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PubMed1980

Naturally occurring alterations of cortical layers surrounding the fissura prima of rat cerebellum.

We have regularly observed alterations in the three-layered arrangement of cerebellar cortex surrounding fissura prima in normal adult and neonatal rats. In 90 of 110 rat brains analyzed, the cortical layers surrounding fissura prima were found to be altered from the four-layered (neonatal) or three-layered (adult) arrangement found in the majority of the remainder of cerebellar cortex. This common alteration extended long distances (as much as 320 microns) on either side of the midline, causing fissura prima to become more and more shallow from its lateral to medial extent. In sagittal sections at the lateral edge of the alteration in neonatal cerebellum, the external granular layer and pial cells disappeared, leaving an expanse of molecular layer lying between internal granular layer cells of lobules V and VI. Proceeding medially toward the midsagittal region, the cells of the internal granular layer of lobules V and VI were situated closer together and often merged. In such sections Purkinje cells did not usually remain in a monolayer, but were displaced, and clusters of these cells were sometimes found within the white matter. Various complex configurations of internal granular layer, molecular layer, and Purkinje cell groups surrounding fissura prima were commonplace in regions of cerebellum as far lateral as 320 microns on either side of the midsagittal plane. The greatest dorsoventral extent of such alterations measured was 400 microns. The presence of these previously unreported deviations is unrelated to experimental stress, as they occur spontaneously, possibly due to a vestigeal disorganization left in midline zones after early cell migration phases.

Animals↗
PubMed1995

Phaseolus vulgaris-leucoagglutinin tracing of commissural fibers to the rat dentate gyrus: evidence for a previously unknown commissural projection to the outer molecular layer.

Numerous studies have shown a lamina-specific termination of commissural fibers to the dentate gyrus in the inner molecular layer. However, the exact course and arborization pattern of individual fibers remained unknown. In this study, the commissural fiber tract to the dentate gyrus of the rat has been studied using the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L), which labels individual axons and their collaterals. Following iontophoretic application of the tracer, anterogradely labeled fibers were followed through the posterior basal fornix and medial fimbria where they formed a dense fiber bundle. Labeled fibers then entered the dentate gyrus close to the medial blade of the granule cell layer where they separated and traversed the hilus. Only in those cases where the injection also involved CA3 pyramidal cells could axons arborizing in the hilus be observed. Typically, fibers that continued into the molecular layer did not arborize in the hilus. Upon their entrance into the molecular layer, these fibers changed direction, gave off several collaterals, and followed a new path parallel to the granule cell layer where they preferentially formed en passant contacts. These commissural fibers to the inner molecular layer terminated in a wide septotemporal (longitudinal) extension. However, a considerable number of fibers reached the outer molecular layer where some of them formed extensive arborizations. Moreover, these commissural fibers to the outer molecular layer appeared to be restricted to the hippocampal lamella, corresponding to the level of the contralateral injection site. These data suggest the existence of three commissural projections to the rat dentate gyrus: (1) commissural fibers to the hilus arising from CA3 neurons, (2) commissural fibers to the inner molecular layer, and, (3) commissural fibers to the outer molecular layer.

Animals↗
PubMed1995

Intrinsic circuit organization of the major layers and sublayers of the dorsolateral prefrontal cortex in the rhesus monkey.

