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B D Burns

Publications and source records attributed to B D Burns.

At least 19 recordsLinked to original sources
PubMed1992

Morphological correlates of protein kinase C induced potentiation in the chick brain slice.

Continuous perfusion of a chick brain slice with 10 microM 4 beta phorbol 12,13 diacetate (PDAc) produces a significant increase in the amplitude of the response to electrical stimulation at 0.1 Hz recorded within the intermediate and medial part of the hyperstriatum ventrale (IMHV). This PDAc-induced potentiation and that induced by tetanising stimulation appear to share similar mechanisms. Quantitative electron microscopy of synapses within the IMHV from slices in which a PDAc induced potentiation had been produced 30 minutes earlier showed that compared with control slices there was a significant increase in the size of the postsynaptic density of spine synapses. The change was greater in magnitude than that observed in spine synapses following tetanically induced potentiation. No other synaptic parameters were affected.

Animals↗
PubMed1992

Protein kinase activity and synaptic plasticity in a chick brain slice.

In an in vitro slice preparation of the chick brain it is possible to record responses to single electrical stimuli from within the intermediate and medial part of the hyperstriatum ventrale (IMHV), a region known to be involved in learning. The amplitude of such responses is significantly increased by superfusion of the slice with 10 microM 4 beta-phorbol 12,13 diacetate (PDAc), a phorbol ester which stimulates protein kinase activity. The ability of PDAc to induce potentiation is greatest in chicks less than 6 days old. Administration of the kinase antagonist H7 prevents the induction of persistent potentiation and in fact produces a long lasting depression of response amplitude. H7 also produces a short term increase in excitability within the IMHV and results in increased expression of N-methyl-D-aspartate receptor activity.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Potentiation of synaptic responses in slices from the chick forebrain.

Coronal slices, containing part of the medial hyperstriatum ventrale (MHV), were cut from the left forebrains of domestic chicks and maintained in vitro. Records were made of the field responses evoked in the MHV by local electrical stimuli provided at 0.1 Hz. Two 1 min periods of stimulation at 5 Hz, separated by 10 min, were used in attempts to induce a persistent increase in the size of the postsynaptic response to test stimulation at 0.1 Hz. This procedure produced a potentiation which usually lasted longer than 2 h. The probability of inducing this persistent potentiation of the response (PPR) is not distributed evenly over the whole anteroposterior length of the MHV but is higher in slices that also contain the septo-mesencephalic tract ventrally. These are the slices that contain the intermediate part of the medial hyperstriatum ventrale (IMHV); an area that is essential for early behavioural learning. At this level PPR is not confined to the IMHV. It can also be produced in the lateral neostriatum in response to similar local stimulation at 5 Hz. No PPR was observed in either the caudal ectostriatum, or the paleostriatum.

Animals↗
PubMed1991

The effects of age and visual experience on potentiation of responses in slices from the chick forebrain.

A single coronal slice, containing the intermediate part of the medial hyperstriatum ventrale (IMHV) was cut from the left forebrain of a series of domestic chicks and maintained in vitro. Records were made of field responses evoked in the IMHV by local electrical stimuli. Two 1-min periods of 5 Hz stimulation, separated by 10 min, were used in attempts to induce persistent potentiation of the responses (PPR) to test stimulation at 0.1 Hz. In dark-hatched chicks the probability of producing PPR is much higher in slices from chicks aged 2-5 days post-hatch than in those from either younger or older birds. As an independent measure of plasticity in dark-hatched chicks, the probability of eliciting unit responses to repeated stimulation of remote sites in the slice at 3.3 Hz was analysed. This probability was greater in slices from chicks aged 2-5 days than in those from either younger or older birds. In light-hatched chicks the probability of inducing PPR is significantly higher during the first day post-hatch, than in dark-hatched chicks of this age. The probability of producing PPR in slices from light-hatched chicks aged 2-3 days is less than that in slices from either younger or older birds. It is clear that both the age and past experience of the domestic chick affect the neurophysiological properties of slices of brain, tested in vitro.

Age Factors↗
PubMed1991

Morphological correlates of persistent potentiation in the chick brain slice.

In an in-vitro slice preparation of the chick brain it is possible to induce persistent potentiation of responses to single electrical stimuli by giving two bursts of 300 stimuli at 5 Hz separated by ten minutes of control stimulation at 0.1 Hz. We investigated the morphological correlates of this potentiation in a group of 2 day old chicks using quantitative electron microscopical techniques. It was found that in slices which showed a clearly potentiated response there was a significant increase in the size of the postsynaptic densities of synapses on spines in the left hyperstriatum ventrale (IMHV). No such increases were seen in a control group nor in slices which failed to potentiate. These results provide further evidence for the lability of synapses in the IMHV.

Animals↗
PubMed1990

Local circuitry in the IMHV of the domestic chick (Gallus domesticus).

The responses to local stimulation have been recorded from neurons in the intermediate part of the medial hyperstriatum ventrale (IMHV) of the domestic chick, by using an in vitro slice preparation. When the slice is bathed in gassed Krebs' solution, a single stimulus evokes a short-lasting diphasic response. The first phase is negative and lasts some 3 ms, whereas the second, positive phase is often of lower amplitude and usually persists for about 15 ms. The first phase is little altered by perfusion with either Ca2(+)-free Krebs' solution or Krebs' solution containing a high concentration of Mg2+. In contrast, the second phase is abolished by these procedures. The post-synaptic phase is positive when it is recorded anywhere between 0.1-1.25 mm from the stimulated point; however, in the immediate vicinity (0.0-0.1 mm) of the stimulating electrodes, the post-synaptic response is strongly negative. A pair of stimuli has to be separated by at least 10 s to guarantee complete recovery of excitability of the post-synaptic response. The recovery curve for this response shows a refractory period of some 5 ms, a peak of excitability at an interval of about 20 ms, and then a sharp trough of relative inexcitability at about 200 ms. The post-synaptic response is considerably reduced in magnitude and duration by the addition of AP-5 to the perfusion fluid; the remaining post-synaptic response is completely abolished by kynurenic acid. The addition of bicuculline methiodide in concentrations of at least 1 x 10(-6) M increases both the magnitude and duration of the second, positive phase of the response to single stimuli. This extended positive response (which may last from 500-800 ms) is abolished by perfusion with bicuculline dissolved in Ca2(+)-free Krebs' solution. For the entire duration of the extended post-synaptic positive response produced by bicuculline, the irregular discharge of single neurons can be recorded. Like the post-synaptic positive response in Krebs' solution, the much larger response produced by bicuculline shows a very localized negativity beneath the stimulating electrodes and displays an almost identical time-course for the recovery of excitability following a single stimulus. The bicuculline induced positive response is also considerably reduced by the presence of AP-5; the addition of kynurenic acid abolishes the remaining post-synaptic response completely. A post-synaptic response, similar to that produced under bicuculline, can be produced by the addition of a maximally effective dose of d-tubocurarine.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1989

Perceptual and motor factors in the imitation of simple temporal patterns.

This study investigated the relative importance of perceptual and motor factors in the imitation of simple temporal patterns. Previous research in which subjects tap out interval sequences using one finger has suggested that perceptual factors play an important role in response timing. Studies of bimanual tapping, in contrast, stress the importance of motor interactions between the two hands. In this experiment we compared the ability of subjects to tap out two-interval sequences using one finger, two fingers on one hand, and two fingers on opposite hands. The results showed almost identical performance under the three response conditions. It is suggested that the perceptual relations between intervals in a pattern were the main determinant of performance in this experiment.

Adult↗
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↗