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PubMed1994

Synaptic physiology of horizontal afferents to layer I in slices of rat SI neocortex.

Layer I is a dense synaptic zone ubiquitous in cerebral cortex. Here we describe a novel in vitro preparation of rat somatosensory (SI) neocortical slices that isolates the fibers that extend horizontally through layer I, and allows intracellular and extracellular analysis of synaptic input to dendrites in layer I. Current source-density analysis of this isolated horizontal layer I input reveals monophasic current sinks restricted to layer I and the most superficial part of layer II. The layer I synaptic response of each neuron was correlated with its morphology by filling penetrated cells with biocytin. All filled cells that responded to horizontal layer I inputs were pyramidal neurons in layers II, III, or V with distal apical dendrites in layer I. There was no evidence of antidromic activation from isolated layer I stimulation, and HRP injected into layer I was not transported via the isolated layer I pathway to cortical neurons within the slice. Therefore, this preparation provides a unique way to study an extrinsic synaptic input localized to the most distal apical dendrites of many pyramidal neurons. In contrast to the EPSP-IPSP sequence characteristically evoked by deep layer stimulation, horizontal layer I inputs evoked long-lasting EPSPs (approximately 50 msec); IPSPs were observed only rarely, in the most superficial neurons. Horizontal layer I-evoked EPSPs were blocked by the non-NMDA glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. Consistent with the very distal site of layer I inputs to layer V pyramidal neurons, the amplitudes of initial EPSPs were insensitive to manipulations of the somatic membrane potential. However, these distal EPSPs were greatly attenuated when combined with IPSPs evoked by deep layer stimulation, indicating that the proximal inputs may modulate distal EPSPs with shunting inhibition. In many layer V neurons, the initial EPSP evoked by horizontal layer I stimulation was followed by a variable late depolarization that was blocked by the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid. Since these late depolarizations were enhanced by somatic depolarization and abolished by hyperpolarization, they appeared to be generated postsynaptically at a site more proximal than the initial EPSP that was insensitive to these manipulations. Synaptic inputs to the distal tufts of pyramidal neurons may trigger active currents along the apical dendrites that amplify the EPSP on its way to the soma.

2-Amino-5-phosphonovalerate↗
PubMed1978

Golgi studies of the neurons in layer II of the dorsal horn of the medulla (trigeminal nucleus caudalis).

The translucent band which lies just beneath the spinal V tract at the lower end of the spinal trigeminal nucleus (nucleus caudalis) can be divided into three layers. These three layers are distinguished by textural differences in their neuropil and by the morphology and laminar distribution of the axons and dendrites of their neurons. Layer II contains four different kinds of interneurons. Stalked cells are named after their short, stalk-like branches. Their cell bodies are found in greatest numbers in the outer half of layer II. Their coneshaped dendritic arbors extend medially across layers II and III and sometimes extend into layer IV. Their axons form extensive, canopy-like arborizations in layer I. Stalked cells are considered to be excitatory interneurons receiving input on their dendritic spines from primary axonal endings in the layers II and III glomeruli and transferring it to the dendrites of the layer I projection neurons. Layer II contains three kinds of Golgi type II inteneurons, i.e, neurons whose axons branch repeatedly within the confimes of their dendritic arbors. Islet cells similar to those found in layer III (Gobel), '75a), are found in small clusters in layer II. Their dendrites and axons are largely confined in layer II. The dendrites of the arboreal cell burst, in tree-like fashion, into highly focal dendritic arbors confined largely in layer II while the extensive rostral and caudal dendritic arbors of the II-III border cell lie largely in layers II and III with a few branches extending into layer I. The axons of both of these interneurons arborize in layers II and III with a few collaterals extending into layer I. Islet cells, arboreal cells and II-III border cells are considered to be inhibitory interneurons. They are strategically situated to interrupt transmission between primary axonal endings in layers II and III and the layer I projection neurons by altering the output of the stalked cells.

Animals↗
PubMed1984

The pyramidal neurons in layer III of cat primary auditory cortex (AI).

