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Biomedical subjects

R W Williams

Publications and source records attributed to R W Williams.

At least 127 records · Page 7Linked to original sources
PubMed1988

Elimination of neurons from the rhesus monkey's lateral geniculate nucleus during development.

The timing, magnitude, and spatial distribution of neuron elimination was studied in the dorsal lateral geniculate nucleus of 57 rhesus monkeys (Macaca mulatta) ranging in age from the 48th day of gestation to maturity. Normal and degenerating cells were counted in Nissl-stained sections by using video-enhanced differential interference contrast optics and video-overlay microscopy. Before embryonic day 60 (E60), the geniculate nucleus contains 2,200,000 +/- 100,000 neurons. Roughly 800,000 of these neurons are eliminated over a 40- to 50-day period spanning the middle third of gestation. Neurons are lost at an average rate of 300 an hour between E48 and E60, and at an average rate of 800 an hour between E60 and E100. Very few neurons are lost after E100, and as early as E103 the population has fallen to the adult average of 1,400,000 +/- 90,000. Degenerating neurons are far more common in the magnocellular part of the nucleus than in the parvicellular part. In 20 of 29 cases, the number of neurons is greater on the right than on the left side. The right-left asymmetry averages about 8.5% and the difference is statistically significant (phi 2 = 38, p less than .001). The period of cell death occurs before the emergence of cell layers in the geniculate nucleus, before the establishment of geniculocortical connections, and before the formation of ocular dominance columns (Rakic, '76). Most important, the depletion of neurons in the geniculate nucleus begins long before the depletion of retinal axons. The number of geniculate neurons is probably a key factor controlling the number of the retinal cells that survive to maturity.

Animals↗
PubMed1988

The control of neuron number.

In comparing strategies used to control neuron number, we find it useful to view nervous system development as occurring in three phases. The phases overlap--each is a process, not an event. The first phase is the development of a genetic nervous system. This is a nervous system of simple genetic intention, not a blueprint or pile of bricks. Its characteristics are abstract: How many neurons in this stem cell destined to produce, which cells are programmed to die, how much target does this cell need to survive. At the level of the individual, the genetic nervous system is essentially fixed, but over generations it is fluid. As this genetic intent interacts within a world of cells, a real brain appears. A new set of rules only tacitly present in the genome is expressed--the embryonic nervous system emerges. The interaction of its parts defines the shape and size of the nervous system. Neuron numbers are adjusted interactively by changes in proliferative potential and the severity of cell death. Cell fates are established in part through interactions with other cells and with hormones. Glial cell numbers are adjusted to match the neuron populations. This phase of brain development is what the embryologist sees under the microscope. The third and final phase of development begins when the brain starts to function and the animal starts to deal with its world. Small changes in neuron number may occur during this period, but these changes are generally of minor functional importance. At this point, the smaller elements of neuronal organization are refined in shape, number, and distribution. Axons are lost or rearranged; dendrites grow, branch, and retract; synapses are fine-tuned; and finally, receptor densities and transmitter titres are adjusted. Some of these interactions and numerical adjustments continue until the animal dies.

Animals↗
PubMed1987

Raman spectroscopy of interferon-induced 2',5'-linked oligoadenylates.

Raman spectra of model compounds and of 2',5'-oligoadenylates in D2O were utilized to assign the Raman bands of 2',5'-oligoadenylates. The Raman spectra of A2'pA2'pA, pA2'pA2'pA, and pppA2'pA2'pA contained features that were similar to those of adenosine, adenosine 5'-monophosphate (AMP), and adenosine 5'-triphosphate, respectively. When AMP and pA2'pA2'pA were titrated from pH 2 to 9, the normalized Raman intensity of their ionized (980 cm-1) and protonated (1080 cm-1) phosphate bands revealed similar pKa's for the 5'-monophosphates. The Raman spectrum of pA2'pA2'pA was altered slightly by elevations in temperature, but not in a manner supporting the postulate that 2-5A possesses intermolecular base stacking. Major differences in the Raman spectrum of 2',5'- and 3',5'-oligoadenylates were observed in the 600-1200-cm-1 portion of the spectrum that arises predominately from ribose and phosphate vibrational modes. Phosphodiester backbone modes in A3'pA3'pA and pA3'pA3'pA produced a broad band at 802 cm-1 with a shoulder at 820 cm-1, whereas all 2',5'-oligoadenylates contained a major phosphodiester band at 823 cm-1 with a shoulder at 802 cm-1. The backbone mode of pppA2'pA2'pA contained the sharpest band at 823 cm-1, suggesting that the phosphodiester backbone may be more restrained in the biologically active, 5'-triphosphorylated molecule. The Raman band assignments for 2',5'-oligoadenylates provide a foundation for using Raman spectroscopy to explore the mechanism of binding of 2',5'-oligoadenylates to proteins.

