Zones Of Junctions Research Articles

Synaptic Vesicles Having Large Contact Areas with the Presynaptic Membrane are Preferentially Hemifused at Active Zones of Frog Neuromuscular Junctions Fixed during Synaptic Activity.

Synaptic vesicles dock on the presynaptic plasma membrane of axon terminals and become ready to fuse with the presynaptic membrane or primed. Fusion of the vesicle membrane and presynaptic membrane results in the formation of a pore between the membranes, through which the vesicle’s neurotransmitter is released into the synaptic cleft. A recent electron tomography study on frog neuromuscular junctions fixed at rest showed that there is no discernible gap between or merging of the membrane of docked synaptic vesicles with the presynaptic membrane, however, the extent of the contact area between the membrane of docked synaptic vesicles and the presynaptic membrane varies 10-fold with a normal distribution. The study also showed that when the neuromuscular junctions are fixed during repetitive electrical nerve stimulation, the portion of large contact areas in the distribution is reduced compared to the portion of small contact areas, suggesting that docked synaptic vesicles with the largest contact areas are greatly primed to fuse with the membrane. Furthermore, the finding of several hemifused synaptic vesicles among the docked vesicles was briefly reported. Here, the spatial relationship of 81 synaptic vesicles with the presynaptic membrane at active zones of the neuromuscular junctions fixed during stimulation is described in detail. For the most of the vesicles, the combined thickness of each of their contact sites was not different from the sum of the membrane thicknesses of the vesicle membrane and presynaptic membrane, similar to the docked vesicles at active zones of the resting neuromuscular junctions. However, the combined membrane thickness of a small portion of the vesicles was considerably less than the sum of the membrane thicknesses, indicating that the membranes at their contact sites were fixed in a state of hemifusion. Moreover, the hemifused vesicles were found to have large contact areas with the presynaptic membrane. These findings support the recently proposed hypothesis that, at frog neuromuscular junctions, docked synaptic vesicles with the largest contact areas are most primed for fusion with the presynaptic membrane, and that hemifusion is a fusion intermediate step of the vesicle membrane with the presynaptic membrane for synaptic transmission.

The Recovery Territories of the Рaradynamyc Anthropogenic Landscape System of the Ecological Network of Murovanokurylovetsky District of Vinnytsia Region

Purpose. To identify the peculiarities of the recovery territories of the paradynamyc anthropogenic landscape system (PDALS) of the ecological network of Murovanokurylovetsky district of Vinnytsia region. Methods: field, theoretical generalization, analytical and cartographic analysis, logic, finding of empirical relationships, cartographic. Results. It was discovered that the areas of relative-natural landscapes occupy only a few percent of the area of ​​ Murovanokurylovetsky district of Vinnytsia region. Therefore, under such conditions, it was offered to form an ecological network as a paradynamyc anthropogenic landscape system. This allows to include valuable territories of different levels of anthropogenization in the ecological network. In the article, the ecological network is considered as a holistic paradynamyc anthropogenic landscape system of key, connecting and buffer territories, zones of potential renaturalization, eco-technical junctions and interactive elements. They are related to each other by the common genesis, simultaneity or sequence of origin and development, dynamic connections. The important structural elements of the paradynamyc anthropogenic landscape system of ecological networks are recovery territories (zones of potential renaturalization). Publications devoted to their description are currently single. Nevertheless, measures of renaturalization within the recovery territories allow to restore and introduce valuable nature sites into the structure of environmental protection systems. Therefore, the study of recovery territories is very relevant. The structure of the nature-protective paradynamyc anthropogenic landscape system of the ecological network of Murovanokurylovetsky district of Vinnytsia region identified the following recovery territories: Konyschivska, Zhytnykivska, Verbovetska, Vynohradnivska, Naddnistrianska, Zhvanska, Halaykivetska, Volodymyrivska, Murovanokurylovetska, Posuhivska, Dereshovska, Myhaylivetska, Yaltushkivska, Bilyanska, Karayetska, Nyshivetska, Kotyuzhanska, Blakitnivs'ka, Gorayska and Glibokodolinska. The characteristic features of the recovery territories of the nature-protective paradynamyc anthropogenic landscape system of the ecological network of Murovanokurylovetsky district of Vinnytsia region are analyzed in the article. It was discovered that natural components and landscape complexes within the zones of potential renaturalization have undergone a significant transformation under the influence of human anthropogenic activity. They are often polluted and devoid of original state. However, areas with remnants of landscape complexes that are close to natural ones are preserved in these territories. Under the conditions of total anthropogenic transformation of nature, recovery territories are one of the few centers of the existence of valuable species of vegetation and wildlife. The species of plants and animals of the Red Books of Vinnytsia region and Ukraine are found here. The article suggests renaturalization measures for each recovery territory of the nature-protective paradynamyc anthropogenic landscape system of the ecological network of Murovanokurylovetsky district of Vinnytsia region. The main environmental measures within the zones of potential renaturalization are overcoming erosion processes, restoration, care and protection of forest, meadow, steppe, wetland and meadow-steppe vegetation. The paradynamyc connections between zones of potential renaturalization and surrounding anthropogenic landscapes, local biocentres, regional and local ecocorridors, and other recovery territories are considered in detail. Conclusion. Consequently, 20 recovery territories are identified within the paradynamyc anthropogenic landscape system of the ecological network of Murovanokurylovetsky district of Vinnytsia region. Their total area is 6222.16 hectares, which is 7.02 % of the area of ​​the district. They cover the sources of the tributaries of the main rivers in the area, the steep slopes of the river valleys with erosion forms of relief, forest, meadow, meadow-steppe and wetland landscape complexes. Nature-protective measures within them will allow the degraded areas of nature to be restored. By intermediation of paradynamyc connections, they will improve the state of the environment. Under the conditions of renaturalization on the basis of the recovery territories, it will be possible to form new and expand existing biocentres, buffer zones, create interactive elements, and optimize local ecological corridors. This will improve the habitat of living organisms and ensure their recovery and conservation.

