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Biomedical subjects

M M Black

Publications and source records attributed to M M Black.

At least 19 recordsLinked to original sources

Tau is enriched on dynamic microtubules in the distal region of growing axons.

It is widely held that tau determines the stability of microtubules in growing axons, although direct evidence supporting this hypothesis is lacking. Previous studies have shown that the microtubule polymer in the distal axon and growth cone is the most dynamic of growing axons; it turns over more rapidly and is more sensitive to microtubule depolymerizing drugs than the polymer situated proximally. We reasoned that if the stability of axonal microtubules is directly related to their content of tau, then the polymer in the distal axon should have less tau than the polymer in the proximal axon. We tested this proposition by measuring the relative tau content of microtubule along growing axons of cultured sympathetic neurons immunostained for tau and tubulin. Our results show that the tau content of microtubules varies along the axon, but in the opposite way predicted. Specifically, the relative tau content of microtubules increases progressively along the axon to reach a peak near the growth cone that is severalfold greater than that observed proximally. Thus, tau is most enriched on the most dynamic polymer of the axon. We also show that the gradient in tau content of microtubules does not generate corresponding gradients in the extent of tubulin assembly or in the sensitivity of axonal microtubules to nocodazole. On the basis of these findings, we propose that tau in growing axons has functions other than promoting microtubule assembly and stability and the key sites for these functions are the distal axon and growth cone.

Adrenergic Fibers

Microtubule assembly and turnover in growing axons.

We have shown previously that axonal microtubules (MTs) are composite, consisting of two distinct domains that differ in their content of tyrosinated alpha-tubulin (tyr-tub). One domain is poor in tyr-tub and is situated at the minus end of the MT. The other domain is rich in tyr-tub and extends from the plus end of the tyr-tub-poor domain to the end of the MT. We have proposed that the spatial variation in the relative content of tyr-tub along individual MTs reflects corresponding variations in their dynamic properties. The present experiments have tested this hypothesis directly by microinjecting biotin-labeled tubulin (Bt-tub) into cultured sympathetic neurons and then quantifying the appearance of Bt-tub in the tyr-tub-rich and tyr-tub-poor polymer of the axon. Bt-tub appeared in axonal MTs with a half-life (t1/2) of approximately 2.2 hr. This time course reflected an average of two distinct components corresponding to the tyr-tub-rich and tyr-tub-poor polymer that had apparent t1/2 values of approximately 1.3 and 3.3 hr, respectively. In individual MTs, Bt-tub first appeared in the tyr-tub-rich domain and then only later appeared in the tyr-tub-poor domain. Also, the appearance of Bt-tub in the tyr-tub-rich polymer typically began precisely at its origin from the tyr-tub-poor domain, indicating that the tyr-tub-poor polymer is assembly-competent and nucleates the assembly of tyr-tub-rich polymer locally within the axon. The stability properties of axonal MTs are discussed in terms of organizing MT assembly locally in the axon and generating long MTs for growing long axons.

Animals

97-kDa linear IgA bullous dermatosis (LAD) antigen localizes to the lamina lucida of the epidermal basement membrane.

Linear IgA bullous dermatosis (LAD) is an autoimmune blistering disease in which IgA autoantibodies develop against the epidermal basement membrane zone. Target antigens of the circulating autoantibodies are thought to be heterogeneous, and their ultrastructural localization has not been fully elucidated. Previous studies with immunoblotting have demonstrated that the 97-kDa autoantigen is detected most frequently in patients' sera and is thought to be a major LAD antigen. Although a recent report suggests that the 97-kDa antigen localized to the hemidesmosomal plaques and the adjacent lamina lucida, discrepancies still exist among previous immunoelectron microscopic findings. To identify the precise localization of the 97-kDa LAD antigen, we used two different low-temperature immunoelectron microscopic techniques. For immunolabeling, we selected five LAD sera that had a high titer of autoantibodies against the 97-kDa LAD antigen. A post-embedding method with cryofixation and freeze substitution failed to immunolabel the 97-kDa LAD antigen. Cryoultramicrotomy with immunoelectron microscopy succeeded in preserving the antigenicity of the 97-kDa LAD antigen. In all cases, the majority of labeling occurred in the lamina lucida beneath the hemidesmosomes. No specific labeling was observed in the hemidesmosomal attachment plaques or the lamina densa or sublamina densa region, including anchoring fibrils. These results indicate that the 97-kDa LAD antigen is a component of the lamina lucida.

