Biomedical subjects

D L Sherman

Publications and source records attributed to D L Sherman.

30 records · Page 2Linked to original sources

PubMed1995

Novel E-cadherin-mediated adhesion in peripheral nerve: Schwann cell architecture is stabilized by autotypic adherens junctions.

Previous studies (Blank, W. F., M. B. Bunge, and R. P. Bunge. 1974. Brain Res. 67:503-518) showed that Schwann cell paranodal membranes were disrupted in calcium free medium suggesting that cadherin mediated mechanisms may operate to maintain the integrity of the paranodal membrane complex. Using antibodies against the fifth extracellular domain of E-cadherin, we now show by confocal laser and electron immunomicroscopy that E-cadherin is a major adhesive glycoprotein in peripheral nervous system Schwann cells. E-Cadherin is not found, however, in compact myelin bilayers. Rather, it is concentrated at the paranodes, in Schmidt-Lanterman incisures, and at the inner and outer loops. At these loci, E-cadherin is associated with subplasmalemmal electron densities that coordinate in register across several cytoplasmic turns of a single Schwann cell. F-Actin and beta-catenin, two proteins implicated in cellular signaling, also co-localize to E-cadherin positive sites. These complexes are autotypic adherens-type junctions that are confined to the plasma membrane synthesized by a single Schwann cell; E-cadherin was never observed between two Schwann cells, nor between Schwann cells and the axon. Our findings demonstrate that E-cadherin and its associated proteins are essential components in the architecture of the Schwann cell cytoplasmic channel network, and suggest that this network has specialized functions in addition to those required for myelinogenesis.

Amino Acid Sequence↗

PubMed1995

Periaxin expression in myelinating Schwann cells: modulation by axon-glial interactions and polarized localization during development.

Periaxin is a newly described protein that is expressed exclusively by myelinating Schwann cells. In developing nerves, periaxin is first detected as Schwann cells ensheathe axons, prior to the appearance of the proteins that characterize the myelin sheath. Periaxin is initially concentrated in the adaxonal membrane (apposing the axon) but, during development, as myelin sheaths mature, periaxin becomes predominately localized at the abaxonal Schwann cell membrane (apposing the basal lamina). In permanently axotomized adult nerves, periaxin is lost from the abaxonal and adaxonal membranes, becomes associated with degenerating myelin sheaths and is phagocytosed by macrophages. In crushed nerves, in which axons regenerate and are remyelinated, periaxin is first detected in the adoxonal membrane as Schwann cells ensheathe regenerating axons, but again prior to the appearance of other myelin proteins. Periaxin mRNA and protein levels change in parallel with those of other myelin-related genes after permanent axotomy and crush. These data demonstrate that periaxin is expressed by myelinating Schwann cells in a dynamic, developmentally regulated manner. The shift in localization of periaxin in the Schwann cell after completion of the spiralization phase of myelination suggests that periaxin participates in membrane-protein interactions that are required to stabilize the mature myelin sheath.

Animals↗

PubMed1994

Periaxin, a novel protein of myelinating Schwann cells with a possible role in axonal ensheathment.

We report the cloning and subcellular localization of a novel Schwann cell-specific protein of 147 kd that we have named periaxin. Periaxin has a remarkable domain of repetitive pentameric units in the primary sequence. It is expressed in the first uncompacted whorls of membrane that ensheathe the axon, and further synthesis of the protein in the rat sciatic nerve parallels the deposition of myelin. In mature myelin, periaxin colocalizes with the myelin-associated glycoprotein in the cytoplasm-filled periaxonal regions of the sheath but is excluded from compact myelin. We propose that periaxin has a role in axon-glial interactions, possibly by interacting with the cytoplasmic domains of integral membrane proteins such as myelin-associated glycoprotein in the periaxonal regions of the Schwann cell plasma membrane.

Amino Acid Sequence↗

PubMed1994

Intracellular transport of newly synthesized varicella-zoster virus: final envelopment in the trans-Golgi network.

