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Biomedical subjects

J E Nelson

Publications and source records attributed to J E Nelson.

At least 55 records · Page 3Linked to original sources
PubMed1992

Developmental staging in a marsupial Dasyurus hallucatus.

In a marsupial, Dasyurus hallucatus, pouch-young of various ages from newborn to 55 days were embedded in wax and serially sectioned. On the basis of the relative development of external and internal characteristics, they were placed in the Carnegie staging system developed by Streeter and elaborated by O'Rahilly and associates. Birth occurred at stage 15, and the end of embryogenesis (stage 23) was reached about day 33. Whereas stage 23 is characterised in all eutherians by the closure of the secondary palate, this occurs before stage 15 in D. hallucatus. Since most other characters of the newborn are at a stage 15 level of development, there has been a relative acceleration of development of the secondary palate (and forelimb) in D. hallucatus that allows it to suckle and breathe at the same time. Between D. hallucatus and eutherians, there is general agreement in the sequence of development and in the relative degree of most structures at each stage. Further marsupials should be examined to see if the minor differences noted are peculiar to D. hallucatus or apply to marsupials generally.

Animals↗
PubMed1992

Development of the urinary system of the marsupial native cat Dasyurus hallucatus.

The development of the mesonephros and metanephros was examined in the marsupial Northern native cat, Dasyurus hallucatus, from birth through to the end of lactation. The mesonephros was present at birth, reached a maximum volume 11 days after birth and had regressed completely by day 30. The metanephros was present on day 2; glomeruli were first seen on day 8, and nephrogenesis continued until day 89 post partum. The newborn native cat is at a very primitive stage of development compared to other marsupials. However, at weaning, like other marsupial species, the native cat has developed a fully morphological and functional urinary system.

Animals↗
PubMed1991

Particle concentration fluorescence immunoassay of gentamicin.

We report the development of a particle concentration fluorescence immunoassay (PCFIA) for gentamicin using commercially available reagents. The solid phase consists of 0.8 microns polystyrene spheres to which gentamicin antibody is noncovalently bound. Fluorescein-labeled gentamicin serves as the tracer. The assay is carried out on 96-well reaction plates and read using an automated instrument. The assay is accurate over the range of gentamicin concentrations commonly encountered in clinical practice, with day-to-day coefficients of variation of 3-7%. As little as 0.01 mg/L of gentamicin can be detected when sample predilution is omitted. PCFIA is compared with Abbott TDX fluorescence polarization immunoassay for the measurement of serum gentamicin concentrations in routine clinical specimens.

Fluorescence Polarization Immunoassay↗
PubMed1989

"Pilot" studies.

Explore the source record for details and available documents.

Drug Evaluation↗
PubMed1989

Auditory forebrain organization of an Australian marsupial, the northern native cat (Dasyurus hallucatus).

Structures and connections of auditory forebrain regions of the Northern native cat, a member of one of the most primitive families among Australian marsupials, have been examined anatomically by using anterograde and retrograde tracing techniques with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) after defining the acoustically responsive neocortical area physiologically. The structure of the medial geniculate body (MG) was similar to that described in other species. The results obtained from a case with a WGA-HRP injection into the MG showed that the MG strongly projects to the lateral amygdaloid nucleus (LAmy) and the putamen as well as the auditory neocortex (ACx). Results obtained from other cases with WGA-HRP injections into the physiologically defined ACx show also that the ACx is connected not only with the ipsilateral MG and the contralateral ACx but also with the LAmy both bilaterally and reciprocally. The regions within the LAmy in which the MG-LAmy projection fibers terminate largely overlap with those in which the ACx-LAmy fibers terminate and the LAmy-ACx pathway originates. The connectional relationships revealed in the present study--that the LAmy receives auditory information from the MG and reciprocates auditory information with the ACx bilaterally--strongly suggest that, in some primitive mammals with small neocortical areas, a specific portion of noncortical telencephalon functions as an auditory center and occupies a relatively large volume of space in the forebrain. It is possible that the auditory sector of noncortical telencephalon in some primitive mammals such as the American Didelphidae and the Australian Dasyuridae is homologous with part of the auditory sector of the dorsal ventricular ridge (DVR) in reptiles and birds and also may have functions shared with the auditory primary and association neocortex in advanced mammals such as the domestic cat and the monkey (Kudo et al., '86a).