The neuronal architecture of pyramidal cells in layer III of the primary auditory cortex (AI) of adult cats was examined as a prelude to connectional and fine structural studies; in a further paper, the results of parallel studies of non-pyramidal layer III cells are presented. Layer III is about 400 micron thick, comprises about one-quarter of the thickness of AI, and lies some 400-800 micron deep to the pial surface. It is distinguished in Nissl, fiber, and Golgi preparations from layers II and IV, and also on connectional grounds, since its neurons are one of the principal inputs to the contralateral AI. Layer III may be divided into two roughly equal tiers on the basis of its neuronal and cytoarchitecture. Layer IIIa is populated by small cells with oval somata and many tiny pyramidal cells; the fiber architecture is dominated by radial bundles of medium-sized axons interspersed among columns of apical dendrites arising from deeper-lying pyramidal cells. In layer IIIb medium-sized and large pyramidal cells are more numerous, and the fiber architecture has a different, much denser texture, including extensive lateral components which invade layer IV, and large contingents of descending, probably corticofugal, axons. Five kinds of pyramidal neurons occur in Golgi preparations. Most numerous are the small, medium-sized, and large pyramidal cells; the two types of star pyramidal neurons are less common. The small pyramidal cell has a limited dendritic field and rather delicate dendrites; all but the apical one usually end in layer III. The medium-sized pyramidal cell is the most common neurons, and its rich basilar dendritic arbors are conspicuous, with their many dendritic appendages, in the layer III neuropil; their distal dendrites spread into layer IV. The largest pyramidal cells lie mainly in layer IIIb, and their lateral dendrites often mark the layer IIIb-IVa border. The apical dendrites of medium-sized and large pyramidal cells often extend to layer Ib, where they branch obliquely. The axons of these cells branch laterally after descending through layer III and toward the white matter. Often secondary or tertiary branches reascend to layer IV and more superficially; there is considerable stereotypy in this branching pattern. These numerous secondary branches contribute heavily to the layer IIIb-IVa lateral fiber plexus. The fourth variety of pyramidal cell has a round soma and a stellate dendritic field whose distal branches extend from layer V to layer I, but whose axon is chiefly in layer III. Finally, a star pyramidal cell with long lateral basilar arbors but rather smooth dendrites completes the picture.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMedDate not supplied

Interlaminar connections of the superior colliculus in the tree shrew. II: Projections from the superficial gray to the optic layer.

This study of the tree shrew, Tupaia belangeri, provides evidence for an intracollicular pathway that arises in the superficial gray layer and terminates in the optic layer. As a first step, Nissl, myelin, and cytochrome oxidase stains were used to identify the layers of the superior colliculus in the tree shrew. Second, anterograde and retrograde axonal transport methods were used to determine relationships between laminar borders and patterns of connections. Intraocular injections of wheat germ agglutinin conjugated to horseradish peroxidase showed that the border between the superficial gray and optic layers in the tree shrew is marked by a sharp decrease in the density of retinotectal projections. The optic layer also could be distinguished from the subjacent intermediate gray layer by differences in connections. Of the two layers, only the intermediate gray layer received projections following injections of wheat germ agglutinin conjugated to horseradish peroxidase within substantia nigra pars reticulata. Similarly, following injections of horseradish peroxidase or biocytin in the paramedian pons, the intermediate gray but not the optic layer contained labeled cells of origin for the main premotor pathway from the tectum, the predorsal bundle. Next, cells in the superficial gray layer were intracellularly injected with biocytin in living brain slices. Axons were traced from narrow and wide field vertical cells in the deep part of the superficial gray layer to the gray matter surrounding the fiber fascicles of the optic layer. Small extracellular injections of biocytin in brain slices showed that the optic layer gray matter contains a population of stellate cells that are in position to receive the input from the superficial layer. Finally, small extracellular injections of biocytin in the intermediate gray layer filled cells that sent prominent apical dendrites into the optic layer, where they may be directly contacted by the superficial gray layer cells. Taken together, the results support the hypothesis that the optic layer is functionally distinct from its adjacent layers, and may provide a link in the transfer of information from the superficial, retinal recipient, to the intermediate, premotor, layer of the superior colliculus.