Animals

Biochemical properties of cortical allograft bone using a new method of bone strength measurement. A comparison of fresh, fresh-frozen and irradiated bone.

There have been conflicting reports on the effects of gamma irradiation on the material properties of cortical allograft bone. To investigate changes which result from the method of preparation, test samples must be produced with similar mechanical properties to minimise variations other than those resulting from treatment. We describe a new method for the comparative measurement of bone strength using standard bone samples. We used 233 samples from six cadavers to study the effects of irradiation at a standard dose (28 kGy) alone and combined with deep freezing. We also investigated the effects of varying the dose from 6.8 to 60 kGy (n = 132). None of the treatments had any effect on the elastic behaviour of the samples, but there was a reduction in strength to 64% of control values (p < 0.01) after irradiation with 28 kGy. There was also a dose-dependent reduction in strength and in the ability of the samples to absorb work before failure. We suggest that irradiation may cause an alteration in the bone matrix of allograft bone, but provided it is used in situations in which loading is within its elastic region, then failure should not occur.

Adolescent

A comparison of valve resistance, the continuity equation, and the Gorlin formula against directly observed orifice area in bioprosthetic valves in the mitral position: an in vitro study.

BACKGROUND AND AIMS OF THE STUDY: There is no consensus over how to describe forward flow through valves in the mitral position. There are three main candidate hydraulic formulae; resistance, the Gorlin formula and the continuity equation. However, virtually no work has been performed to validate resistance and the continuity equation for valves in the mitral position. The aim of this study, therefore, was to compare the three formulae against an independent standard provided by directly observed orifice areas. MATERIALS AND METHODS: Five bioprosthetic valves with orifice areas between 0.14 cm2 and 2.33 cm2 were studied in a pulse simulator at up to 20 different stroke volume/rate combinations using quasi-physiologic flow curves. Orifice areas were measured using a video camera, pressure difference using strain gauge transducers and Doppler signals using a 1.9 MHz Pedoff probe with a Vingmed SD50 system. RESULTS: The Gorlin ratio (flow/square root of mean delta P) had a direct curvilinear relationship with the orifice area (log(y) = 0.31 + 0.36x; r = 0.94, SEE 0.08 cm2, p < 0.0001). Resistance (mean delta P/flow) had an indirect curvilinear relationship (log(y) = 0.19 - 0.55x, r = -0.93, SEE 0.13 cm2, p < 0.0001). The continuity equation was directly related to observed orifice area although with high scatter (y = 1.13 + 0.79x; r = 0.90, SEE 0.23 cm2, p < 0.0001). Although both the Gorlin ratio and resistance changed with flow, there was also a tendency for observed orifice areas to increase with flow. Empirical effective orifice areas calculated using the regression equations closely resembled observed orifice areas and agreement was reasonable, with 95% limits of -0.33 cm2 to +0.33 cm2 (Gorlin), -0.41 cm2 to +0.42 cm2 (resistance) and -0.40 cm2 to +0.48 cm2 (continuity). CONCLUSION: In conclusion, no single formula adequately predicted all observed orifice areas although resistance and the Gorlin formula gave useful predictions after empirical correction.

Bioprosthesis

Endothelial cell activation in cutaneous vasculitis.

