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Biomedical subjects

A Whyte

Publications and source records attributed to A Whyte.

At least 37 records · Page 2Linked to original sources
PubMed1995

The hypoglossal canal: normal MR enhancement pattern.

PURPOSE: To review the anatomy of the hypoglossal canal and present the normal precontrast and postcontrast MR appearance of axial posterior fossa images. METHODS: Thirty-one axial MR examinations of the normal posterior fossa were retrospectively reviewed. RESULTS: The hypoglossal canals are well seen on 3-mm-thick axial MR images of the posterior fossa (28 [90%] of 31 patients). Symmetric intense intracanalicular enhancement after intravenous administration of gadopentetate dimeglumine is routine, typically with minor anterior extension into the nasopharyngeal region (28 [100%] of 28). A linear filling defect traversing the enhanced canal often is seen (21 [75%] of 28) and may represent hypoglossal nerve rootlets. Circumferential enhancement of the meninges at the level of the foramen magnum was a common finding (19 [64%] of 28). CONCLUSION: Enhancement within the hypoglossal canal with anterior extension beneath the skull base is a normal finding. This pattern is characteristic enough on MR imaging to aid interpretation of skull base lesions and to exclude the possibility of a mass within the hypoglossal canal.

Adult↗
PubMed1995

Differences in E-selectin expression and leucocyte infiltration induced by inflammatory agents in a novel subcutaneous sponge matrix model.

We have developed a novel subcutaneous sponge matrix model in major histocompatibility complex (MHC) homozygous SLAb/b inbred pigs to study lymphocyte-endothelial cell interactions during inflammation. Polyether sponges were implanted subcutaneously and left for 12 days before injection of proinflammatory agonists. Implanted sponges became highly vascularized and showed markedly increased uptake of i.v.-injected 51Cr-labelled lymphocytes 5 hr after injection of tumour necrosis factor-alpha (TNF-alpha) (3000 U) or phytohaemagglutinin (PHA) (37 micrograms). Lower levels of traffic were seen in sponges 5 hr after injection with interleukin-1 alpha (IL-1 alpha) (3000 U) and no significant traffic occurred in sponges injected with phorbol 12-myristate 13-acetate (PMA) (15 ng) at 5 hr or PHA at 24 hr (compared to sponges injected with medium alone). Electron microscopy of control sponges revealed low numbers of infiltrating leucocytes and relatively 'flat' endothelium. Many more infiltrating leucocytes were present in PHA-injected sponges. However, no ultrastructural evidence was seen of any significant difference between control and activated endothelium. Immunocytochemistry of frozen sections from sponges showed that E-selectin expression was up-regulated markedly by TNF-alpha and PHA at 5 hr, only moderately by IL-1 alpha at 5 hr, and not at all by PMA at 5 hr. By 24 hr in PHA-injected sponges E-selectin expression had fallen markedly from the level seen at 5 hr. Flow cytometric analysis of cellular infiltrates dispersed from sponges injected with TNF-alpha, PHA, IL-1 alpha or medium alone, revealed differences in lymphocyte subset populations. The infiltrate in sponges injected with TNF-alpha 5 hr before removal was dominated by high numbers of CD2+ lymphocytes, whereas the infiltrate induced by PHA showed relatively higher levels of CD2- CD4-CD8- gamma delta T-cell receptor+ (TCR+) T cells revealed by population-specific monoclonal antibodies (mAb). This model, which permits harvesting of leucocytes and endothelial cells for manipulation in vitro, will be useful for the study of leucocyte-endothelial cell interactions in subacute and chronic inflammation.

Animals↗
PubMed1995

Cannabinoids modulate voltage sensitive potassium A-current in hippocampal neurons via a cAMP-dependent process.