Animals↗
PubMed2004

Calculation of colour resulting from composite/compomer layering techniques.

This study determined the influence of optical properties of constituent layers on the colour of double-layer aesthetic filling materials. Multiple regression equations for the Commission Internationale de I'Eclairage (CIE) L*, a* and b* of layered materials were calculated from the optical values of the covering and underlying layers. Specimens (10 mm diameter, 1 mm thickness) of two light-cured resin composites and one compomer of seven to 11 shades were used. CIE L*, a* and b* values of each specimen were measured with a colour spectrophotometer backed by a standard white background. The scattering coefficient (S), absorption coefficient (K), contrast ratio (C) and translucency parameter (T) were calculated. Double-layered specimens were formed in optical contact by joining two different shades from the same material, or resin composite as covering with a compomer underlying layer. Each of the L*, a* and b* of layered material was used as a dependent variable, and 14 optical values of underlying and covering layers were used as independent variables in forward regression analysis (P = 0.01). CIE L* after layering had a positive correlation with S of covering layer (correlation coefficient; beta = 0.79-0.91, P < 0.01) and a correlation with L* of underlying layer (beta = 0.14-0.16). CIE a* after layering had a correlation with a* of covering layer (beta = 0.83-0.94) and a correlation with a* of underlying layer (beta = 0.30-0.56). CIE b* after layering had a correlation with b* of covering layer (beta = 0.77-0.90) and a correlation with T of covering layer (beta = 0.40-0.59). The layered colour of these materials can be predicted by the derived regression equations within the limitations of this study. CIE L*, a* and b* values of double-layer material are mainly influenced by S, CIE a* and b* of covering layer, respectively.

Colorimetry↗
PubMed1998

Prenatal development of layer-specific local circuits in primary visual cortex of the macaque monkey.

Previous studies have demonstrated that axonal arbors specific for the four main cortical layers - 2/3, 4, 5, and 6 - develop precisely from the outset using activity-independent cues. In macaque primary visual cortex (V1), layer 2/3 is subdivided into layers named 2/3A, 3B, 4A, and 4B, and layer 4 is subdivided into 4Calpha and 4Cbeta. Individual neurons in V1 of mature macaques have axonal arbors that are highly specific for these sublayers. We have studied the prenatal development of laminar and sublaminar specificity of local circuits in macaque V1. Two-hundred thirty-eight neurons were labeled intracellularly in living brain slices prepared from V1 of five prenatal macaque monkeys aged 100 to 145 d postconception (E100-E145). Axonal and dendritic arbors of labeled neurons were reconstructed to assess their relationships to the cortical layers. We find that developing spiny neurons in layers 2-4B and layer 5 specifically target superficial and deep layers without forming "incorrect" branches in layer 4C. Similarly, layer 6 pyramidal neurons that target layer 4C do not form "incorrect" branches in layer 5. These results indicate that specific projections to the main cortical layers develop with a high degree of selectivity, as in other species. However, the development of sublayer-specific projections was not always precise from the outset. Unlike postnatal animals, axons of some prenatal layer 4Cbeta spiny neurons branch in layer 4B. At similar ages, many pyramidal neurons in the upper half of layer 6 have axonal branches in layer 4Calpha as well as 4Cbeta; these projections are specific for 4Cbeta in more mature animals. Also, there is similar "exuberance" in axonal arbors of other layer 6 cell types. Transient projections were also observed in the subplate and to the white matter for cells from all layers, except 4Cbeta. These observations indicate that at least some sublayer-specific projections emerge by elimination of exuberant axonal branches and suggest that they may use activity-dependent mechanisms to identify "correct" target layers. Such cues could be provided by laminar differences in the patterns of spontaneous prenatal activity in the retino-geniculo-cortical network.

Animals↗
PubMed1990

Sublaminar organization within layer VI of the striate cortex in Galago.