Intrinsic connections are likely to play important roles in cognitive information processing in the prefrontal association cortex. To gain insight into the organization of these circuits, intracortical connections of major laminar and sublaminar divisions were retrogradely labeled in Walker's area 9 and 46 in rhesus monkeys by using cholera toxin (B-subunit) conjugated to colloidal gold. Microinjections placed within particular cortical laminae produced unique patterns of retrograde labeling. Injections in layers II/III yielded labeling which was laterally widespread (2-7 mm) in supragranular layers, and more narrowly focused, i.e., conforming to a column, in layers IV-VI. In contrast, local circuits associated with layers IV and Vb displayed a regular, cylindrical organization, whereas intrinsic connections of layer Va were laterally extensive (3-5 mm) in layers III and Va. Finally, injections in layer VI gave rise to a narrow column of cell labeling traversing all layers, augmented by laterally extensive labeling (approximately 7 mm) in layer VI. The intrinsic connections of the prefrontal cortex were arrayed within mediolaterally elongated stripes which were often distributed asymmetrically in either the medial or lateral direction. In addition, labeled cells within these mediolaterally oriented fields were frequently grouped within discrete clusters or narrow bands. The intrinsic connections identified in this study differ from the local circuits of corresponding layers reported for primary visual cortex; the unique intrinsic wiring diagram of the prefrontal cortex may be related to its specialized cognitive and mnemonic functions.

Animals↗
PubMed1995

Compartmental organization of layer IVA in human primary visual cortex.

Immunostaining for three neuronal proteins, nonphosphorylated neurofilament protein (with antibody SMI-32), calbindin, and parvalbumin, was used to examine the organization of layer IV in human primary visual cortex (area 17 or V1) specifically to determine whether, similar to the case in macaque V1, layer IVA is present and is divided into neurochemically distinct compartments. All three proteins are expressed by neurons that are unevenly distributed in layer IV of human V1; immunostaining for each protein includes a thin band corresponding to layer IVA of classic cytoarchitectonic studies. In this band, nonphosphorylated neurofilament protein immunoreactivity is present in relatively broad clusters of pyramidal cell somata and dendrites that appear as upwardly protruding parts of intense immunostaining in layer IVB, whereas immunoreactivity for calbindin and parvalbumin exists in somata of nonpyramidal neurons and in thin, dense clusters of punctate profiles. In tangential sections through layer IVA, the three proteins are seen in distinct compartments. Calbindin- and parvalbumin-immunostained neurons make up a thinly walled honeycomb or lattice, whereas neurons immunostained for nonphosphorylated neurofilament protein occupy the central lacunae. Direct comparison shows that neurons immunostained for calbindin occupy regions in layer IVA complementary to those immunostained for nonphosphorylated neurofilament protein. These data demonstrate a basic similarity in the organization of layer IV in macaques and humans. Layer IVA specifically is organized into complementary and neurochemically distinct compartments, including what appears to be a geniculocortically innervated and parvicellular-driven lattice and the interstitial lacunae formed by the periodic, upward protrusion of magnocellular-dominated layer IVB neurons.

Aged↗
PubMed2002

Three classes of pyramidal neurons in layer V of rat perirhinal cortex.

Whole-cell recordings from 140 pyramidal neurons in layer V of rat perirhinal cortex (PR) revealed three distinct firing patterns: regular spiking (RS, 76%), burst spiking (BS, 9%), and late spiking (LS, 14%). LS neurons have not previously been reported in layer V of any cortical region. LS cells in layer V of PR exhibited delays of up to 12 s from onset of a depolarizing current step to spike threshold, followed by sustained firing. In contrast, pyramidal cells in layer V of other cortical regions contain only RS and BS cells. Within PR, the percentage of LS neurons in layer V differs markedly from what we previously observed in layers II/III (50% LS) and VI (90% LS). Morphologically, BS neurons in layer V of PR had thick primary apical dendrites that terminated in a tuft within layer I, whereas RS and LS cells had relatively thin primary apicals that terminated either diffusely or in a layer I tuft. At holding potentials near rest, PR neurons exhibited small (approximately 15 pA), inward, spontaneous postsynaptic currents (PSCs) that were indistinguishable among the three cell types. Currents evoked by minimal stimulation of layer I were about 2.8 times larger than the spontaneous PSCs. Evoked currents had unusually long onset latencies with little variation in latency, consistent with monosynaptic responses evoked by stimulation of unmyelinated fibers. The prevalence of LS cells in combination with the long-latency monosynaptically evoked PSCs suggested that PR is not a region of rapid throughput. This is consistent with anatomical data suggesting that PR is a higher-level association cortex. These data further advance an emerging picture of PR as a cortical region with a unique distribution of cell types different from other cortical regions.

