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Biomedical subjects

D M Taylor

Publications and source records attributed to D M Taylor.

At least 73 records · Page 4Linked to original sources

Halothane, but not the nonimmobilizers perfluoropentane and 1,2-dichlorohexafluorocyclobutane, depresses synaptic transmission in hippocampal CA1 neurons in rats.

UNLABELLED: Volatile anesthetics may decrease synaptic transmission at central neurons by presynaptic and/or postsynaptic actions. Nonimmobilizers are volatile compounds with lipophilicities that suggest that they should (but do not) prevent motor responses to surgical stimuli. However, nonimmobilizers interfere with learning and memory, and, thus, might be predicted to depress synaptic transmission in areas of the brain mediating memory (e.g., hippocampal CA1 neurons). To test this possibility, we stimulated the Schaffer collaterals of rat hippocampal slices and recorded from stratum pyramidale of CA1 neurons. At approximately 0.5 MAC (MAC is the minimum alveolar anesthetic concentration at one standard atmosphere that is required to eliminate movement in response to noxious stimulation in 50% of subjects), halothane decreased population spike amplitude 37% +/- 21% (mean +/- SD), increased latency 15% +/- 9%, and decreased excitatory postsynaptic potentials 16% +/- 10%. In contrast, at concentrations below (0.4 times) predicted MAC, the nonimmobilizer, 1,2 dichlorohexafluorocyclobutane (2N), slightly (not significantly) increased population spike amplitude, decreased population spike latency 9% +/- 4%, and increased excitatory postsynaptic potentials 22% +/- 16%. At concentrations above (2 times) predicted MAC, 2N did not significantly increase population spike, decreased latency 10% +/- 4%, and did not significantly change excitatory postsynaptic potentials. At 0.1 predicted MAC, a second nonimmobilizer, perfluoropentane, tended (P = 0.05) to increase (11% +/- 9%) population spike amplitude, decreased population spike latency 8% +/- 2%, and tended (P = 0.06) to increase excitatory postsynaptic potentials (9% +/- 8%). We conclude that clinically relevant concentrations of halothane depress synaptic transmission at Schaffer collateral-CA1 synapses and that the nonimmobilizers 2N and perfluoropentane have no effect or are excitatory. The Schaffer collateral-CA1 synapse may serve as a useful model for the production of immobility by volatile anesthetics, but is flawed as a model for the capacity of volatile anesthetics to interfere with memory and learning. IMPLICATIONS: Halothane, but not the nonimmobilizers 1,2-dichlorohexafluorocyclobutane and perfluoropentane, inhibits hippocampal synaptic transmission at Schaffer collateral-CA1 synapses.

Action Potentials↗

A comparison of Australasian and United States emergency medicine training programs.

Training programs in emergency medicine differ from country to country. This article compares the allopathic training programs of Australasia and the United States. The perceived advantages of these programs are highlighted, but no attempt is made to determine which is the better program. The Australasian program is significantly longer and places a greater emphasis on the basic clinical sciences, physical examination skills, and academic output. Australasian College for Emergency Medicine (ACEM) regulations are relatively flexible and allow trainees to design their own programs. Trainees are encouraged to arrange accredited positions in a variety of hospitals. Overseas and part-time training may be acceptable. In the United States, trainees rotate within and from one parent institution, which provides a rigid teaching structure for a "critical mass" of trainees, based on a "core" curriculum. Rotations tend to be much shorter but ensure exposure to a broader range of clinical experience. Evaluation of trainees and teaching faculty is more frequent and documentation of procedural and resuscitation skills is required. Trainees are under the close supervision of teaching faculty at all times when working in an ED.

Accreditation↗

Current outpatient management of asthma shows poor compliance with International Consensus Guidelines.

