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PubMed1985

Critical dependence of calcium-activated force on width in highly compressed skinned fibers of the frog.

Force development by skinned frog semitendinosus fibers was studied at various levels of lateral compression to compare the results with intact fibers and to evaluate the limits on cross-bridge movements during isometric contraction. The skinned fibers were compressed osmotically using a high molecular weight polymer, dextran T500. Ca-activated force remained constant down to 58% of the fiber width (w0) after skinning, corresponding to a nearly twofold change in separation between the thin and thick filaments in the myofilament lattice. This agrees with the earlier result on intact fibers, and gives additional evidence that the cross-bridge mechanism for force generation is relatively insensitive to large changes in interfilament separation. Further compression, below 0.58 w0, produced a sharp drop in force, and the force was practically zero at a fiber width of 50%. The effect at high compression was the same at all pCa's, which indicates that the Ca sensitivity of the myofilaments is unaffected by radial compression. The stiffness of the fiber remained high in rigor in the presence of dextran, which indicates that the rigor cross-bridge attachment is not inhibited, and actually may be improved, with decreases in the interfilament space. Also, the drop in active force with the highest compression was similar when the compressed fibers were put in rigor before contraction, which suggests that the force drop also was not due to a hindrance to cross-bridge attachment. The results appear to exclude large motions such as tilting and rocking of the bridge as a rigid molecule, but suggest that at least some molecular movement is essential for force development; they also raise the possibility that there is a critical interfilament separation in the fiber, below which the cross-bridge cannot function.

Animals↗

PubMed1997

Microbial and animal limitations to fiber digestion and utilization.

The ruminal microbial populations attack, degrade and ferment structural carbohydrates in forage cell walls and thereby provide volatile fatty acids and protein to the host animal. Microbial colonization of fiber is quite rapid; however, the rate and extent to which fiber is degraded is determined to a considerable degree by factors such as microbial accessibility to substrate, physical and chemical nature of the forage and kinetics of ruminal digestion. The physical and chemical nature of forages can present a barrier to their complete digestion in the rumen, especially the association of lignin with polysaccharide constituents. Adhesin proteins allow bacteria with cell-bound enzymes to come into intimate contact with their substrates, ensuring that the degradation products are preferentially available. Research on various fibrolytic enzymes and cellulose binding domains may allow for the transfer of novel genetic material to bacteria for enhancing the hydrolysis of plant cell walls. Fungi may also play an important synergistic role in the ruminal digestion of forages by physically disrupting the lignified stem tissue. This allows the ruminal microbes greater access to the plant stem and the digestible portions of the plant. New developments in fiber utilization by ruminants are currently under investigation and include genetic manipulation of ruminal bacteria, chemical and biological treatments of forages, and manipulation of dietary inputs and feeding management.

Animal Feed↗

PubMed1993

Actions of cholinergic agonists and antagonists on sensory nerve endings in rat skin, in vitro.

1. Cholinergic effects on primary sensory afferents were investigated in a superfused skin-saphenous nerve preparation of the rat that allows the application of chemicals topically to the corium side of identified receptive fields. 2. The acetylcholine analogue carbachol (carbamoylcholine) selectively excited cutaneous C-fibers of nociceptive character; in proportion, almost half of the mechanoheat sensitive ("polymodal," C-MH, n = 27), and a third of the mechanocold sensitive (C-MC, n = 10), and high-threshold mechanosensitive (C-HTM, n = 6) C-fibers were activated. 3. None of slowly and rapidly adapting A beta fibers, low and high threshold mechanoreceptive A delta fibers (n = 19) gave a response to high concentrations (< or = 10(-4) M) of carbachol. 4. The carbachol threshold concentrations of C-nociceptors ranged between 10(-7) and 10(-4) M; 10(-6) M was most frequently encountered. 5. The carbachol-induced discharges showed a dose-response relationship without obvious "ceiling" from 10(-6) to 10(-4) M. Tachyphylaxis was not prominent; the fibers mostly developed ongoing activity after exposure to carbachol. 6. Repeated carbachol treatment of C-MH units left with a marked and sustained desensitization to mechanical (von Frey) stimulation, while the heat responsiveness remained unchanged. 7. In a group of carbachol-sensitive C-nociceptors (n = 4), two units could also be excited with muscarine (10(-6) M), one with nicotine (10(-6) M), and one unit with both substances.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1992

Bravo/Nr-CAM is closely related to the cell adhesion molecules L1 and Ng-CAM and has a similar heterodimer structure.