Foraging areas of streaked shearwater Calonectris leucomelas nesting on the Karamzin Island (Peter the Great Bay, East Sea)

Karamzin Island (the Peter the Great Bay, the East Sea) is the only nesting point of streaked shearwaters in Russian Federation. To understand and determine distribution patterns of streaked shearwaters along the Eastern Sea waters during nesting period, the Trackers WT-300 were set to 10 adult birds. Over the observation period (from 5 July 2016 to 7 January 2017), 4812 locations were registered. Analysis of data obtained revealed that main feeding points of colony studied were situated in the Peter the Great Bay along 50 m isobath and, to the less extension, near the eastern coast of Korean Peninsula. It was determined that streaked shearwaters most frequently visited waters with circular flows or zones of junctions of multidirectional flow. It was also shown that these zones had high concentrations of zooplankton.

Hysteresis loop and scanning curves of argon adsorption in closed-end wedge pores.

The hysteresis loop and scanning curves for argon adsorbed in a wedge pore with one end closed are studied with grand canonical Monte Carlo simulation. We have found multiple hysteresis loops for pores with either the narrow end or the wider end closed. In pores with the narrow end closed, adsorption and desorption exhibits a two-stage sequence of rapid change, followed by a gradual change in adsorbate density. The pore can be divided into zones of commensurate packing and junctions of incommensurate packing. A striking feature is that the sequence of these two stages is opposite for the adsorption and desorption processes. This can be explained by cohesion in the adsorbate, in which a steep condensation process is associated with the zones and a steep evaporation process is associated with the junctions between them. For pores with the wider end closed, the processes of adsorption and desorption from various zones are correlated with each other. In pores with the narrow end closed, the scanning curves trace reversibly along the segment of the isotherm, where the isotherm shows gradual change, and when the scanning curve reaches a point between the gradual change segment and the sharp change segment, the scanning curve crosses from one boundary of the hysteresis loop to the corresponding point on the other boundary. This indicates that the condensation and evaporation states are not affected by scanning but that, in scanning across the hysteresis loop, the adsorbate passes through a sequence of metastable states as the distribution of density is rearranged, without any significant change in the overall density. In contrast, for pores with the wider end closed, both the descending curve from a partially filled pore and the ascending curve are identical to the desorption branch of the corresponding pore with its narrow end closed.

