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Biomedical subjects

B D Burns

Publications and source records attributed to B D Burns.

At least 37 records · Page 2Linked to original sources
PubMed1988

Response characteristics of neurons in chick forebrain slices.

Coronal sections were taken from the forebrains of domestic chicks, aged 1-20 days, and maintained in vitro. Extracellular recordings of neural activity were made from the intermediate part of the medial hyperstriatum ventrale (IMHV). Spontaneous activity was rarely recorded, but neuronal responses could be evoked by stimulation of various sites. Each recording point was surrounded by an arc of sites which, when stimulated, typically elicited a short-latency field potential. These 'local responses' could be recorded in slices from chicks of any age. Stimulation of more distant sites failed to evoke field potentials from the IMHV. Instead, trains of large, unit action potentials appeared on an undisturbed baseline. Such 'unit' responses could only be evoked by stimuli delivered at specific frequencies. They required facilitation, were of variable latency, and often finally decayed. The number of sites capable of evoking a 'unit' response from the IMHV fell dramatically in slices taken from chicks older than 4 days.

Aging↗
PubMed1988

Transmission of burst responses through slices of rat cerebral cortex.

1. Slices of rat's forebrain, 400 micron thick, have been cut and maintained in a bath perfused with warm oxygenated Krebs solution. Records were made with extracellular micropipettes of the neural responses to local stimulation of the cortex itself or the underlying white matter. 2. Single stimuli at either of these sites could produce an all-or-nothing burst response among nearby neurones. This response usually lasted 0.2-0.5 s during which repetitively discharging cortical units could be recorded at all cortical depths. 3. This burst response was transmitted from the stimulated point across the cortex in all directions with a velocity of roughly 0.1 m s-1. 4. Complete recovery of excitability among neurones generating the burst response took about 10 s. 5. Removal of Ca2+ from the perfusate prevented transmission of this response, as did a high concentration of Mg2+ or 160 mg/100 ml of ethanol. 6. Propagation of the burst response was not dependent upon the integrity of the underlying white matter; it required only that any 20% of the cortical thickness was intact and undamaged. 7. In coronal sections of brain the response could be transmitted from one hemisphere to the other provided that the corpus callosum was intact.

Action Potentials↗
PubMed1987

The effects of arginine-8 vasopressin on blood vessels supplying the cerebral cortex.

A videocamera and a dissecting microscope have been used to record the effects of arginine-8 vasopressin (AVP) upon pial blood vessels in anaesthetised rats. Topical application of AVP caused a contraction of pial arteries, but had no measureable effect upon the diameter of veins. The smallest concentration of AVP that was effective in contracting arteries was 10(-7) mU/microliter. Stronger solutions (10(-5) to 2.0 mU/microliter) produced approximately the same (45%) reduction of external diameter. Contraction was maximal 0.25-1.0 min after application of the hormone, had almost recovered (10% contraction) after 10 min, and showed complete recovery by 30 min. Concentrations of AVP that were greater than 10(-3) mU/microliter produced tachyphylaxis, so that a second application of AVP 30 min later had considerably less effect. Concentrations less than 10(-3) mU/microliter produced no detectable tachyphylaxis. These results suggest that blood flow to the normal cerebral cortex may be partly under tonic control by the local concentration of AVP.

Animals↗
PubMed1986

The effects of arginine-8 vasopressin on the cerebral cortex of rats anaesthetised with urethane.

The effects of arginine-8 vasopressin (AVP) on the spontaneous electrical activity of the cerebral cortex were investigated in rats anaesthetised with urethane. Direct application of a relatively large concentration of AVP (0.5-2.0 mU AVP/microliter; 1.25-5.00 ng AVP/microliter) to the pial surface of a small area of the parietal cortex produced a complete cessation of spontaneous neural activity, which was often preceded by a short-lasting increase in frequency of discharge. There was also a decline in the number of large waves in the local electrocorticogram. These changes occurred after 1-4 min. A slow recovery began 10-30 min later, but was sometimes still incomplete after more than an hour. Only the first application of AVP produced the local effects described above. A second application, 2 hr later, was without effect. Direct application to a small area of one hemisphere did not alter the electrical activity of the contralateral cortex. Smaller concentrations of AVP (0.005-0.200 mU AVP/microliter; 12.5 pg-0.5 ng AVP/microliter) were variable in their actions. Occasionally, no effect at all was seen, while sometimes the cells stopped firing completely. However, the most usual consequence was a reduction in discharge frequency, the magnitude of which appeared to be related to the concentration of AVP applied. A second application of a small concentration of AVP usually failed to reduce the rate of spontaneous discharge.

Animals↗
PubMed1979

The effects of sleep on neurons in isolated cerebral cortex.

