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Biomedical subjects

A Matthews

Publications and source records attributed to A Matthews.

At least 19 recordsLinked to original sources
PubMed2002

Cortical activation associated with midtrial change of instruction in a saccade task.

The appearance of a visual stimulus in the peripheral visual field can elicit different saccade responses depending on prior instruction. This flexibility is commonly attributed to differences in motor set. Little is known about how the brain switches between one saccade response and another. To investigate the neural processes associated with switches between saccade motor sets, we recorded event-related potentials (ERPs) in 13 subjects, in three tasks that required subjects to generate prosaccades to a visual stimulus on 75% of the trials. On 25% of the trials, the color of the fixation point (FP) changed 300 ms prior to stimulus presentation. In the "ANTI" task, the change of the FP was the instruction to generate an antisaccade; in the "NOGO" task, subjects were instructed to maintain fixation; and in the "PRO" task, subjects were instructed to generate a prosaccade. The switch in motor set from prosaccades to antisaccades in the ANTI task and the cancellation of the prosaccade motor set in the NOGO task modulated frontal and frontocentral channels. Futhermore, the ANTI task but not the NOGO task was associated with differences at central and parietal channels compared with the PRO task. We hypothesize that the frontal activation in the ANTI and NOGO task reflects inhibition and task-switching processes, whereas the parietal activation reflects the preparation of this area for the sensorimotor transformation process that is necessary for the generation of an antisaccade.

Adult↗
PubMed2001

Effects of solution pH and electrical parameters on hydroxyapatite coatings deposited by a plasma-assisted electrophoresis technique.

Hydroxyapatite (HA) coatings can be deposited using a hybrid process of plasma electrolysis and electrophoresis, called plasma-assisted electrophoretic deposition (PEPD). HA aqueous suspensions with various pH values were prepared using a modified ultrasonic cleaning bath as an agitator/stirrer. Both DC and unbalanced AC power supplies were used to bias the titanium alloy substrate materials employed in this work. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to observe and analyze coating morphology and microstructure. It was shown that the morphology and composition of the calcium phosphate coatings were significantly influenced by solution pH values; the level of "pure" HA in the coatings' composition corresponded to both solution pH and the type of power supply employed. Loss of hydroxyl radials (i.e., dehydroxylation), which degrades the performance of the hydroxyapatite coating in terms of long-term chemical and mechanical stability, can be virtually eliminated by a combination of high pH and unbalanced AC plasma power. In addition, the underlying TiO2 coatings used to support the HA layer (preproduced by plasma electrolysis process) have a nanoscaled (10-20 nm) polycrystalline structure. TEM studies also revealed a dense, continuous amorphous titania layer (10 nm in thickness) at the interface between the Ti alloy substrate and the TiO2 layer, which may play a role in improving the corrosion resistance of the substrate. Such a nanophase TiO2 layer (if used as a coating alone) may also provide a further improvement in osteoinductive properties, compared to a conventional TiO2 coating on the Ti alloy substrate.

Alloys↗
PubMed2001

Lack of cross-species transmission of porcine endogenous retrovirus infection to nonhuman primate recipients of porcine cells, tissues, or organs.

BACKGROUND: Nonhuman primates (NHPs) have been widely used in different porcine xenograft procedures inevitably resulting in exposure to porcine endogenous retrovirus (PERV). Surveillance for PERV infection in these NHPs may provide information on the risks of cross-species transmission of PERV, particularly for recipients of vascularized organ xenografts for whom data from human clinical trials is unavailable. METHODS: We tested 21 Old World and 2 New World primates exposed to a variety of porcine xenografts for evidence of PERV infection. These NHPs included six baboon recipients of pig hearts, six bonnet macaque recipients of transgenic pig skin grafts, and nine rhesus macaque and two capuchin recipients of encapsulated pig islet cells. Serologic screening for PERV antibody was done by a validated Western blot assay, and molecular detection of PERV sequences in peripheral blood mononuclear cells (PBMCs) and plasma was performed using sensitive polymerase chain reaction and reverse transcriptase-polymerase chain reaction assays, respectively. Spleen and lymph node tissues available from six bonnet macaques and three rhesus macaques were also tested for PERV sequences. RESULTS: All plasma samples were negative for PERV RNA suggesting the absence of viremia in these xenografted animals. Similarly, PERV sequences were not detectable in any PBMC and tissue samples, arguing for the lack of latent infection of these compartments. In addition, all plasma samples were negative for PERV antibodies. CONCLUSION: These data suggest the absence of PERV infection in all 23 NHPs despite exposure to vascularized porcine organs or tissue xenografts and the use of immunosuppressive therapies in some animals. These findings suggest that PERV is not easily transmitted to these NHP species through these types of xenografts.