Action Potentials↗
PubMed2006

Corrosion test, cell behavior test, and in vivo study of gradient TiO2 layers produced by compound electrochemical oxidation.

This paper describes efforts to improve implant biocompatibility and durability by applying a hybrid technique using composite oxidation. Pure titanium was used as the substrate material. A porous oxide film as the outer layer was produced by micro-arc oxidation and a dense oxide film as the inner layer was produced by pre-anodic oxidation. In this study, physicochemical characteristics, corrosion test, cell attachment behavior, and in vivo studies were used to compare this gradient layer with untreated titanium. The results revealed that the gradient layer was composed of two layers of oxide films which were made up of rutile and anatase and the surface was porous with calcium and phosphor. The corrosion resistance of the gradient layer was improved remarkably, which was about three times the values for titanium and two times the value for the dense layer. The cell-material interaction study indicated that L929 cells seeded and cultured on the gradient layer appeared to attach well and the rate of proliferation was the greatest. The study in vivo showed that the gradient layer had good biocompatibility. This gradient layer provides a material with high corrosion resistance, bioactivity, and biological properties suitable for tissue engineering applications.

Animals↗
PubMed2003

Synthesis and secretion of molecules exhibiting the HL1 epitope during development of the hyaline layer of the asteroid Pisaster ochraceus.

A complex ECM layer called the hyaline layer (HL) surrounds embryos and larvae of the starfish Pisaster ochraceus. When preserved by freeze substitution, the HL of a bipinnaria larva consists of six sublayers. From the plasmalemma outwards these are the intervillous layer (iv), the H3, H2, H1 sublayers that make up the supporting layer, a boundary layer (b) and the coarse outer meshwork (cm). HL development begins at fertilization when exocytosis of the cortical granules releases ECM into the perivitelline space and elevates the fertilization membrane. Over the course of early development the layers are added in a sequential manner and by hatching the embryo is surrounded by a thin HL containing most if not all of the layers. The layers thicken over the next few days. By the bipinnaria stage the larvae are surrounded by a thick six-layered HL. HL1 is a monoclonal antibody that reacts against an epitope found in all regions of the HL of the bipinnaria larva except the H2 sublayer. Western blots show that it is present on several molecules during HL development. The number and pattern of the HL1-labeled molecules change during development, suggesting that either new molecules are being produced or that some molecules are precursors of others. Light (immunofluorescence) and TEM (immunogold) studies using HL1 in the early stages of development show that HL1-positive material is not present in the corticle granules and that it only begins to be manufactured and secreted in quantity in the blastula stage at 18-20 h. Following this it continues to be secreted at least as far as the bipinnaria stage. Molecules containing the HL1 antigen therefore do not appear to play a major role in early development of the HL but are necessary for later events. The results suggest that, like the sea urchin HL, the starfish HL undergoes a sequential organization of the different HL layers from ECM components, which are released into the perivitelline space.

Animals↗
PubMed1999

Structural Conformation of Bovine Serum Albumin Layers at the Air-Water Interface Studied by Neutron Reflection.