Previous studies have shown that cannabinoid receptor analogs increase voltage-dependent potassium A-current (IA) in cultured hippocampal cells. Because cannabinoid receptors inhibit adenylate cyclase, the present study explored whether cAMP played a role in mediating this effect on IA. The specific issue of whether cannabinoid receptor modulation of voltage-dependent IA acts via a cAMP-dependent process was investigated. The cAMP analog, 8-bromo-cAMP, as well as the adenylate cyclase stimulant forskolin, produced concentration-dependent shifts in IA that were opposite those produced by cannabinoid receptor ligands. Moreover, the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine also produced a marked negative shift in the steady-state voltage dependence of IA and increased the effect of forskolin on IA. As shown in previous studies, the cannabinoid agonist WIN 55,212-2 increased IA via a decrease in steady-state voltage-dependent inactivation of IA. WIN 55,212-2 also reversed the effects of forskolin on IA. The electrophysiological studies were paralleled by direct assays of cAMP in these cells, where cannabinoids inhibited forskolin-stimulated cAMP by 50% in a pertussis toxin-sensitive manner. The results confirmed that pertussis toxin-sensitive cannabinoid receptor-mediated changes in IA were probably the result of inhibition of adenylate cyclase. The findings are discussed in terms of modulation of IA conductance properties via cannabinoid receptor-mediated inhibition of cAMP levels within the cell.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Genetically determined CD45 variant of value in leucocyte tracing in vivo in the pig.

This paper describes a monoclonal antibody (mAb), anti-pig CD45 (MAC323), that is directed against a polymorphic determinant. A monomorphic anti-pig CD45 mAb (K252.1E4) bound strongly to leucocytes from both MAC323+ and MAC323- pigs, demonstrating the absence of the epitope rather than the CD45 molecule. The MAC323 determinant was present on all leucocytes in positive pigs, exhibiting different expression levels on subsets (monocytes > lymphocytes > polymorphs), but was absent on red blood cells. Pigs lacking this determinant were healthy and grew normally. Careful selection of male and female SLAb/b pigs produced families that were either positive or negative for this epitope. Interbreeding within these families identified the genetic segregation of this variation, which is consistent with the CD45(323) epitope being inherited as a simple dominant autosomal gene. The lack of this determinant in certain lines of inbred pigs has been used to study the homing, lifespan and tissue distribution of donor unlabelled MAC323+ leucocytes and their subsets (using single- and two-colour immunocytological techniques) in MAC323- recipients after either intravenous injection or exchange transfusion. These results, identifying trafficking areas and subsets in constitutive lymphoid and inflammatory tissues, obtained using this genetic marker, extend those obtained previously using fluorescein isothiocyanate (FITC)-labelled donor cells.

Animals↗
PubMed1995

Distribution of gamma delta T cells in the pig foetus.

The distribution of gamma delta T cells during different developmental stages of pig foetuses was studied using monoclonal antibodies directed against a ruminant WC1 antigen, a T-cell receptor (TCR) subset epitope, and pig Null T-cell antigen. Binding was revealed by the avidin/biotin/peroxidase technique on cryostat sections and flow cytometry analysis. The extrathymic origin of gamma delta T cells was confirmed: gamma delta T cells appeared in the liver, spleen and peripheral blood sooner than in the thymus. In the course of the second half of gestation, these T cells were found in the dermis and intestinal mucosal compartments which represented the predominant loci of gamma delta T cells after birth.

Animals↗
PubMed1994

Adhesion molecule expression and infiltrating maternal leucocyte phenotypes during blastocyst implantation in the pig.

