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Biomedical subjects

G Shaw

Publications and source records attributed to G Shaw.

At least 73 records · Page 4Linked to original sources
PubMed2000

Noise suppression of transient-evoked otoacoustic emissions. II. Derived narrow-band contributions.

Transient-evoked otoacoustic emissions (TEOAEs) were decomposed into cochlear place specific components using high-pass noise suppression. This was performed using high-pass filtered noise with cut-off frequencies between 0.7 and 5.6 kHz in 0.5-octave steps. Subtraction of the TEOAEs obtained in the presence of two high-pass noise suppressors with 0.5-octave difference in their cut-off frequencies, f(A) and f(B), should theoretically result in TEOAE components with frequencies between f(A) and f(B). The reconstructed wide-band emission power spectrum obtained by summing the narrow-band emission power spectra, was nearly identical to the power spectrum of the original wide-band emission. This suggests that no phase-cancellation occurs and that the individual narrow-band TEOAEs are uncorrelated, and thus that their generators are potentially independent. About 66% of the derived narrow-band emissions had spectral components that extended below the cut-off frequency of the lower high-pass noise filter. These tail components were interpreted as resulting from high-frequency side suppression of the high-pass noise on the click emission and potentially distortion product components from the TEOAE.

Acoustic Stimulation↗
PubMed2000

Noise suppression of transient-evoked otoacoustic emissions. I. A comparison with the non-linear method.

A new method to record transient-evoked otoacoustic emissions (TEOAEs) is introduced. Click stimuli were presented both with and without a simultaneously presented wide-band noise burst. Subtraction of the recorded signal evoked by the noise burst plus click from the signal evoked by the click alone, cancelled the eardrum reflection components of the response and resulted in a measure of the emission. This was used to obtain the TEOAEs from 21 subjects for peak click stimulus levels of 48-66 dB SPL. The root-mean-square (RMS) level of the noise burst was set 10 dB higher than the peak click level, and resulted in suppression of the TEOAE by up to 20 dB. The TEOAE waveforms obtained by the new method were compared to those obtained with Kemp's non-linear method, and were indistinguishable in 20 of the 21 subjects. On basis of the emission spectra, they were indistinguishable in 18 out of 21 subjects. The latencies of narrow-band filtered components from the TEOAEs obtained with the two methods were also similar. This suggests that this noise-suppression method produces similar results as Kemp's non-linear method with the advantage that emission components with very short latencies can be obtained.

Acoustic Stimulation↗
PubMed2000

beta-adrenergic mechanisms in cardiac diseases: a perspective.

Several lines of evidence show that neurohumoral systems, especially those involving catecholamines, play a crucial role in cardiac diseases. Changes in the beta-adrenergic receptor (beta-AR) system such as receptor down-regulation, uncoupling from G-proteins, receptor internalization and receptor degradation may account for some of the abnormalities of contractile function in this disease. Increases in the level of inhibitory G-protein subunits also appears to be involved in attenuating the beta-AR signal. Finally beta-AR signalling is strongly regulated by members of the G-protein-coupled receptor kinase family (GRKs), the best known of which is beta-adrenergic receptor kinase 1 (beta-ARK1). beta-ARK1 mRNA, protein level and enzymatic activity is increased in heart disease, further contributing to an attenuation in beta-AR signalling. The combination of these negative alterations are presumably related to the contractile dysfunction seen in human heart disease. The combination of biochemical, physiological and molecular biological studies bearing on the normal function and regulation of these various molecules should provide strategies for elucidating the pharmacological basis of the regulation of myocardial contractility in the normal and failing heart.

Adenylyl Cyclases↗
PubMed2000

Contraceptive effects of levonorgestrel implants in a marsupial.

The effect of subcutaneous levonorgestrel implants on reproduction in female tammar wallabies was investigated during the breeding and non-breeding season. Female tammars were given either a control or a levonorgestrel implant and their pouch young were removed to terminate embryonic diapause. Both the control and the levonorgestrel-implant animals treated during the months of May and June gave birth, demonstrating that levonorgestrel does not prevent the reactivation of the diapausing blastocyst or its subsequent development when given at these times. However, none of the levonorgestrel-treated animals mated post partum, whereas all of the control females that gave birth had a post partum oestrus and mated. Control animals gave birth again when the neonate was removed, and continued to breed normally during the following 36 months of the investigation. None of the levonorgestrel-treated animals gave birth again or mated during the next 36 months. Animals given control implants during December did not reactivate or give birth until the normal start of the breeding season in late January. Animals treated with levonorgestrel implants during December did not reactivate with the control animals at the beginning of the breeding season and did not give birth during the next 36 months. There were no effects of levonorgestrel treatment on early lactation. Levonorgestrel implants were removed from six females and four of these animals resumed reproductive activity, confirming that the contraceptive effect of the implants is reversible. Levonorgestrel implants therefore provide a highly effective, reversible and long-term method of contraception for tammar wallabies. This contraceptive system appears to offer a method of population control for the management of overabundant captive and selected wild populations of macropodid marsupials.

