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Biomedical subjects

J Millar

Publications and source records attributed to J Millar.

At least 127 records · Page 7Linked to original sources
PubMed1982

The responses of neurones of the superficial dorsal horn to ionophoretically applied glutamate ion.

Extracellular spikes were recorded from neurones in the marginal zone and substantia gelatinosa of the cat lumbar spinal cord using low-noise carbon fibre microelectrodes. Ionophoretic ejection of glutamate ion was used to distinguish soma/dendrite from axon spikes. The receptive fields of the units and their response to percutaneous electrical stimulation was investigated. The majority of units had low-threshold receptive fields on the hair and skin of the toes and foot. The receptive fields indicated a convergence of different modality afferents onto single cells. Ionophoretic glutamate acted synergistically with the action of the natural transmitter from the low-threshold afferents onto the substantia gelatinosa cells.

Action Potentials↗
PubMed1981

Quantitative ionophoresis of catecholamines using multibarrel carbon fibre microelectrodes.

Carbon fibre microelectrodes can be used to measure the local concentration of ionophoretically ejected catecholamines in vitro or in vivo. The method can also be used to measure the transport number for the materials. The concentration measurement takes about 20 ms and can be repeated at up to about 10 Hz without electrode poisoning or deterioration. This paper describes in detail the methodology of the technique and the apparatus required.

Animals↗
PubMed1980

Quantification of noradrenaline iontophoresis.

Several problems are encountered when iontophoresis is used to study the effects of putative neurotransmitters. The most significant is that it is not usually practical to estimate the concentration of drug obtained at the tip of the microelectrode by a current of a given strength. The usual methods, albeit rarely used, include measurement of transport numbers, the use of ion-sensitive microelectrodes and quantitative fluorescent microscopy. With the exception of the ion-sensitive microelectrodes developed for acetylcholine, these techniques are elaborate and time consuming, and cannot be routinely applied to every electrode used. Furthermore, conventional multibarrel microelectrodes have high-impedance recording barrels and thus often display low signal-to-noise ratios when recording single-cell activity, the noise being increased during iontophoresis. We describe here a technique with largely overcomes the problem of low spike signal-to-noise ratio in conventional multibarrel electrodes, and which, unlike the latter, also allows precise determination of the concentration of noradrenaline in the environment of the cells, which affects its excitability. The recording and iontophoretic properties of these electrodes have been described previously. The use of these electrodes to quantify precisely iontophoresed noradrenaline by adapting polarographic techniques is described.

Animals↗
PubMed1980

Contralateral and long range ipsilateral receptive fields of fibres in the central ends of divided dorsal roots.

Action potentials were recorded in the central ends of transected feline lumbosacral dorsal rootlets after all the ipsilateral lumbar and sacral dorsal and ventral roots had been divided. A few fibres had receptive fields on the contralateral hindlimb. A smaller number had receptive fields on the ipsilateral forelimb. Percutaneous electrical stimulation was able to drive some fibres at such high frequencies that the fibres were considered to be branches of the distant afferent. Other fibres were probably synaptically coupled to the afferent. These results are discussed in the context of an hypothesis that primary afferents form many extraneous or aberrrant branches in the spinal cord.

Action Potentials↗
PubMed1980

Computer measurement of dynamic compliance: technique and reproducibility in man.

A computer program was developed to calculate the frequency dependence of dynamic compliance (Cdyn) using continuous data analysis. Cdyn was measured repeatedly in eight normal human subjects over a 2-yr period. Comparison with Cdyn results measured manually showed that the computer program improved 10-fold the ratio of variance within subjects to between subjects of the compliance at specific frequencies, but there was only slight improvement in indices of the slope of the frequency dependence of compliance. We suggest that the absolute compliance at specific frequencies merits further consideration as a pathophysiological measurement and that, if the frequency dependence of compliance continues to be used, standardization of its calculation should be applied and the wide normal range should be more widely appreciated. Measurements of Cdyn in subjects breathing 80% helium-20% oxygen confirm that inertia is insignificant when breathing with tidal volumes of less than 500 ml and frequency of less than 1.5 Hz.

Diagnosis, Computer-Assisted↗
PubMed1980

Mycoplasma pneumonia: failure of erythromycin therapy.

Two cases of mycoplasma pneumonia are described which failed to respond to prolonged treatment with erythromycin. The substitution of oxytetracycline therapy resulted in rapid clinical and radiological resolution.

Adult↗
PubMed1980

Fibre size distribution in the elbow joint nerve of the cat.

The elbow joint nerve, a small branch of the musculocutaneous nerve in the cat, was investigated with low power transmission electron microscopy. By taking a series of overlapping photographs a montage was constructed of the cross section appearance of the complete nerve. Thus, a complete count of the number and sizes of myelinated and unmyelinated fibres was obtained. Two peaks in the distribution of myelinated fibres were consistently found, one at 2-5 micrometers and the other at 8-11 micrometers. The number of unmyelinated fibres was much larger than the number of myelinated fibres, with an average ratio of 4.4:1. This proportion of unmyelinated fibres is higher than that found by earlier workers, but is comparable with that in other peripheral nerves.

Animals↗
PubMed1979

The effect of bilateral ventral noradrenaline bundle lesions on lever pressing for food in rats.

Food reward has been associated with activation of noradrenergic mechanisms in the brain. Using rats trained to press a lever for food reward, we have investigated the effects of 6-hydroxydopamine lesions, which severly depleted hypothalamic noradrenaline, on the willingness of the rats to press the lever for food reward. We found that performance in the food-rewarded task was significantly impaired following such lesions, and that this was especially marked when the task was made more difficult. From our results we suggest that ventral noradrenaline bundle lesions can decrease the rewarding nature of food, thus making the animals less willing to work for food reward.

Animals↗
PubMed1979

Carbon fibre microelectrodes.

A technique for making recording microelectrodes containing an ultrafine carbon fibre is described. This technique can be used for single- and multi-barrel microelectrodes. These microelectrodes not only have a very low signal-to-noise ratio comparable with that found in tungsten microelectrodes but are simpler to make. When used in a multi-barrel array for iontophoretic application of drugs the carbon fibre microelectrode has many advantages over a fluid electrolyte-filled recording barrel, including very high signal-to-noise ratio and relative immunity to spike distortion during application of iontophoretic current.

Animals↗
PubMed1979

Receptive fields of fibres in the central ends of divided dorsal roots.

1. Action potentials were recorded from single fibres in the central ends of divided lumbar dorsal root filaments in anaesthetized cats. 2. Six classes of receptive field could be identified in such fibres, which corresponded very closely to the receptive fields of single primary afferent fibres. 3. For fibres with superficial receptive fileds (cutaneous or hair), a percutaneous electrical stimulation was used to drive the afferents at sustained high frequencies (100, 200 or 300 Hz), and the ability of the recorded fibre to follow the stimulation monitored. About one half of fibres with superficial receptive fields could be driven at sustained high frequencies. 4. The shape of the action potential from the fibre was analysed at different distances from the spinal cord. Close to the spinal cord a clear action potential could be recorded, but further out along the filament the action potential was often attenuated or absent. 5. It is suggested that some at least of these fibres are recurrent collaterals of primary afferent fibres, that taper in size after leaving the spinal cord. The function of such fibres is discussed.

Action Potentials↗