists should offer mental health services to older adults and that the primary care system is a good focus of such efforts. Three issues deserve more prominence in their review. First, their argument that older adults are averse to mental health services seems incorrect, given research indicating that older adults prefer psychotherapy to medication for treatment of depression. Second, psychologists working in primary care need to be aware of new Current Procedural Terminology (CPT) codes that allow documentation of psychological work in medical settings. Third, Speer and Schneider allude to interdisciplinary team functioning, but provide little information about models of team care or issues in developing a well-functioning interdisciplinary team; this commentary expands on those topics.     

Caffeine and histamine-induced oscillations of K(Ca) current in single smooth muscle cells of rabbit cerebral artery

In the present experiment, we characterized the intracellular Ca²⁺ oscillations induced by caffeine (1 mM) or histamine (1–3 M) in voltage-clamped single smooth muscle cells of rabbit cerebral (basilar) artery. Superfusion of caffeine or histamine induced periodic oscillations of large whole-cell K⁺ current with fairly uniform amplitudes and intervals. The oscillatory K⁺ current was abolished by inclusion of ethylenebis(oxonitrilo)tetraacetate (EGTA, 5 mM) in the pipette solution. Caffeine- and histamine-induced periodic activation of the large-conductance Ca²⁺-activated K⁺ [K_(Ca)] channel was recorded in the cell-attached patch mode. These results suggest that the oscillations of K⁺ current are carried by the K_(Ca) channel and reflect the oscillations of intracellular Ca²⁺ concentration ([Ca²⁺]_i). Ryanodine (1–10 M) abolished both caffeine- and histamine-induced oscillations. Caffeine- induced oscillations were abolished by the sarcoplasmic reticulum Ca²⁺-adenosine 5-triphosphatase (Ca²⁺-ATPase) inhibitor, cyclopiazonic acid (10 M), and a high concentration of caffeine (10 mM). Inclusion of heparin (3 mg/ml) in the pipette solution blocked histamine-induced oscillations, but did not block caffeine-induced oscillations. By the removal of extracellular Ca²⁺, but not by the addition of verapamil and Cd²⁺, the caffeine-induced oscillations were abolished. Increasing Ca²⁺ influx rate increased the frequencies of caffeine-induced oscillations. Spontaneous oscillations were also observed in cells that were not superfused with agonists, and had similar characteristics to the caffeine-induced oscillations. From the above results, it is concluded, that in smooth muscle cells of the rabbit cerebral (basilar) artery, ryanodine-sensitive Ca²⁺-induced Ca²⁺ release pools play key roles in the generation of caffeine- and histamine-induced intracellular Ca²⁺ oscillations.     

Measurement of current spread from microelectrodes when stimulating within the nervous system

Summary Tungsten stimulating microelectrodes have been tested in monopolar, bipolar and concentric configurations for the extent to which unwanted current spread occurred. Current spread from monopolar electrodes in close conformity with the predictions of the inverse square law, both in vitro and in vivo. The bipolar and concentric configurations, tested only in vitro, had current-spread characteristics which did not follow the inverse square law so closely. The bipolar configuration gave little reduction in spread, compared with a monopolar electrode, but the concentric configuration did reduce the extent of stimulus spread. The extent of spread depends greatly upon a number of experimental variables, including the dimensions of the microelectrode tip. For studies requiring precise localization, with low stimulus currents, it is advisable to determine the inverse square law constant for each experimental situation. For more generalized stimulation purposes within the mammalian C.N.S., employing monopolar microelectrodes of moderate tip size, brief pulses of 10 A can be expected to stimulate myelinated axons within about 0.15 mm of the tip, and 100 A will stimulate within a radius of about 0.5 mm.The work was all done while E.V.B. was on Industrial Training leave from the North-East Polytechnic, Romford Road, London E. 15     

极低频磁场对胞内钙振荡影响的机理分析

基于双钙库模型,本文以离子跨过细胞膜、细胞器膜迁移的几率作为细胞对电磁场的响应因子,来调制流过膜通道的离子的速率,进而影响细胞内钙离子的浓度。数值分析表明:在极低频磁场的作用下,一定能量因子下的频率条件或是一定频率因子下的能量条件可引起钙振荡形式的变化;窗效应是频率因子和能量因子共同作用的结果。