Diverse cell-surface molecules of the nervous system play an important role in specifying cell interactions during development. Using a method designed to generate mAbs against neural surface molecules of defined molecular weight, we have previously reported on the surface protein, Bravo, found in the developing avian retinotectal system. Bravo is immunologically detected on developing optic fibers in the retina, but absent from distal regions of the same fibers in the tectum. We have isolated cDNA clones encompassing the entire coding region of Bravo, including clones containing five alternative sequences of cDNA. These putative alternatively spliced sequences encode stretches of polypeptide ranging in length from 10-93 amino acids and are predicted to be both extra- and intracellular. The deduced primary structure of Bravo reveals that, like the cell adhesion molecules (CAMs) chicken Ng-CAM and mouse L1, Bravo is composed of six Ig-like domains, five fibronectin type III repeats, a transmembrane domain, and a short cytoplasmic region. Recently, the cDNA sequence of a related molecule, Nr-CAM, was reported and its possible identity with Bravo discussed (Grumet, M., V. Mauro, M. P. Burgoon, G. E. Edelman, and B. A. Cunningham. 1991. J. Cell Biol. 113:1399-1412). Here we confirm this identity and moreover show that Bravo is found on Müller glial processes and end-feet in the developing retina. In contrast to the single polypeptide chain structure of Nr-CAM reported previously, we show that Bravo has a heterodimer structure composed of an alpha chain of M(r) 140/130 and a beta chain of 60-80 kD. As with L1 and Ng-CAM, the two chains of Bravo are generated from an intact polypeptide by cleavage at identical locations and conserved sites within all three molecules (Ser-Arg/Lys-Arg). The similar domain composition and heterodimer structure, as well as the 40% amino acid sequence identity of these molecules, defines them as an evolutionarily related subgroup of CAMs. The relationship of Bravo to molecules known to be involved in cell adhesion and process outgrowth, combined with its pattern of expression and numerous potential isoforms, suggests a complex role for this molecule in cell interactions during neural development.

Amino Acid Sequence↗

PubMed1996

Integrated optical NIR-evanescent wave absorbance sensorfor chemical analysis.

A new, long-path integrated optical (IO) sensor for the detection of non-polar organic substances is described. The sensing layer deposited on a planar multimode IO structure is built by a suitable silicone polymer with lower refractive index (RI). It acts as a hydrophobic matrix for the reversible enrichment of non-polar organic contaminants from water or air. Light from the near-infrared (NIR) range is coupled into the planar structure and the evanescent wave part of the light field penetrating into the silicone layer interacts with the enriched organic species. As a result, light is absorbed at the characteristic frequencies of the corresponding C-H, N-H or O-H overtone and combination band vibrations of the analytes. To perform evanescent field absorbance (EFA) measurements, the arc-shaped strip waveguide structure of 172 mm interaction length was adapted to a tungsten-halogen lamp and an InGaAs diode array spectrograph over gradient index fibers. Dimethyl-co-methly(phenyl)polysiloxanes with varying degrees of phenylation were prepared and used as sensitive coating materials for the IO structure. Light attenuation in the arc-shaped waveguides is high and typical insertion losses in the range of 14-18 dB were obtained. When the coated sensors were brought in contact with aqueous samples, the light transmission decreases, which is due to the formation of H(2)O micro-emulsions in the silicone superstrates. Nevertheless, after reaching constant light transmissions, absorbance spectra of aqueous trichloroethene samples were successfully collected. For gas measurements, where water cross sensitivity problems are absent, the sensitivity of the IO device for trichloroethene was tested as a function of the RI of the silicone superstrate. The slope of the TCE calibration function increases by a factor of 10 by using a poly(methylphenylsiloxane) layer with a RI of 1.449 instead of poly(dimethylsiloxane) (RI: 1.41). A comparison of the IO-EFA and an earlier developed fiber-optic EFA sensor for trichloroethene measurements in the gas phase showed an increase in sensitivity per unit length of the waveguide by a factor of up to 120.

