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Biomedical subjects

B Matthews

Publications and source records attributed to B Matthews.

At least 19 recordsLinked to original sources
PubMed1992

Drosophila single-minded gene and the molecular genetics of CNS midline development.

Our goal is to understand the molecular mechanisms that govern the formation of the central nervous system. In particular, we have focused on the development of a small group of neurons and glia that lie along the midline of the Drosophila CNS. These midline cells possess a number of unique attributes which make them particularly amenable to molecular, cellular, and genetic examinations of nervous system formation and function. In addition, the midline cells exhibit distinctive ontogeny, morphology, anatomical position, and patterns of gene expression which suggest that they may provide unique functions to the developing CNS. The single-minded gene encodes a nuclear protein which is specifically expressed in the midline cells and has been shown to play a crucial role in midline cell development and CNS formation. Genetic experiments reveal that sim is required for the expression of many CNS midline genes which are thought to be involved in the proper differentiation of these cells. In order to identify additional genes which are expressed in some or all of the midline cells at different developmental stages, a technique known as enhancer trap screening was employed. This screen led to the identification of a large number of potential genes which exhibit various midline expression patterns and may be involved in discrete aspects of midline cell development. Further molecular, genetic, and biochemical analyses of sim and several of the enhancer trap lines are being pursued. This should permit elucidation of the genetic hierarchy which acts in the specification, differentiation, and function of these CNS midline cells.

Animals↗
PubMed1992

Fluid flow through cat dentine in vivo.

An outward flow of fluid through exposed dentine was demonstrated in anaesthetized cats. The flow was measured by observing the movement of the fat droplets of dilute milk in a glass capillary (i.d. 30 microns) with a microscope. The capillary was sealed to the dentine with a plastic cap. The resting flow rate through dentine exposed by fracturing off the tip of a cat's canine ranged from 2.8 to 50.9 pl.s-1.mm-2 (mean 18.1, SD 15.9, n = 12). Raising the pressure at the dentine surface to about 15 cmH2O stopped the flow. Immediately after cutting the pulp at the root apex, in 11 of 12 preparations, the flow reversed. The average flow rate was then 3.8 pl.s-1.mm-2 inward (range 8.4 outward to 15.9 inward, SD 5.4, n = 12). The inward flow after pulp section suggests that an osmotic effect may contribute to the net pressure causing flow. The average hydraulic conductance of the exposed dentine was 1.6 x 10(-8) m.s-1.kPa-1 (range 0.5-2.9, SD 0.8) before pulp section. After pulp section, it increased to an average of 2.5 x 10(-8) m.s-1.kPa-1 (range 0.8-5.2, SD 1.3).

Absorption↗
PubMed1992

Modulation by peripheral conditioning stimuli of the responses of trigeminal brain stem neurones and of the jaw opening reflex to tooth pulp stimulation in chronically prepared, anaesthetized cats.

The effects of peripheral conditioning stimuli on the thresholds of the jaw opening reflex (JOR) and of trigeminal brain stem neurones to tooth pulp stimulation were examined in chronically prepared, anaesthetized cats. High intensity electrical conditioning stimuli applied to the ipsilateral forepaw produced an increase in the thresholds of both responses, with the JOR thresholds being elevated significantly more, and remaining elevated for significantly longer, than those of the neurones. These findings suggest that the elevation of the JOR cannot be explained just by inhibitory effects on the brain stem neurones.

Animals↗
PubMed1992

The vascularity of dental pulp in cats.

The fraction of the volume of the coronal pulp of cat canines that is occupied by blood vessels was estimated by measurement of the cross-sectional areas of all the vessels in a complete transverse section of the pulp from each of four teeth. The sections were taken 0.5 mm from the pulp cornu. Overall, 14.4% of the area of the pulp was occupied by vessels. In the core of the pulp, the average value was 42.9%, and superficially, near the odontoblast layer, it was between 5 and 10%. The average capillary density was 1402/mm2, which is higher than in most other tissues. Laser Doppler flow meters can be used for recording blood flow from the coronal pulp of intact teeth, but these instruments are linear only if the moving blood cells occupy no more than 1% of the tissue volume. The present results suggest that this figure is exceeded in pulp.

Animals↗
PubMed1992

Evidence that nitric oxide or a related substance is a neurovasodilator in the submandibular gland of the cat.

Close-arterial injection of L-NG-nitro arginine methyl ester, a compound that inhibits the synthesis of nitric oxide (NO), caused a dose-dependent reduction in both the parasympathetic and sympathetic (rebound) nerve-induced vasodilatation within the submandibular gland of the cat. At the same time, salivary secretion produced by each nerve was relatively unaffected, and the sympathetic vasoconstriction was enhanced. These results suggest that NO or a related compound may be either a neurotransmitter or neuromodulator contributing to the autonomic nerve-induced vasodilatation in the submandibular gland of the cat.