The adsorption of bovine serum albumin (BSA) at the air-water interface has been studied by specular neutron reflection. The variation of the adsorbed amount and the total thickness of the BSA layer with respect to bulk BSA concentration was determined at pH 5, close to its isoelectric point (IP). While the surface excess showed a steady increase with bulk concentration the thickness of the protein layer was found to be close to the short axial length of 40 Å of the globular solution structure of BSA at concentrations below 0.1 g dm-3, suggesting that BSA molecules adsorb with their long axes parallel to the surface of water. At 1 g dm-3 the adsorbed layer can be modeled as an upper layer of 40 Å with a volume fraction of 0.4 and a sublayer of 30 Å underneath the top main layer with a volume fraction of 0.12. The results suggest that, although there is some structural deformation accompanying adsorption, there is no denaturation. The extent of immersion of the BSA in water was determined by performing the measurements in D2O and in a mixture of H2O and D2O whose contrast matches that of BSA. The signal is then only from the part of the layer out of water. At pH 5 this layer was about 10 +/- 5 Å at a bulk concentration of 5 x 10(-4) g dm-3 and decreased to 5 +/- 3 Å at 1 g dm-3. The fraction of the BSA layer immersed in water therefore varies from about 70 to over 90%. The effect of pH on the adsorption was examined at two BSA concentrations. While pH had little effect on the adsorption at a low BSA concentration of 5 x 10(-3) g dm-3, both surface excess and layer thickness showed pronounced peaks at pH 5 at the higher concentration of 1 g dm-3. The increased adsorption at pH 5 is attributed to the reduced lateral electrostatic repulsion around the IP. This adsorption pattern became less pronounced when the total ionic strength was increased from 0.02 to 1 M, indicating that the electrolyte screens the electrostatic repulsions within the adsorbed layer. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Adsorption and Exchange Dynamics in Aging Hydroxyethylcellulose Layers on Silica.

The adsorption kinetics of hydroxyethylcellulose (HEC) on silica and relaxations in adsorbed HEC layers were probed using total internal reflectance fluorescence and near-Brewster reflectivity. Like many random-coil polymers, HEC was found to adsorb at the transport-limited rate. Relaxations occurred at nearly constant interfacial mass when HEC layers were exposed to aqueous solvent, causing the subsequent exchange of chains between the layer and the free solution to become increasingly hindered. Eventually, on the time scale of a day, layers became immobilized and unable to accommodate chains from free solution. A continued fluorescence decay, beyond time scales that could be probed with self exchange, suggested further relaxations of the adsorbed HEC. The polydisperse HEC system (with an average molecular weight near 450,000) behaved qualitatively similar to molecular weight standard polyethylene oxide (PEO) layers on silica. For instance, relaxations in PEO layers occurred on a time scale of 10-20 h, like the HEC layers. Young layers of the latter, however, exhibited self-exchange kinetics that were an order of magnitude slower than PEO layers of similar age. This difference in adsorbed layer dynamics was attributed to HEC's stiffer backbone, compared with flexible PEO. Copyright 2000 Academic Press.

Journal Article↗
PubMed2002

Grand canonical Monte Carlo simulation for determination of optimum parameters for adsorption of supercritical methane in pillared layered pores.

A grand canonical Monte Carlo (GCMC) method is carried out to determine optimum adsorptive storage pressures of supercritical methane in pillared layered pores. In the simulation, the pillared layered pore is modeled by a uniform distribution of pillars between two solid walls. Methane is described as a spherical Lennard-Jones molecule, and Steele's 10-4-3 potential is used for representing the interaction between the fluid and a layered wall. The site-site interaction is also used for calculating the interaction energy between methane molecules and pillars. An effective potential model that reflects the characteristics of a real pillared layered material is proposed here. In the model, a binary interaction parameter, k(fw), is introduced into the combining rule for the cross-energy parameter for the interaction between the fluid and a layered wall. Based on the experimental results for the Zr-pillared material synthesized and characterized by Boksh, Kikkinides, and Yang, the binary interaction parameter, k(fw), is determined by fitting the simulation results to the experimental adsorption data of nitrogen at 77 K. Then, by taking it as a model of pillared layered material, a series of GCMC simulations have been carried out. The excess adsorption isotherms of methane in a pillared layered pore with three different pore widths and porosities are obtained at three supercritical temperatures T=207.3, 237.0, and 266.6 K. Based on the simulation results at different porosities, various pore widths and different supercritical temperatures, the pillared layered pore with porosity psi=0.94 and pore width hsigma(p)=1.02 nm is recommended as adsorption storage material of supercritical methane. Moreover, the optimum adsorption pressure is determined at a given temperature and a fixed width of the pillared layered pore. For example, at temperature T=207.3 K, the optimum adsorption pressures are 3.1, 3.7, and 4.5 M Pa at H=1.02, 1.70, and 2.38 nm, respectively. In summary, the GCMC method is a useful tool for optimizing adsorption storage of supercritical methane in pillared layered material.