Journal Article↗

PubMed1992

Development of cerebral arterial innervation: synchronous development of neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-containing fibers and some observations on growth cones.

The pre- and postnatal development of sympathetic fibers containing neuropeptide Y (NPY) and parasympathetic fibers containing vasoactive intestinal polypeptide (VIP) supplying the cerebral arteries were studied with immunohistochemistry in rats. The innervation patterns and densities of NPY and VIP fibers were similar at all stages of development and similar to that previously reported for norepinephrine (NE). There was a striking reorganization of the innervation pattern of all three fiber systems between the first and second postnatal weeks. At all stages of development prior to the first postnatal week, growth cones were present on individual fibers at the distal part of major cerebral arteries and the middle segment of the basilar artery. The growth cones had a range of shapes from blunt to stellate, lanceolate or filiform. NPY and VIP immunoreactive granules were commonly present. The present results taken with our earlier developmental study of NE fibers (J. Comp. Neurol., 271 (1988) 435-444), demonstrate that: (1) both sympathetic and parasympathetic perivascular nerves on immature cerebral vessels develop with similar sequences: first longitudinal fibers and fiber bundles are present; these transform to a meshwork pattern and finally transform again into the mature, predominantly circumferential pattern; (2) both the classical (NE) and peptidergic transmitters (NPY) within the sympathetic system appear to develop identically in terms of time of appearance, innervation patterns, densities and reorganization.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic Fibers↗

PubMed1975

Development of the triadic junction in skeletal muscle fibers of fetal and postnatal rats.

Electron microscope examinations of the developing triadic junction in fibers from leg muscles of fetal and postnatal rats reveal a range of complexity from no structural connections across the space between apposed membranes of T and SR to all of the junctional structures visible in adult rat muscle fibers. In triads showing no connections, faintly stained projections from the apposed membranes of T and SR are seen. The simplest form of junctional structure is a series of faintly stained strands that make connections across the space between apposing membranes. Junctional structures stained more intensely show periodic bridges traversing the space plus an intermediate dense line (intermediate density) running parallel to the apposed membranes of T and SR and bisecting the space between apposed membranes. The intermediate density is continuous across the periodic bridges and interbridge spaces and it appears to be connected to the apposed membranes of T and SR. It is suggested that projections from T and SR are precursors of the connections and that the projections interact to form the intermediate density. It is also suggested that bridge and interbridge junctional structures might form compartments isolated from the sarcoplasm and thus enhance the flow of electrical current from T to apposed SR by reducing low-resistance shunting of current flow into the sarcoplasm,

Animals↗

PubMed1987

Molding of laser energy by shaped optic fiber tips.

The development of a new technique for laser recannalizing atheromatous vessels has inherent problems concerning heat damage to the vessel walls. A theoretical analysis of 2,100 light rays in large bulb end (output end) fibers compared to a standard flat end fiber showed (1) a much higher-intensity focus; (2) a 125.4% increase in number of output rays (with respect to number of input rays) in the convergent output beam, due to multiple reflections/refractions ("stars" and "triangles") and standing waves, in the large bulb end, compared to 48.6% in the flat end; (3) 83.69% energy in the converging beam of the large bulb end, compared to 46.1% energy in the flat end; and (4) a rapidly divergent beam after focus. Hence, theoretically a wide area of plaque could be burnt off more rapidly with less heat conduction into the vessel walls. Coupling efficiency was experimentally shown to be greatly increased by also having a bulb at the optic fiber input end.

Arteriosclerosis↗

PubMed1981

Histochemical differentiation of fiber types in neonatal canine skeletal muscle.