Animals↗
PubMed1992

Changes in pulpal blood flow and in fluid flow through dentine produced by autonomic and sensory nerve stimulation in the cat.

We have recorded the flow of fluid through exposed dentine in cat canines. The effects on this flow of electrical stimulation of the cervical sympathetic trunk (CST) and of the inferior alveolar nerve (IAN) were investigated. In some preparations, pulpal blood flow was also monitored with a laser Doppler flow meter and the compound action potentials evoked by IAN stimulation were recorded from the tooth. CST stimulation (0.5-5/s) resulted in a significant decrease in the rate of outward flow of fluid through the dentine or, with the higher frequencies tested, a reversal of the flow. CST stimulation also produced vasoconstriction. IAN stimulation caused a significant increase in the rate of outward flow of fluid from the dentine. This effect required the recruitment of A delta fibres: A beta fibres alone had no effect. Pulpal vasodilatation occurred with the same threshold. Mechanical stimulation of dentine in an acutely denervated tooth also caused vasodilatation, indicating that pulpal afferents were involved. The results show that the rate of fluid flow through dentine, and hence the rate of inward diffusion of chemicals from the oral cavity, can be influenced by changes in the state of the pulpal microvasculature.

Action Potentials↗
PubMed1991

The permeability of cat dentine in vivo and in vitro.

The apparent impermeability of dentinal tubules to chemicals applied to exposed dentine in vivo was investigated. It was shown that whereas Evans' blue diffused readily into dentine in extracted teeth, it did not do so in visible amounts when it was applied in vivo. In the in vitro experiments, decreasing the pressure of the Evans' blue solution to 20 cmH2O below atmospheric apparently prevented the dye entering the tubules, while increasing the pressure of the solution to 15 cmH2O or more above atmospheric in vivo resulted in the dye penetrating the dentine in high concentrations. It is concluded that, in cat dentine in vivo, there is an outward flow of fluid through exposed dentinal tubules, and that this flow is sufficient to substantially reduce diffusion into the tubules of chemicals such as Evans' blue.

Animals↗
PubMed1991

Methods for recording the jaw-opening reflex to tooth-pulp stimulation in awake cats.

Techniques are described for use in awake, unrestrained cats which enable recordings to be made from the digastric muscle, electrical stimuli to be applied to the teeth, and intravenous injections to be made via an indwelling cannula. A headpiece was fixed to the skull of the animal and leads were passed subcutaneously from it to electrodes in the muscle and the teeth. A silicone rubber cannula was inserted into the external jugular vein and connected to an injection port in the headpiece. The headpiece incorporated a miniature 9-way connector which was connected to the electrode leads.

Animals↗
PubMed1991

A technique for recording from brain-stem neurones in awake, unrestrained cats.

A method is described which enables single unit recordings to be made from neurones over a wide area of the brain-stem of awake, unrestrained cats. A small headpiece, made from titanium and acrylic, was fixed to the skull over a craniotomy at pre-set stereotaxic co-ordinates. Between recording sessions the craniotomy was sealed. During recording, a miniature micro-manipulator and adjustable titanium support was screwed into the headpiece and recordings were made with tungsten electrodes.

Animals↗
PubMed1991

Section 136 and African/Afro-Caribbean minorities.

Social, demographic and clinical information was collected retrospectively on all 99 people referred to a South London hospital in 1986 under Section 136 of the Mental Health Act (1983), this being the last complete year before local changes in the procedure for assessment of Section 136 cases were initiated. An over-representation of Afro-Caribbeans was confirmed and this seemed to be accounted for largely by young men under the age of 30 who with Africans had very high rates of previous Section 136 referral, were more likely to be perceived as threatening, incoherent and disturbed but less clearly diagnosed with a mental illness, and were more likely than the Caucasian sample to be living in stable accommodation. The implications of these results are discussed.

Adolescent↗
PubMed1990

The thresholds of the jaw-opening reflex and trigeminal brainstem neurons to tooth-pulp stimulation in acutely and chronically prepared cats.

Electrical stimuli were applied to tooth-pulp in cats and the thresholds of the jaw-opening reflex and of neurons in the trigeminal sensory nuclei were determined. The effects of the method of preparation of the animal for stereotaxic recording were determined by making observations on animals set up in one of three ways: acutely in the usual manner; chronically, three to five days before recording; and acutely with precautions to minimize nociceptive input to the central nervous system. The threshold of the jaw-opening reflex increased progressively during the setting up of the normal, acute preparations and at the time brainstem recording began was significantly higher in these than in either the chronic or low-trauma acute preparations. Previous studies have shown that the increase in threshold is maintained for several hours and is not due to the effects of the anaesthetic. In normal acute preparations, few units (27/154) were found that had thresholds below 50 microA, 0.1 ms, whereas many units were encountered that responded to such a stimulus in chronic (147/152) and low-trauma acute (99/127) animals. In the chronic and in low-trauma acute preparations, there was no significant difference between the thresholds of the units in the main sensory trigeminal nucleus and spinal subnucleus oralis compared with those in subnucleus caudalis. Thus the preparation of an animal for stereotaxic recording can cause a severe and long-lasting depression in the excitability of neurons in the trigeminal sensory nuclei and an increase in the threshold of the jaw-opening reflex. This effect will have influenced the results of previous studies on the responses evoked in central neurons by stimulation of tooth-pulp, and may have similarly affected recordings from other regions.

