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PubMed1994

Physiological consequences of the S-layer of Aeromonas salmonicida in relation to growth, temperature, and outer membrane permeation.

S-layers are paracrystalline protein multimers that cover the entire cell surface of many bacterial species. The presence of an S-layer in Aeromonas salmonicida (also known as A-layer) predisposed this bacterium to apparently unrelated physiological consequences: inhibition of growth at 30 degrees C, enhanced cell filamentation at 37 degrees C, and enhanced uptake of the hydrophobic antibiotics streptonigrin and chloramphenicol. Growth inhibition or enhanced filamentation was not observed when the native A-layer was missing or its arrangement altered, as in Ca(2+)-limited or Ca(2+)- and Mg(2+)-limited cells, in A-layer-negative (A-) cells with an artificially reconstituted A-layer, or in mutants unable to correctly assemble this layer. A-layer-positive cells (A+) were far more sensitive to the intracellularly acting antibiotics streptonigrin and chloramphenicol than were A- cells, and streptonigrin-resistant mutants were predominantly A-. Hemin, a compound known to specifically bind to the A-layer, alleviated streptonigrin toxicity to A+, but not A-, cells. As well, Ca(2+)- and Mg(2+)-limited cells, or mutants harboring A-layer defects had a reduced sensitivity to streptonigrin, and A- cells with reconstituted A-layers remained resistant to streptonigrin and chloramphenicol. Thus, the presence of a native A-layer arrangement on the cell surface, and not the mere presence of A-layer protein subunits, predisposed A. salmonicida toward the aforementioned physiological consequences. The A-layer is suggested to specifically effect these consequences, in particular the permeation of streptonigrin or chloramphenicol, by a specific interaction of A-layer subunits with the outer membrane.

Aeromonas↗
PubMed2006

Layer-specific properties of the persistent sodium current in sensorimotor cortex.

We evaluated the characteristics of the persistent sodium current (I(NaP)) in pyramidal neurons of layers II/III and V in slices of rat sensorimotor cortex using whole cell patch-clamp recordings. In both layers, I(NaP) began activating around -60 mV and was half-activated at -43 mV. The I(NaP) peak amplitude and density were significantly higher in layer V. The voltage-dependent I(NaP) steady-state inactivation occurred at potentials that were significantly more positive in layer V (V(1/2): -42.3 +/- 1.1 mV) than in layer II/III (V(1/2): -46.8 +/- 1.6 mV). In both layers, a current fraction corresponding to about 25% of the maximal peak amplitude did not inactivate. The time course of I(NaP) inactivation and recovery from inactivation could be fitted with a biexponential function. In layer V pyramidal neurons the faster time constant of development of inactivation had variable values, ranging from 158.0 to 1,133.8 ms, but it was on average significantly slower than that in layer II/III (425.9 +/- 80.5 vs. 145.8 +/- 18.2 ms). In both layers, I(NaP) did not completely inactivate even with very long conditioning depolarizations (40 s at -10 mV). Recovery from inactivation was similar in the two layers. Layer V intrinsically bursting and regular spiking nonadapting neurons showed particularly prolonged depolarized plateau potentials when Ca2+ and K+ currents were blocked and slower early phase of I(NaP) development of inactivation. The biexponential kinetics characterizing the time-dependent inactivation of I(NaP) in layers II/III and V indicates a complex inactivating process that is incomplete, allowing a residual "persistent" current fraction that does not inactivate. Moreover, our data indicate that I(NaP) has uneven inactivation properties in pyramidal neurons of different layers of rat sensorimotor cortex. The higher current density, the rightward shifted voltage dependency of inactivation as well the slower kinetics of inactivation characterizing I(NaP) in layer V with respect to layer II/III pyramidal neurons may play a significant role in their ability to fire recurrent action potential bursts, as well in the high susceptibility to generate epileptic events.

Action Potentials↗
PubMed1994

Sonography of the stomach: an in vitro study to determine the anatomic cause of inner hyperechoic and hypoechoic layers of the gastric wall.