STUDY OBJECTIVE: This study aimed to establish whether the outpatient management of patients presenting with an asthma exacerbation to the emergency department (ED) was in compliance with the 1992 guidelines of the "International Consensus Report on the Diagnosis and Management of Asthma." DESIGN: Prospective, observational study using a researcher-administered questionnaire. SETTING: University tertiary referral ED. PATIENTS: Convenience sample of asthmatics (aged 18 to 54 years) presenting for asthma treatment between July 1, 1997, and June 30, 1998. RESULTS: Eighty-five asthmatic patients were enrolled. Of these, 34 patients (40%) smoked, 53 patients (62%) were undertreated with medication when compared to the consensus guidelines, and 74 patients (87%) had no written "plan of action." During an asthma attack, 9 patients (11%) did not use a bronchodilator as first-line action and 76 patients (89%) did not commence or increase the use of an inhaled steroid. Forty-nine patients (58%) did not know that bronchospasm occurred in asthma, and 53 patients (62%) did not know that bronchial swelling occurred. Twenty-six patients (31%) thought short-acting bronchodilator drugs were asthma preventers. Sixty-two patients (73%) could not adequately define peak expiratory flow (PF), 41 patients (48%) did not own a PF meter, and only 8 patients (9%) determined their PF daily. Fifty-three patients (62%) were reviewed by a physician once a year or less, and 18 patients (21%) noted family and friends as their only source of asthma education. CONCLUSIONS: The outpatient management of most asthma patients presenting to the ED did not comply with the consensus guidelines, and asthma knowledge was poor.

Adolescent↗

The fibrinogen gamma chain dodecapeptide inhibits agonist-induced aggregation of rabbit platelets and fibrinogen binding to rabbit glycoprotein IIb-IIIa.

The HHLGGAKQAGDV (H12) sequence at the carboxyl termini of the y chains and the RGD sequences in the Aalpha chains of human fibrinogen are potential recognition sites for the binding of soluble fibrinogen to glycoprotein IIb-IIIa (GPIIb-IIIa) on activated human platelets. Thus, addition of either H12 or RGD-containing peptides inhibits aggregation of and fibrinogen binding to human platelets. In contrast, we reported previously that RGDS had relatively little inhibitory effect on these functions of rabbit platelets. In the present study, we found that H12 inhibited ADP- and thrombin-induced aggregation of rabbit platelets in a dose-dependent manner. Specificity was demonstrated by the failure of the variant HHLGGAKQAGEV peptide to inhibit ADP-induced aggregation. Furthermore, flow cytometric analyses demonstrated that H12 inhibited the binding of FITC-fibrinogen to ADP-activated rabbit platelets in a dose-dependent manner. To examine the direct interaction of H12 with rabbit GPIIb-IIIa, we performed affinity chromatography by applying an octylglucoside extract of rabbit platelet proteins onto an affinity matrix containing the fibrinogen gamma chain sequence. Proteins of approximately 135 kDa and approximately 95 kDa were specifically eluted by soluble H12, and the 95 kDa protein band was immunoblotted by anti-LIBS1, a monoclonal antibody against human GPIIIa. In control samples, no detectable protein from rabbit platelet lysates was eluted from an RGD affinity matrix by GRGDSP. Collectively, our results demonstrated that H12 inhibits aggregation of and fibrinogen binding to rabbit platelets by directly interacting with rabbit GPIIb-IIIa. These findings suggest that rabbit platelets would serve as a suitable thrombosis model for testing the efficacy of peptide mimetics derived from H12.

Animals↗

An analysis of the demand for and cost of preimplantation genetic diagnosis in the United Kingdom.

Research in the field of preimplantation genetic diagnosis (PGD) has concentrated on increasing the number of diseases diagnosed, different strategies for single cell analysis and improving efficiency and reliability. Of equal importance are clinical issues such as the demand for and cost of PGD. This study assesses patient awareness of PGD and its potential benefits; additionally the awareness, attitudes and referral patterns of Assisted Conception Units, Regional Genetics Centres and Health Authorities (funding bodies) have been analysed to establish the demand for PGD within the United Kingdom. The licensed units are able to perform 128 cycles of PGD annually, however 256 cases were referred within the last year. It is clear that the currently licensed units operating at their present capacity are unable to meet the demand for PGD in the U.K. Concerns raised by this study include the unequal geographical distribution of PGD services and the lack of a uniform funding policy by Health Authorities. The investment in personnel and technology to establish a PGD service is considered and a costing provided. We estimate an initial investment in the region of 139,000 Pounds with annual running costs of 55,000 Pounds. This information should contribute towards an appropriate allocation of resources at a national level in the U.K.

Awareness↗

Solvent extraction as an adjunct to rendering: the effect on BSE and scrapie agents of hot solvents followed by dry heat and steam.