In this study we examined the organization of projections from the striate cortex to the dorsal lateral geniculate (GL) and pulvinar (PUL) nuclei in the prosimian Galago by using retrograde transport methods. Injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the PUL labeled two bands of cells in the striate cortex: the first consisted of large pyramidal cells in the upper half of layer V; the second consisted of small and medium-size pyramidal cells located in the deepest part of layer VI. The location of cells within layer VI coincided with a clear cytoarchitectonic sublayer, VIb, which contains fewer and paler staining cells than VIa. Injections of WGA-HRP involving all layers of the GL produced an uninterrupted band of pyramidal cells distributed throughout layer VI (a and b), including the region labeled after injections into the PUL. Thus as a first approximation, layer VI can be divided into an upper tier (VIa) that projects only to the GL and a lower tier (VIb) that projects to both the GL and PUL. Injections of WGA-HRP that were restricted to one or a few GL layers revealed a further refinement of the subdivisions within layer VI. Injections into the parvicellular and intercalated (or koniocellular) layers of the GL labeled neurons predominantly in the upper half of layer VIa, whereas injections restricted to the magnocellular layers labeled neurons in the lower half of layer VIa and in layer VIb. In order to determine whether individual neurons in layer VIb send axon collaterals to both the GL and PUL, we injected WGA-HRP into one nucleus and fluorescent rhodamine latex beads into the other. In three experiments, we found only one double-labeled cell. In sum, the results provide evidence that layer VI is divided into at least three sublayers: upper VIa, which projects to the intercalated and parvicellular GL layers; lower VIa, which projects to the magnocellular GL layers; and VIb, which sends separate projections to the magnocellular layers of the GL and to the PUL. The segregation observed is sufficiently discrete to propose the existence of multiple, descending pathways from layer VI of the striate cortex that complement those ascending from the GL and PUL.

Animals↗
PubMed1978

Morphological and biochemical studies on isolated molecular and granular layers from bovine cerebellum.

Molecular layer, granular layer and white matter are dissected from bovine cerebellum under optical microscope and without freezing under conditions which preserve their main anatomical features. Polyacrylamide gel electrophoresis in sodium dodecyl sulphate of the isolated layers reveal that the P400 protein characteristic of the Purkinje cells is found in the isolated molecular layer and in the molecular layer free from Purkinje cell soma, but not in the granular layer or white matter. The histones (F1, F2A1,2, F2B, F3) are abundant in the granular layer and myelin proteins in the white matter. The DNA content per wet weight is 10 times greater in the isolated granular layer than in the other layers and the RNA content twice as great in the granular layer than in any other layer. The specific activity of acetylcholinesterase is 4 times greater in the granular layer than in the other layers. Homogenates of the isolated layers take up labeled amino-acids and the velocity of glutamate incorporation is 9 times greater in the molecular layer than in the granular layer, while GABA incorporation is about twice as great in the granular layer than in the molecular layer. Homogenates of isolated molecular layer are centrifuged on discontinuous Ficoll gradient after incubation with L[3H]glutamate and [14C]GABA. The analysis of the distribution of glutamate and GABA after centrifugation reveals that the particles which incorporate glutamate can be separated from those which take up GABA.

Acetylcholinesterase↗
PubMed2002

S-layers on cell walls of cyanobacteria.