OBJECTIVE: Sonography of the normal gastric wall delineates five distinct layers: from the luminal side, a first, inner hyperechoic layer; a second, hypoechoic layer; a third, middle hyperechoic layer; a fourth, hypoechoic layer; and a final, outer hyperechoic layer. The anatomic origin of the inner two sonographic layers has been a matter of controversy. To verify the histologic origin of the inner two sonographic layers, we attempted to correlate sonographic and histologic layers of resected gastric specimens. Because we hypothesized that the fluid covering the mucosa and the mucosa may be responsible for the sonographic inner two layers of the stomach, we selected specimens in which the mucosa was sloughed or thickened. MATERIALS AND METHODS: We selected five resected gastric specimens with ulcerative carcinoma in which the mucosa was totally sloughed, one specimen with a mucosal polyp, and two specimens with a polypoid lesion and partial surface ulceration. The gastric specimens were immersed in normal saline and examined with 5-MHz high-resolution sonographic equipment. Sonographic findings were correlated with gross and microscopic pathologic findings. Two phantoms were immersed in normal saline and examined with the same technique to evaluate the thickness of the sonographic interface between water and phantoms. RESULTS: The inner hyperechoic layer was constant in thickness, measuring 1 mm, and covered the surface of the normal areas and the areas where the mucosa was lost or thickened. The hypoechoic layer underlying the hyperechoic layer was obliterated where the mucosa was defective and thickened where the mucosa was thickened. The sonographic interface between water and phantoms was 1 mm thick. CONCLUSION: Our results show that the inner hyperechoic layer of the stomach seen on sonograms is due to echoes arising from the interface between fluid in the gastric lumen and the mucosal surface. The underlying hypoechoic layer is caused by the mucosa itself.

Carcinoma↗
PubMed1998

Functional streams and local connections of layer 4C neurons in primary visual cortex of the macaque monkey.

The primate visual system is composed of multiple, functionally specialized cortical areas. The functional diversity among areas is thought to reflect different contributions from early parallel visual pathways to the area V1 neurons providing input to "higher" cortical areas. The M pathway is believed to provide information about motion and contrast, via layer 4B of V1, to dorsal visual areas. The P pathway is believed to provide information about shape and color, via layer 2/3 of V1, to ventral visual areas, with specialized contributions from cytochrome-oxidase (CO) blob versus interblob neurons. However, the detailed anatomical relationships between the M and P pathways and the neurons in V1 that provide input to higher extrastriate cortical areas are poorly understood. To study these relationships, spiny stellate neurons in the M- and P-recipient layers of V1, 4Calpha and 4Cbeta, respectively, were intracellularly labeled, and their axonal and dendritic arbors were reconstructed. We find that neurons with dendrites in upper layer 4Calpha project axons to layer 4B and CO blobs in layer 2/3, thus relaying M input to these regions. Other neurons in lower layer 4Calpha provide M input to interblobs. These cells have either (1) dendrites restricted to lower layer 4Calpha and axons specifically targeting layer 2/3 interblobs, or (2) dendrites in lower 4Calpha and 4Cbeta and axons targeting blobs and interblobs. P-recipient layer 4Cbeta neurons have dense axonal arbors in both blobs and interblobs but not layer 4B. Quantitative analyses reveal that 4Calpha cells provide approximately five times more synapses than 4Cbeta cells to layer 4B, whereas 4Cbeta cells provide five times more synapses than 4Calpha cells to layer 2/3. These observations imply that M input is dominant in layer 4B. In layer 2/3, both blobs and interblobs receive M and P input, but the P input is dominant, and M input to interblobs derives exclusively from a subpopulation of M afferents that targets lower 4Calpha, not from afferents targeting only upper 4Calpha (cf. Blasdel and Lund, 1983). We speculate that the M and P pathways to interblobs are "X-like" linear systems, whereas blobs also receive nonlinear "Y-like" M input.

Animals↗
PubMed1996

Interneurons of the ganglionic layer in the mormyrid electrosensory lateral line lobe: morphology, immunohistochemistry, and synaptology.