Animals↗
PubMed1989

Peripheral and central auditory specialization in a gliding marsupial, the feathertail glider, Acrobates pygmaeus.

Two specialized features are described in the auditory system of Acrobates pygmaeus, a small gliding marsupial. Firstly, the ear canal includes a transverse disk of bone that partly occludes the canal near the eardrum. The resultant narrow-necked chamber above the eardrum appears to attenuate sound across a broad frequency range, except at 27-29 kHz at which a net gain of sound pressure occurs. Secondly, the lateral medulla is hypertrophied at the level of the cochlear nucleus, forming a massive lateral lobe comprised of multipolar cells and granule cells. This lobe has connections with the auditory nerve and the cerebellum. Speculations are advanced about the functions of these structures in gliding behaviour and predator avoidance.

Animals↗
PubMed1988

Assay of stable isotope labelled urea in biological fluids by selected ion monitoring.

A selected ion-monitoring method, incorporating an internal standard, was developed to allow the direct and simultaneous measurement of stable isotope-labelled urea and unlabelled urea concentrations in biological specimens. After cyclization of urea with malonaldehyde bis(dimethylacetal) to form 2-hydroxypyrimidine, the volatile heptafluorobutyryl derivative was made in a two-step process utilizing a trimethylsilyl intermediate. The internal standard, 4-methyl-2-hydroxypyrimidine, was found to be stable under the cyclization conditions. The structures of the internal standard and urea derivatives were confirmed by electron impact and chemical ionization mass spectrometry. This method was applied to the measurement of [15N2]urea concentrations in dog plasma.

Body Fluids↗
PubMed1988

Afferent input for target survival in marsupial visual development.

The influence of afferent input on the survival of target neurons in mammals has been examined by the removal of one eye of pouch young of the marsupial native cat (Dasyurus hallucatus). The ages at eye removal spanned the period of neurogenesis of the ascending visual pathway, and were earlier than the time of maximal axon number in the optic nerve. Autoradiography following the injection of tritiated proline into the intact eye of adult animals shows that the lateral geniculate nucleus contralateral to the injected eye of the earliest enucleates retains its laminated structure, despite the total absence of binocular competition throughout development. However, we find a dramatic, age-related reduction in the volume of those parts of the lateral geniculate nucleus and superior colliculus which would normally receive a contralateral-only projection from the enucleated eye. The effects of the enucleation are not restricted to the primary termination sites of the optic axons but ramify throughout a large part of the neo- and archicortex.

Age Factors↗
PubMed1987

Retinogeniculate patterns in diprotodont marsupials.

The pattern of retinogeniculate connections has been examined in a range of diprotodont marsupials, including wallabies, possums, forest wombat and koala. The lateral geniculate nucleus (LGd) in most species has alternating bands of ipsilateral and contralateral retinal terminal fields, with considerable interspecific variability. The number of terminal bands of retinogeniculate input varies from eight to eleven in most species, with little binocular overlap. By contrast in one species, the feather-tailed glider, the most significant feature of LGd organisation is binocular overlap. No relationship is apparent between LGd organisation and the life-style of the animals.

Animals↗
PubMed1987

Theophylline distribution kinetics analyzed by reference to simultaneously injected urea and inulin.

Theophylline distribution kinetics were studied after i.v. injection in five anesthetized dogs. [14C]Urea and inulin were injected simultaneously as reference compounds to measure body fluid spaces and to calculate compartmental blood flows and permeability coefficient-surface area products for transcapillary exchange. The distribution of all three compounds was modeled with three-compartment systems in which the central compartment corresponds to intravascular space. The total volume of theophylline distribution averaged 0.72 +/- 0.09 liters/kg (+/- S.D.), indicating net tissue binding as reflected in a tissue/intracellular water partition coefficient of 1.17 +/- 0.10. Cardiac output measurements averaged 4.78 +/- 0.95 liters/min and were similar to the sum of compartmental blood flows estimated from the intercompartmental clearances of urea and inulin (4.62 +/- 1.10 liters/min) and to the sum of theophylline intercompartmental clearances (5.10 +/- 1.29 liters/min). Theophylline intercompartmental clearance to each peripheral compartment was faster than expected from its free-water diffusion coefficient and was similar to estimated compartmental blood flow. It is possible that theophylline transcapillary exchange is carrier mediated and that its rapidity contributes to the frequency of adverse reactions after i.v. administration of this drug.