Active zones of mammalian neuromuscular junctions: formation, density, and aging

Presynaptic active zones are synaptic vesicle release sites that play essential roles in the function and pathology of mammalian neuromuscular junctions (NMJs). The molecular mechanisms of active zone organization use presynaptic voltage-dependent calcium channels (VDCCs) in NMJs as scaffolding proteins. VDCCs interact extracellularly with the muscle-derived synapse organizer, laminin β2 and interact intracellularly with active zone-specific proteins, such as Bassoon, CAST/Erc2/ELKS2alpha, ELKS, Piccolo, and RIMs. These molecular mechanisms are supported by studies in P/Q- and N-type VDCCs double-knockout mice, and they are consistent with the pathological conditions of Lambert-Eaton myasthenic syndrome and Pierson syndrome, which are caused by autoantibodies against VDCCs or by a laminin β2 mutation. During normal postnatal maturation, NMJs maintain the density of active zones, while NMJs triple their size. However, active zones become impaired during aging. Propitiously, muscle exercise ameliorates the active zone impairment in aged NMJs, which suggests the potential for therapeutic strategies.

Single-Pixel Optical Fluctuation Analysis of Calcium Channel Function in Active Zones of Motor Nerve Terminals

We used high-resolution fluorescence imaging and single-pixel optical fluctuation analysis to estimate the opening probability of individual voltage-gated calcium (Ca(2+)) channels during an action potential and the number of such Ca(2+) channels within active zones of frog neuromuscular junctions. Analysis revealed ∼36 Ca(2+) channels within each active zone, similar to the number of docked synaptic vesicles but far less than the total number of transmembrane particles reported based on freeze-fracture analysis (∼200-250). The probability that each channel opened during an action potential was only ∼0.2. These results suggest why each active zone averages only one quantal release event during every other action potential, despite a substantial number of docked vesicles. With sparse Ca(2+) channels and low opening probability, triggering of fusion for each vesicle is primarily controlled by Ca(2+) influx through individual Ca(2+) channels. In contrast, the entire synapse is highly reliable because it contains hundreds of active zones.

Ultrastructure of the ovarian follicles, oviducts and oocytes of Gyrocotyle urna (Neodermata: Gyrocotylidea)

An ultrastructural study of the ovarian follicles and their associated oviducts of the cestode Gyrocotyle urna Grube et Wagener, 1852, a parasite from the spiral valve of the rabbit fish, Chimaera monstrosa L., was undertaken. Each follicle gives rise to follicular oviduct, which opens into one of the five collecting ducts, through which pass mature oocytes. These collecting ducts open into an ovarian receptacle which, in turn, opens via a muscular sphincter (the oocapt) to the main oviduct. The maturation of oocytes surrounded by the syncytial interstitial cells within the ovarian follicles of G. urna follows a pattern similar to that in Eucestoda. The ooplasm of mature oocytes contain lipid droplets (2.0 x 1.8 microm) and cortical granules (0.26 x 0.19 microm). The cytoplasm of primary and secondary oocytes contains centrioles, indicating the presence of the so-called "centriole cycle" during oocyte divisions. A morphological variation between different oviducts was observed. The luminal surface of the follicular and the collecting oviducts is smooth. The zones of the septate junctions are present within the distal portion of the net-like epithelial wall of the collecting ducts close to the ovarian receptacle. The syncytial epithelial lining of the ovarian receptacle, oocapt and main oviduct is covered with lamellae and cilia. Cortical granules secreted from mature oocytes occur freely within the lumen of the main oviduct that functions as a fertilisation canal. A division of the ovary into separated parts with their own collecting ducts as that typical of Gyrocotyle has been observed in neodermates, basal monogenean family Chimaericolidae, and Neoophora (some Proseriata and Fecampiidae). Ultrastructural data thus reveal several unique morphological characteristics of gyrocotylideans, the most basal taxon of tapeworms (Cestoda).

The Ig cell adhesion molecule Basigin controls compartmentalization and vesicle release at Drosophila melanogaster synapses

Synapses can undergo rapid changes in size as well as in their vesicle release function during both plasticity processes and development. This fundamental property of neuronal cells requires the coordinated rearrangement of synaptic membranes and their associated cytoskeleton, yet remarkably little is known of how this coupling is achieved. In a GFP exon-trap screen, we identified Drosophila melanogaster Basigin (Bsg) as an immunoglobulin domain-containing transmembrane protein accumulating at periactive zones of neuromuscular junctions. Bsg is required pre- and postsynaptically to restrict synaptic bouton size, its juxtamembrane cytoplasmic residues being important for that function. Bsg controls different aspects of synaptic structure, including distribution of synaptic vesicles and organization of the presynaptic cortical actin cytoskeleton. Strikingly, bsg function is also required specifically within the presynaptic terminal to inhibit nonsynchronized evoked vesicle release. We thus propose that Bsg is part of a transsynaptic complex regulating synaptic compartmentalization and strength, and coordinating plasma membrane and cortical organization.