This is the second paper in a series that describes the morphology, immunohistochemistry, and synaptology of the mormyrid electrosensory lateral line lobe (ELL). The ELL is a highly laminated cerebellum-like structure in the rhombencephalon that subserves an active electric sense: Objects in the nearby environment of the fish are detected on the basis of changes in the reafferent electrosensory signals that are generated by the animal's own electric organ discharge. The present paper describes interneurons in the superficial (molecular, ganglionic, and plexiform) layers of the ELL cortex that were analyzed in the light and electron microscopes after Golgi impregnation, intracellular labeling, neuroanatomical tracing, and gamma-aminobutyric acid (GABA) immunohistochemistry. The most numerous interneurons in the ganglionic layer are GABAergic medium-sized ganglionic (MG) cells and small ganglionic (SG) cells. MG cells have 10-20 spiny apical dendrites in the molecular layer, a cell body of 10-12 microns diameter in the ganglionic layer, a single basal dendrite that gives rise to fine, beaded, axon-like branches in either the plexiform layer (MG1 subtype) or the deeper granular layer (MG2 subtype), and an axon that terminates in the plexiform layer. Their apical dendritic tree has 12,000-22,000 spines that are contacted by GABA-negative terminals, and it receives, 1,250-2,500 GABA-positive contacts on the smooth dendritic surface between the spines. The average ratio of GABA-negative to GABA-positive contacts on the interneuron apical dendrites (14:1) is significantly higher than that for the efferent projection cells that have been described previously (Grant et al. [1996] J. Comp. Neurol., this issue). The somata and basal dendrites of MG cells receive a low to moderate density of GABAergic synaptic input, and their axons make GABAergic synaptic contacts with the somata and cell bodies of MG as well as with large ganglionic (LG) cells. SG cells probably represent immature, growing MG cells. Other interneurons in the superficial ELL layers include GABAergic stellate cells in the molecular layer, two types of non-GABAergic cells with smooth dendrites in the deep molecular layer that are named thick-smooth dendrite cells and deep molecular layer cells, and horizontal cells that are encountered particularly in the plexiform layer. Comparison with the ELL of waveform gymnotiform fish, which is another group of active electrolocating teleosts that has been investigated thoroughly, shows striking differences. In these fish, no GABAergic interneurons are found in the ganglionic (pyramidal) layer of the ELL, and GABA-negative interneurons with smooth dendrites in the molecular layer also seem to be lacking. At present, the phylogenetic origin of the described superficial interneurons in the mormyrid ELL is uncertain.

Animals↗
PubMed1999

Layer VI in cat primary auditory cortex: Golgi study and sublaminar origins of projection neurons.

The organization of layer VI in cat primary auditory cortex (AI) was studied in mature specimens. Golgi-impregnated neurons were classified on the basis of their dendritic and somatic form. Ipsilateral and contralateral projection neurons and the corticogeniculate cells of origin were labeled with retrograde tracers and their profiles were compared with the results from Golgi studies. Layer VI was divided into a superficial half (layer VIa) with many pyramidal neurons and a deeper part (layer VIb) that is dominated by horizontal cells. Nine types of neuron were identified; four classes had subvarieties. Classical pyramidal cells and star, fusiform, tangential, and inverted pyramidal cells occur. Nonpyramidal neurons were Martinotti, multipolar stellate, bipolar, and horizontal cells. This variety of neurons distinguished layer VI from other AI layers. Pyramidal neuron dendrites contributed to the vertical, modular organization in AI, although their apical processes did not project beyond layer IV. Their axons had vertical, intrinsic processes as well as corticofugal branches. Horizontal cell dendrites extended laterally up to 700 microm and could integrate thalamic input across wide expanses of the tonotopic domain. Connectional experiments confirmed the sublaminar arrangement seen in Nissl material. Commissural cells were concentrated in layer VIa, whereas corticocortical neurons were more numerous in layer VIb. Corticothalamic cells were distributed more equally. The cytological complexity and diverse connections of layer VI may relate to a possible role in cortical development. Layer VI contained most of the neuronal types found in other layers in AI, and these cells form many of the same intrinsic and corticofugal connections that neurons in other layers will assume in adulthood. Layer VI, thus, may play a fundamental ontogenetic role in the construction and early function of the cortex.

Animals↗
PubMed2000

Predominant information transfer from layer III pyramidal neurons to corticospinal neurons.