The study was designed to determine the effect on bovine spongiform encephalopathy (BSE) and scrapie agents of the solvent extraction processes used in the past by British renderers. The raw material was mouse spleen infected with either the 22A strain of scrapie agent or the 301V strain of BSE agent. Samples were exposed to hexane, heptane, petroleum spirit or perchlorethylene at the relevant temperatures for the appropriate times. Control samples were exposed to the same range of temperatures for the same range of times in saline. Other samples were exposed to the hot solvents, followed by treatment with dry heat at 100 degrees C for 30 minutes and steam at 100 degrees C for 30 minutes. Further samples were exposed only to the dry heat and steam cycles. No single complete process was significantly more effective than any of the others, and they all produced only slight inactivation, less than one log on average for both strains of agent. The average degree of inactivation produced by exposure to hot saline was generally comparable to that produced by exposure to the hot solvents. This was also true for the samples exposed only to dry heat and steam compared with those exposed to hot solvent before treatment with dry heat and steam, and suggests that the slight inactivation was caused by the heat rather than by the solvents. It is concluded that the solvent extraction processes used by renderers in Britain had little capacity to inactivate BSE and scrapie agents.

Abattoirs↗

An open rectifier potassium channel with two pore domains in tandem cloned from rat cerebellum.

Tandem pore domain K+ channels represent a new family of ion channels involved in the control of background membrane conductances. We report the structural and functional properties of a TWIK-related acid-sensitive K+ channel (rTASK), a new member of this family cloned from rat cerebellum. The salient features of the primary amino acid sequence include four putative transmembrane domains and, unlike other cloned tandem pore domain channels, a PDZ (postsynaptic density protein, disk-large, zo-1) binding sequence at the C terminal. rTASK has distant overall homology to a putative Caenorhabditis elegans K+ channel and to the mammalian clones TREK-1 and TWIK-1. rTASK expression is most abundant in rat heart, lung, and brain. When exogenously expressed in Xenopus oocytes, rTASK currents activate instantaneously, are noninactivating, and are not gated by voltage. Because rTASK currents satisfy the Goldman-Hodgkin-Katz current equation for an open channel, rTASK can be classified an open rectifier. Activation of protein kinase A produces inhibition of rTASK, whereas activation of protein kinase C has no effect. rTASK currents were inhibited by extracellular acidity. rTASK currents also were inhibited by Zn2+ (IC50 = 175 microM), the local anesthetic bupivacaine (IC50 = 68 microM), and the anti-convulsant phenytoin ( approximately 50% inhibition at 200 microM). By demonstrating open rectification and open probability independent of voltage, we have established that rTASK is a baseline potassium channel.

Acids↗

Assessment of the reliability of single blastomere analysis for preimplantation diagnosis of the delta F508 deletion causing cystic fibrosis in clinical practice.

Following the birth of a baby girl confirmed to be homozygous normal for the delta F508 deletion causing cystic fibrosis (CF), many single-gene defects have been diagnosed by polymerase chain reaction (PCR) for preimplantation genetic diagnosis (PGD). A few misdiagnoses have been reported but no large-scale studies have been performed to assess the accuracy of diagnosis in a clinical setting. Here we focus on a series of 15 delta F508 PGD cycles performed at the Hammersmith hospital in an 18 month period. All the spare embryos that had not been selected for transfer after clinical diagnosis were disaggregated and the blastomeres were analysed individually to confirm the clinical results and assess the reliability of single blastomere analysis by the nested PCR method. A total of 484 blastomeres from 112 embryos of different delta F508 genotypes were analysed. The amplification rate for nucleated blastomeres was 95 per cent and the overall accuracy of diagnosis was 89 per cent. Using these figures, we calculate that the chance of selecting an affected embryo instead of a homozygous unaffected or heterozygous carrier is 1.3 per cent, and 0.3 per cent of selecting an affected embryo as unaffected when heterozygotes were not considered for transfer. Misdiagnoses risks were negligible when embryos were considered for transfer after obtaining two concordant results from the same embryo. This study highlights the fact that heterozygous carrier embryos are more often associated with misdiagnoses, due to the failure of amplification of one of the two alleles in heterozygous cells (allele dropout (ADO)) and undetected contamination. In a recessive condition such as CF, ADO cannot result in a serious error. Misdiagnoses due to contamination are potentially more dangerous, they, however, can be limited by only selecting homozygous unaffected embryos for transfer as the risks are quadrupled when heterozygotes are also considered for transfer. For diagnoses of dominant conditions we strongly recommend the systematic analysis of two blastomeres per embryo and the transfer of only embryos with two independent concordant results.