Influence of electronic states on precipitation of metallic As clusters in LT-GaAs

The influence of electronic states of the semiconductor matrix on the precipitation of metallic As clusters in GaAs epilayers grown by molecular beam epitaxy at low temperatures were studied. From x-ray diffraction and Hall effect measurements, the presence of free carriers was found to occur in a certain time after the start of the coarsening stage of the precipitation. Transmission electron microscope observations indicate that redistributions of As clusters between the doped and undoped regions starts at the same time with the appearance of free carriers. Redistributions of As clusters occurs in pn junction structures in such a way that depletion zones of the pn junctions become free from As clusters, leading to close correlation of widths of precipitate free zones with those of the depletion zones of the pn junctions for various dopant concentrations. These observations are explained with a tendency of As metal clusters of reducing free carriers in the surrounding semiconductor matrix and hence keeping it as an intrinsic semiconductor.

Motor nerve terminals on abdominal muscles in larval flesh flies, Sarcophaga bullata: Comparisons with Drosophila

Motor nerve terminals on abdominal body-wall muscles 6A and 7A in larval flesh flies were investigated to establish their general structural features with confocal microscopy, transmission electron microscopy, and freeze-fracture procedures. As in Drosophila and other dipterans, two motor axons supply these muscles, and two morphologically different terminals were discerned with confocal microscopy: thin terminals with relatively small varicosities (Type Is), and thicker terminals with larger varicosities (Type Ib). In serial electron micrographs, Type Ib terminals were distinguished from Type Is terminals by their larger cross-sectional area, more extensive subsynaptic reticulum, more mitochondrial profiles, and more clear synaptic vesicles. Type Ib terminals possessed larger synapses and more synaptic contact area per unit terminal length. Although presynaptic dense bars of active zones were similar in mean length for the two terminal types, there were almost twice as many dense bars per synapse for Type Ib terminals. Freeze-fractures through the presynaptic membrane showed particle-free areas indicative of synapses on the P-face, within which were localized aggregations of large intramembranous particles indicative of active zones. These particles were similar in number to those found at active zones of several other arthropod neuromuscular junctions. In general, synaptic structural parameters strongly paralleled those of the anatomically homologous muscles in Drosophila melanogaster. In live preparations, simultaneous focal recording from identified varicosities and intracellular recording indicated that the two terminals produced excitatory junction potentials of similar amplitude in a physiological solution similar to that used for Drosophila. J. Comp. Neurol. 402:197–209, 1998. © 1998 Wiley-Liss, Inc.

Motor nerve terminals on abdominal muscles in larval flesh flies,Sarcophaga bullata: Comparisons withDrosophila

Motor nerve terminals on abdominal body-wall muscles 6A and 7A in larval flesh flies were investigated to establish their general structural features with confocal microscopy, transmission electron microscopy, and freeze-fracture procedures. As in Drosophila and other dipterans, two motor axons supply these muscles, and two morphologically different terminals were discerned with confocal microscopy: thin terminals with relatively small varicosities (Type Is), and thicker terminals with larger varicosities (Type Ib). In serial electron micrographs, Type Ib terminals were distinguished from Type Is terminals by their larger cross-sectional area, more extensive subsynaptic reticulum, more mitochondrial profiles, and more clear synaptic vesicles. Type Ib terminals possessed larger synapses and more synaptic contact area per unit terminal length. Although presynaptic dense bars of active zones were similar in mean length for the two terminal types, there were almost twice as many dense bars per synapse for Type Ib terminals. Freeze-fractures through the presynaptic membrane showed particle-free areas indicative of synapses on the P-face, within which were localized aggregations of large intramembranous particles indicative of active zones. These particles were similar in number to those found at active zones of several other arthropod neuromuscular junctions. In general, synaptic structural parameters strongly paralleled those of the anatomically homologous muscles in Drosophila melanogaster. In live preparations, simultaneous focal recording from identified varicosities and intracellular recording indicated that the two terminals produced excitatory junction potentials of similar amplitude in a physiological solution similar to that used for Drosophila.