Connections of layer III pyramidal neurons to corticospinal neurons of layer V and corticothalamic neurons of layer VI in the rat primary motor cortex were examined in brain slices by combining intracellular staining with Golgi-like retrograde labeling of corticofugal neurons. Forty layer III pyramidal neurons stained intracellularly were of the regular-spiking type, showed immunoreactivity for glutaminase, and emitted axon collaterals arborizing locally in layers II/III and/or V. Nine of them were reconstructed for morphologic analysis; 15.2% or 3.8% of varicosities of axon collaterals of the reconstructed neurons were apposed to dendrites of corticospinal or corticothalamic neurons, respectively. By confocal laser scanning and electron microscopy, some of these appositions were revealed to make synapses. These findings suggest that corticospinal neurons receive information from the superficial cortical layers four times more frequently than corticothalamic neurons. The connections were further examined by intracellular recording of excitatory postsynaptic potential (EPSP) that were evoked in layer V and layer VI pyramidal neurons by stimulation of layer II/III. EPSPs evoked in layer V pyramidal neurons showed short and constant onset latencies, suggesting their monosynaptic nature. In contrast, most EPSPs evoked in layer VI pyramidal neurons had long onset latencies, showed double-shock facilitation of onset latency, and were largely suppressed by an N-methyl-D-aspartic acid receptor blocker, suggesting that they were polysynaptic. The results suggest that information from the superficial cortical layers is transferred directly and efficiently to corticospinal neurons in layer V and thereby exerts an important influence on cortical motor output. Corticothalamic neurons are, in contrast, considered relatively independent of, or indirectly related to, information processing of the superficial cortical layers.

Animals↗
PubMed2006

Development of layer-specific axonal arborizations in mouse primary somatosensory cortex.

In the developing neocortex, pyramidal neurons use molecular cues to form axonal arbors selectively in the correct layers. Despite the utility of mice for molecular and genetic studies, little work has been done on the development of layer-specific axonal arborizations of pyramidal neurons in mice. We intracellularly labeled and reconstructed the axons of layer 2/3 and layer 5 pyramidal neurons in slices of primary somatosensory cortex from C57Bl6 mice on postnatal days 7-21. For all neurons studied, the development of the axonal arborizations in mice follows a pattern similar to that seen in other species; laminar specificity of the earliest axonal branches is similar to that of mature animals. At P7, pyramidal neurons are very simple, having only a main descending axon and few primary branches. Between P7 and P10, there is a large increase in the total number of axonal branches, and axons continue to increase in complexity and total length from P10 to P21. Unlike observations in ferrets, cats, and monkeys, two types of layer 2/3 pyramidal neurons are present in both mature and developing mice; cells in superficial layer 2/3 lack axonal arbors in layer 4, and cells close to the layer 4 border have substantial axonal arbors within layer 4. We also describe axonal and dendritic arborization patterns of three pyramidal cell types in layer 5. The axons of tall-tufted layer 5 pyramidal neurons arborize almost exclusively within deep layers while tall-simple, and short layer 5 pyramidal neurons also project axons to superficial layers.

Animals↗
PubMed1993

Intrinsic connections of layer III of striate cortex in squirrel monkey and bush baby: correlations with patterns of cytochrome oxidase.

This study used biocytin and horseradish peroxidase (HRP) to examine the intrinsic connections of the cytochrome oxidase (CO) rich blob and CO poor nonblob zones within layer III of striate cortex in two primate species, nocturnal prosimian bush babies (Galago crassicaudatus) and diurnal simian squirrel monkeys (Saimiri sciureus). Our main objective was to determine whether separate classes of lateral geniculate nucleus (LGN) cells projected to separate superficial layer zones or layers in either species. There were three significant findings. First, we confirm that layer III consists of three sublayers, IIIA, IIIB, and IIIC in both species. Layer IIIA receives input from layers IIIB, IIIC, and V, with little or no input from LGN recipient layers IV and VI. Layer IIIB receives its input from nearly every cortical layer. Layer IIIC, receives input principally from layers IV alpha [which receives its input from magnocellular (M) LGN cells] and from layers V and VI. Taken together with other findings on the extrinsic connections of these layers, our data suggest that IIIA and IIIC provide output to separate hierarchies of visual areas and IIIB acts as a set of interneurons. Second, we find that, as in macaque monkeys, cells in both IV beta and IV alpha of bush babies and squirrel monkeys project to layer IIIB, converging within the blobs. These results suggest that information from all LGN cell classes [parvocellular (P), M, and the Koniocellular (K) or their equivalents] may be integrated within the blobs. Thus, blobs in all of these primates may perform a function that transcends visual niche differences. Third, our data show a species specific difference in the connections of the IIIB nonblobs; nonblobs receive indirect input via IV alpha from the LGN M pathway in bush babies but receive indirect input via IV beta from the LGN parvocellular (P) pathway in squirrel monkeys. These findings indicate that the role of nonblob zones within striate cortex differs from that of blob zones and takes into account visual niche differences.