Anesthesia↗
PubMed1990

The effect of bacterial products on human fibroblast and keratinocyte detachment and viability.

An in vitro model has been developed to study the effect of soluble bacterial products on the viability and detachment of skin cell types utilized cultured grafts. Microbial products prepared from clinical isolates of bacterial species which most commonly colonize burn lesions showed marked variation in their ability to detach and kill both keratinocytes and fibroblasts. All three isolates of Acinetobacter spp. tested were effective in causing detachment and death of keratinocytes and fibroblasts, whereas Escherichia coli, Proteus mirabilis and Enterobacter spp. tested had little, or no, effect on detachment or viability for either skin cell type. Four Staphylococcus aureus isolates elicited variable strain-dependent results with regard to detachment and viability. One isolate possessed activity specific for keratinocyte detachment and death. These results indicate the possible undesirable effects such bacterial species may have on graft success in colonized burn wounds.

Bacteria↗
PubMed1989

myc-related proteins and DNA sequences in Trypanosoma brucei.

The cAMP content of Trypanosoma brucei increases in parallel with ascending mammalian parasitemia to very high levels just before differentiation of the long-slender to the short-stumpy bloodstream form. Because expression of myc oncogenes is required for vertebrate cells to interpret proliferation signals and declines in response to cAMP mediated differentiation, we investigated whether T. brucei also harbored myc-like proteins and genes. Accordingly, we probed lysates of long-slenders, short-stumpies and procyclics (insect midgut stage) with antibody to myc proteins and also hybridized myc gene family sequences to procyclic DNA. We found that antibody to myc-family proteins of mammals reacts with 40 kDa and 55 kDa proteins in all three life cycle stages, and that procyclic DNA contains three EcoRI fragments that are homologous to a v-myc probe. One of these fragments also hybridizes to a synthetic 25-mer oligonucleotide deduced from a consensus sequence in the second exon of the myc family and expresses a 3.2 kb mRNA transcript in Northern blots of procyclic RNA. The conservation of myc-family homologous across the broad phylogenetic gap between mammals and trypanosomes illustrates ancient evolutionary relationships and raises the possibility of stage-specific expression of myc genes during the life cycle of T. brucei.

Animals↗
PubMed1989

Genetic transfer systems in Bacteroides: cloning and mapping of the transferable tetracycline-resistance locus.

Conjugation systems that transfer antibiotic resistance in the absence of detectable plasmids are common in Bacteroides, but the mechanism of transfer is poorly understood. We found that linked transfer of tetracycline (TcR) and clindamycin (ClR) resistance by Bacteroides fragilis strain 1126 is induced by growth in either Tc or Cl. We cloned the transferable TcR locus as a 13 kb fragment on the shuttle vector pPH6 in Escherichia coli and showed that this region expresses TcR in Bacteroides but not E. coli. The TcR gene was mapped to a 3 kb region and the ClR gene was shown not to be present in the 13 kb insert. Homologous TcR genes are found in B. fragilis V479 and 1792. Using pulsed-field electrophoresis, the transferable TcR gene was shown to be physically associated with high molecular-weight DNA, suggesting that it is located on the chromosome. A new TcR shuttle vector, pPH7 delta 1.1, was constructed to facilitate use of this selective marker in Bacteroides genetics.

Bacteroides↗
PubMed1989

Autonomic mechanisms in oral sensations.

Sympathetic fibres reach the oro-facial region by several routes, the main one being via the carotid nerve and the trigeminal or facial nerves. Sensory receptors in this region may be affected non-specifically by activity in these fibres as a result of, for example, changes in local blood flow or contraction of pilo-erector muscles. There is evidence that the responses of intradental receptors and periodontal mechanoreceptors may change during stimulation of the cervical sympathetic trunk, but these effects are probably not due to specific modulatory mechanisms. There is no evidence that the parasympathetic nervous system affects the properties of oral receptors. Patients with Horner's syndrome appear to have no sensory abnormalities, apart from pain which is sometimes associated with the onset of the condition. Reflex sympathetic dystrophy seems to be rare in the oro-facial region.

Dental Pulp↗