Adenine Nucleotides↗
PubMed1987

Secondary structure predictions and medium range interactions.

Several authors have proposed that predictions of protein secondary structure derived from statistical information about the known structures can be improved when information about neighboring residues participating in short and medium range interactions is included. A substantial improvement shown here indicates that current methods of including this information are not more successful than methods that do not. Evaluations of the Chou and Fasman method (Adv. Enzymol. 47 (1978) 45-148), that does not include information about interactions (except in averaging), have shown it to be about 49% correct for three states (helix, beta-sheet and undefined). In comparison, the method of Garnier et al. (J. Mol. Biol. 120 (1978) 97-120), that explicitly includes information about neighboring residues, has an accuracy of 57% residues correct for three states. However, we have obtained an 8% improvement for predictions of secondary structure based on the algorithm by Chou and Fasman. The improvements are obtained by eliminating many rules and by choosing the best decision constants for structure assignments. The simplified method described here is 57% correct for three states using preference values calculated in 1978.

Amino Acids↗
PubMed1987

Formation of retinal ganglion cell topography during prenatal development.

A fundamental feature of the mammalian visual system is the nonuniform distribution of ganglion cells across the retinal surface. To understand the ontogenetic processes leading to the formation of retinal ganglion cell topography, changes in the regional density of these neurons were studied in relation to ganglion cell loss and the pattern of retinal growth in the fetal cat. Midway through the gestation period, the density of these neurons was only two to three times greater in the area centralis than in the peripheral retina, whereas shortly before birth this central-to-peripheral difference was nearly 20-fold. Age-related changes in the ganglion cell distribution were found not to correspond in time or magnitude to the massive loss of ganglion cells that occurs during prenatal development. Rather, the formation of ganglion cell density gradients can be accounted for by unequal expansion of the growing fetal retina-peripheral regions expand more than the central region, thereby diluting the peripheral density of ganglion cells to a greater degree. Nonuniform growth, in conjunction with differential periods of neurogenesis of the different types of retinal cells, appears to be a dominant factor regulating overall retinal topography. These results suggest that the differential regional expansion of the fetal retina underlies the formation of magnification factors in the developing visual system.

Animals↗
PubMed1987

Mutagenicity in salmonella of hazardous wastes and urine from rats fed these wastes.

15 hazardous industrial waste samples were evaluated for mutagenicity in the Salmonella plate-incorporation assay using strains TA98 and TA100 in the presence and absence of Aroclor 1254-induced rat liver S9. Dichloromethane/methanol extracts of the crude wastes were also evaluated. 7 of the crude wastes were mutagenic, but only 2 of the extracts of these 7 wastes were mutagenic; extracts of 2 additional wastes also were mutagenic. In addition, 10 of the crude wastes were administered by gavage to F-344 rats, and 24-h urine samples were collected. Of the 10 raw urines evaluated, 3 were mutagenic in strain TA98 in the presence of S9 and beta-glucuronidase. The 3 crude wastes that produced these 3 mutagenic urines were, themselves, mutagenic. Adequate volumes of 6 of the 10 raw urines were available for extraction/concentration. These 6 urines were incubated with beta-glucuronidase and eluted through Sep-Pak C18 columns; the methanol eluates of 3 of the urines were mutagenic, and these were the same 3 whose raw urines also were mutagenic. In general, the C18/methanol extraction procedure reduced the cytotoxicity and increased the mutagenic potency of the urines. To our knowledge, this is the first report of the mutagenicity of urine from rodents exposed to hazardous wastes. Based on the present results, the use of only strain TA98 in the presence of S9 might be adequate for general screening of hazardous wastes or waste extracts for genotoxicity. The urinary mutagenesis assay does not appear to be a useful adjunct to the Salmonella assay for screening hazardous wastes. The problems associated with chemically fractionating diverse types of hazardous wastes for bioassay are also discussed.