Animals↗
PubMed1986

Frequency representation in auditory cortex of the common marmoset (Callithrix jacchus jacchus).

The location and characteristics of the primary auditory cortex of the common marmoset, Callithrix jacchus jacchus, were determined in five anesthetized male adult animals by mapping the responses of cortical units and unit clusters to pure tone stimuli presented to the contralateral ear. The primary auditory cortex lies largely ventral to the lateral sulcus, the only major fissure on the lateral cortex of this smooth-brained primate, but in some animals it may extend significantly down the ventral bank of this sulcus. Responses are distributed such that low best frequencies are found rostroventrally whereas high best frequencies occur caudally. The disposition of frequency-band contours is fan-shaped, with contours separating low-frequency octaves nearly parallel to the lateral sulcus and high-frequency (greater than 8 kHz) contours perpendicular to that sulcus. Best frequencies range from 0.6 to 30 kHz across the primary field, but there is a disproportionate representation of the three octaves between 2 and 16 kHz. The most sensitive thresholds (as low as -2 dB SPL) are found between 7 and 9 kHz. The primary auditory cortex is similar in cytoarchitecture to that reported for the cat, showing a blurring of lamination in the middle layers (II-IV) and a preponderance of small cells in these merged layers, giving a highly granular appearance. The accessibility of the cochlear representation on the gyral surface makes the marmoset an attractive animal for studies of primate auditory cortex.

Animals↗
PubMed1986

Visual acuity of the northern native cat (Dasyurus hallucatus)--behavioural and anatomical estimates.

Behavioural estimates of the visual acuity of the Northern Native Cat (or Northern Quoll)--Dasyurus hallucatus--were made using the Mitchell jumping stand technique. A value of 2.3-2.8 cycles per degree was obtained. This functional acuity compared well with predictions based on the peak ganglion cell density (2600 cells/mm2) determined from the retinal ganglion cell density map.

Animals↗
PubMed1986

Brain stem auditory nuclei and their connections in a carnivorous marsupial, the northern native cat (Dasyurus hallucatus).

The cytoarchitecture and connections of the brain stem auditory nuclei in the marsupial native cat (Dasyurus hallucatus) were studied using Nissl material in conjunction with the retrograde transport of horseradish peroxidase injected into the inferior colliculus. Some features different from those of Eutheria include the disposition of the cochlear nuclear complex medial to the restiform body, a lack of large spherical cells in the anteroventral cochlear nucleus, a small medial superior olive, and a large superior paraolivary nucleus.

Animals↗
PubMed1986

Frequency representation in the auditory midbrain and forebrain of a marsupial, the northern native cat (Dasyurus hallucatus).

The representation of sound frequency was examined in the auditory cortex and inferior colliculus of anaesthetized marsupial native cats (Dasyurus hallucatus) using microelectrode mapping techniques. The tonotopic organizations of these two auditory regions are grossly similar to those described in brush-tailed possums and in Eutheria. There appears to exist a biased representation of high frequencies (greater than 10kHz) in native cats and a paucity of frequencies below 1 kHz. Unit threshold audiograms indicate minimum thresholds between 7 and 12kHz and high thresholds above 30kHz.

Animals↗
PubMed1981

Drug abusers on the job.

Drug abusers in the working population range from the functional to the dysfunctional. Functional drug-abusing employees may work as productive members of a company for years without incident or detection. Cases have been documented of long-term heroin addicts with stable 10- and 20-year work histories., Studies of drug addicts in treatment with known work histories reveal that such persons can, and do, hold a broad range of jobs in the work force. In a study by Levy of 95 former addicts with histories of simultaneous employment and undetected drug abuse (including on-the-job use by 91 of the 95 addicts), the following occupations were found: bank teller; mail clerk; secretary; delivery man; stock clerk; college registrar; typist; baker; nurses aide; medical supply clerk; messenger; pharmacy clerk; receptionist; teletype operator; men's clothing salesman; truck driver; busboy; telephone installer; roofer; clothing designer; assembly line worker; waitress; auto mechanic; security officer; postal worker; credit collector; plant manager; and rigger. Reports from CODAP, a Federal statistical system covering drug treatment programs, indicate that about 20% of opiate users admitted to treatment were employed full time at the time of admission. Caplovitz found that the stable worker-addict is more similar in basic characteristics to other workers than to nonworking addicts.

Costs and Cost Analysis↗