Identification of types II, IX and X collagens at the insertion site of the bovine achilles tendon

Achilles tendinous collagen fibrils insert into the calcaneus by first passing through a zone that is defined histologically as fibrocartilaginous. This zone consists of four regions: tendon proper, non-mineralized and mineralized fibrocartilage and bone. The function of this zone has not yet been clearly defined. To gain more insight into the role of this fibrocartilaginous zone, collagens present in the zone of the Achilles tendon-calcaneus interface were isolated and characterized. Types II, IX and X collagens were identified in the pepsin digests of the tissue harvested from the bovine Achilles tendon-calcaneus interface. Western blotting using specific antisera to types II, IX and X collagens confirmed the identity of these collagens. Immunofluorescence localization placed type X collagen predominantly in the mineralized zone of the tendon-calcaneus junction, while type IX collagen was distributed throught the the insertion site. The presence of the cartilage-specific collagens at the Achilles tendon-calcancus-interface suggests that this zone is cartilaginous in nature. The presence of type X collagen at this junction is not clear, but our present findings go along with the previous report which showed that type X collagen is present in the mineralized zone of the medial collateral ligament femoral insertion site. These data suggest that type X collagen may be a resident of mineralized fibrocartilaginous zones of tendon or ligament-bone junctions and may participate in anchoring ligament or tendon to bone.

Identification of types II, IX and X collagens at the insertion site of the bovine achilles tendon.

Achilles tendinous collagen fibrils insert into the calcaneus by first passing through a zone that is defined histologically as fibrocartilaginous. This zone consists of four regions: tendon proper, non-mineralized and mineralized fibrocartilage and bone. The function of this zone has not yet been clearly defined. To gain more insight into the role of this fibrocartilaginous zone, collagens present in the zone of the Achilles tendon-calcaneus interface were isolated and characterized. Types II, IX and X collagens were identified in the pepsin digests of the tissue harvested from the bovine Achilles tendon-calcaneus interface. Western blotting using specific antisera to types II, IX and X collagens confirmed the identity of these collagens. Immunofluorescence localization placed type X collagen predominantly in the mineralized zone of the tendon-calcaneus junction, while type IX collagen was distributed throughout the the insertion site. The presence of the cartilage-specific collagens at the Achilles tendon-calcaneus-interface suggests that this zone is cartilaginous in nature. The presence of type X collagen at this junction is not clear, but our present findings go along with the previous report which showed that type X collagen is present in the mineralized zone of the medial collateral ligament femoral insertion site. These data suggest that type X collagen may be a resident of mineralized fibrocartilaginous zones of tendon or ligament-bone junctions and may participate in anchoring ligament or tendon to bone.

THE EFFECT OF OXYGEN TENSION ON PROTEOGLYCAN SYNTHESIS AND AGGREGATION IN MAMMALIAN GROWTH PLATE CHONDROCYTES

Growth plate chondrocytes isolated from the proliferative and hypertrophic zones of bovine costochondral junctions were grown in vitro in the presence of various oxygen tensions ranging from 3 to 60%. Using [35S] sulfate as an index of glycosaminoglycan synthesis, incorporation was found to be maximal at 21% O2. In contrast, proteoglycan aggregation under the same conditions was found to be maximal at 3% O2. There were no consistent differences in response between cells from the different morphologic zones even though they are exposed to different oxygen tensions in situ. These results show that proteoglycan synthesis and aggregation in growth plate chondrocytes in vitro are differentially affected by the ambient oxygen environment.

The effect of oxygen tension on proteoglycan synthesis and aggregation in mammalian growth plate chondrocytes

Growth plate chondrocytes isolated from the proliferative and hypertrophic zones of bovine costochondral junctions were grown in vitro in the presence of various oxygen tensions ranging from 3 to 60%. Using [35S] sulfate as an index of glycosaminoglycan synthesis, incorporation was found to be maximal at 21% O2. In contrast, proteoglycan aggregation under the same conditions was found to be maximal at 3% O2. There were no consistent differences in response between cells from the different morphologic zones even though they are exposed to different oxygen tensions in situ. These results show that proteoglycan synthesis and aggregation in growth plate chondrocytes in vitro are differentially affected by the ambient oxygen environment.