S-layers are surface layers of bacterial cell walls. They are formed by two-dimensional, monomolecular crystalline arrays of identical units of protein or glycoprotein macromolecules (subunits). In general, each S-layer exhibits one of four possible 2-D lattice types: oblique (p1 or p2 symmetry), triangle (p3 symmetry), square (p4 symmetry) or hexagonal (p6 symmetry). The S-layer protein compasses up to 15% of the total protein of the bacterial cell and thus represents its major protein. Since 1972, S-layers have also been found in cyanobacteria. So far, they have been observed in 60 strains (isolates) of 23 species, belonging to 12 genera of unicellular Chroococcales and in just five strains or isolates (four species, four genera-only with p1 and p4 lattice symmetry) of filamentous Oscillatoriales; in further families of filamentous cyanobacteria (Nostocales, Stigonematales) they have not been detected, although filamentous cyanobacteria have been frequently studied in the electron microscope. In Chroococcales, relatively large cells of planktonic genera harbouring gas vesicles, S-layers are often present, while picoplanktonic species without gas vesicles usually do not have them. The p6 lattice symmetry appears to be the most common in cyanobacteria, having been found in 41 out of the 60 S-layers observed. All cells of a given strain, all strains capable of forming S-layers and all S-layer forming species of a given genus (as far as it is known) form S-layers of the same lattice type. Hence, the ability to form an S-layer appears to be useful as a supportive morphological marker for species classification. In 41 S-layer formers, the center-to-center spacing of their lattice unit arrays has been measured; the lattice constants range from 5 to 22nm, measured directly on surface of fixed cells. Coarse S-layers of p6 symmetry are the most frequent (with spacing of 15.0-22.0nm); p1 and p2 S-layers are the finest ones (with spacing of 5.0-10.0nm). Medium-spaced lattices (11.0-14.0nm) may be both of the p4 or p6 symmetry types. When measured on isolated S-layers, the spacings show a 10-60% higher value. All the hexagonal unit lattices have the same molecular architecture. Each S-layer unit resembles a truncated cone with an axial pore and with six protein subunits symmetrically placed around its opening. Adjoining units are interspaced by relatively fine channels. The fine detail of every S-layer of every individual strain is unique. Only the S-layer protein subunits of Synechococcus sp. strain GL24 have been analysed by electrophoresis. When incorporated into the S-layer units they confer a net neutral charge to the cell surface. This cyanobacterium induces mineralization of fine-grain gypsum and calcite in a saturated lake fresh water solution. This process is involved in the formation of stromatolites.

Cell Wall↗
PubMed1992

Evidence for an S-layer protein pool in the peptidoglycan of Bacillus stearothermophilus.

Intact cells of Bacillus stearothermophilus PV72 revealed, after conventional thin-sectioning procedures, the typical cell wall profile of S-layer-carrying gram-positive eubacteria consisting of a ca. 10-nm-thick peptidoglycan-containing layer and a ca. 10-nm-thick S layer. Cell wall preparations obtained by breaking the cells and removing the cytoplasmic membrane by treatment with Triton X-100 revealed a triple-layer structure, with an additional S layer on the inner surface of the peptidoglycan. This profile is characteristic for cell wall preparations of many S-layer-carrying gram-positive eubacteria. Among several variants of strain PV72 obtained upon single colony isolation, we investigated the variant PV72 86-I, which does not exhibit an inner S layer on isolated cell walls but instead possesses a profile identical to that observed for intact cells. In the course of a controlled mild autolysis of isolated cell walls, S-layer subunits were released from the peptidoglycan of the variant and assembled into an additional S layer on the inner surface of the walls, leading to a three-layer cell wall profile as observed for cell wall preparations of the parent strain. In comparison to conventionally processed bacteria, freeze-substituted cells of strain PV72 and the variant strain revealed in thin sections a ca. 18-nm-wide electron-dense peptidoglycan-containing layer closely associated with the S layer. The demonstration of a pool of S-layer subunits in such a thin peptidoglycan layer in an amount at least sufficient for generating one coherent lattice on the cell surface indicated that the subunits must have occupied much of the free space in the wall fabric of both the parent strain and the variant. It can even be speculated that the rate of synthesis and translation of the S-layer protein is influenced by the packing density of the S-layer subunits in the periplasm of the cell wall delineated by the outer S layer and the cytoplasmic membrane. Our data indicate that the matrix of the rigid wall layer inhibits the assembly of the S-layer subunits which are in transit to the outside.

Cell Wall↗
PubMed2003

Long term potentiation varies with layer in rat visual cortex.

Long term potentiation (LTP) in various layers of rat visual cortex was studied in 90 cells with visually identified, whole-cell recordings. LTP was induced in layer II/III, layer V or layer VI with theta burst stimulation (TBS), but was not observed in layer IV. In the presence of a NMDA antagonist, D-AP5, in the bath solution, potentiation was blocked in layer II/III, some depression was seen in layer V, and potentiation still remained in layer VI. After addition of a specific mGluR1 antagonist, LY367385, to the bath solution, LTP was reduced in layer II/III and layer V, and was blocked in layer VI. After a specific mGluR5 antagonist, MPEP was applied in the bath solution, LTP was enhanced in layer VI, and blocked in layer V. We conclude that: (1) LTP in layer VI is different from other layers, depending on mGluR1, but not NMDA receptors. (2) In layer II/III, LTP is NMDA-dependent and is not blocked by group I mGluR antagonists. (3) LTP in layer V is both NMDA receptor and mGluR5 receptor-dependent. (4) LTP was not induced in layer IV with TBS.