Animals↗
PubMed1986

The secondary structure of calcium pump protein in light sarcoplasmic reticulum and reconstituted in a single lipid component as determined by Raman spectroscopy.

Raman spectra have been measured of the following samples: active calcium pump protein in light sarcoplasmic reticulum (SR) membranes, lipids extracted from light SR membranes, active calcium pump protein reconstituted in dielaidoylphosphatidylcholine (DEPC), and pure DEPC. The spectra of native SR lipids and of pure DEPC are different, and yet when these spectra are subtracted from the spectra of the respective protein-lipid complexes, the resulting amide I spectra of the calcium pump protein are the same, indicating that appropriate criteria have been chosen for subtraction of the spectrum of a lipid. This spectrum has been analyzed for secondary structure with the following results. The SR calcium pump protein contains 51 +/- 5% helix, in agreement with a prediction of secondary structure obtained from an analysis of the sequence, and 21 +/- 4% beta-strand. In addition, the presence of protein broadens and lowers the main melting transition of DEPC.

Animals↗
PubMed1986

Secondary structure of calsequestrin in solutions and in crystals as determined by Raman spectroscopy.

Calsequestrin has been precipitated with calcium into five different crystal forms: cruciform twins, flat rectangles, thin needles, bipyramids, rectangular prisms, and a sixth precrystalline form, spheres. Raman spectra of the spheres and the cruciform twins are the same. The Raman spectrum of a physiological concentration (10%) of calsequestrin in calcium-free solution is the same as the spectrum of calcium precipitated calsequestrin in the amide I region, and in the C-C stretching region, but these spectra are different in the amide III region. The Raman spectrum of unfolded calsequestrin in 5 M guanidine hydrochloride is quite different from the other spectra, but it is not similar to the spectra of other unfolded proteins. Estimates of secondary structure from the amide I region indicate that calsequestrin in calcium-free solution and calcium-precipitated forms has 40 +/- 5% helix, 30 +/- 4% beta-strand, and 18 +/- 2% reverse turn. Secondary structure estimates calculated from the amide III region are not significantly different. They indicate 41 +/- 5% helix and 36 +/- 6% beta-strand for the precipitated forms, and 32 +/- 5% helix and 39 +/- 6% beta-strand for solutions. Calsequestrin unfolded in 5 M guanidine hydrochloride at 100 mg/ml gives 24 +/- 5% helix and 48 +/- 6% beta-strand.

Calsequestrin↗
PubMed1986

Growth cones, dying axons, and developmental fluctuations in the fiber population of the cat's optic nerve.

We have studied the rise and fall in the number of axons in the optic nerve of fetal and neonatal cats in relation to changes in the ultrastructure of fibers, and in particular, to the characteristics and spatiotemporal distribution of growth cones and necrotic axons. Axons of retinal ganglion cells start to grow through the optic nerve on the 19th day of embryonic development (E-19). As early as E-23 there are 8,000 fibers in the nerve close to the eye. Fibers are added to the nerve at a rate of approximately 50,000 per day from E-28 until E-39--the age at which the peak population of 600,000-700,000 axons is reached. Thereafter, the number decreases rapidly: About 400,000 axons are lost between E-39 and E-53. In contrast, from E-56 until the second week after birth the number of axons decreases at a slow rate. Even as late as postnatal day 12 (P-12) the nerve contains an excess of up to 100,000 fibers. The final number of fibers--140,000-165,000--is reached by the sixth week after birth. Growth cones of retinal ganglion cells are present in the optic nerve from E-19 until E-39. At E-19 and E-23 they have comparatively simple shapes but in older fetuses they are larger and their shapes are more elaborate. As early as E-28 many growth cones have lamellipodia that extend outward from the core region as far as 10 microns. These sheetlike processes are insinuated between bundles of axons and commonly contact 10 to 20 neighboring fibers in single transverse sections. At E-28 growth cones make up 2.0% of the fiber population; at E-33 they make up about 1.0%; from E-36 to E-39 they make up only 0.3% of the population. Virtually none are present in the midorbital part of the nerve on or after E-44. At all ages growth cones are more common at the periphery of the nerve than at its center. This central-to-peripheral gradient increases with age: at E-28 the density of growth cones is two times greater at the edge than at the center but by E-39 the density is four to five times greater. Necrotic fibers are observed as early as E-28 in all parts of the nerve. Their axoplasm is dark and mottled and often contains dense vesiculated structures.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Does axonal branching contribute to the overproduction of optic nerve fibers during early development of the cat's visual system?