Ultrastructure of the Rat Mesencephalic Trigeminal Nucleus

The subcellular morphology of the mesencephalic trigeminal (Me5) nucleus in the rat was studied by transmission electron microscopy. Most neurons in the thin rostral as well as in the major caudal part of Me5 appeared as large (40-50 microns), round- to ovoid-shaped unipolar cells. A few neurons (estimated 5%) appeared to be multipolar, usually bipolar. The Me5 neurons had a large, round, centrally located nucleus, and their cytoplasm was characterized by a dense network of lamellar granular endoplasmic reticulum, an abundant Golgi apparatus, many mitochondria and neurofilaments suggesting very active cells with a high rate of synthesis and axoplasmatic transport. Numerous small spinous processes covered the surface of the Me5 neurons. Clustering of 2 or 3 cells was accomplished by maculae, i.e. zones of gap junctions and close cell appositions. Boutons contacting the soma of Me5 neurons and boutons contacting large and small dendrites were defined as axosomatic and axodendritic synapses, respectively. Four types of synaptic boutons were distinguished: (1) S boutons, with round vesicles and asymmetrical as well as symmetrical synapses, (2) F boutons, with pleomorphic admixture of flattened and spherical vesicles and asymmetrical synapses, (3) P boutons, which resembled the F-type boutons but contained predominantly spherical vesicles and symmetrical synapses, and (4) G boutons, characterized by a heterogeneous population of vesicles. This description of the Me5 nucleus is particularly useful for future studies that attempt to correlate the structure of a particular synapse with its function.

Presynaptic active zones at neuromuscular junctions of larval frogs

Freeze-fractured presynaptic membranes at tadpole neuromuscular junctions display small clusters of large P-face particles, including short double linear arrays. Short pairs of double particle rows are randomly oriented at some junctions. At others, presynaptic membranes are crossed at regular intervals by long pairs of double rows indistinguishable from those characterizing the active zones of adult amphibian neuromuscular junctions. Formation of double particle rows, pairing of the double rows, and transverse alignment of the pairs are shown to be independent processes.

Normal variations in presynaptic active zones of frog neuromuscular junctions

Neuromuscular junctions of frog cutaneous pectoris muscles were examined by the complementary-replica freeze-fracture technique. The large number of active zones revealed in this way permitted quantitation of normal and disrupted zones in control muscles and in muscles deprived of external calcium for periods of up to eight hours. Although some 87% of the active zones examined had the usual appearance of two double rows of intramembrane particles flanking a low ridge, several varieties of disrupted active zones appeared in which the rows were interrupted, dispersed, rotated, or reduced to single rows. The frequency of disruptions was not increased by calcium deprivation. Disorganized active zones at tips of neuromuscular junctions may represent normal remodelling of the junctions.

Decreased sprouting and degeneration of nerve terminals of active muscles in aged rats.