Journal Article↗
PubMed2000

Zooarchaeological and taphonomic analysis of the Die Kelders Cave 1 layers 10 and 11 Middle Stone Age larger mammal fauna.

Middle Stone Age (MSA) and Middle Paleolithic (MP) faunal assemblages have gained widespread attention due to their relevance to the debate over the modernity of hominid behavior during the MSA/MP. A recent critique of the scavenging argument for MSA/MP behavior drew on a summary presentation of the skeletal abundance and surface modification data from Die Kelders Cave 1 Layer 10 (Marean, 1998). This paper provides a more complete presentation of those data, adds the smaller Layer 11 sample, and provides a detailed analysis of the taphonomic history of both samples.Bone fragment density is higher in Layer 10 than in Layer 11. Bone densities vary horizontally as well, with Layer 10 showing greater deposition in the exposed areas of the cave. An analysis of long bone breakage patterns indicates that non-nutritive breakage on the Layers 10 and 11 samples was present but not intense. Size 1 mammals were predominantly accumulated by owls and/or other large raptors, not hominids, in Layer 10. Hominids were the predominant accumulator of Sizes 2-4 mammals in Layers 10 and 11 as indicated by the frequency of hammer-stone percussion marks and carnivore toothmarks. After discard by hominids, a significant portion of these remains were discovered and scavenged by carnivores. Overall, the larger mammal fauna of Layer 10 is dominated by Sizes 3 and 4 bovids, mostly young and adult eland, and thus hominids were focusing on the high-ranked prey items. Shaft portions of long bones, the portions with the most flesh, have the highest frequencies of cutmarks. A comparison of the Layers 10 and 11 cutmark frequencies to Selvaggio's (1998) scavenging model shows that the frequencies are significantly outside the range of variation documented in Selavaggio's scavenging sample.

Animals↗
PubMed1989

Actions of excitatory amino acid antagonists on synaptic potentials of layer II/III neurons of the cat's visual cortex.

Actions of excitatory amino acid (EAA) antagonists on the responses of cells in layers II/III and IV of the cat's visual cortex to stimulation of layer VI and the underlying white matter were studied in slice preparations. Antagonists used were 2-amino-5-phosphonovalerate (APV), a selective antagonist for the N-methyl-D-aspartate (NMDA) type of EAA receptors, and kynurenate, a broad-spectrum antagonist for the three types of EAA receptors. In extracellular recordings it was demonstrated that most of the layer II/III cells were sensitive to APV, while the great majority of the layer IV cells were not. By contrast, kynurenate suppressed the responses completely in both layers. Excitatory post-synaptic potentials (EPSPs) evoked by stimulation of layer VI and the while matter were recorded intracellularly from layer II/III neurons. To determine whether the EPSPs were elicited mono- or polysynaptically, the synaptic delay for each EPSP was calculated from a pair of onset latencies of EPSPs evoked by stimulation of the two sites. Forty-two percent of the layer II/III cells were classified as having monosynaptic EPSPs. In 60% of these monosynaptic cells, the rising slope of the EPSPs was reduced by APV while in the other 40%, it was not. In the former (APV-sensitive cells), subtraction of the APV-sensitive component from the total EPSP indicated that the onset latency of the NMDA receptor-mediated component was roughly equal to that of the non-NMDA component. In the latter (APV-resistant cells), only the slowly-decaying component was in part mediated by NMDA receptors. The conduction velocities of the afferent fibers innervating APV-resistant cells were slower than those of the APV-sensitive cells, suggesting that both types of cells are innervated by different types of afferents. The polysynaptic EPSPs of almost all layer II/III cells were sensitive to APV. The subtraction method indicated that the NMDA component had about the same magnitude as the non-NMDA components. When the slices were superfused by a Mg2+-free solution, the EPSPs were potentiated dramatically, but this potentiation was reduced to the control level during the administration of APV. Similarly, APV-sensitive components were potentiated during the administration of bicuculline, a selective antagonist for gamma-aminobutyric acid receptors of A type. These results suggest that NMDA receptors participate, at varying degrees, in excitatory synaptic transmission at most layer II/III cells in the cat's visual cortex, and their actions appear to be regulated by intracortical inhibition.