The maturation and envelopment of varicella-zoster virus (VZV) was studied in infected human embryonic lung fibroblasts. Transmission electron microscopy confirmed that nucleocapsids acquire an envelope from the inner nuclear membrane as they enter the perinuclear-cisterna-rough endoplasmic reticulum (RER). Tegument is not detectable in these virions; moreover, in contrast to the mature VZV envelope, the envelope of VZV in the RER is not radioautographically labeled in pulse-chase experiments with [3H]mannose, and it lacks gpI immunoreactivity and complex oligosaccharides. This primary envelope fuses with the RER membrane (detected in cells incubated at 20 degrees C), thereby releasing nucleocapsids to the cytosol. Viral glycoproteins, traced by transmission electron microscopy radioautography in pulse-chase experiments with [3H]mannose, are transported to the trans-Golgi network (TGN) by a pathway that runs from the RER through an intermediate compartment and the Golgi stack. At later chase intervals, [3H]mannose labeling becomes associated with enveloped virions in post-Golgi locations (prelysosomes and plasma membrane). Nucleocapsids appear to be enveloped by wrapping in specialized cisternae, identified as the TGN with specific markers. Tegument-like material adheres to the cytosolic face of the concave surface of TGN sacs; nucleocapsids adhere to this protein, which is thus trapped between the nucleocapsid and the TGN-derived membrane that wraps around it. Experiments with brefeldin A suggest that tegument may bind to the cytosolic tails of viral glycoproteins. Fusion and fission convert the TGN-derived wrapping sacs into an inner enveloped virion and an outer transport vesicle that carries newly enveloped virions to cytoplasmic vacuoles. These vacuoles are acidic and were identified as prelysosomes. It is postulated that secreted virions are partially degraded by their exposure to the prelysosomal internal milieu and rendered noninfectious. This process explains the cell-associated nature of VZV in vitro; however, the mechanism by which the virus escapes diversion from the secretory pathway to the lysosomal pathway in vivo remains to be determined.

Cell Line↗

PubMed1993

Structural abnormalities associated with congenital megacolon in transgenic mice that overexpress the Hoxa-4 gene.

Congenital megacolon develops in transgenic mice that overexpress the homeobox-containing gene, Hoxa-4. The current study was done to identify abnormalities of the terminal colon that might account for the phenotype. The terminal bowel of transgenic mice was compared with that of control and lethal spotted (ls/ls) mice, a strain in which megacolon also develops. The terminal colon of the transgenic mice contained fewer ganglia than that of controls, but was hypoganglionic, rather than aganglionic like that of ls/ls mice. The neurons present in the adult transgenic colon were significantly increased in size and a subset of very large neurons (> 40 microns in maximum diameter) were observed. Electron microscopic studies of young adult transgenic mice revealed that the ganglia and nerves of the myenteric plexus had the ultrastructure of extraenteric peripheral nerve rather than that of the enteric nervous system (ENS). The myenteric ganglia in the transgenic animals contained Schwann cells associated with a basal lamina that enveloped axons completely and individually, instead of glia. Although collagen is excluded from the ganglia and thin nerve fibers of the normal ENS, a collagen-containing endoneurium surrounded each of the axon-Schwann cell units of the abnormal nerve fibers of the transgenic colon. Some of the neurons of the transgenic mice were located in these nerve bundles rather than in ganglia. There were also smooth muscle abnormalities in the terminal bowel of the transgenic mice. Wide gaps were present in the longitudinal muscle of the transgenic mice; these gaps contained ganglia that were in contact with the adventitia. These longitudinal smooth muscle cells were more irregular than those of controls and they contained fewer puncta adherens; moreover, a larger proportion of the volume of the cytoplasm of transgenic smooth muscle cells was occupied by organelles. Finally, an extensive thickening and reduplication of the basal lamina surrounding the smooth muscle cells of the muscularis mucosa was observed in the transgenic colon and resembled that found in ls/ls mice. These data suggest that both smooth muscle and the innervation of the terminal bowel of neonatal Hoxa-4 transgenic mice are structurally abnormal. Although some of the abnormalities seen in Hoxa-4 transgenic mice are similar to those which arise in ls/ls mice, the two conditions are not identical. In both animals, the data are consistent with the hypothesis that the defects arise as a result of a defective interaction between the precursors of enteric neurons and smooth muscle.

Acetylcholinesterase↗

PubMed1992

Schwann cells of the myelin-forming phenotype express neurofilament protein NF-M.