Markers of endothelial cell activation were measured in 28 patients presenting with various forms of limited or focal type cutaneous vasculitis. Plasma levels of tissue plasminogen activator antigen (t-PA:Ag), plasminogen activator inhibitor type 1 antigen (PAI-1:Ag) and PAI-1 activity, fibrin plate, von Willebrand factor antigen (vWF:Ag), tissue factor (TF) and soluble thrombomodulin (sTM) were measured. In comparison with the control group (n = 20) there was a significant increase in t-PA:Ag, vWF:Ag and TF (P < 0.05, Mann-Whitney U-test) in the cutaneous vasculitis group. This study confirms that measurable degrees of endothelial activation occur in cutaneous vasculitis. Cutaneous vasculitis includes a diverse group of clinical conditions, which are associated with inflammatory changes in cutaneous blood vessels with local fibrin deposition. The aetiology and pathogenesis of the majority of these entities remain unknown. Causative mediators are thought to include immune complexes, anti-endothelial cell antibodies, cytotoxic lymphocytes and viruses. Histologically, immune complexes and complement are frequently detected on the vessel wall, and serologically anti-endothelial antibodies are often detected in patients with vasculitis and in systemic lupus erythematosus (SLE) which correlate with the severity of cutaneous vasculitis, arthritis and nephritis. Lymphocyte-mediated toxicity to endothelial cells has been reported in a small number of patients with giant cell arteritis and Takayasu's arteritis. The vascular endothelium plays a central part in the control of haemostasis. Under physiological conditions endothelial cells present an anticoagulant surface to blood constituents, partially due to surface expression of heparan sulphate and thrombomodulin (TM). Heparan sulphate binds antithrombin III (ATIII), thereby accelerating inactivation of intrinsic coagulation enzymes. Thrombomodulin is an endothelial cell surface glycoprotein which promotes anticoagulation by forming a complex with thrombin which then activates protein C. Activated protein C together with a cofactor, protein S, inactivates FVa and FVIIIa. von Willebrand factor (vWF) is synthesized by endothelial cells, stored in Weibel-Palade bodies and released into the circulation upon endothelial stimulation. vWF mediates the binding of platelets to the subendothelium and is the carrier molecule for FVIIIC. The endothelium controls fibrinolysis by producing t-PA and its inhibitor PAI-1. Inflammatory cytokines such as interleukin-1 (IL-1) and tumour necrosis factor (TNF) activate endothelial cells, causing a shift from an antithrombotic to prothrombotic state, including expression of tissue factor, increased synthesis of PAI-1 and decreased expression of TM. Fibrin deposition and intravascular thrombosis are seen in cutaneous vasculitis syndromes, suggesting local endothelial cell activation. The aim of this pilot study was to assess whether perturbation of the endothelium in cutaneous vasculitis could be detected in the patients' plasma samples. If so, further studies to assess any correlation in levels of these markers with disease activity might prove useful in the future.

Adult

Characterization of paraneoplastic pemphigus autoantigens by immunoblot analysis.

We investigated the antigen molecules for six clinically typical cases of paraneoplastic pemphigus (PNP) using immunofluorescence, immunoprecipitation, and immunoblotting. All the PNP sera showed a clear reactivity with transitional epithelia of rat urinary bladder and immunoprecipitated the 250-kD, 230-kD, 210-kD, 190-kD, and 170-kD proteins in various combinations, confirming the diagnosis of PNP. Immunoblot analysis demonstrated slightly different reactivity from that of immunoprecipitation. With immunoblotting of normal human epidermal extract, bovine desmosome preparation, and extract of cultured squamous cell carcinoma cells, all the PNP sera reacted with a characteristic doublet of the 210-kD and 190-kD proteins. However, immunoblotting detected the 250-kD desmoplakin I and the 230-kD bullous pemphigoid antigen less frequently and did not detect the 170-kD protein. Further immunoblot studies indicated that the 210-kD protein is different from desmoplakin II and that the 190-kD protein is most frequently detected by PNP sera. Two of the six PNP sera specifically reacted with the extracellular domain of recombinant pemphigus vulgaris antigen protein, indicating that pemphigus vulgaris antigen may be involved in PNP. In future studies to unravel the complex mechanisms of the PNP antigens, the immunoblot technique may be a useful tool.

Autoantigens

Generalized granuloma annulare sparing vaccination sites.

Generalized granuloma annulare (GA) is a chronic and widespread form of GA, less common than the localized type, in which the primary papular lesions may be arranged in either predominantly annular or non-annular configurations. Associations with numerous systemic disorders, including malignancies of the haematopoietic system, have been reported. There is a marked tendency to show the isomorphic or Koebner phenomenon. We report a most unusual case of generalized non-annular GA associated with chronic myelomonocytic leukaemia and myelodysplasia, in which the eruption showed striking sparing of vaccination sites.

Aged

Management of the immunobullous disorders. II. Pemphigus.

In the second of our reviews on the management of the immunobullous disorders, we review the therapy of pemphigus disorders, including pemphigus vulgaris, pemphigus vegetans, pemphigus foliaceus, pemphigus erythematosus, pemphigus herpetiformis, drug-induced pemphigus, IgA pemphigus and paraneoplastic pemphigus.