Animals↗
PubMed2005

Fundamental differences in spontaneous synaptic inhibition between deep and superficial layers of the rat entorhinal cortex.

We have previously shown that there are clear differences between spontaneous excitatory synaptic currents recorded in layers V and II of the rat entorhinal cortex (EC) in vitro, and have suggested that these might contribute to a more pronounced susceptibility of the deeper layer to epileptogenesis. In the present study, we have made a detailed comparison of spontaneous synaptic inhibition between the two layers by recording spontaneous inhibitory synaptic currents (sIPSCs) using whole-cell patch-clamp techniques in EC slices. Pharmacological studies indicated that sIPSCs were mediated exclusively by gamma-aminobutyric acid (GABA)(A) receptors. There was little difference in average amplitudes, rise or decay times of sIPSCs in layer II compared with layer V. However, in the former, events occurred at 4-5 times the frequency seen in the latter, and frequencies of </=40 Hz were not uncommon. When activity-independent, miniature IPSCs were isolated in tetrodotoxin (TTX), the frequency in layer V was more than halved, but in layer II only a small reduction was seen, and the frequency remained very high. In terms of kinetics, while averaged sIPSCs in each layer were very similar, detailed comparison of individual sIPSCs within layers revealed distinct differences, possibly reflecting inputs from different subtypes of interneurons or inputs at different somatodendritic locations. In layer V, sIPSCs could be divided into three groups, one with slow rise and decay kinetics and a second with fast rise kinetics, further distinguished into two groups by either fast or slow decay kinetics. The distinction between events in layer II was simpler, one group having both fast rise and decay times and the second with both parameters much slower. Finally, IPSCs could occur in high-frequency bursts in both layers, although these were much more prevalent in layer II. The results are discussed in terms of the overall level of background inhibition in the two layers, as well as how this might relate to their susceptibilities to epileptogenesis.

Anesthetics, Local↗
PubMed2001

Rheology of PVC Plastisol: Formation of Immobilized Layer in Pseudoplastic Flow.

Hoffman in the early 1970s examined mechanism of dilatancy and fracture of plastisol under high-shear conditions. The samples were monodispersed spherical particles of PVC. He discovered formation of immobilized layer in the pseudoplastic flow preceding dilatancy and subsequent destruction of the layer at the fracture. However, his analysis was focused primarily on the mechanism of the fracture, and the mechanism of pseudoplastic flow remains unexplored. The present work begins with analyses of Hoffman's data to show that pseudoplastic flow, i.e., the decrease of viscosity with the increase of shear rate, is a result of the development of the immobilized layer and creation of a mobile layer of low-viscosity fluid. Hoffman took the mobile layer to consist of pure plasticizer. The present work shows that the mobile layer contains PVC particles. The thickness of mobile layer decreases (and the thickness of immobilized layer increases) with the increase of shear rate. The particle concentration and hence viscosity of the mobile layer decrease with the increase of shear rate. Similar analyses of our dynamic viscosity-frequency relationship show that (1) the pseudoplastic behavior is a result of formation of immobilized layer, which grows thicker with the increasing frequency, and (2) the mobile layer contains dispersed particles, the concentration of which decreases with increasing frequency. (3) A presence of coarse particles results in a tighter packing of the immobilized layer and lower viscosity of the mobile layer for a given volume fraction of particles. This explains why the presence and the amount of the coarse particles are important parameters in plastisol formulation. The elastic modulus-frequency relationship is also interpreted with the development of the immobilized layer, giving strain amplification. Copyright 2001 Academic Press.