Differentiation of fiber types in developing canine skeletal muscle was studied, using morphologic, morphometric, and histochemical techniques. Sample collections were made from 6 muscles from the pectoral and pelvic limbs of 16 healthy pups between 1 day and 12 weeks of age. In newborn pups, 90% to 95% of the fibers in the 6 muscles were classified as undifferentiated or type IIC; the remaining fibers were classified either normal or large-size type I. Large-size type I fibers usually accounted for 2% to 4% of the total population and were considered analogous with the B fiber of Wohlfart. These fibers were larger than all other fiber types and disappeared after pups reached 4 to 5 weeks of age. After 2 to 4 weeks, the number of undifferentiated fibers decreased with the appearance of, and the concomitant numerical increases of, normal size type I and type IIA fibers. The percentages of type I and IIA fibers approached proportions of the adult dog by 12 weeks, at which time a type IIA fiber predominance was present in biceps femoris, lateral head of the gastrocnemius, cranial tibial, and long head of the triceps. Type I fibers predominated in medial head of the triceps and superficial digital flexor after 4 to 5 weeks. The mean fiber diameters of type I and IIA fibers were similar to any given muscle throughout the postnatal development. All fiber types stained uniformly with the oxidative stain nicotinamide adeninedinucleotide-tetrazolium reductase during the first 12 weeks of life, whereas a distinction between type I and II fibers was evident after 3 to 4 weeks with the periodic acid-Schiff stain reaction.

Adenosine Triphosphatases↗

PubMed1990

Substance P- and opioid-immunoreactive structures in olfactory centers of the cat: adult pattern and postnatal development.

Substance P (SP)-ir and opioid-ir structures were studied in the cat main olfactory bulb (MOB), accessory olfactory bulb (AOB), and olfactory peduncle. In the MOB, the opioid-ir and the majority of the SP-ir neurons belong to the granule cell type. SP-ir granule cells reside in the deeper granule cell layer, whereas opioid-ir granule cells reside in the superficial granule cell layer, internal plexiform, and mitral cell layer. Many granule cells are observed in the external plexiform and glomerular layer. Other granule cells were found in the bulbar/peduncular white matter, the taenia tecta, and the genu of the corpus callosum. A new substance P-ir cell type was identified in the glomerular layer. This cell type was also identified by using the technique of intracellular injection of Lucifer Yellow. The cell type corresponds neither to the external tufted type nor to the short axon cell types described so far. The AOB resembles the MOB with respect to large numbers of SP-ir and opioid-ir granule cells. In addition, a few opioid-ir neurons, probably superficial mitral cells, were found in the glomerular layer. The AOB is surrounded by islands of immunoreactive granule cells, which connect to the granule cell layer by extremely long processes. Opioid-ir and SP-ir beaded axons pass through the olfactory peduncle terminating on granule cells, and ascend as far as the glomerular layer. All subdivisions of the anterior olfactory nucleus (AON) contain immunoreactive terminal fields. Afferent fibers and terminal plexuses derive from a population of immunoreactive neurons located predominantly in the region of the septo-olfactory junction. They have large somata. Their axons form recurrent collaterals, some of which run rostrally in the peduncular white matter. Others ascend caudally towards the septal region. The fibers seem to remain ipsilaterally, since the olfactory limb of the anterior commissure and the commissure proper are devoid of SP-ir and opioid-ir fibers. During development SP and opioid immunoreactivity were found only in differentiated granule cells. The peptides were not detectable in migrating or immature granule cells, as identified in Golgi-impregnated material. The granule cell population largely develops during postnatal life. The number of opioid-ir granule cells increases slowly and continuously, reaching the adult level not before the sixth postnatal month. Strikingly, SP-ir granule cell number increases fast and reaches a transient peak during the second month. Thereafter it declines (40% decrease) to the adult density, which is similar to that of opioid-ir granule cells.

Afferent Pathways↗

PubMed2002

Evidence that phosphate release is the rate-limiting step on the overall ATPase of psoas myofibrils prevented from shortening by chemical cross-linking.