Animals↗
PubMed2005

Composite structure of the crystalline epicuticular wax layer of the slippery zone in the pitchers of the carnivorous plant Nepenthes alata and its effect on insect attachment.

The slippery zone situated below the peristome inside pitchers of most carnivorous plants from the genus Nepenthes is covered with a thick layer of epicuticular wax. This slippery zone is reported to play a crucial role in animal trapping and prey retention. In N. alata, the wax coverage consists of two clearly distinguished layers. These layers differ in their structure, chemical composition and mechanical properties, and they reduce the insect attachment in different ways. The lower layer resembles foam, composed of interconnected membraneous platelets protruding from the surface at acute angles. The upper layer consists of densely placed separate irregular platelets, located perpendicular to the subjacent layer. Crystals of the upper layer bear small stalks, directed downwards and providing connections to the lower layer. These morphological distinctions correlate with differences in the chemical composition of waxes. The compound classes of alkanes, aldehydes, primary alcohols, free fatty acids, esters and triterpenoids occurred in extracts from both wax layers, but in different proportions. Chain length distributions in aliphatics were different in extracts from the lower and the upper wax layers. Waxes of the upper and lower layers exhibited different mechanical properties: wax of the lower layer is harder and stiffer than that of the upper layer. Moreover, crystals of the upper layer are brittle and may be easily exfoliated or broken to tiny pieces. Laboratory experiments using tethered insects showed that both wax layers reduce the attachment force of insects. It is assumed that a decrease in insect attachment on the two distinct wax layers is provided by the two different mechanisms: (1) crystals of the upper wax layer contaminate insects' adhesive pads; (2) the lower wax layer leads to a reduction of the real contact area of insects' feet with the plant surface.

Animals↗
PubMed1996

Development of axonal arbors of layer 6 pyramidal neurons in ferret primary visual cortex.

We followed the development of axonal arbors of layer 6 pyramidal neurons in ferret striate cortex to determine whether early developing axon collaterals are formed specifically in the correct target layers from the outset or achieve their adult specificity by the elimination of initially exuberant projections. These neurons were chosen for study because they are amongst the first to be generated in the developing ferret's striate cortex, and, in mature animals, these cells have axonal arbors that are highly specific for layer 4 and to a lesser extent layers 2/3 but have few collateral branches in layer 5. The axonal arbors of individual layer 6 pyramidal neurons were reconstructed following labeling in living slices prepared from the striate cortex of ferrets aged 13-35 days postnatal (P13-35). At the earliest ages (P13-15), axonal arbors consisted of a simple axon extending from the base of the cell body into the subplate or white matter and usually forming a few collateral branches but never ascending into layer 5. By P19-20, about one-half of the cells had extended axon collaterals into layer 5 or higher, and these already appeared to branch preferentially in layer 4. All of the cells from older animals had substantial axonal arbors in layers 2-4. By P26-28, there were approximately ten times as many axonal branches in layer 4 as in layer 5. Between P26-28 and P35, there was no significant change in the number of branches in layer 5, but the numbers of both branches and of axon collateral terminations in layer 4 approximately doubled. Thus, the extent of axonal arborization in layer 4 increases dramatically between P13 and P35, and growth is highly specific for correct target layers, with few branches formed in layer 5.

Animals↗
PubMed2002

In Patas monkey, glutamic acid decarboxylase-67 and reelin mRNA coexpression varies in a manner dependent on layers and cortical areas.

