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Biomedical subjects

H C Jones

Publications and source records attributed to H C Jones.

16 recordsLinked to original sources
PubMed1992

Effect of histamine and antagonists on electrical resistance across the blood-brain barrier in rat brain-surface microvessels.

The effect of histamine on blood-brain barrier permeability was investigated using in situ measurement of transendothelial electrical resistance in brain-surface microvessels of anaesthetized rats. Mean resistance of vessels superfused with artificial cerebrospinal fluid was 1500 omega.cm2, indicating a tight barrier with low ion permeability. The addition of 10(-4) M histamine resulted in a 75% decrease in resistance, in both arterial and venous vessels, indicating a marked increase in barrier permeability. To determine the nature of the response to histamine, rats were given presurgical intraperitoneal injections of promethazine (H1 receptor antagonist), cimetidine (H2 receptor antagonist) or indomethacin (cyclo-oxygenase inhibitor), singularly and in combinations. Cimetidine completely blocked the histamine-mediated increase in barrier permeability whereas promethazine only had a small effect and indomethacin was ineffective. In addition, cimetidine treatment resulted in a 100% increase in basal resistance in both arterial and venous vessels, suggesting endogenous histamine was acting to increase blood-brain barrier permeability. It is concluded that histamine causes an increase in blood-brain barrier permeability which is mediated via endothelial H2 receptors, and that the electrical resistance in cimetidine-treated rats most closely represents the true permeability of the blood-brain barrier.

Animals↗
PubMed1992

MR imaging for measurements of ventricles and cerebral cortex in postnatal rats (H-Tx strain) with progressive inherited hydrocephalus.

As part of a wider investigation on brain structure and function in young rats with inherited hydrocephalus, this study was undertaken to develop a technique to monitor, and quantify, progressive changes in ventricle and cortical dimensions in hydrocephalic rats in vivo. Magnetic resonance images were obtained with a T1-weighted protocol and a multislice variant of the inversion recovery sequence which displayed optimal contrast between cerebrospinal fluid and brain parenchyma. Rats were imaged at 7, 14, and 21 days after birth by taking 10 contiguous 2.0-mm coronal slices. Area and distance measurements were taken from the displayed images, enabling calculation of ventricle volumes, cortical length, and cortical thickness. The lateral ventricle volume, which was already 100-fold larger than control at 7 days, increased to over 1000 mm3 at 21 days. The anterior-posterior length of the cortex was up to 27% larger in hydrocephalics and the cortical mantle was up to 75% thinner, particularly in the posterior cortex. Subsequent fixation and histological sectioning of two 21-day-old rats showed that the smaller dimensions, which were obtained from analysis of the sections, could be accounted for by shrinkage of the tissue during dehydration and wax embedding.

Aging↗
PubMed1991

The cerebral cortex in congenital hydrocephalus in the H-Tx rat: a quantitative light microscopy study.

Hydrocephalus in the H-Tx rat first develops in late gestation and causes death at 4-7 weeks. The effect of hydrocephalus on overall cortical dimensions and on five specific regions (frontal, sensory-motor, parietal, auditory and visual) has been studied by quantitative light microscopy at 10 and 30 days after birth. The lateral ventricle volumes in hydrocephalic rats were about 40 x larger than controls and increased fourfold between 10 and 30 days. Cortical volume was reduced by a small amount at 10 days but was larger in hydrocephalics at 30 days. Thinning of the cortical mantle was severe with disruption of the laminar structure, particularly in the auditory and visual regions, where it was already present at 10 days. The density of cortical cells (neurones and glia) was not altered in hydrocephalics at 10 days but was reduced in all regions at 30 days. Estimates of total cell number suggest that the lower density was not associated with an overall loss of cells. Capillary numerical density was not affected by the hydrocephalus at 10 days after birth but by 30 days it was significantly lower, particularly in the worst-affected posterior regions. The results show that the cerebral cortex is severely distorted and that in advanced hydrocephalus, although overall cell number is not affected, both cell density and capillary density are lower by up to 30%.

Aging↗
PubMed1991

Cerebrospinal fluid pressure in 10-day-old rats with congenital hydrocephalus.

Rats from the H-Tx strain develop hydrocephalus through a developmental obstruction of the cerebral aqueduct. The progressive ventriculomegally is accompanied by thinning of the cerebral cortex which is already present 10 days after birth. However, a previous study found that the CSF pressure was not significantly raised until 21 days after birth. New experiments have now been performed over a 90 min. period using control and hydrocephalic 10-day-old rats under light pentobarbitone anaesthesia, in order to study the level, time-course and morphology of the resting intraventricular pressure. The mean pressure and its fluctuations were calculated for each minute. Control rats had a mean pressure of 19.3 +/- 1.23 (SEM) mm H2O (n = 9, range: 13.6-24.7) and in hydrocephalic rats, pressure was significantly higher at 23.5 +/- 1.13 mm H2O (n = 9, range: 18.1-28.3). There was no consistent trend with time and no significant difference between groups in pressure fluctuations, but at least two of the hydrocephalic rats showed episodic waves similar to "B"-waves in humans.