Animals↗
PubMed2000

Aquatic toxicology.

Australia is blessed with a great diversity of unique species in its fresh waters and in the marine environment around its coast. There is evidence that human and natural events are impacting on these species. Such impacts are associated with various agricultural, industrial, and domestic practices and with natural and anthropogenically driven climate change. Among the species most affected are those living in aquatic and marine environments. Some of these, such as cyanobacteria and dinoflagellates, have the potential for toxicity. Linked to this, there is the potential benefit of harnessing the pharmacologic potential of these toxins.

Animals↗
PubMed2000

Diapause.

Embryonic diapause, or delayed implantation as it is sometimes known, is said to occur when the conceptus enters a state of suspended animation at the blastocyst stage of development. Blastocysts may either cease cell division so that their size and cell numbers remain constant, or undergo a period of very slow growth with minimal cell division and expansion. Diapause has independently evolved on many occasions. There are almost 100 mammals in seven different mammalian orders that undergo diapause. In some groups, such as rodents, kangaroos, and mustelids, it is widespread, whereas others such as the Artiodactyla have only a single representative (the roe deer). In each family the characteristics of diapause differ, and the specific controls vary widely from lactational to seasonal, from estrogen to progesterone, or from photoperiod to nutritional. Prolactin is a key hormone controlling the endocrine milieu of diapause in many species, but paradoxically it may act either to stimulate or inhibit growth and activity of the corpus luteum. Whatever the species-specific mechanisms, the ecological result of diapause is one of synchronization: It effectively lengthens the active gestation period, which allows mating to occur and young to be born at times of the year optimal for that species.

Animals↗
PubMed2000

Useful Microsoft Word Macros for molecular biologists and protein chemists.

Biologists today make extensive use of word processing programs for the production of research reports, literature reviews and grant proposals. Frequently, such programs become the default platform for viewing and the later publication of protein and nucleic acid sequence data. Thus, researchers often switch between their word processor and more specialized programs designed to analyze protein and nucleic acid sequences. It would be more convenient to perform these simple sequence analyses using the word processor without switching to another program. The focus here is on the use of the Visual Basic programming language, which is built into all recent versions of Microsoft Word to generate surprisingly complex and useful macros that can conveniently analyze several important features of protein and nucleic acid sequences. The standard Word interface can also be easily modified to display and run these macros from a pull-down menu. Several examples of this approach are provided.

Amino Acid Sequence↗
PubMed2000

Mercury modeling to predict contamination and bioaccumulation in aquatic ecosystems.

In response to increasing scientific evidence of the environmental toxicity of mercury and its organic compounds, this study reviews the state of knowledge about the mercury cycle in aquatic systems. It describes the aquatic chemistry of mercury and discusses the importance of biological and physicochemical parameters such as pH, temperature, dissolved organic carbon, oxygen concentration, mercury and methylmercury concentration and availability, as well as sulfate, manganese, and iron concentration in surfaced waters. There is still a paucity of information on environmental dependency of factors that regulate the formation, destruction, and trophic transfer of methylmercury. This lack has led to numerous studies to define the factors that can influence its bioconcentration and bioaccumulation. This review presents some alternative models for mercury cycling, speciation, and partitioning based on the trend toward "site-specific water quality standards," in which chemical speciation is considered on a site-by-site basis.

Animals↗
PubMed1999

Prognostic significance of DNA ploidy in endometrial cancer.