Animals↗
PubMed2001

Evidence of porcine endogenous retroviruses in porcine factor VIII and evaluation of transmission to recipients with hemophilia.

Since 1984, unheated porcine clotting factor VIII (Hyate:C) has been used to treat severe bleeding episodes in persons with hemophilia who have antibodies to human clotting factor. We document the presence of porcine endogenous retrovirus (PERV) in plasma samples of pigs and in clinical lots of Hyate:C. Both gag and pol PERV RNA sequences were detected by reverse-transcriptase (RT) polymerase chain reaction in 13 of 13 lots of Hyate:C tested. Among 10 of these lots, RT activity also was detected, which confirms the presence of retroviral particles. To assess the transmission of PERV to Hyate:C recipients, we tested serum specimens from 88 recipients of Hyate:C and 23 noninfused control subjects for anti-PERV antibodies by using a Western blot assay. None of the samples was positive. Our data document that PERV particles are a common contaminant of Hyate:C products and suggest that the risk of PERV transmission from these percutaneous exposures is very low.

Animals↗
PubMed2001

Prestimulus cortical potentials predict the performance in a saccadic distractor paradigm.

OBJECTIVE: In distractor paradigms, subjects sometimes respond to the wrong stimulus in a reflex-like manner. It is poorly understood why these errors occur. METHODS: To investigate the cortical processes possibly responsible for these errors, we recorded event-related potentials (ERPs) in human subjects performing a distractor saccade task in which subjects had to select a saccade target based on the colour of the initial fixation point and ignore a distractor on the opposite side. The initial fixation point disappeared 200 ms before the presentation of the visual stimuli (gap period). We compared the ERPs between correct trials in which subjects looked to the correct stimulus with error trials in which they looked towards the wrong stimulus. RESULTS: Correct response trials and error response trials showed a negative potential at the end of the gap period with the greatest amplitude over the fronto-central cortex. However, this potential had a lower amplitude in error response trials compared to correct response trials. CONCLUSION: These findings suggest that task-specific preparatory cortical processes in the frontal lobe prior to stimulus presentation have a major influence on the performance in distractor paradigms.

Adult↗
PubMed2001

Family-based transmission disequilibrium test (TDT) and case-control association studies reveal surfactant protein A (SP-A) susceptibility alleles for respiratory distress syndrome (RDS) and possible race differences.

A key cause of respiratory distress syndrome (RDS) in the prematurely born infant is deficiency of pulmonary surfactant, a lipoprotein complex. Both low levels of surfactant protein A (SP-A) and SP-A alleles have been associated with RDS. Using the candidate gene approach, we performed family-based linkage studies to discern linkage of SP-A to RDS and identify SP-A susceptibility or protective alleles. Moreover, we performed case-control studies of whites and blacks to detect association between RDS and SP-A alleles. Transmission disequilibrium test (TDT) analysis revealed that the frequency of transmission (from parent to the offspring with RDS) of alleles 6A(2) and 1A(0) and of 1A(0)/6A(2) haplotype in RDS was increased, whereas transmission of alleles 1A(5) and 6A(4) and of haplotype 1A(5)/6A(4) was decreased. Extended TDT analysis further strengthened the observations made. The case-control studies showed that in whites or blacks with RDS the frequencies of specific genotypes, 1A(0) and 6A(2) or 1A(0), were increased, respectively, but the frequency of specific 6A(3) genotypes was increased in certain white subgroups and decreased in blacks. Regression analysis revealed gestational age (GA) and 6A(3) genotypes are significant factors in blacks with RDS. In whites with RDS, GA and antenatal steroids are important factors. The data together indicate linkage between SP-A and RDS; certain SP-A alleles/haplotypes are susceptibility (1A(0), 6A(2), 1A(0)/6A(2)) or protective (1A(5), 6A(4), 1A(5)/6A(4)) factors for RDS. Some differences between blacks and whites with regard to SP-A alleles may exist.

Alleles↗
PubMed2001

Training in obstetric sonography for radiology residents and fellows in the United States.