2-Amino-5-phosphonovalerate↗
PubMed1975

[A device for the measurement of the horny layer transparency. The stripping method].

A new measuring device for the determination of transparency of horny layer material stripped off the skin surface with adhesive tape is being described. This method enables a differentiated and reproducible objectification of light absorption of stripped horny layer material. The horny layer is being fixed on a glass plate and then conducted past a light source and a photo cell at constant speed, whereby the respective light-current-variation caused by the varying degrees of light permeability of the horny layer material is being synchroniously registered by a continuous-line-recording instrument thereby serving as a parameter for each respective strip sample. The systematic evaluation of the original curves takes into consideration amplitude, angle of climb and medium route and results in a horny layer sample-obtained successively from one and the same horny layer strip-series test area-impressioned by individual and regional horny layer conditions. This permits conclusions concerning not only the horny layer transparency but also the horny layer solidity and stripping capability. Thus, the procedure opens new horizons for experimental and clinical questions regarding horny layer diagnostics.

Dermatology↗
PubMed1982

Effects of feeder layers made of human, mouse, hamster, and rat cells on the cloning efficiency of transformed human cells.

The effect of feeder layers on cloning efficiency of transformed human cells was investigated. Embryonic human skin or lung fibroblasts; adult human skin fibroblasts; early passage cells from embryos of mouse, rat, and hamster; established mouse cell lines; 3T3 and 10T1/2 were used as feeder layers after they were lethally exposed to Co-60 gamma-rays at 3,000 rad. As test cells to study the effect of feeder layers on cloning efficiency, WI-38 CT 1 cells transformed in vitro by Co-60 gamma-rays and HGC cells cultured from a human gastric cancer were used. The effect of feeder layers on the cloning efficiency of the test cells was dependent on cell density of feeder layer cells, sources of the feeder layer cells, and kinds of test cells. An optimal density of feeder cells produced cloning efficiencies 3 to 15 times higher than in cultures without a feeder layer. Generally, high density of cells in feeder layers decreased the cloning efficiency of the test cells, presumably owing to contact inhibition of growth and depletion of essential nutrients by the feeder layer cells. Regarding the effect of the feeder layers made of human fibroblasts, there were no significant differences in population doubling levels; tissue origins of fibroblasts, or fibroblasts derived from normal individuals, patients with cancer, or with a genetically high familial incidence of cancer, hereditary adenomatosis of the colon and rectum.

Animals↗
PubMed2004

Gallbladder wall thickening: MR imaging and pathologic correlation with emphasis on layered pattern.

The aim of this study was to correlate MR findings of gallbladder wall thickening with pathologic findings on the basis of the layered pattern and to evaluate the diagnostic value of MR imaging in gallbladder disease. We retrospectively evaluated the source images of HASTE sequences for MR cholangiography in 144 patients with gallbladder wall thickening. The layered pattern of thickened wall was classified into four patterns. Type 1 shows two layers with a thin hypointense inner layer and thick hyperintense outer layer. Type 2 has two layers of ill-defined margin. Type 3 shows multiple hyperintense cystic spaces in the wall. Type 4 shows diffuse nodular thickening without layering. MR findings of a layered pattern of thickened gallbladder were well correlated with histopathology. Chronic cholecystitis matched to type 1, acute cholecystitis corresponded to type 2, adenomyomatosis showed type 3, and the gallbladder carcinomas showed type 4. All four layered patterns were associated with PPV of 73% or greater, sensitivity of 92% or greater and specificity of 95% or greater. Our results indicate that MR findings of gallbladder wall thickening are characteristic in each entity and correlate well with pathologic findings. The classification of the layered pattern may be valuable for interpreting thickened gallbladder wall.