Immature Schwann cells of the rat sciatic nerve can differentiate into myelin-forming or non-myelin-forming cells. The factors that influence this divergent development are unknown but certain markers such as galactocerebroside distinguish the two cell populations at an early stage of Schwann cell differentiation. Because myelination requires extensive changes in cell morphology, we have investigated the composition and structure of the Schwann cell cytoskeleton at a time when these cells become committed to myelination. Here we show that Schwann cells express a cytoskeletal protein of M(r) 145 before diverging into the myelin-forming path, i.e., before they acquire cell-surface galactocerobroside. The p145 protein has the characteristics of an intermediate filament (IF) protein and immunoelectron microscopy shows that it colocalizes with vimentin, which suggests that these two proteins can coassemble into IFs. Elevated intracellular cAMP levels, which can mimic some of the early effects of axons on Schwann cell differentiation, induced p145 synthesis, therefore, we conclude that myelin-forming Schwann cells express this protein at a very early stage in their development. Immunological comparisons with other IF proteins revealed a close similarity between p145 and the neurofilament protein NF-M; the identification of p145 as NF-M was confirmed by isolating and sequencing a full-length clone from a Schwann cell cDNA library. These data demonstrate that Schwann cells remodel their IFs by expressing NF-M before acquiring the myelin-forming phenotype and that IF proteins of the neurofilament-type are not restricted to neurons in the vertebrate nervous system.

Amino Acid Sequence↗

PubMed1991

Expression of a neurally related laminin binding protein by neural crest-derived cells that colonize the gut: relationship to the formation of enteric ganglia.

In order to give rise to the enteric nervous system (ENS), cells migrating from the neural crest must find the bowel and cease migrating at appropriate locations within the gut. Previous studies of the development of the ENS in a mutant mouse have led to the hypothesis that laminin in the enteric mesenchyme may act as a signal to crest-derived cells to cease migrating and extend neurites (or glial processes). Implied in this hypothesis is the idea that crest-derived cells, as a prelude to their participation in ganglion formation, acquire a neurally related laminin receptor, which they do not express at pre-enteric stages of migration. As a partial test of this hypothesis, single and double label immunocytochemistry at light and electron microscopic (EM) levels were used to study the expression of cell surface laminin binding proteins by crest-derived cells in the process of migrating to or within the developing chick gut. Two antibodies (called 3070 and alpha-110) raised against neuronal cell surface laminin binding proteins were employed for this purpose. Laminin binding protein immunoreactivity was found to be expressed within the bowel and ganglion of Remak by a subset of crest-derived cells (identified immunocytochemically with NC-1/HNK-1 antibodies) and by all of those developing as neurons (identified immunocytochemically with antibodies to neurofilament-associated proteins). Laminin binding protein immunoreactivity was also found to be expressed in fixed neural structures elsewhere in the embryos, including cranial and spinal roots, nerves, and ganglia. In contrast, laminin binding protein immunoreactivity was not expressed by migrating crest-derived cells in the vicinity of the vagal or sacral regions of the neuraxis (from which the precursors of the ENS take origin); nor was it expressed by juxta-pharyngeal vagal crest-derived cells migrating to the foregut through the caudal branchial arches or by the caudal stream of sacral crest-derived cells approaching the hindgut. EM immunocytochemistry confirmed that laminin binding protein immunoreactivity in the bowel was located on the surfaces of crest-derived cells, and was exhibited both by those cells that could only be distinguished from their neighbors by their NC-1/HNK-1 immunoreactivity and by cells developing as neurons or glia. EM immunocytochemistry also revealed that the surfaces of crest-derived cells migrating through the enteric mesenchyme were contacted by many small osmiophilic "puffs" of laminin-immunoreactive extracellular material. These puffs coincided in location with membrane sites that expressed the immunoreactivity of the laminin binding protein. These observations are consistent with the hypothesis that laminin plays a role in the formation of enteric ganglia.

Animals↗

PubMed1990

Type-specific localization of monoamine oxidase in the enteric nervous system: relationship to 5-hydroxytryptamine, neuropeptides, and sympathetic nerves.