OBJECTIVE: The aim of this study was to analyze the prognostic significance of DNA ploidy in patients with endometrial cancer. METHODS: Between October 1988 and January 1997, DNA ploidy was determined prospectively in 208 women who were staged surgically by a standard protocol that included pelvic and para-aortic lymphadenectomy. Median follow-up was 48 months. RESULTS: Diploid tumors were identified in 154 (74%) patients and aneuploid tumors in 54 (26%). Patients with aneuploid tumors had a significantly higher prevalence of metastases to the cervix, adnexa, and omentum, malignant pelvic cytology, and advanced surgical stage. Patients with aneuploid tumors had a 4.5 times higher prevalence of pelvic lymph node metastases and a 5.8 times higher prevalence of para-aortic lymph node metastases. A significantly higher proportion of patients with aneuploid tumors was diagnosed with recurrent or progressive endometrial cancer (22.2 versus 6.5%, P = 0.002). Patients with aneuploid tumors had a significantly lower rate of survival from cancer death (P = 0.038) with 83% versus 94% surviving 5 years. CONCLUSION: Patients with aneuploid tumors are at high risk for lymph node metastases and should be surgically staged, including pelvic and para-aortic lymphadenectomy. Aneuploidy confers a risk for endometrial cancer death and these patients should be candidates for clinical trials evaluating treatment following surgery.

Aged↗
PubMed1999

Comparison of dopamine receptor antagonists on hyperlocomotion induced by cocaine, amphetamine, MK-801 and the dopamine D1 agonist C-APB in mice.

RATIONALE: Direct or indirect stimulation of dopamine receptors increases locomotor activity in mice. Determining the role played by D1 and D2 dopamine receptors in the mediation of this activity can be difficult due to the wide variety of experimental paradigms used to investigate these phenomena. OBJECTIVES: This study set out to compare the role of selective antagonism of dopamine D1 and D2 receptors on the hyperactivity induced by a range of stimulants. METHODS: Mice were habituated to perspex locomotor activity boxes (30 x 30 x 30 cm) and activity was measured via photobeam interrupts. RESULTS: Haloperidol and clozapine both reduced the hyperactivity induced by MK-801. Haloperidol did so only at a dose that also decreased spontaneous activity (0.1 mg/kg), whereas clozapine reduced MK-801-induced hyperactivity at a dose that had no effect on spontaneous activity (1.25 mg/kg). The D1 antagonist SCH23390 (0.01 mg/kg) reduced hyperlocomotion induced by amphetamine (2.5 mg/kg), cocaine (10 mg/kg) and C-APB (1.0 mg/kg) at doses that did not consistently alter spontaneous activity, whereas the selective D2 antagonist raclopride only attenuated the hyperlocomotion induced by amphetamine, cocaine and C-APB at doses in excess of the minimum dose required to attenuate spontaneous locomotor activity significantly. The latency to peak levels of hyperlocomotion induced by MK-801 (0.3 mg/kg) was delayed by SCH23390 (0.1 mg/kg) but peak levels of activity were not reduced. CONCLUSIONS: The results of the present study suggest that selective blockade of D1 receptors suppresses amphetamine and cocaine-induced hyperactivity in mice but not MK-801-induced locomotor activity.

Amphetamine↗
PubMed1999

Development of the penis and clitoris in the tammar wallaby, Macropus eugenii.

The development of the phallus from the indifferent stage to sexual dimorphism has not been described in any marsupial. This study describes the morphological and histological changes occurring in the development of the phallus of the tammar wallaby. The development of the penis and clitoris in the tammar closely follow the most widely accepted model for the development of the same organs in eutherian mammals. The urogenital plate that is present in both sexes at birth hollows out to form a urogenital groove at approximately 70 days postpartum (p.p.). There is then greater growth of the phallus in males than in females, which results in sexual dimorphism in length approximately 100 days p.p. In males, the urogenital groove secondarily closes over at this time and fuses in the midline and by 128 days p.p. the penile urethra is fully formed. In females, the groove remains open. The clitoris changes little morphologically from the time of formation of the urogenital groove until adulthood. The pattern of development of the penis in the tammar is similar to that seen in eutherian mammals. There is strong evidence that penis development is androgen-dependent in the tammar, yet unusually it becomes sexually dimorphic at a time when androgen content of the developing testis is low.

Animals↗
PubMed1999

5-HT2 receptor antagonism reduces hyperactivity induced by amphetamine, cocaine, and MK-801 but not D1 agonist C-APB.