Biopsy↗

Observations on thermostable subpopulations of the unconventional agents that cause transmissible degenerative encephalopathies.

When scrapie agent is exposed to partially inactivating autoclave cycles, the fraction of infectivity that survives remains thermostable during relatively long periods of autoclaving. This resistant subpopulation can also be differentiated from the main population by its prolonged incubation periods in assay animals, compared with control material. Stabilisation of this subpopulation may occur through the smearing and drying of infected tissue that can occur prior to autoclaving, in which the disease-specific form of PrP protein (PrP(Sc)) could become rapidly heat-fixed. This may paradoxically be what protects this fraction of PrP(Sc) from further inactivation during autoclaving. Data are presented showing that the thermostability acquired by the resistant subpopulation is a stable characteristic; autoclaving for a second time results in very little further loss of infectivity. These observations suggest that inactivation procedures that do not involve rapid and effective fixation of PrP(Sc) may be better candidates for dealing effectively with scrapie-like agents.

Animals↗

Deliberate self-inflicted trauma: population demographics, the nature of injury and a comparison with patients who overdose.

Self-inflicted harm, whether by trauma or drug overdose, is not uncommon, and has important social consequences. This study was a retrospective record analysis of patients who presented to an emergency department after deliberate self-inflicted harm. Over the two-year study period, there were 175 self-inflicted trauma and 441 overdose presentations. The self-inflicted trauma patients were a heterogeneous group and included patients who displayed suicide-related behaviour and behaviour not related to suicide. The self-inflicted traumatic injuries tended to be either relatively minor or potentially very serious. Lacerations to the upper limb were seen most frequently. The trauma and overdose groups were almost mutually exclusive populations and showed some significant differences. The trauma group was smaller, contained a significantly greater proportion of younger patients and males, presented more commonly in the late evening and early morning hours and ultimately received less psychiatric counselling. Research of this type has problems of underreporting and data bias. Prospective studies of self-inflicted trauma would improve the identification of patients after self-harm and improve the understanding of the relationship between the patterns of injury psychiatric diagnosis and the long-term risk of future self-harm.

Adolescent↗

Recurrent overdose: patient characteristics, habits, and outcomes.

OBJECTIVES: Patients who overdose repeatedly on drugs and poisons (repeaters) are of major concern. This study aimed to examine the demographics, types of drugs ingested, associated self inflicted trauma, and medium term outcome of repeaters and to compare these patients with those who overdosed on one occasion only (single presenters) during the study period. METHODS: The study was undertaken in the emergency department of a large, provincial Australian hospital. A retrospective case note examination was made for all patients who presented, after drug overdose, during the two year study period. These patients were also followed up for a further 12 months after the study period. RESULTS: The study identified 335 single presenters and 46 repeaters. Females formed about two thirds of each group but repeaters tended to be older (p > 0.05) and to present more frequently before midnight (p > 0.05). Significantly more repeat presentations were triaged to the low priority categories 4 or 5 (odds ratio (OR) 0.48; 95% confidence interval (CI) 0.26 to 0.90, p = 0.023) and this group required fewer admissions to the hospital (OR 1.85; 95% CI 1.16 to 2.93, p = 0.009). Repeaters tended to take single drug overdoses. There were significantly more paracetamol only overdoses (OR 0.54; 95% CI 0.32 to 0.92, p = 0.024) and neuroleptic only overdoses (OR 0.27; 95% CI 0.11 to 0.67, p = 0.005) in the repeater group. More repeaters caused self inflicted trauma during the study period (OR 0.20; 95% CI 0.06 to 0.64, p = 0.007). No repeater completed suicide during the study or the 12 month follow up periods but repeaters presented more frequently, after overdose, during follow up (OR 0.38; 95% CI 0.13 to 1.11, p = 0.078). CONCLUSIONS: The study concludes that there are some significant differences between patients who overdose repeatedly and those who overdose on one occasion only. The study findings suggest that the medium term suicidal risk for repeaters is relatively low. However, this risk will vary and individual patients must be assessed thoroughly and managed accordingly.