The localization in the guinea pig enteric nervous system (ENS) of monoamine oxidase (MAO) types A and B was investigated at the light and electron microscopic levels. Immunocytochemistry was used to visualize the enzyme protein and histochemistry was employed to study catalytic activity. Type specificity was achieved in histochemical studies by using deprenyl (0.5 microM) to inhibit MAO-B or clorgyline (0.1 microM) to inhibit MAO-A. The distribution of MAO-B immunoreactivity in the ENS corresponded to that of the sites of MAO activity found histochemically to be inhibited by deprenyl, but not clorgyline. MAO-B was observed to be the primary type of MAO found in the intrinsic elements of the ENS and was located in subsets of neurons in both submucosal and myenteric plexuses. MAO-B was not demonstrated immunocytochemically or histochemically in enteric glia, nor, at the light microscopic level, was there significant MAO-B activity or immunoreactivity in serotonin (5-HT)-immunoreactive neuronal cell bodies. In the submucosal plexus about 50% of the neurons expressed MAO-B; these neurons also contained neuropeptide y (NPY) and/or calcitonin gene related peptide (CGRP), but not substance P or vasoactive intestinal polypeptide (VIP). About 10% of myenteric neurons were intensely reactive for MAO-B; again MAO-B was co-localized with NPY and/or CGRP. In contrast to intrinsic neurons, extrinsic CGRP-immunoreactive nerve fibers contained no demonstrable MAO activity or immunoreactivity. Moreover, the sympathetic innervation, identified as varicose axons that degenerated after administration of 6-hydroxydopamine, contained abundant MAO-A, but no MAO-B activity or immunoreactivity. It is concluded that MAO-B is characteristic of a subset of intrinsic enteric neurons, while MAO-A is confined to the sympathetic innervation, which is extrinsic. At the electron microscopic level individual cells varied greatly in their degree of immuno- or cytochemically demonstrable MAO-B, which was most concentrated on the outer membranes of mitochondria. MAO-B immunoreactivity (but not cytochemical activity) was found on mitochondria in some serotoninergic perikarya identified by the simultaneous radioautographic detection of the uptake of 3H-5-HT. Mitochondria in most serotoninergic axon terminals displayed both MAO-B activity and immunoreactivity. Neurons receiving serotoninergic synapses often, but not invariably, contained MAO-B. Inhibition of neither MAO-B nor MAO-A appeared to slow the disappearance of 3H-5-HT loaded into enteric neurons significantly, even when intraneuronal storage of 5-HT was inhibited with tetrabenazine.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Noradrenergic innervation of serotoninergic neurons in the myenteric plexus.

The monoaminergic innervation of the guinea pig small intestine was investigated to determine if there is an anatomical basis for the hypothesis that serotoninergic and noradrenergic neurons physiologically interact in the enteric nervous system. Initial rates of uptake of tritiated 5-hydroxytryptamine (3H-5-HT) or norepinephrine (3H-NE) by segments of guinea pig small intestine were measured in order to estimate the regional density of the serotoninergic and noradrenergic innervation. No change was found in the uptake of 3H-5-HT as a function of distance between duodenum and ileum, whereas the relative uptake of 3H-NE declined. The pattern of serotoninergic elements demonstrated radioautographically was compared with that obtained by visualizing 5-HT immunoreactivity. Both methods revealed that a small number of serotoninergic neurons, located in 35.3% +/- 1.5% of myenteric ganglia, give rise to many fibers that form thick bundles in interganglionic connectives. Moreover, there was a pronounced heterogeneity in the serotoninergic innervation of individual myenteric neurons and ganglia. In material fixed with aldehydes and postfixed with NaMnO4, noradrenergic axon terminals were identified by their characteristic small dense-cored vesicles. Following incubation with 3H-NE only terminals with small dense-cored vesicles were radioautographically labeled, confirming that these terminals are noradrenergic. When 3H-5-HT was substituted for 3H-NE, noradrenergic terminals were not labeled, showing that nonspecific uptake of 3H-5-HT into noradrenergic axons did not occur in the presence of 5-hydroxydopamine. The combination of aldehyde-NaMnO4 fixation with the radioautographic localization of 3H-5-HT thus permitted the simultaneous identification of serotoninergic and noradrenergic neural elements. Serotoninergic varicosities were found to differ from noradrenergic varicosities in the size, appearance, and packing density of their synaptic vesicles. In addition, recognizable but rudimentary pre- and postsynaptic membrane specializations were associated with serotoninergic but not noradrenergic varicosities. Most serotoninergic neuronal cell bodies were contacted both by serotoninergic synapses and noradrenergic varicosities. Similar appositions of noradrenergic varicosities with nonserotoninergic neurons appeared to be rare. In view of earlier observations that sympathetic nerves affect the release of 5-HT from stimulated enteric serotoninergic neurons, it seems likely that the noradrenergic appositions with serotoninergic neurons are the anatomical substrate for this effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic Fibers↗

PubMed1982

Identification of and interactions between noradrenergic and serotonergic neurites in the myenteric plexus.