The hyperlocomotion induced by the noncompetitive NMDA antagonist MK-801 (0.3 mg/kg SC) in mice was attenuated by the nonselective 5-HT2 antagonist ritanserin (0.12 and 0.25 mg/kg SC) and by the 5-HT2A selective antagonist MDL100907 (0.05 and 0.1 mg/kg SC). SB242084 (0.25-1.0 mg/kg), a selective 5-HT(2C) antagonist, had no effect on MK-801-induced hyperactivity. These same doses of ritanserin and MDL100907 reduced the hyperactivity induced by cocaine (10 mg/ kg). Amphetamine (2.5 mg/kg SC) induced hyperlocomotion that was also attenuated by ritanserin (0.064).25 mg/kg SC). The hyperlocomotion induced by the D1 agonist C-APB (1.0 mg/kg) is not altered by pretreatment with ritanserin or MDL100907. This suggests that compounds that increase locomotor activity via indirectly increasing dopaminergic activity (either by increased release or blockade of reuptake) require the activation of a 5-HT2A receptor. Activity of compounds that act directly at the postsynaptic dopamine receptors such as C-APB is not dependent on such a mechanism. This suggests a selective involvement of 5-HT2A receptors but not 5-HT2c receptors in the mediation of the behavioral effects of compounds that increase synaptic concentration of dopamine but not directly acting agonists. This implies that the 5-HT2A receptors modulate elevation of extracellular dopamine, not the postsynaptic sensitivity of dopamine neurons.

Aminopyridines↗
PubMed1999

Radioactive contamination: state of the science and its application to predictive models.

Information on environmental levels and transport processes of natural and anthropogenic radioactivity, although plentiful, is widely scattered, and relatively few attempts have been made to summarize and synthesize this information. Furthermore, most experimental observations and experiments on environmental radioactivity have been designed for documentation or testing of specific hypotheses, rather than for providing key information for transport simulation models or on fundamental processes which such models seek to represent. This paper examines three basic questions, namely (1) what is the current state of the science of radioecology?; (2) how well is this science being incorporated into predictive models?; and (3) how well are the models being used to guide and improve the science? These discussions will be preceded by a brief description of the field of radioecology, and comments on its relevance to other sciences as well as to major societal problems stemming from environmental releases of radioactivity. In addition to assessing the current state of the science and its use in predictive models, specific ideas for improving both the science and its associated models will be advanced. These ideas fall under the categories of (1) environmental transport processes and model parameters, (2) estimating exposure and dose to human and ecological receptors, and (3) dose-effect relationships for plants and animals.

Journal Article↗
PubMed1999

Production of prostaglandin f2alpha and its metabolite by endometrium and yolk sac placenta in late gestation in the tammar wallaby, Macropus Eugenii.

In this study, we investigated production of prostaglandin (PG) F2alpha and its metabolite, PGFM, by uterine tissues from tammar wallabies in late pregnancy. Endometrial explants were prepared from gravid and nongravid uteri of tammars between Day 18 of gestation (primitive streak) and Day 26.5 (term) and were incubated in Ham's F-10 medium supplemented with glutamine and antibiotics for 20 h. PGF2alpha and PGFM in the medium were assayed by specific, validated RIAs. Control tissues (leg muscle) did not produce detectable amounts of either PG. Both gravid and nongravid endometria secreted PGF2alpha, and production increased significantly in both gravid and nongravid uteri towards term. PGFM was produced in small amounts by both gravid and nongravid uteri, and the rate of production did not increase. Neither oxytocin nor dexamethasone stimulated PG production in vitro in any tissue at any stage. Thus, the surge in peripheral plasma PGFM levels seen at parturition may arise from increased uterine PG production, but further study is needed to define what triggers this release.

Animals↗
PubMed1999

Cortisol in fetal fluids and the fetal adrenal at parturition in the tammar wallaby (Macropus eugenii).

Glucocorticoid hormones may play a critical role in initiating parturition in tammar wallabies. In this study, we investigated the concentration of cortisol in fetal fluids and cortisol production by fetal adrenals over the last 3 days of the 26-day pregnancy and within 24 h postpartum. The fetal adrenals almost doubled in size between Days 24 and 26 of pregnancy, and their cortisol content increased over 10-fold during this period, from 10 pg to over 100 pg per adrenal pair. After birth, neonatal adrenals continued to grow, but cortisol content fell dramatically to 20 pg. The prepartum increase in adrenal cortisol was reflected by a substantial rise in cortisol concentrations in yolk sac fluid, allantoic fluid, and fetal blood, which were below 10 ng/ml on Day 24 and rose to over 40 ng/ml by Day 26. Cortisol concentrations in neonatal blood decreased postpartum, mirroring decreased cortisol content in neonatal adrenals. Cortisol production by the fetal adrenal was stimulated in vitro by ACTH and prostaglandin E2, suggesting that the in vivo increase may be stimulated by release of ACTH from the fetal hypothalamic-pituitary axis and prostaglandin E2 from the placenta. These results indicate that increasing cortisol production by the fetal adrenal is a characteristic of late pregnancy in the tammar wallaby and support the suggestion that fetal cortisol may trigger the initiation of parturition in this marsupial species.

Adrenal Glands↗