Animals↗
PubMed1979

The structure of the roof of the fourth ventricle in pigeon and chick brains by light and electron microscopy.

The hindbrains and meninges of the pigeon and chick have been examined by light and electron microscopy. Serial section histology of the skull with the brain and meninges intact has shown that the caudal end of the roof of the fourth ventricle consists of an extensive membranous pouch which projects caudally and dorsally into the subarachnoid space. Electron microscopy of selected areas of the membranous pouch in pigeon has shown it to consist of two components: ependymal cells and pial tissue. The membrane ependymal cells are squamous, adjacent cells being linked by intermediate junctions. At the junction with the surface of the medulla the ependymal cells are continuous with the ventricular ependyma, and at the choroid plexus they are continuous with the choroid plexus epithelium. These results are discussed in relation to the fluid spaces in and around the hindbrain.

Animals↗
PubMed1978

Continuity between the ventricular and subarachnoid cerebrospinal fluid in an amphibian, Rana pipiens.

Continuity between the ventricular and subarachnoid cerebrospinal fluid has been investigated in Rana pipiens. The structure of the posterior tela, a deficient membrane situated at the extreme caudal end of the roof of the fourth ventricle, has been studied using whole membrane mounts and by light microscopy of resin embedded tissue. The ependymal component consists of columnar and rounded cells which form a regular 'syncytium' enclosing round and oval fenestrations. Small fenestrations are covered on the subarachnoid side by elongated pial cells and thus do not give total continuity between the fourth ventricle and the subarachnoid space. Large fenestrations, on the other hand, are accompanied by equivalent pial fenestrations giving direct access between the fluid compartments. Towards the caudal end the fenestrations break up and the numbers of ependymal and pial cells decrease, the caudal end itself being characterised by a small remaining clump of ependyma and pia or of pia alone. Flow through the tela has been studied using fluorescein-labelled dextran placed in the intraventricular space. Infusion into the lateral ventricle and subsequent localisation by fluorescence microscopy shows the marker to be in the fourth ventricle, in the fenestrations of the posterior tela and in the subarachnoid space overlying the tela. Infusion of the marker followed by freezing and examination of the cut heads on a freezing microtome, shows fluorescence throughout the ventricular system, in the subarachnoid space adjacent to the posterior tela and also along the dorsal subarachnoid space of the spinal cord.

Animals↗
PubMed1978

Adaptation of the acoustic reflex.

The characteristics of acoustic reflex adaptation were studied in human subjects. Contralateral stapedial reflex measurements were made by monitoring changes in acoustic conductance and susceptance with a 220-Hz probe. The reflex activators included four tonal stimuli (500, 1000, 2000, and 4000 Hz) and broadband noise presented for 180 s at 96, 104, and 112 dB SPL. The data are presented as change in acoustic admittance and in percent of maximum admittance change. The static admittance of the ear was found to drift systematically toward lower admittance values in the absence of contralateral stimulation. All stimulus conditions demonstrated some reflex adaptation. The half-life and time of onset of adaptation were found to vary directly with intensity and inversely with frequency. The effects of stimulus parameters on the rates of reflex adaptation are discussed. A previously described exponential model of reflex adaptation provided a reasonable first approximation to the data.

Acoustic Stimulation↗
PubMed1976

The value of self-test items in tape--slide instruction.

Two tape-slide sequences in general pathology were used in an experiment to assess the value of self-test items and to determine whether it is better to intersperse the self-test items in the programme or place them all at the end of the sequence. The programmes were presented to a random sample of thirty-six students from a class of 149 in one of three forms: version 1, tape-slide programme without self-test items; version 2, tape-slide programme with self-test items interspersed between sections of the sequence; and version 3, tape-slide programme with all self-test items at the end of the sequence. Each student worked a pre-test before studying versions 1, 2 or 3 of a programme. A week later they worked through the post-test which was identical to the pre-test. At the same time they filled in a short attitude questionnaire on the teaching method. All students learned from the programmes. There was improvement in the post-test on the mean pre-test scores for all versions of both programmes. For one programme there was no significant difference between the mean post-test scores for students studying versions 1, 2 or 3, but for the other programme there was a significant difference between the versions. In this case the inclusion of self-test items was better for learning than no self-test items, and it was better if the self-test items were placed at the end of the sequence. A highly favourable attitude to the method is reported.

Audiovisual Aids↗