It has been suggested that the mechanical condition determines the rate-limiting step of the ATPase of the myosin heads in fibers: when fibers are isometrically contracting, the ADP release kinetics are rate-limiting, but as the strain is reduced and the fibers are allowed to shorten, the ADP release kinetics accelerate and P(i) release becomes rate-limiting. We have put this idea to the test with myofibrils as a model because with these both mechanical and chemical kinetic measurements are possible. With relaxed or rapidly shortening myofibrils, P(i) release is rate-limiting and (A)M.ADP.P(i) states accumulate in the steady state [Lionne, C., et al. (1995) FEBS Lett. 364, 59]. We have now studied the kinetics of P(i) release with chemically cross-linked myofibrils that, when adequately cross-linked, appear to be a good model for isometric contraction. By using a method that is specific for free P(i) and rapid quench flow that measures the amount of (A)M.ADP.P(i) states and free P(i), we show that (A)M.ADP.P(i) states predominate which suggests that the overall ATPase is limited by P(i) release kinetics. Therefore, under our experimental conditions with myofibrils prevented from shortening, the concentration of (A)M.ADP states is low, as with rapidly shortening and relaxed myofibrils. This result is difficult to reconcile with the sensitivity of force development in fibers and myofibrils to P(i) which implies interaction of P(i) with an (A)M.ADP state. We discuss two models for accommodating the mechanical and chemical kinetics with reference to the duty cycle in skeletal muscle.

Adenosine Diphosphate↗

PubMed2002

Functional properties and [Ca(2+)](i) metabolism of creatine kinase--KO mice myocardium.

One major function of the creatine kinase system is to maintain energy demand of myofibrillar contraction processes. Loss of the CK-system led to adaptations in skeletal muscle. To analyze the impact on myocardial function contractile parameters and intracellular calcium metabolism of transgenic mice lacking mitochondrial CK (ScCKmit(-/-)) alone or both mitochondrial and cytoplasmic ScCK (CK(-/-)) were investigated compared to wild type at various workload conditions using isolated intact muscle fibers. Force development at baseline conditions, force-frequency relationship (60-600/min), and rapid frequency switch (60-600/min) were unaltered in myocardium of transgenic mice compared to wild type. Intracellular calcium metabolism revealed unchanged amplitude of the intracellular calcium transients (ICT), refilling of the sarcoplasmic reticulum (calcium reuptake, post-rest behavior) in the ScCKmit(-/-) and CK(-/-) mice. The results demonstrate the effectiveness of myocardial energy-recruiting compensatory mechanisms at baseline as well as under stress conditions in CK depleted myocardium of transgenic mice.

Adaptation, Physiological↗

PubMed1995

TrkB-like immunoreactivity in trigeminal sensory nerve fibers of the rat molar tooth pulp: development and response to nerve injury.

The localization of TrkB, a signal transducing receptor for brain-derived neurotrophic factor and neurotrophin-4, was studied in the rat mandibular molar pulp during development and following nerve injury. Sections were incubated with rabbit polyclonal antiserum against the catalytic part of the TrkB receptor, thus only binding to full-length TrkB receptors, and examined by immunofluorescence microscopy and EM immunocytochemistry. At embryonic day 17, strongly TrkB-positive fibers were located in mandibular nerve trunks, in nerve fibers of deeper mesenchyme in close spatial relation to sites of future tooth development and in subepithelial nerve plexa. At postnatal days 1-12 intensely TrkB-positive nerve fibers surrounded and eventually invaded the developing dental papillae and pulps. In the normal adult pulp TrkB-immunoreactive axons were seen extending through the radicular pulp into the coronal areas. Double labelling demonstrated a considerable overlap between TrkB-like immunoreactivity and low affinity neurotrophin receptor-like immunoreactivity in the pulp, although some low affinity neurotrophin receptor-positive nerve fibers lacked TrkB-like immunoreactivity. Immunogold electron microscopy showed TrkB-like immunoreactivity in myelinated as well as in unmyelinated axons. One week following inferior alveolar nerve injury there was a dramatic decrease in the level of TrkB-like immunoreactivity labelling in the pulp, which paralleled an increase in the expression of Schwann cell low affinity neurotrophin receptor-like immunoreactivity. The first signs of regenerating TrkB-positive nerve fibers were found at 4 weeks post-operative, and at 9 weeks the distribution of pulpal TrkB-like immunoreactivity had returned to normal. These data indicate that brain-derived neurotrophic factor and/or neurotrophin-4 could be target-derived factors involved in sensory trigeminal tooth pulp nerve fiber development, differentiation or regeneration.

Aging↗

PubMed2000

Hydrostatic pressure stimulates synthesis of elastin in cultured optic nerve head astrocytes.