Journal Article↗
PubMed1986

Neurons accumulating [3H]gamma-aminobutyric acid (GABA) in supragranular layers of cat primary auditory cortex (AI)

The classes of neurons accumulating exogenously injected, tritiated gamma-aminobutyric acid [( 3H]GABA) were studied in the supragranular layers in the primary auditory field of the adult cat. The size, laminar locus, and somatodendritic profiles of labeled neurons were studied light microscopically in frozen- or Vibratome-sectioned, 30 micron thick material, and in semithin, 1-2 micron thick, plastic-embedded high-resolution autoradiographic preparations. The chief goals of the study were to determine which types of cells could be identified as accumulating [3H]GABA in layers I, II and III, and to establish possible relationships between these cells and neurons described in Golgi studies of these layers, and the neurons found, in parallel investigations of the connections of the primary auditory field, to participate as ipsilateral corticocortical and commissural cells of origin. The principal findings are: that neurons in every layer in the primary auditory field take up tritiated gamma-aminobutyric acid; that their Nissl-counterstained somata have a smaller average area, and a smaller range of areas, than do the unlabeled cells; that more than one type of labeled neuron-as defined by somatic size and shape, height:width ratios, and nuclear membrane morphology-could be identified in each layer; that none of the labeled neurons had a soma with a pyramidal configuration; that the labeled cells are comparable in size, shape, and laminar distribution to some populations of non-pyramidal ipsilateral corticocortical cells of origin in layers II and III, and perhaps to certain classes of commissurally projecting, layer III non-pyramidal neurons; and finally, that only a rather small proportion-perhaps 10% or less, except in layer I-of the supragranular cells appear to accumulate labeled material. With regard to the identity of particular classes of neurons accumulating silver grains above background in the individual layers, in layer I, 2 of the 4 types of neurons characterized in Golgi preparations take up gamma-aminobutyric acid and the remaining 2 types may also, and the relative number of labeled cells appears to be higher than in the other layers; in layer II, 2 of the 9 varieties are labeled, and 4 other types may also be; and in layer III, 2 of the 11 types take up gamma-aminobutyric acid, and 5 other varieties may as well. Three types of non-pyramidal layer II cells that project ipsilaterally from AI to the second auditory cortical field, AII, possibly accumulate gamma-aminobutyric acid; 3 types of commissural non-pyramidal cells of origin linking AI to AI appear to be labeled by gamma-aminobutyric acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Corticocortical and thalamocortical projections to layer I of the frontal neocortex in rats.

Layer I of the neocortex is a dense synaptic zone consisting of horizontal corticocortical and widespread layer VII projections, in addition to thalamic inputs. In order to determine the origin and extent of corticocortical and thalamocortical projections to layer I of the frontal/premotor area M2 of the rat neocortex, we have used fluorescent anatomical tracing methods to determine the precise sources of cortical and thalamic input to the rostral and caudal aspects of layer I of M2. Retrograde tracer diamidino yellow (DY), applied directly to the pial surface on rostral or caudal areas of rat M2 (RM2 and CM2, respectively) labeled cells ipsilaterally throughout layers II/III, V, and VII of the adjacent primary motor area and the parietal areas (SI and SII). In addition, retrograde transport labeled contralateral CM2 or RM2 in layers II/III and V at sites homotopic to either CM2 or RM2 application sites. Contralateral layer VII was retrogradely labeled by the application to layer I of CM2, but not by the RM2 application. Retrograde DY transport from layer I of RM2 or CM2 of was seen in the ventral medial (VM), ventral lateral (VL), and posterior (Po) thalamic nuclei. However layer I transport from CM2 additionally labeled the thalamic central medial (CM) nucleus, while the RM2 labeled the mediodorsal (MD) thalamic nucleus. Upon determination that thalamic nuclei VM and VL were of primary interest in this study, due to their dense retrograde labeling, injections of anterograde tracer rhodamine dextranamine (RDA) into VM or VL were performed in order to study the projection patterns of these nuclei to layer I of the frontal cortex. RDA injections into VM labeled fibers extending through layer I of both RM2 and CM2 and throughout the cingulate cortex. Injections of RDA into VL consistently labeled dense fibers in layer I of both CM2 and RM2, although labeling was sharply decreased anterior to CM2. This study adds to a growing body of evidence that projections to layer I from all sources of cortical input make a significant contribution to integration throughout the neocortex.