In nonhuman and human primates, reelin immunoreactivity is expressed consistently in gamma-aminobutyric acid (GABA)-ergic interneurons of the three upper cortical layers (Impagnatiello et al. [1998] Proc. Natl. Acad. Sci. U S A 95:15718-15723; Rodriguez et al. [2000] Proc. Natl. Acad. Sci. U S A 97:3550-3555). To understand in detail the pattern of reelin synthesis in GABAergic interneurons of primate neocortex, a quantitative analysis of reelin and of glutamic acid decarboxylase-67 (GAD(67)) mRNA-positive neurons as well as a quantitative analysis of total neuronal density measured by neuron-specific nuclear protein (NeuN) immunoreactivity was carried out in Patas monkey neocortex (Brodmann's areas 2, 3, 4, 6, 9, 17, 18, and 24). Reelin mRNA is expressed in every cortical area and layer studied, but layer II of each cortical area consistently revealed the largest neuronal population expressing reelin mRNA compared with other layers. The percentages of GAD(67)-positive neurons in each layer of the eight cortical areas were 83-98% in layer I, 55-64% in layer II, 37-49% in layer III, 71-89% in layer IV, 54-68% in layer V, and 71-85% in layer VI. The percentages of GABAergic neurons expressing reelin were 86-100% in layer I, 76-84% in layer II, 52-96% in layer III, 23-33% in layer IV, 33-57% in layer V, and 34-54% in layer VI. These findings suggest that there may be two classes of GABAergic neurons that can be differentiated by their ability to express reelin mRNA and reelin protein. This differentiation may have a functional significance, considering that reelin is secreted into the extracellular matrix, where it plays a putative role in the maturation of newly formed dendritic spines and binds selectively to dendritic shafts and to spine postsynaptic densities and presumably to integrin receptors, including alpha(3) subunits (Rodriguez et al. [2000]).

Animals↗
PubMed1992

Excitatory inputs to layer V pyramidal cells of rat primary visual cortex revealed by acetylcholine activation.

Cells in layers II-III or VI were activated by microdrop application of acetylcholine (ACh), while monitoring the intracellular response of layer V pyramidal cells. This enabled the tracing of functional connections between the cells of layers II-III or VI with those of layer V. ACh activation of layer II-III or VI cells resulted in a small depolarization of these cells, accompanied by a burst of excitatory postsynaptic potentials (EPSPs) from layer V pyramidal cells. These effects of ACh were blocked by tetrodotoxin (TTX), suggesting the involvement of action potentials in their production. The input resistance of layer V pyramidal cells during and after the EPSP burst was not significantly different from control values, further suggesting an indirect effect of ACh on layer V pyramidal cells. Isolation of the supragranular layer, by horizontal cutting, did not prevent the EPSP burst evoked by ACh application to the lower layer VI, suggesting a direct input from layer VI to layer V pyramidal cells. ACh applied near pyramidal cells in layers II-III, V or VI caused transient hyperpolarization associated with a decrease in input resistance followed by a large depolarization, an increase in input resistance, and action potential discharges. The ACh-mediated hyperpolarization and the train of action potentials of layer II-III pyramidal cells were blocked by TTX. Thus the ACh-activated cells in layers II-III and VI make an excitatory synaptic contact with layer V pyramidal cells, producing the EPSP burst observed in layer V.

Acetylcholine↗
PubMed2002

Microtubule associated protein (MAP-2) expression defines the companion layer of the anagen hair follicle and an analogous zone in the nail unit.