Elastin is a major component of the extracellular matrix (ECM) of the lamina cribrosa in the optic nerve head in humans and nonhuman primates. The lamina cribrosa appears to be the site of damage to the retinal ganglion cell axons in glaucomatous optic neuropathy, characterized in many patients by elevated intraocular pressure (IOP). Type 1B astrocytes are the major cell type in the lamina, synthesize elastic fibers during development, express increased elastin mRNA, and synthesize abnormal elastin in glaucoma. In this study, we determined the effect of elevated hydrostatic pressure on the synthesis of elastin by type 1B astrocytes in culture. Type 1B astrocytes were exposed to gradients of hydrostatic pressure and tested for proliferation, morphology, synthesis, and deposition of elastin. Trichloroacetic acid (TCA) and immunoprecipitation of radiolabeled protein determined total new protein and elastin synthesis. Proteins from the conditioned media were analyzed by Western blot. Levels of elastin mRNA were determined by in situ hybridization. Cell proliferation increased approximately 2-fold after exposure to pressure for one day, approximately 5-fold after 3 and 5 days of exposure to pressure. Confocal and electron microscopic cytochemistry showed a marked increase in intracellular elastin in astrocytes exposed to pressure, as compared with controls. Intracellular elastin was associated with the RER-Golgi region and with the cytoskeleton. Total protein and elastin synthesis increased significantly (P < 0.05) at 3- and 5-day exposure to pressure, as well as the level of elastin mRNA. Elastin protein in the media increased with the level of pressure. These results indicate that hydrostatic pressure stimulates type 1B astrocytes to synthesize and secrete soluble elastin into the media. In glaucoma, type 1B astrocytes may respond to IOP-related stress with increased expression of elastin and formation of elastotic fibers leading to loss of elasticity and tissue remodeling.

Adolescent↗

PubMed1986

Slow-like electrostimulation switches on slow myosin in denervated fast muscle.

Adult fast and slow skeletal muscles are composed of a large number of fibers with different physiological and biochemical properties that under neuronal control can respond in a plastic manner to a variety of stimuli. Although muscle cells synthesize muscle-specific contractile proteins in the absence of motoneurons, after innervation the neuron controls the particular set of isoforms subsequently synthesized. However, agreement has not been reached on the mechanism, either chemotrophic or impulse-mediated, by which the nerve influences gene expression in the muscle. Here we report the effect on isomyosins of continuous, low-frequency (a protocol mimicking the discharge pattern of the slow motoneuron) direct electrical stimulation of a permanently denervated fast muscle, the extensor digitorum longus of adult rat. After several weeks, unlike sham-stimulated muscle, the stimulated muscle showed a dramatic increase of the slow myosin light and heavy chains. Myosin light chains were identified by two-dimensional gel electrophoresis. The slow myosin heavy chain was clearly distinguished from fast and embryonic types by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and orthogonal peptide mapping. The myosin change could be restricted to a portion of the muscle by the position of the stimulating electrodes. Taking into account the morphologic appearance of the electrostimulated muscle and the large body of evidence demonstrating the absolute dependence of slow myosin on specific innervation, our observations indicate that at least the slow motoneuron influences the isomyosin genes' expression by the kind of activity it imposes on developing muscle fibers.

Animals↗

PubMed1990

Effect of optic nerve lesions and intraocular colchicine on cell proliferation in the germinal zone of the optic tectum and in the torus longitudinalis in the goldfish.

Postembryonic development of the optic tectum occurs in part through proliferation of cells in the germinal zone located at the caudal edges of each lobe. Autoradiography experiments by others have shown that [3H]thymidine labeling in the germinal zone is decreased following optic nerve crush or enucleation and restored above normal levels during optic nerve regeneration. The present autoradiography experiments examined the relationship between retinal innervation and the rate of mitotic activity in the tectum germinal zone and in the torus longitudinalis. The fish received optic nerve crush to temporarily deafferent the tectum, enucleation for permanent deafferentation, or an intraocular injection of 0.01-1.0 microgram of colchicine to reversibly inhibit axonal transport in the optic nerve. Thymidine labeling in the tectum germinal zone showed that nerve crush resulted in decreased mitotic activity in most fish within 6 days followed by recovery by 21 days; enucleation decreased mitotic activity more uniformly and for more than 42 days with recovery by 84 days postaxotomy; colchicine produced a dose-dependent inhibition of mitotic activity which was reversed by 42 days postinjection. Axonal transport was restored by 42 days postinjection. In the torus longitudinalis, nerve crush produced a brief increase in mitotic activity followed by a return to normal; enucleation and colchicine resulted in a lasting decrease in mitotic activity and atrophy indicating a loss of cells or neuropil. The data are consistent with the proposal that cell proliferation in the tectum germinal zone is stimulated by the accretion of fibers from developing retinal ganglion cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Identification of an elastin cross-linking domain that joins three peptide chains. Possible role in nucleated assembly.