Adolescent↗

Apolipoprotein(a) enhances platelet responses to the thrombin receptor-activating peptide SFLLRN.

Elevated levels of lipoprotein(a) [Lp(a)] are correlated with an increased risk of atherosclerotic disease. We examined the effect of recombinant apolipoprotein(a) [r-apo(a)] and Lp(a) on responses of washed human platelets, prelabeled in the dense granules with [14C]serotonin and suspended in Tyrode's solution, to ADP and the thrombin receptor-activating peptide SFLLRN. No effect of the 17 kringle (K), 12K, or 6K r-apo(a) derivatives (at concentrations of 0.35 and 0.7 micromol/L) or Lp(a) (up to 0.1 micromol/L) on primary ADP-induced platelet aggregation was observed. In contrast, weak platelet responses stimulated by 7.5 micromol/L SFLLRN were significantly enhanced by the r-apo(a) derivatives; eg, 0.7 micromol/L 17K r-apo(a) increased aggregation from 15+/-4% to 58+/-6%, release of [14C]serotonin from 9+/-3% to 36+/-6%, and formation of thromboxane A2, measured as its stable metabolite thromboxane B2, from 7+/-1 to 29+/-5 ng/10(9) platelets (n=3; P<0.04 to 0.015). Significant enhancement of aggregation and release of granule contents was observed at a concentration of 17K r-apo(a) as low as 0.175 micromol/L. Purified Lp(a) (0.25 to 0.1 micromol/L) also enhanced SFLLRN-induced aggregation and release in a dose-dependent manner. Although plasminogen (0.7 and 1.5 micromol/L) and low density lipoprotein (0.025 to 0.1 micromol/L) both exhibited potentiating effects on SFLLRN-mediated platelet aggregation, the magnitude of the responses was less than that observed with either the r-apo(a) derivatives or Lp(a). The enhanced responses of platelets via the protease-activated receptor- thrombin receptor in the presence of Lp(a) may contribute to the increased risk of thromboembolic complications of atherosclerosis associated with this lipoprotein.

Adenosine Diphosphate↗

Undergraduate procedural skills training in Victoria: is it adequate?

OBJECTIVES: To assess the experience in basic and advanced clinical procedures of recently graduated medical students and to identify deficiencies in procedural skills training. DESIGN: An anonymous, voluntary, questionnaire-based survey. SETTING: The 13 hospitals in the State of Victoria that employ their own interns. SUBJECTS: New interns, immediately before starting their intern year in 1996. RESULTS: One hundred and seventy-four interns participated. They reported that they had had few opportunities to practise some procedures during their medical courses. By their own report, 3% had never sutured a patient, 10% had never drawn blood gases, 16% had never applied a limb plaster, 18% had never inserted a catheter and 37% had never intubated a patient. Twenty-nine per cent perceived their proficiency in basic procedural skills to be inadequate and 43% perceived their training in basic skills to have been inadequate. Except for intravenous cannulation, there was a significant association (P < 0.01) between the number of procedures performed and perceived proficiency in that procedure. The new interns reported that they had been taught mainly by residents and registrars in the emergency department. "Doctors performing most procedures" and "limited access to patients" were considered the main obstacles to procedural training. Fewer than 50% of interns had spent extra time improving their procedural skills. CONCLUSION: Undergraduate training in procedural skills in Victoria is inadequate. Comprehensive training programs appear to be lacking and clinical schools have few techniques for quality assurance. RECOMMENDATION: Victorian clinical schools need to review their procedural skills training programs.

Clinical Competence↗

Paternal transcripts for glucose-6-phosphate dehydrogenase and adenosine deaminase are first detectable in the human preimplantation embryo at the three- to four-cell stage.