Slabs of cat parietal cortex with some 2 mm of underlying white matter were surgically isolated from the rest of the nervous system, without interference with the superficial blood supply. Wire micro-recording electrodes were inserted into the isolated cortex; bone, muscle and skin wounds were repaired and the animal allowed to recover from anaesthesia. The adequacy of surgical isolation was examined histologically 8--12 weeks after operation. Only one of the six preparations reported here showed surviving neural connections with the rest of the brain. Soon after operation, spontaneous bursts of neural activity appeared within the isolated area. These became more frequent until neural discharge was continuous but irregular. Our records were made from this time onwards. The interval distributions obtained from neurons within the isolated area did not differ significantly from log-normal curves. When the unrestrained animal fell asleep, there was no significant alteration in the model interval or geometric standard deviation of interval distributions recorded from cells in isolated cortex. The interval distributions of neurons in isolated cerebral cortex resembled those of neurons in the intact cortex of an alarmed animal. It is concluded that the reduction of modal interval that is shown by neurons in intact cortex when an animal falls asleep is probably due to the neural influence of infracortical structures.

Action Potentials↗
PubMed1979

The correlation between discharge times of neighbouring neurons in isolated cerebral cortex.

The purpose of the experiments was to find out whether neighbouring neurons in chronic preparations of neurally isolated cerebral cortex are more likely to fire synchronously than are similar neurons in the intact brain. Chronically implanted extracellular microelectrodes were used to obtain simultaneous records of the spontaneous discharges of neighbouring neurons in the suprasylvian gyrus of the unanesthetized, unrestrained cat. We have examined multi-unit records obtained from neurons in islands of neurally isolated cortex; these records have been compared with similar records from neurons in the same cortical region of the intact brains of control animals. In isolated cortex, neighbouring neurons showed a tendency to discharge in near synchrony. In contrast, there was a random temporal relation between the firing times of adjacent nerve cells of intact cortex, provided the cat was awake. These results, taken together with the relevant observations of other workers, may indicate the manner in which biologically important information is transmitted within the mammalian brain.

Action Potentials↗
PubMed1972

Responses of neurones in the cat's visual cerebral cortex to relative movement of patterns.

1. We have investigated the responses of single neurones in the visual cerebral cortex of the unanaesthetized, isolated cat's forebrain to excitation of one retina with patterned light. The responses of twenty-six cells to the relative movement of two patterns in the visual field have been recorded.2. We used several forms of relative movement for stimulation, but all of them involved a change in the separation of two parallel and straight light-dark edges.3. Responses to this form of stimulation were compared with the responses of the same cells to simple movement, that is, movement of the same patterns without change of distance between their borders.4. All cells showed a response to relative movement that differed from their response to simple movement.5. The time-locked phasic response differed in 54% of the cells tested. Of cells responding in this way, 83% of tests produced an increased phasic response.6. Relative movement brought about changes in the mean frequency of discharge in 96% of the cells tested. 82% of these cells responded with an increased rate of firing.7. Movement relative to a coarse background pattern affected more neurones and produced a greater change in their behaviour than did movement relative to a fine-grained pattern.8. The neurones tested represented the central part of the visual field (0-10 degrees ); while all were affected by relative movement, those representing points furthest from the optic axis appeared to be most susceptible (we found no correlation between size of receptive field and distance from the optic axis).

Animals↗
PubMed1971

Geometrical illusions and the response of neurones in the cat's visual cortex to angle patterns.

1. This report describes the responses of thirty-six single neurones in the primary visual area of the cat's neurologically isolated and unanaesthetized forebrain, to movements of thin white lines across the visual field. The experiments were designed to record the effects upon the response to a single test line of an added line, which was either parallel to the test line or joined it, making an angle-pattern of 30 degrees . Unit responses were measured in terms of the peak probability of firing derived from a post-stimulus histogram.2. All of the cortical neurones tested exhibited a preferred orientation for stimulation by the test line, i.e. an orientation of the line which produced a maximal response when the line passed through the centre of the unit's receptive field.3. There was no evidence that the orientation of a single test line preferred by cortical neurones was different from that preferred by the same cell when excited by an angle pattern, one arm of which was the original test line.4. The position of a test line (with preferred orientation) in the visual field that produced a maximal response from cortical neurones, was not always the same as the position for maximal response, when a second line was added to make either an angle pattern or to make a pattern of two parallel lines.5. Where the two lines of these patterns were close together and separated by less than the radius of the receptive field, the position for maximal response to the test line was shifted towards the added line. Where the two lines were further apart than this but separated by less than a receptive field diameter, the optimal position for the test line was displaced away from the added line.6. Some evidence was found of a lateral inhibition in the visual system, sufficient to account for the displacements described in paragraphs 4 and 5 above.7. It is concluded that the tip of an angle pattern of 30 degrees produces a distorted cortical image within the primary visual area.8. This neural distortion of sensory information seems adequate to explain the well known illusions of orientation that are associated with human perception of patterns containing acute angles.

Action Potentials↗