Adrenal Cortex Hormones

Class II MHC typing in pemphigoid gestationis.

Pemphigoid gestationis (PG) is a rare, autoimmune skin disease associated with pregnancy or the immediate post-partum period, previously shown to be associated with the HLA class II antigens DR3 and DR4. Advances in molecular analytical techniques now allow the identification of HLA alleles previously difficult to define by serological assays. Unsuspected polymorphism within the HLA-DR3 and DR4 classes can, therefore, be identified. The aim of our study was to apply these newer techniques to the question of genetic predisposition in PG by re-evaluating the association with DR3 and by studying a possible link with DQ. We have investigated by restriction fragment length polymorphism, the DQA, and by sequence specified oligonucleotide probing the DQB and DRB1 (HLA DR) specificities of 41 women with immunofluorescence-confirmed PG. The principal finding of this study is that there is an association between PG and DRB1*0301 (DR3) and DRB1*0401/040X (DR4). Although there is also an increase (P = 0.06) in the concurrent presence of both antigens, this appears to be due to the association with either antigen alone. We also found an increase in the frequency of DQA1*2 (P = 0.016 vs. control) and a decrease in frequency of DQB1*0201 (P = 0.022 vs. controls) and DQB1*0602 (P = 0.026 vs. controls).

Case-Control Studies

The use of Michel's transport medium for immunofluorescence and immunoelectron microscopy in autoimmune bullous diseases.

We report the use of Michel's solution, already a well established transport medium, in the combined use of direct immunofluorescence (IMF) and pre-embedding immunoelectron microscopy in 3 subepidermal bullous diseases--bullous pemphigoid (BP), epidermolysis bullosa acquisita (EBA) and dermal binding linear IgA disease (LABD). Our studies demonstrated that electron microscopy of normal skin maintained in Michel's medium for up to 28 days showed remarkable preservation of all components of the basement membrane zone, including the ultrastructure of the basal keratinocytes, dermoepidermal junction and papillary dermis. However, epidermal cell cytolysis occurred after just 48 hours. Immunoelectron microscopy using a gold probe has enabled us to localise the immunoreactants in bullous pemphigoid, epidermolysis bullosa acquisita and dermal-binding linear IgA bullous dermatoses. Our findings are comparable to and as equally reliable as those on immunoelectron microscopy of fresh skin biopsies with no loss of antigen deposition, and demonstrate an effective new use of a well established transport medium.

Epidermolysis Bullosa Acquisita

A randomized clinical trial of home intervention for children with failure to thrive.

OBJECTIVE: To evaluate the efficacy of a home-based intervention on the growth and development of children with nonorganic failure to thrive (NOFTT). DESIGN: Randomized clinical trial. PARTICIPANTS: The NOFTT sample included 130 children (mean age, 12.7 months; SD, 6.4) recruited from urban pediatric primary care clinics serving low income families. All children were younger than 25 months with weight for age below the fifth percentile. Eligibility criteria included gestational age of at least 36 weeks, birth weight appropriate for gestational age, and no significant history of perinatal complications, congenital disorders, chronic illnesses, or developmental disabilities. Children were randomized into two groups: clinic plus home intervention (HI) (n = 64) or clinic only (n = 66). There were no group differences in children's age, gender, race, or growth parameters, or on any of the family background variables. Most children were raised by single, African-American mothers who received public assistance. Eighty-nine percent of the families (116 of 130) completed the 1-year evaluation. INTERVENTIONS: All children received services in a multidisciplinary growth and nutrition clinic. A community-based agency provided the home intervention. Families in the HI group were scheduled to receive weekly home visits for 1 year by lay home visitors, supervised by a community health nurse. The intervention provided maternal support and promoted parenting, child development, use of informal and formal resources, and parent advocacy. MEASUREMENTS: Growth was measured by standard procedures and converted to z scores for weight for height and height for age to assess wasting and stunting. Cognitive and motor development were measured with the Bayley Scales of Infant Development, and language development was measured by the Receptive/Expressive Emergent Language Scale. Both scales were administered at recruitment and at the 12-month follow-up. Parent-child interaction was measured by observing mothers and children during feeding at recruitment and at the 12-month follow-up, and the quality of the home was measured by the Home Observation Measure of the Environment 18 months after recruitment. ANALYSES: Repeated-measures multivariate analyses of covariance were used to examine changes in children's growth and development and parent-child interaction. Analyses of covariance were used to examine the quality of the home. Independent variables were intervention status and age at recruitment (1.0 to 12.0 vs 12.1 to 24.9 months). Maternal education was a covariate in all analyses. When changes in developmental status and parent-child interaction were examined, weight for height and height for age at recruitment were included as covariates. RESULTS: Children's weight for age, weight for height, and height for age improved significantly during the 12-month study period, regardless of intervention status. Children in the HI group had better receptive language over time and more child-oriented home environments than children in the clinic-only group. The impact of intervention status on cognitive development varied as a function of children's ages at recruitment, with younger children showing beneficial effects of home intervention. There were no changes in motor development associated with intervention status. During the study period, children gained skills in interactive competence during feeding, and their parents became more controlling during feeding, but differences were not associated with intervention status. CONCLUSIONS: Findings support a cautious optimism regarding home intervention during the first year of life provided by trained lay home visitors. Early home intervention can promote a nurturant home environment effectively and can reduce the developmental delays often experienced by low income, urban infants with NOFTT: Subsequent investigations of home intervention should consider alternative options for toddlers with NOFTT:

Child Development

Services for adult family members with mental retardation: perceptions of accessibility and satisfaction.

Caregivers' satisfaction with and perceptions of the services received by their adult family member with mental retardation were examined. Most caregivers were satisfied with the services, regardless of the type of services received. Access variables, including the assistance provided in acquiring services, were better predictors of satisfaction than were aspects of the services. Demographic variables did not predict ratings of accessibility or satisfaction.

Adult

Prosthetic heart valves--the integration of analysis with design.

In this paper some of the issues associated with the application of computational fluid dynamics (CFD) to the design of prosthetic heart valves are discussed. The intentions are to emphasise that, for best effect, the analysis should integrate smoothly into the design process, and to illustrate the usefulness of the technique in providing detailed spatial and temporal resolution of quantities that are otherwise difficult to measure. The vehicle for the discussion is a chronological review of some valve analyses performed by the Sheffield group over the period from 1990 to 1994.

Biomedical Engineering

Anal intercourse among preadolescent and early adolescent low-income urban African-Americans.

OBJECTIVE: The purpose of this study, which was conducted as part of a larger study on adolescent risk behaviors, was to determine the frequency of anal intercourse among preadolescent and early adolescent youths. DESIGN: Survey. SUBJECTS: Three hundred fifty-one low-income urban African-American youths aged 9 to 15 years. MAIN OUTCOME MEASURES: A questionnaire assessing self-reported acquired immunodeficiency syndrome-risk behaviors was administered via a "talking" computer. The outcome measure was anal intercourse. RESULTS: Of the 137 youths (39%) who had engaged in any sexual intercourse (vaginal or anal), 50 (36%) had engaged in anal intercourse, including 41 (35%) sexually active boys and nine (43%) sexually active girls. Youths who had engaged in anal intercourse were significantly more likely to report having been sexually molested and having engaged in several delinquent behaviors than were virgins or youths who had engaged in coitus only. CONCLUSIONS: Efforts at preventing acquired immunodeficiency syndrome that target low-income urban African-American early adolescents should include the high-risk nature of anal intercourse.

Acquired Immunodeficiency Syndrome

Mechanical and other problems of artificial valves.

This chapter has discussed the design, development, laboratory testing and clinical performance of artificial heart valve replacements. The published material on this subject is extensive and clearly this present chapter represents only a limited selection of the many topics and researchers associated with the production of clinically implantable valves. Any omissions should not be regarded as a criticism, but simply the result of economy of space. The field is still developing and the situation regarding the advantages and disadvantages of the various types of valves as illustrated in Table 3 still obtains notwithstanding the many improvements which have been made with current designs. Valve development is, and will continue to be, closely allied to advances in our understanding of the behaviour of the materials of construction. Ultimately, improved haemodynamic performances of the various valve configurations will result from designs based on data from computerised fluid dynamic analysis combined with finite element stress analysis according to recognised engineering design principles.

Biomechanical Phenomena