OBJECTIVE: The purpose of our study was to assess the current experience of radiology residents and fellows in obstetric sonography. SUBJECTS AND METHODS: Written surveys were sent to the directors of 206 accredited radiology residency programs and 85 fellowship programs in the United States. The surveys encompassed obstetric sonographic experience during routine working hours and after hours, the level of supervision, the types of scanning performed, and the extent of formal lectures available during training. Additional questions concerned the relative knowledge of laboratory accreditation processes and training of faculty covering obstetric sonography. RESULTS: Sixty (29%) of 206 accredited radiology residency programs and 24 (28%) of 85 fellowship programs returned surveys. The experience among residency programs was similar, providing fewer than 4 weeks per year of obstetric sonography, usually within their own department of radiology. Residents were more likely to be sent to outside departments for second or third trimester sonography experience. A decrease in scanning assistance was reported for examinations performed after hours, more so for second or third trimester studies. Lecture topics revealed similar deficiencies for residency and fellowship programs. CONCLUSION: Greater emphasis on the performance of prenatal sonographic examinations may be warranted during formal sonography rotations. Current levels of experience in obstetric sonography may not be providing sufficient experience to allow residents to appropriately manage call cases or for practicing radiologists to provide such services after their training is completed.

Data Collection↗
PubMed2000

Partner violence, social support, and distress among inner-city African American women.

This study examined the role of social support in the partner violence-psychological distress relation in a sample of African American women seeking medical care at a large, urban hospital (n = 138). Results from bivariate correlational analyses revealed that partner violence was related to lower perceived social support and greater psychological distress, and lower social support was related to more distress. Furthermore, findings based on path analysis indicated that low levels of social support helped account for battered women's increased distress. Findings point to the need for service providers to screen for partner violence in nontraditional sites, such as hospital emergency rooms, and to address the role of social support resources in preventive interventions with African American battered women.

Adult↗
PubMed1999

Effects of di-isononyl phthalate (DINP) on peroxisomal markers in the marmoset-DINP is not a peroxisome proliferator.

In the present study the systemic toxic potential of di-isononyl phthalate (DINP) was assessed in a 13-week study in marmosets. Particular attention was given to its potential for hepatic peroxisome proliferation. Three groups of four male and four female marmosets received DINP, by oral gavage administration, at dosages of 100, 500 or 2500 mg/kg/day for 13 weeks. A fourth group served as a concurrent Control group and received the vehicle (1% methylcellulose and 0.5% Tween) only. A fifth group received clofibrate at a dosage of 500 mg/kg/day to provide a positive Control for liver peroxisome activity. At the end of the treatment period, the animals were killed and their livers were removed. 3000 x g supernatant and microsomal subcellular fractions were prepared from homogenised liver by differential centrifugation. The peroxisomal marker enzyme activity, cyanide-insensitive palmitoyl CoA oxidase, was assayed in the former, while cytochrome P450 concentration and lauric acid 11- and 12-hydroxylase activities (selective for CYP2E1 and 4A, respectively) were assayed in the microsomes. No statistically significant changes were seen in any of these parameters measured following DINP treatment, compared with the Control. Clofibrate treatment resulted in an approximately 100% increase (p < 0.01) in both male and female marmoset cyanide-insensitive palmitoyl CoA oxidase activity and a similar increase (p < 0.05) in male (only) lauric acid 11-hydroxylase activity. No other changes were statistically significant at the 5% level. These data provide no evidence that DINP was acting as a peroxisome proliferator when administered to marmosets under the conditions of the study.

Animals↗
PubMed1998

The cloning and expression of a new guanylyl cyclase orphan receptor.

A novel membrane form of guanylyl cyclase (GC-G) has been identified through the isolation of a full-length cDNA clone; it is predicted to contain an extracellular ligand binding domain, a single transmembrane segment, and intracellular protein kinase-like and cyclase catalytic domains. That GC-G represents a guanylyl cyclase was confirmed by both transient expression in COS-7 cells and stable expression in H293 cells. Endogenous cyclic GMP concentrations of transfected or stable cells, however, were much higher than control cells, suggesting an inability of the cells to effectively regulate GC-G cyclase activity. Of six Cys residues found within the extracellular domain of guanylyl cyclase-A (GC-A), the receptor for atrial natriuretic peptide, five are conserved within GC-G. Ligands for the other cyclase receptors, nevertheless, failed to stimulate GC-G expressed in transient or stable cells, suggesting that the unknown ligands possess a structure different from the natriuretic peptides or heat-stable enterotoxins. 125I-ANP also failed to bind to H293 cells overexpressing GC-G. Based on Northern hybridization, mRNA for GC-G was predominantly expressed in lung, intestine, and skeletal muscle. Using the candidate gene approach to potentially define function, the gene for GC-G was mapped to the distal region of mouse chromosome 19 (syntenic with human chromosome 10q), but no human genetic defect has been ascribed to the GC-G locus. The finding of a new membrane form of guanylyl cyclase in peripheral tissues suggests the existence of another family or subfamily of ligands that signal through elevations of cGMP.