Amidines↗
PubMed1997

Layer-specific differential regulation of transcription factors Zif268 and Jun-D in visual cortex V1 and V2 of macaque monkeys.

To investigate intracellular mechanisms of cortical layer-specific gene regulation, we quantitatively examined the expression of two transcription factors, Zif268 and JunD, and compared their expression levels in each layer of the primary visual cortex (VI) and visual area 2 (V2) of macaque monkeys (Macaca fuscata). The brain sections were immunohistochemically stained for determination of the percentage of Zif268- or JunD-expressing neurons in the total neuronal population. We found area- and layer-specific expression of these transcription factors; Zif268 tended to be expressed at high levels in layers on the parvocellular pathway in V1, whereas JunD did not show such an expression pattern. In V1, many Zif268-immunopositive neurons were observed in layers II/III, IVC beta and VI. The percentage of Zif268-immunopositive neurons was highest in layer IVC beta and lowest in layer IVC alpha. JunD-immunopositive neurons were fewest in layer IVC beta and most abundant in layer VI. In V2, the level of expression of Zif268 was almost the same as that of JunD in layer II/II. However, layer IV of V2 tended to contain more Zif268-immunopositive neurons than JunD-immunopositive neurons, whereas layer VI contained more JunD-immunopositive neurons than Zif268-immunopositive neurons. Although it has been reported that the same extracellular signals induce both Zif268 and JunD, the present results indicate that the expression of these transcription factors is differentially controlled in each layer of the primate visual cortical areas. Furthermore, the present results suggest that these transcription factors contribute to area- and layer-specific gene regulation by mediating transmission of extracellular signals to the nucleus via different intracellular signalling pathways.

Animals↗
PubMed2000

S-layer-supported lipid membranes.

Many prokaryotic organisms (archaea and bacteria) are covered by a regularly ordered surface layer (S-layer) as the outermost cell wall component. S-layers are built up of a single protein or glycoprotein species and represent the simplest biological membrane developed during evolution. Pores in S-layers are of regular size and morphology, and functional groups on the protein lattice are aligned in well-defined positions and orientations. Due to the high degree of structural regularity S-layers represent unique systems for studying the structure, morphogenesis, and function of layered supramolecular assemblies. Isolated S-layer subunits of numerous organisms are able to assemble into monomolecular arrays either in suspension, at air/water interfaces, on planar mono- and bilayer lipid films, on liposomes and on solid supports (e.g. silicon wafers). Detailed studies on composite S-layer/lipid structures have been performed with Langmuir films, freestanding bilayer lipid membranes, solid supported lipid membranes, and liposomes. Lipid molecules in planar films and liposomes interact via their head groups with defined domains on the S-layer lattice. Electrostatic interactions are the most prevalent forces. The hydrophobic chains of the lipid monolayers are almost unaffected by the attachment of the S-layer and no impact on the hydrophobic thickness of the membranes has been observed. Upon crystallization of a coherent S-layer lattice on planar and vesicular lipid membranes, an increase in molecular order is observed, which is reflected in a decrease of the membrane tension and an enhanced mobility of probe molecules within an S-layer-supported bilayer. Thus, the terminology 'semifluid membrane' has been introduced for describing S-layer-supported lipid membranes. The most important feature of composite S-layer/lipid membranes is an enhanced stability in comparison to unsupported membranes.

Bacterial Proteins↗
PubMedDate not supplied

Contributions of individual layer 2-5 spiny neurons to local circuits in macaque primary visual cortex.

