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Biomedical subjects

A K Wright

Publications and source records attributed to A K Wright.

33 records · Page 2Linked to original sources
PubMed1978

The striatonigral fibres and the feedback control of dopamine metabolism.

It proved possible to make lesions which interrupted the striatonigral GABA-containing pathway in the rat brain without causing concomitant damage to the nigrostriatal dopamine containing system. Estimations of striatal concentrations of dopamine (DA), dihydroxyphenyl-acetic acid (DOPAC) and homovanillic acid (HVA) inducated that these lesions had no influence either on normal striatal DA turnover or on the enhancement of DA turnover induced by neuroleptics. Behavioural experiments suggested a motor output function for the striatonigral pathway.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1978

Topographical organization of the striatonigral pathway revealed by anterograde and retrograde neuroanatomical tracing techniques.

L-[4,5-3H]leucine was injected stereotaxically into various regions of the rat neostriatum. Light microscopic autoradiographic techniques were used to plot the entire efferent pathways of the neostriatum, and in particular, the projections to the substantia nigra (SN). The terminal distribution of the pathways projecting to the ipsilateral SN was predominantly restricted to the zona reticulata region. The dorsal part of the head of the striatum was found to innervate the anterior and medial portions of the zona reticulata, while the ventral area of the head projected to more posterior regions of the SN. A pathway from the tail of the striatum to the lateral and dorsal parts of SN was also demonstrated. Horseradish peroxidase injections, restricted to different areas of the SN, led to retrograde labelling of neurons in the striatum whose distribution confirmed the topographic organization of the striatonigral pathway demonstrated in the autoradiographic studies.

Animals↗
PubMed1977

A proposed model for rhodopsin in photoreceptor membranes.

Transient electric birefringence studies have been made on bovine rhodopsin solubilized in the detergent lauryldimethylamine oxide from glutaraldehyde fixed rod outer segment (ROS) membranes. It was found that fixation caused no appreciable differences in the measured relaxation times when compared with unfixed ROS. On the basis of these findings a model for the orientation of rhodopsin in photoreceptor membranes is proposed which accounts for translational diffusion and two modes of rotational diffusion. The proposed model is related to a number of experimentally determined biophysical properties reported in the literature.

Membrane Proteins↗
PubMed1976

A study of rhodopsin-detergent micelles by transient electric birefringence.

The hydrodynamic method of transient electric birefringence has been used to study bovine rhodopsin solubilized in two detergents, 0.02% Ammonyx LO and 0.045% digitonin. All measurements are interpreted as the sum of two exponentials by which the relaxation times yield the rotary diffusion coefficients for ellipsoids of revolution. The semi-major and minor axes for prolate ellipsoid models have been calculated and their axial ratio, 6.8, in both detergents, is in line with recent reports on the structure of rhodopsin. Studies on bleached rhodopsin showed a large increase in axial ratio in 0.02% Ammonyx LO.

Binding Sites↗
PubMed1976

Numerical inversion of the Perrin equations for rotational and translational diffusion constants by iterative techniques.

An iterative numerical technique is presented which allows the semiaxes for prolate and oblate ellipsoids to be determined from the Perrin equations for rotational and translational diffusion constants. The use of this inversion technique is illustrated by application to the proteins: lysozyme, bovine serum albumin, human transferrin, and bovine rhodopsin solubilized in digitonin.

Diffusion↗
PubMed1975

A study of protein-sodium dodecyl sulfate complexes by transient electric birefringence.

The method of transient electric birefringence has been applied to study the conformation of protein-sodium dodecyl sulfate complexes. A model of a deformable prolate ellipsoid has been proposed for the protein-dodecyl sulfate complex. This model is compared to the models proposed by J. A. Reynolds and C. Tanford (1970), J. Biol. Chem. 245, 5161) and K. Shirahama, K. Tsujii, and T. Takagi (1974, J. Biochem. 75, 309). Differences between these latter two models are resolved by the model presented here. In addition, it has been demonstrated that protein molecular weights may be obtained from the slow relaxation time for transient electric birefringence of protein-dodecyl sulfate complexes.

Animals↗
PubMed1975

Hydrodynamic structure of bovine serum albumin determined by transient electric birefringence.

Birefringence relaxation studies on bovine serum albumin (BSA) reveal transient decay described by a double exponential process. The values of the relaxation times lead to estimation of the size of the equivalent ellipsoid of revolution for BSA. Previous measurements of transient birefringence for BSA have shown a single relaxation process, since the apparatus used in obtaining those data was not fast enough to detect the faster relaxation process.

Animals↗
PubMed1973

A numerical inversion of the perrin equations for rotational diffusion constants for ellipsoids of revolution by iterative techniques.

The rotational diffusion coefficients R(1) and R(3) for ellipsoids of revolution are shown to represent another pair of hydrodynamic data to obtain size and shape with theories by Sadron and Scheraga-Mandelkern. An iterative numerical technique is presented which allows the semiaxes to be determined from the Perrin equations for rotational diffusion constants. The use of this inversion technique is illustrated by application to literature data from dielectric dispersion studies.

Computers↗
PubMedDate not supplied

Some non-fluorescent connections of the nigro-neostriatal dopamine neurones.

This study of the relationships between cells identified by their catecholamine fluorescence and their less fortunate neighbours became possible with the advent of autoradiographic tracing methods. A major output from the neostriatum returns to the substantia nigra where it fills the pars reticulata. Outputs from this area of substantia nigra are present on both sides of the brain in the thalamus, in parts of parafascicular, intralaminar, and mediodorsal nuclei, and the superior colliculi in the deeper layers. Mainly unilateral pathways reach the ventromedial nucleus of thalamus and also pass under the lateral part of the colliculus to reach the region of the nucleus pendunculo-pontinus among the fibres of the brachium conjunctivum. The roles of those areas in the transmission of the output of the basal ganglia to the motor system of the animal, however, remain obscure.

Animals↗