Decreased sprouting and degeneration of nerve terminals of active muscles in aged rats.D O Smith, and J L RosenheimerD O Smith, and J L RosenheimerPublished Online:01 Jul 1982https://doi.org/10.1152/jn.1982.48.1.100MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByPresynaptic active zones of mammalian neuromuscular junctions: Nanoarchitecture and selective impairments in agingNeuroscience Research, Vol. 127Age-related changes in the structure and function of mammalian neuromuscular junctions31 December 2017 | Annals of the New York Academy of Sciences, Vol. 1412, No. 1Regulation of Synaptic Transmission by Adenosine at the Neuromuscular JunctionPredicting recovery from deep neuromuscular block by rocuronium in the elderlyJournal of Clinical Anesthesia, Vol. 15, No. 5Localization of mRNAs for calpain and calpastatin in the adult rat brain by in situ hybridization histochemistryMolecular Brain Research, Vol. 23, No. 1-2Age-induced alteration of neuromuscular transmission: effect of halothaneEuropean Journal of Pharmacology, Vol. 254, No. 1-2Age-related changes in maturation of regenerated motor innervationJournal of the Neurological Sciences, Vol. 114, No. 1Cholinesterase activity in vestibular organs of young and old miceHearing Research, Vol. 58, No. 2Recovery of motor-unit function after peripheral nerve injury in aged ratsNeurobiology of Aging, Vol. 12, No. 4Synaptic terminal degeneration and remodeling at the rat neuromuscular junction resulting from a single exposure to acrylamideToxicology and Applied Pharmacology, Vol. 105, No. 3Morphological changes in the human end plate with ageJournal of the Neurological Sciences, Vol. 95, No. 3Ultraterminal sprouting in innervated and partially denervated adult and aged rat muscleNeuroscience, Vol. 38, No. 3Maintenance of neurite contacts at junctional regions of cultured individual muscle fibers from aged rats is correlated with the presence of a synapse-associated protein, gelasminMechanisms of Ageing and Development, Vol. 49, No. 2Effect of age on collateral reinnervation of sweat glands in the mouseBrain Research, Vol. 463, No. 1The Biology of Aging, with Particular Reference to the Musculoskeletal SystemClinics in Geriatric Medicine, Vol. 4, No. 2Cellular and molecular correlates of aging in the nervous systemExperimental Gerontology, Vol. 23, No. 4-5Non-uniform changes in nerve-terminal calcium homeostasis during agingNeurobiology of Aging, Vol. 8, No. 4Aging of cholinergic synapses in the avian iris. Part I—Biochemical studiesNeurobiology of Aging, Vol. 8, No. 2Strategies for modifying axonal growth, synaptic function, and recovery of neural function after injury to the central nervous system: A conference reportExperimental Neurology, Vol. 93, No. 1Properties of muscle cells and remodeling of neuromuscular junctions as related to age in AplysiaMechanisms of Ageing and Development, Vol. 34, No. 2Sprouting and remodelling at the nerve-muscle junctionProgress in Neurobiology, Vol. 27, No. 3Distribution of calpain I, an enzyme associated with degenerative activity, in rat brainBrain Research, Vol. 347, No. 2Colchicine-induced differential sprouting of the endplates on fast and slow muscle fibers in rat extensor digitorum longus, soleus and tibialis anterior musclesBrain Research, Vol. 329, No. 1-2Regional distribution of soluble calcium activated proteinase activity in neonatal and adult rat brainBrain Research, Vol. 327, No. 1-2Age changes of motor innervation and acetylcholine receptor distribution on human skeletal muscle fibresJournal of the Neurological Sciences, Vol. 66, No. 2-3Restricted diffusion of extracellular potassium at the neuromuscular junction of aged ratsBrain Research, Vol. 239, No. 2 More from this issue > Volume 48Issue 1July 1982Pages 100-9 https://doi.org/10.1152/jn.1982.48.1.100PubMed7119839History Published online 1 July 1982 Published in print 1 July 1982 Metrics

A freeze-fracture study of the topographic relationship between inner enamel-secretory ameloblasts in the rat incisor.

AbstractA correlated study using freeze‐fracture replicas and routine thin sectioning was done on the ameloblasts which secrete inner enamel in the rat incisor. These ameloblasts are columnar cells aligned in rows parallel to the cross‐sectional plane of the incisor. Each cell has a Tomes' process at its distal end which is contained within a cavity of interrod enamel. Tomes' processes of a particular row of cells are inclined towards the mesial side of the tooth, while those of the next row are inclined towards the lateral side, so that the processes cross each other at 90°. Freeze‐fracture replicas were used to examine the surfaces of ameloblasts between adjacent rows and the surfaces of the cells within the row. Replicas of the surfaces between rows showed that ameloblasts are curved so that their proximal and distal ends (Tomes' processes) are both directed towards the same side of the tooth. The surface of each row bears the impression left upon it by the cells in the adjacent row which have been fractured away. This cell‐impression is also curved, but in the opposite direction to the cells which it crosses. It was thus shown that not only the Tomes' processes of adjacent rows but the entire cell bodies cross one another. This crossing is slight at the proximal ends of the cells, but marked at the level of the distal junctional complex. At this level a cell from a particular row curves across several cells of the neighbouring row and forms large tight junctions with at least two cells in that row. The proximal and distal junctional complexes form zones of tight junctions around the cell. The distal complex is more extensive than the proximal and the tight junctions are better developed between adjacent rows. Gap junctions are, however, larger between cells within the rows. The study demonstrated the effectiveness of freeze‐fracture replicas in obtaining 3‐dimensional details about ameloblast shape, and this information was used to evaluate the supposed movement of ameloblasts during inner enamel formation.