We studied excitatory local circuits in the macaque primary visual cortex (VI) to investigate their relationships to the magnocellular (M) and parvocellular (P) streams. Sixty-two intracellularly labeled spiny neurons in layers 2-5 were analyzed. We made detailed observations of the laminar and columnar specificity of axonal arbors and noted correlations with dendritic arbors. We find evidence for considerable mixing of M and P streams by the local circuitry in VI. Such mixing is provided by neurons in the primary geniculate recipient layer 4C, as well as by neurons in both the supragranular and infragranular layers. We were also interested in possible differences in the axonal projections of neurons with different dendritic morphologies. We found that layer 4B spiny stellate and pyramidal neurons have similar axonal arbors. However, we identified two types of layer 5 pyramidal neuron. The majority have a conventional pyramidal dendritic morphology, a dense axonal arbor in layers 2.4B, and do not project to the white matter. Layer 5 projection neurons have an unusual "backbranching" dendritic morphology (apical dendritic branches arc downward rather than upward) and weak or no axonal arborization in layers 2-4B, but have long horizontal axonal projections in layer 5B. We find no strong projection from layer 5 pyramidal neurons to layer 6. In macaque V1 there appears to be no single source of strong local input to layer 6; only a minority of cells in layers 2-5 have axonal branches in layer 6 and these are sparse. Our results suggest that local circuits in V1 mediate interactions between M and P input that are complex and not easily incorporated into a simple framework.

Animals↗
PubMedDate not supplied

Terminal morphology and distribution of corticothalamic fibers originating from layers 5 and 6 of cat primary auditory cortex.

Two types of terminations were observed on corticothalamic fibers arising from cells in different layers of cat auditory cortex. Injections of the anterograde tracers Phaseolus vulgaris leucoagglutinin (PHA-L) or biocytin were made into single cortical loci that included both superficial layer 5 (5a) and layer 6 in the primary auditory cortex (AI). These resulted in labeling of terminal fibers with small (approximately 1 micron) and large (approximately 2 microns) boutons in the medial geniculate complex (MG) and the lateral nucleus of the posterior complex. Large boutons were found in the deep and superficial dorsal nuclei, in the ventrolateral nucleus, and, less frequently, in the medial nucleus of the MG. They usually ended in grape-like clusters of boutons. By contrast, small boutons were found densely in the pars lateralis and pars ovoidea of the ventral nucleus, and to a lesser extent in the medial nucleus of MG. In the anterior third of the ventral nucleus, where the highest density of labeled fibers was observed, the small bouton terminations formed a plate-like plexus. In the inferior colliculus (IC), most terminal boutons on labeled corticotectal fibers were of large size. To reveal the cells of origin of the axons ending in the two different types of corticothalamic terminations, biocytin injections were localized in either layer 5 or layer 6 of AI or PHA-L injections were made into middle layers, including layer 5a but excluding layer 6. Virtually all labeled terminals found in the MG after layer 5 injections were of large size, while those found after layer 6 injections were of small size. The distribution of terminals of single-labeled axons was extensive and variable. For example, an axon recovered after a layer 5 injection of biocytin ended in at least seven patches of clusters of large boutons along much of the anteroposterior axis of MG. Our previous findings showed two neuronal populations situated in superficial layer 5 and in layer 6 of AI and projecting to the thalamus. The axons of these cells had different patterns of collateral distributions in the cortex. The present study shows that the extrinsically projecting axons of these two populations also have different terminal morphologies and distribution patterns in the MG. The findings suggest that the corticothalamic pathway in the cat auditory system consists of at least two feedback projections originating from different cortical layers that exert different influences on distinct thalamic neuronal populations.

Animals↗
PubMed2004

Laminar patterns of local excitatory input to layer 5 neurons in macaque primary visual cortex.

Layer 5 neurons in primary visual cortex make putative reciprocal feedback connections to the superficial layers. To test this hypothesis, we employed scanning laser photostimulation combined with intracellular dye injection to examine local functional excitatory inputs to and axonal projections from individual layer 5 neurons in brain slices from monkey V1. In contrast with previous studies of other V1 neurons, layer 5 neurons received significant input from nearly all of the cortical layers, suggesting individual layer 5 cells integrate information from a broad range of input sources. Nevertheless relative strengths of laminar inputs varied across neurons. Cluster analysis of relative strength of laminar inputs to individual layer 5 neurons revealed four discrete clusters representing recurring input patterns; each cluster included both excitatory and inhibitory neurons. Twenty-five of 40 layer 5 neurons fell into two clusters, both characterized by very strong input from superficial layers. These input patterns are consistent with layer 5 neurons providing feedback to superficial layers. The remaining 15 neurons received stronger input from deep layers. Differences in input from layer 4Calpha versus 4Cbeta also suggest specific associations of the magnocellular and parvocellular visual pathways, with populations receiving stronger input from deep versus superficial cortical layers.

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