The number of axons within the optic nerve of the fetal cat was found to be no greater near the chiasm than near the eye. This suggests that the overabundance of axons present in the developing nerve results from a corresponding excess of retinal ganglion cells, and that the elimination of optic fibers that occurs during normal development is principally due to the loss of ganglion cells and not to the elimination of axonal branches.

Animals↗
PubMed1985

Selectivity of antibody-mediated destruction of axons in the cat's optic nerve.

The purpose of this study was to determine the selectivity with which polyspecific antibodies directed against large retinal ganglion cells destroy axons in the cat's optic nerve. Immune serum prepared against large ganglion cells isolated from ox retinas was injected into 1 eye of each of 2 cats. After more than 1 month, the cats were perfused with mixed aldehydes and the optic nerves were prepared for transmission electron microscopy. On the basis of a large sample of micrographs of transverse thin sections, we estimated that each of the nerves that issued from treated eyes contained approximately 62,500 necrotic fibers, amounting to 42-46% of the total fiber population in 1 case and 39-42% in the other. The diameters of 2900-5000 intact axons from each of 4 nerves (2 from immune-treated eyes and 2 from untreated eyes) were measured. Comparisons of histograms of axon diameter for nerves from treated and untreated eyes revealed that 90-100% of large axons with diameters above 3.5-4.0 micron were eliminated by the antibodies. Between 65 and 70% of medium-sized fibers were also eliminated. The number of small axons--those with diameters less than 1.2-1.6 micron--did not differ appreciably from normal. These results suggest that the immune serum destroyed virtually all alpha cell axons and a substantial fraction of beta cell axons but did not reduce the number of small fibers that largely stem from the gamma class of retinal ganglion cells.

Animals↗
PubMed1985

Secondary structure of human leukocyte interferon from Raman spectroscopy.

Raman spectra were taken of human alpha (leukocyte) interferon subtype A (HuIFN-alpha A) purified from extracts of transformed Escherichia coli. Quantitative analysis of the conformationally sensitive amide I band indicates that IFN (interferon)-alpha A is 75 +/- 5% helical and 7 +/- 4% beta-strand. An independent analysis of the amide III spectrum indicates 71 +/- 5% helix and 10 +/- 6% beta-strand. These results differ with a recently proposed three-dimensional model based on secondary structure predictions derived from sequence and with circular dichroism measurements. The Raman spectrum of IFN-alpha A is compared with the spectra of several other helical proteins: hemerythrin, intestinal calcium-binding protein, melittin, and insulin.

Escherichia coli↗
PubMed1985

Dispersion of growing axons within the optic nerve of the embryonic monkey.

To determine whether individual optic fibers grow along constant sets of neighboring fibers, a group of 160 axons and 25 axonal growth cones were traced through a set of 500 serial electron micrographs of an optic nerve taken from a 39-day-old monkey embryo (Macaca mulatta). In single transverse sections, growth cones contact an average of 7.9 fibers, whereas axons contact 5.3 other fibers. The particular set of fibers in contact with one another changed rapidly, and, on average, growth cones and axons lost half of their original neighbors over a distance of only 8-10 micron. Between the first and last sections of the series, 92% of all initial contacts were lost. Individual axons moved freely between fiber fascicles, and the distance separating initial neighbors increased progressively. Most remarkably, the sets of fibers touched by the tips and the shanks of growth cones had no common neighbors in 17 out of 25 cases. These results demonstrate that, in primates, fibers in the optic nerve do not retain a particular set of immediate neighbors during their outgrowth.

Animals↗