BACKGROUND: Microtubule associated protein 2 (MAP-2) is one of a group of polypeptides that are an integral component of the microtubular cytoskeletal structure of the central and peripheral nervous system. During the course of another investigation that utilized immunohistochemistry, MAP-2 expression was observed in the hair follicle, almost exclusively in the innermost layer of the outer root sheath of the anagen follicle. This innermost layer, the so-called companion layer, has unique properties that clearly distinguish it from the rest of the outer root sheath. Among these are diminished glycogenation and an intimate association with the Henle's layer, which it directly apposes. Numerous intercellular connections exist between the companion layer and Henle's layer and, in fact, the companion layer accompanies Henle's layer during its vertical ascent in the follicle. Circumferentially oriented keratin filaments have also been demonstrated between the companion layer and Henle's layer, apparently providing structural support to the inner root sheath. Experimentally, disturbances in the keratin filaments of the companion layer in animals ultimately results in destruction of the hair follicle and an alopecia. METHODS: Immunohistochemical studies for MAP-2 were performed on 25 additional paraffin-embedded scalp specimens using standard techniques. Because of the parallels between the follicle and nail, MAP-2 expression in the nail unit was also investigated in three specimens. RESULTS: The presence of MAP-2 in the companion layer was confirmed in all cases. Intense MAP-2 expression in the companion layer begins at the B-fringe (the start of the keratogenous zone with cornification of the Henle's layer of the inner sheath) and extends to the level of the isthmus where the inner root sheath exfoliates. MAP-2 is also expressed in the upper layers of the nail matrix. CONCLUSION: The expression of MAP-2 almost exclusively in the companion layer is probably related to the unique cytoskeletal structure of this microanatomic layer. Since experimental evidence has shown that the cell cytoskeleton is important to the integrity of the hair follicle, it is probable that MAP-2 expression is also important and disturbances in its expression could play a role in the pathogenesis of some alopecias. MAP-2 may play a similar role in the nail matrix.

Hair Follicle↗
PubMed1992

Parallel pathways in macaque monkey striate cortex: anatomically defined columns in layer III.

Visual information reaching striate cortex comes from parallel pathways, and the information is organized, or processed, by the layers and columns of striate cortex. To better understand how this is accomplished anatomically, we asked whether parallel pathways originating in the lateral geniculate nucleus (LGN), and terminating separately in layer IV, remain separate in layer III of macaque monkeys. Layer III is of interest since it may play a special role in color and form vision but not in analysis of visual motion. The chief finding was that cells in "blobs" of layer III that stain densely for cytochrome oxidase receive indirect input, via layer IVC, from both LGN magnocellular (M) and parvocellular (P) cells. This is important because the P and M pathways may represent color/form and motion-processing channels, respectively. Interblob cells receive indirect input, via layers IVC and IVA, from the LGN P cells. Also, as suggested by others, our data demonstrate that layer III can be subdivided. The bottom tier, layer IIIB, receives direct projections from all cortical layers. Output from layer IIIB appears to remain intrinsic to striate cortex. In contrast, the top tier, layer IIIA, receives projections from layer IIIB as well as from layers IVA, IVB (blobs only), and V, but it receives no direct projections from LGN recipient layers IVC and VI. Unlike layer IIIB, the output of layer IIIA reaches extrastriate areas. Thus, impulses arriving from parallel LGN pathways may be recombined through serial stages in striate cortex to produce a set of parallel pathways that are qualitatively different from the original LGN set.

Animals↗
PubMed2003

Electrical coupling between the myenteric interstitial cells of Cajal and adjacent muscle layers in the guinea-pig gastric antrum.

Intracellular recordings were made from short segments of the muscular wall of the guinea-pig gastric antrum. Preparations were impaled using two independent microelectrodes, one positioned in the circular layer and the other either in the longitudinal layer, in the network of myenteric interstitial cells of Cajal (ICCMY) or in the circular layer. Cells in each layer displayed characteristic patterns of rhythmical activity, with the largest signals being generated by ICCMY. Current pulses injected into the circular muscle layer produced electrotonic potentials in each cell layer, indicating that the layers are electrically interconnected. The amplitudes of these electrotonic potentials were largest in the circular layer and smallest in the longitudinal layer. An analysis of electrical coupling between the three layers suggests that although the cells in each layer are well coupled to neighbouring cells, the coupling between either muscle layer and the network of ICCMY is relatively poor. The electrical connections between ICCMY and the circular layer did not rectify. In parallel immunohistochemical studies, the distribution of the connexins Cx40, Cx43 and Cx45 within the antral wall was determined. Only Cx43 was detected; it was widely distributed on ICCMY and throughout the circular smooth muscle layer, being concentrated around ICCIM, but was less abundant in the circular muscle layer immediately adjacent to ICCMY. Although the electrophysiological studies indicate that smooth muscle cells in the longitudinal muscle layer are electrically coupled to each other, none of the connexins examined were detected in this layer.

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