Interactions between enteric noradrenergic and serotonergic neurites in the myenteric plexus were examined. The influence of exogenous norepinephrine (NE) and endogenously released NE on the release of 3H-serotonin (3H-5-HT) from electrically stimulated, everted segments of guinea pig small intestine were analyzed. In addition, methods were employed to permit the ultrastructural identification of enteric serotonergic and noradrenergic neurites. These included electron microscopic radioautographic localization of 3H-5-HT in gut from animals treated with 6-hydroxydopamine (6-HD; 100 mg/kg) and examination of NaMnO4-fixed tissue from animals given desmethylimipramine and the indolic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). Exogenous NE antagonized the stimulated release of 3H-5-HT; this action was mediated through alpha adrenoceptors. Evidence was obtained, however, that endogenous NE liberated from sympathetic postganglionic nerve terminals had a different action on the stimulated release of 3H-5-HT from that of exogenous NE. Endogenous NE appeared to facilitate 3H-5-HT release through an action on beta adrenoceptors. Terminals identified as probably serotonergic by radioautographic labeling with 3H-5-HT or by loading with 5,7-DHT were most often found to end on neuronal somata or proximal dendrites. Synaptic specializations were found by radioautography in these locations. Terminals, dendrites, and cell bodies that took up 5,7-DHT could be identified in NaMnO4-fixed material that also permitted the simultaneous recognition of noradrenergic varicosities. Apparent noradrenergic-serotonergic axoaxonic contacts were found by means of this double-labeling technique. Together with the results of the experiments on the release of 3H-5-HT, these anatomical observations suggest that noradrenergic axons form facilitatory axoaxonic synapses with enteric serotonergic neurons.

5,7-Dihydroxytryptamine↗

PubMed1980

Effects of indolic neurotoxins on enteric serotonergic neurons.

The effects of the indolic neurotoxins 5,6- and 5,7-dihydroxytryptamine (5,6-DHT; 5,7-DHT) on the enteric nervous system were examined. 5,6-DHT, in moderate dosage, 40 mg/kg, decreased uptake of tritiated 5-hydroxytryptamine (3H-5-HT) but not that of tritiated norepinephrine (3H-NE). However, selectivity of the neurotoxins for enteric serotonergic rather than adrenergic axons was enhanced by pretreating animals with desmethylimipramine to inhibit the catecholamine uptake mechanism. When this was done, 5,7-DHT was found to prevent the development of 5-HT histofluorescence (following injection of L-tryptophan) without affecting histofluorescence of NE. In contrast, 6-hydroxydopamine virtually abolished NE histofluorescence and uptake of 3H-NE without affecting development of 5-HT histofluorescence or uptake of 3H-5-HT. Electron microscopy revealed that b,7-DHT induced dose-dependent lesions of axonal varicosities in the enteric nervous system. Early lesions, 1--4 hours following injection, resembled cytolysosomes and consisted of membrane enclosed regions of opaque cytoplasm containing synaptic vesicles. Affected varicosities contained a mixed population of large dense cored (approximately 120 nm) and small lucent vesicles (approximately 70 nm) but none exhibited pre- or postsynaptic membrane specializations. After 24 hours terminals degenerated and were engulfed by surrounding supporting cells. It is concluded that peripheral serotonergic neurons resemble central serotonergic neurons in susceptibility to the toxic effects of indolic neurotoxins. These neurotoxins are useful anatomical markers of serotonergic terminal varicosities.

5,6-Dihydroxytryptamine↗

PubMed1977

Uptake of serotonin by intrinsic neurons of the myenteric plexus grown in organotypic tissue culture.

The myenteric plexus contains axons, not found elsewhere in the peripheral nervous system, which are distinguished by a specific, high affinity transport system for serotinin (5-HT). This study was undertaken to determine the location of the cell bodies of origin of these axons. Vagotomy decreased uptake of [3H]5-HT and tritiated norepinephrine ([3H]NE) by the myenteric plexus. However, while examination by histofluorescence revealed the presence of descending vagal adrenergic fibers, no evidence was found for the presence or accumulation of 5-HT above a vagal ligature. Vagus nerves thus contain adrenergic but not serotonergic axons. The gut was also denervated of all extrinsic axons by growth of intestinal explants in organotypic tissue culture for 3 weeks. Uptake of [3H]5-HT persisted while uptake of [3H]NE was lost. Light and quantitative electron microscopic radioautography revealed that, as in intact gut, the elements of the cultures responsible for uptake of [3H]5-HT were axons distinguished by varicosities containing large dense cored vesicles. In conclusion, these experiments establish that the mammalian gut contains intrinsic neurons which selectively take up 5-HT. The capacity of these neurons for 5-HT uptake may be influenced by the vagus nerves.

Animals↗