The transition between dependence on maternal transcripts and proteins inherited in the oocyte and embryonic gene expression in the human preimplantation embryo occurs at the four- to eight-cell stage. Recently, studies using reverse transcriptase polymerase chain reaction (RT-PCR) have detected paternal transcripts for the Y-linked genes, ZFY and SRY, and the myotonic dystrophy associated protein kinase gene, DK, as early as the late pronucleate one-cell stage. However, expression at the protein level has not been demonstrated and its function at these early stages is unknown. Using coding sequence polymorphisms to distinguish maternal and paternal transcripts, we have examined the transcription of two ubiquitously expressed genes: X-linked glucose-6-phosphate dehydrogenase (G6PD) and adenosine deaminase (ADA). Both G6PD and ADA are housekeeping genes with TATA-less promoters which, because of their roles in metabolism and ubiquitous expression, may provide a more reliable indication of the timing of activation of the embryonic genome. They also each have biallelic polymorphisms with a high heterozygosity ratio which can be detected by restriction digestion. Couples undergoing in vitro fertilization (IVF) were screened for these polymorphisms. Individual spare oocytes and embryos at different stages of preimplantation development were analyzed by RT-PCR and appropriate restriction digestion in those cases in which the male partner carried a different allele to the female partner. In addition, since only female embryos inherit the paternal allele of X-linked G6PD, cDNA was also analyzed for ZFX/ZFY transcripts to identify the sex of each embryo. One hundred and twenty three individual oocytes and embryos were analyzed by RT-PCR and restriction digestion to detect the paternal transcripts from the polymorphic alleles. Maternal transcripts for G6PD, ADA, and ZFX were detected in all oocytes and embryos and at all stages. Following restriction digestion, paternal G6PD and ZFY transcripts were first detected at the four-cell stage and paternal ADA transcripts in an embryo at the three-cell stage coinciding with the onset of dependency on transcription from the embryonic genome. This approach should be widely applicable to other genes since similar polymorphisms exist in the coding regions of many genes.

Adenosine Deaminase↗

Inactivation of the 22A strain of scrapie agent by autoclaving in sodium hydroxide.

Samples of macerated mouse-brain infected with the 22A strain of scrapie agent were subjected to gravity-displacement autoclaving at 121 degrees C for 30 minutes in the presence of 2 M sodium hydroxide. No infectivity was detectable by mouse bioassay in samples which were either held for an hour at room temperature before autoclaving, or autoclaved immediately after adding the hydroxide. In contrast, all of the mice injected with a control sample, held for an hour in distilled water before autoclaving, developed scrapie. If adopted as a routine decontamination procedure it is recommended that hydroxide-treated waste should be autoclaved in sealed heat-resistant containers which can withstand the pressures involved. This would make the procedure safer for the operator, and avoid autoclave damage through exposure to sodium hydroxide.

Animals↗

The effect of formic acid on BSE and scrapie infectivity in fixed and unfixed brain-tissue.

Brain-tissue infected with scrapie-like agents remains infectious after histological fixation, and represents a source of occupational exposure. Infectivity titres in formol or paraformaldehyde-lysine-periodate (PLP)-fixed mouse-brains infected with the 301V strain of BSE agent were reduced by around six logs following treatment with formic acid. After PLP fixation and formic acid treatment, no infectivity was detectable in mouse-brain infected with the 87V strain of scrapie agent. Similarly-treated mouse-brain infected with the ME7 strain of scrapie agent showed a titre loss of approximately 5 logs. No infectivity was detectable in PLP-fixed, BSE-infected bovine brain after formic acid treatment, but this was an unreliable result. With unfixed brain homogenates, formic acid reduced the titre of ME7 by > or = 5.0 logs; technical problems limited the measured loss of BSE infectivity to > or = 1.0 logs. These studies confirm that formic acid treatment during fixation of brain-tissue significantly reduces the infectivity titres of scrapie-like agents, thus reducing the level of any occupational exposure.

Animals↗

Why minority group members perceive or do not perceive the discrimination that confronts them: the role of self-esteem and perceived control.

Self-esteem and perceived control were examined to explain why minority group members sometimes perceive discrimination but, more often, minimize the discrimination. Women (Study 1), and Asians and Blacks (Study 2) reacted to negative feedback after information about the probability for discrimination. Minority group members tended to minimize discrimination and attributed their failure to themselves. By perceiving discrimination as a reason for failure, minority group members protected their performance state self-esteem. In contrast, by minimizing discrimination, they protected their social state self-esteem and maintained the perception of control in the performance and social domains. Results suggest that minority group members minimize discrimination because the consequences of doing so are psychologically beneficial.

Adaptation, Psychological↗