Amino Acid Sequence↗
PubMed1998

Accessibility of nucleosomal DNA to V(D)J cleavage is modulated by RSS positioning and HMG1.

B and T cell receptor gene assembly by V(D)J recombination is tightly regulated during lymphoid development. The mechanisms involved in this regulation are poorly understood. Here we show that nucleosomal DNA is refractory to V(D)J cleavage. However, the presence of HMG1, a chromatin-associated nonhistone DNA-binding protein, stimulates V(D)J cleavage of nucleosomal templates. This HMG1 stimulation is differentially affected by the rotational or translational positioning of the recombination signal sequence on the histone octamer, with cleavage of the 12 bp spacer RSS showing sensitivity to rotational position and the 23 bp spacer RSS affected by its displacement from the dyad. These results suggest that V(D)J recombination can be modulated by controlling substrate accessibility and cleavage at the level of an individual nucleosome.

Base Pairing↗
PubMed1998

Pre-hospital emergency medical services, phase I. Role of the Department of Community Health and Psychiatry.

The Department of Community Health and Psychiatry was contracted by the Ministry of Health to assist with the implementation of a pilot programme in the Western Health Region to train fire fighters as basic level Emergency Medical Technicians (EMTs), and was responsible for its design, implementation and monitoring for the first 18 months. The course was covered in 440 hours over a 10 week period, and included training in emergency medical response, driving an emergency medical vehicle, emergency medical dispatching and inventory control. Of 76 fire fighters selected for training, 62 graduated, receiving Certificates of Merit from the Ministry of Health, Jamaica and were deployed into service on 17th April 1996. During the period 17 April to 31 December, 1996, the newly trained EMTs responded to 1,299 calls. Medical and surgical cases represented approximately 55% of all calls, followed by trauma (19%), motor vehicle accidents (9%) and obstetric emergencies (8%). Between 15% and 20% of calls in Montego Bay and Negril involved tourists. This first group of EMTs has performed well and was well received by the communities and the persons who used the service.

Ambulances↗
PubMed1996

Validation of probe EFD52 (D17S26) for forensic DNA analysis.

Validation studies that meet TWGDAM (The Working Group on DNA Analysis Methods) and CAC (California Association of Criminalists) guidelines for RFLP (restriction fragment length polymorphism) analysis were performed with the DNA probe EFD52 (D17S26). These studies demonstrate that the probe EFD52 is suitable for forensic casework. No unexpected DNA banding patterns were obtained from controlled studies examining various tissues, sample consistency over many gels, mixtures of body fluids, various substrates, various contaminants and non-human DNA sources. Of all the animal DNAs tested, only one higher primate yielded a single band to EFD52 hybridization. The sensitivity of EFD52 was shown to be comparable to that of other forensic probes. Population frequency distribution tables were prepared from over 4000 alleles and two-locus studies were conducted on nine forensically useful probes. Black, White, Hispanic and Lumbee Indian populations were found to be in Hardy-Weinberg and linkage equilibrium. Comparisons between victim blood standards and epithelial fractions of mixed strains from sexual assault cases were used to demonstrate the robustness of the EFD52 probe in forensic casework.

Asian People↗
PubMed1996

Development of preterm and full-term infant ability on AB, recall memory, transparent barrier detour, and means-end tasks.

10 preterm and 10 full-term infants were tested longitudinally from 28 to 60 weeks of age on a modified version of the AB task, a nonreaching AB task, a Barrier Detour task, a Means-End task, and Perseveration in the Means-End task. Results show that age-corrected (age since conception) premature infants tolerated longer delays than full-term infants on the modified and nonreaching AB tasks. However, when compared by chronological age (age since birth), there were no group differences on either the reaching or nonreaching AB task. No group differences were found on Barrier Detour, Means-End, or Perseveration in either the age-corrected or chronological age comparisons. The results suggest that the function that mediates modified AB performance is one of memory and not of perseveration or means-end ability. Further, these findings suggest that current proposals about brain development based on single samples of infants may be tenuous. Finally, the results of this study suggest that development of the brain structure(s) that mediate modified AB performance is strongly influenced by experience in the postnatal environment.

Age Factors↗