The alignment of elastin molecules in the mature elastic fiber was investigated by purifying and sequencing cross-link-containing peptides generated by proteolytic digestion incompletely cross-linked insoluble elastin. Peptides of interest were purified by reverse phase and size exclusion high performance liquid chromatography and characterized by amino acid analysis and protein sequencing. One peptide, consisting of the cross-linking domain encoded by exon 10, contained a modified lysine residue that had not condensed to form a polyfunctional cross-link. Although this domain contains the characteristic paired lysine residues found in other cross-linking domains of elastin, protein sequence analysis indicated that the first but not the second lysine had been oxidized by lysyl oxidase. This finding suggests that lysine residues in an individual cross-linking domain may not have equal susceptibility to oxidation by lysyl oxidase. In a second peptide, we found that a major cross-linking site in elastin is formed through the association of sequences encoded by exons 10, 19, and 25 and that the three chains are joined together by one desmosine and two lysinonorleucine cross-links. Past structural studies and computer modeling predict that domains 19 and 25 are linked by a desmosine cross-link, while domain 10 bridges domains 19 and 25 through lysinonorleucine cross-links. These findings, together with the high degree of sequence conservation for these three domains, suggest an important function for these regions of the molecule, possibly nucleating the aggregation and polymerization of tropoelastin monomers in the developing elastic fiber.

Amino Acid Sequence↗

PubMed2001

Microstructural brain development after perinatal cerebral white matter injury assessed by diffusion tensor magnetic resonance imaging.

OBJECTIVE: Brain injury in premature infants is characterized predominantly by perinatally acquired lesions in the cerebral white matter (WM). The impact of such injury on the subsequent development of cerebral WM is not clear. This study uses diffusion tensor magnetic resonance imaging (MRI) to evaluate the effects of cerebral WM injury on subsequent microstructural brain development in different WM areas of the brain. METHODS: Twenty premature infants (gestational age: 29.1 +/- 1.9 weeks) were studied by conventional MRI within the first 3 weeks of life and again at term, with the addition at the latter time of diffusion tensor MRI. Ten of the preterm infants had cerebral WM injury identified by the early MRI and were matched with 10 premature infants of similar gestational age and neonatal course but with normal neonatal MRI scans. Diffusion tensor MRI at term was acquired in coronal and axial planes and used to determine the apparent diffusion coefficient, a measure of overall restriction to water diffusion, and the relative anisotropy (RA), a measure of preferred directionality of diffusion, in central WM, anterior frontal WM, occipital WM, temporal WM, and the posterior limb of the internal capsule. Diffusion vector maps were generated from the diffusion tensor analysis to define the microstructural architecture of the cerebral WM regions. RESULTS: At term, the diffusion tensor MRI revealed no difference in apparent diffusion coefficient among preterm infants with or without perinatal WM lesions. By contrast, RA, the measure of preferred directionality of diffusion and thereby dependent on development of axonal fibers and oligodendroglia, was 25% lower in central WM, the principal site of the original WM injury. However, RA was unaffected in relatively uninjured WM areas, such as temporal, anterior frontal, and occipital regions. Notably, RA values in the internal capsule, which contains fibers that descend from the injured cerebral WM, were 20% lower in the infants with WM injury versus those without. Diffusion vector maps showed striking alterations in the size, orientation, and organization of fiber tracts in central WM and in those descending to the internal capsule. CONCLUSIONS: Perinatal cerebral WM injury seems to have major deleterious effects on subsequent development of fiber tracts both in the cerebral WM and more distally. The ultimate impact of brain injury in the newborn should be considered as a function not only of tissue destruction, but also of impaired subsequent brain development.

Humans↗