During the implantation period (days 14 to 30 post coitum) in Large White pigs substantial numbers of endometrial sub-epithelial leucocytes were observed from about day 18 p.c. These were predominantly MHC Class II+, CD45+ and reactive for an accessory cell determinant carried by polymorphs and macrophages. Maternal lymphocytes of the CD2+, CD4-, CD8-, and a gamma delta TcR+ subtype identified by the mAb 86D, were also present. Few CD4+, CD8+, or double-positive lymphocytes were seen. CD2-CD4-CD8- gamma delta TcR+ "Null" cells were seen in stroma adjacent to endometrial glands, as were CD2+ lymphocytes. There was no apparent up-regulation of CD18, VLA-4 or CD25. E-selectin could not be detected on endothelium within uterine tissues or on trophectoderm, nor was a ligand for L-selectin detectable. The luminal aspect of the uterine epithelium was strongly reactive with anti-CD15 mAb, which was specifically blocked by lacto-N-fucopentaose III, indicating the presence of the LewisX determinant.

Animals↗
PubMed1994

Complications and cardiovascular risk factors in insulin-dependent diabetes--findings in an Irish clinic and in other European centres.

The Eurodiab Insulin Dependent Diabetes (IDDM) Complications Study was a cross-sectional investigation of a stratified random sample of IDDM patients attending 31 clinics in 16 European countries. We compared the findings in the only participating Irish centre (Cork Regional Hospital) with those of the study group as a whole. There were fewer episodes of ketosis but severe hypoglycaemia occurred more frequently in Cork patients, when compared to the full study group. There were no significant differences in the prevalence of background retinopathy, proliferative retinopathy, microalbuminuria, macroalbuminuria or peripheral neuropathy, when the two groups were compared. However, autonomic neuropathy was significantly less common in Cork. The prevalence of cardiovascular disease was slightly lower than the Eurodiab average in Cork patients, and cardiovascular risk factors were more favourable. Waist-hip ratio and total plasma cholesterol were significantly lower than in the full study group. The prevalence of hypertension was similar, but there were fewer smokers in Cork than in most other centres.

Adult↗
PubMed1994

Infiltrating gamma delta T-cells and selectin endothelial ligands in the cutaneous phytohaemagglutinin-induced inflammatory reaction.

The 24 h phytohaemagglutinin-induced skin inflammatory site (intradermal and subcutaneous) was studied in inbred MHC-homozygous (SLAb/b) pigs and it was found, by immunohistology, that the predominant lymphocytes in the infiltrate are CD2-CD4-CD8-sIg-T-cells, the Null/gamma delta T-cell family, identified using the monoclonal antibodies (mAbs) MAC320 and MAC319 (which recognises a subset of MAC320+ cells). A large percentage of the infiltrating cells expressed the gamma delta T-cell receptor phenotype identified by binding of the mAb 86D. Fewer CD2+, CD8+ and CD4+ cells were present and surface immunoglobulin positive (sIg+) cells were virtually absent in the infiltrate. Areas of lymphocytic infiltration were associated with endothelial activation as determined by expression of the E-selectin and a ligand for the L-selectin.

Animals↗
PubMed1994

Phylogenetic analysis of the rpoB gene from the plastid-like DNA of Plasmodium falciparum.

Malaria and other Apicomplexan parasites harbour two extrachromosomal DNAs. One is mitochondrial and the other is a 35-kb circle with some plastid-like features but whose provenance and function is unknown. In addition to genes for rRNAs, tRNAs and ribosomal proteins, the 35-kb circular DNA of Plasmodium falciparum carries an rpoBC operon which encodes subunits of a eubacteria-like RNA polymerase. The phylogenetic analysis of the complete rpoB sequence presented here supports our inference that the 35-kb circle is the remnant of a plastid genome.

Amino Acid Sequence↗
PubMed1994

Beckwith-Wiedemann syndrome: antenatal diagnosis.

The Beckwith-Wiedemann syndrome is an unusual complex with variable features. The major findings include abdominal wall defects, macroglossia and visceromegaly. These features should be amenable to antenatal ultrasound detection. Only a few such cases have been reported to date. Antenatal diagnosis allows optimum perinatal care. Hypoglycaemia in the neonatal period is common in these babies and requires early detection and appropriate management to prevent long-term intellectual complications. We present a case where the diagnosis was suggested prior to delivery.

Adult↗