Adult↗
PubMed1992

Differential projections to the superior collicular layers from the perihypoglossal nuclei in the cat.

The primary objective of the present study is to demonstrate the presence of a projection to the superficial layers of the superior colliculus (SC) from the perihypoglossal nuclei, specifically from the nucleus intercalatus (INT) in the cat. Iontophoretic application of WGA-HRP into the perihypoglossal complex produced orthogradely labeled terminals in the SC contralaterally forming two bands: one is in the superficial gray layer, and the other in the intermediate gray layer. The superficial band was evenly distributed in the upper portion of the superficial gray layers (layers II1-2) and the deeper band existed in the intermediate gray layer (layer IV) being arranged in a discontinuous manner. Injections of the tracer into the superficial layers of the SC yielded retrogradely labeled cells only in the rostral part of the contralateral INT; by contrast, the injection confined to the deep layers produced labeling of cells exclusively in the nucleus prepositus hypoglossi (PH). Thus, the INT and the PH each project separately to the functionally different superficial and intermediate layers of the SC, respectively. On the basis of the present anatomical findings, it is suggested that the perihypoglossal nuclei as a whole contribute not only to the oculomotor but also to the visuosensory regulatory function in the SC.

Afferent Pathways↗
PubMed1988

Comparisons between strychnine and penicillin epileptogenesis suggest that propagating epileptiform abnormalities require the potentiation of thalamocortical circuitry in neocortical layer 4.

Simultaneous recordings from three laminae within the cat visual cortex following differential intralaminar injections of strychnine (i) confirmed that low strychnine concentrations (5 mM) induce interictal-like epileptiform abnormalities (late responses) only when injected into superficial layers 2 and 3, (ii) revealed that these abnormalities are generated locally within these layers, and (iii) showed that they remain local phenomena by not spreading vertically into other cortical layers. Higher strychnine concentrations (20 mM), however, (iv) obscured these laminar differences by increasing layer 4 sensitivity to this agent in addition to the maximally sensitive superficial layers, and further (v) revealed nonlocal, vertically propagating, interictal-like abnormalities (late responses) following layer 4 injections which are preceded by an increase in thalamocortically mediated activity within this layer (enhanced physiologic responses). When penicillin was used as the convulsant, propagated interictal-like responses (late responses) induced in any layer were always preceded by a thalamocortically mediated response from layer 4 (enhanced physiologic responses); a condition clearly unlike the 5 mM but similar to the 20 mM strychnine foci observed in this study. These results suggest that convulsant action upon the thalamocortical circuitry of layer 4 is essential for the development of propagating as opposed to local epileptiform activity. Further, these results may also help explain why some cortical seizure disorders remain localized (focal) whereas others secondarily generalize to distal brain sites (i.e., complex partial seizures of extratemporal origin).

Animals↗
PubMed1989

[3H]muscimol labels neurons in both the superficial and deep layers of cat superior colliculus.

We examined the pattern of [3H]muscimol labeling in cat superior colliculus to determine if it matches that of [3H] gamma-aminobutyric acid ([3H]-GABA) labeling or GABA antibody immunoreactivity. Injections in the superficial layers labeled cell bodies in only the superficial layers. Of 204 labeled cells, 68% were located within the upper 200 microns of the superior colliculus, 31% within the deep superficial gray layer, and only 1% below that layer, a pattern similar to that seen with [3H]GABA labeling. By contrast, an injection in the deep layers of the colliculus resulted in cell labeling in both the superficial and deep layers, including 68% in the superficial gray layer, 24% in the optic layer, and 8% in the intermediate and deep gray layers. This pattern approximates that seen with GABA immunocytochemistry. We conclude that the pattern of accumulation of [3H]muscimol depends critically upon the location of the injection and reasonably matches the pattern of GABA immunoreactivity if the injection involves the deep layers of the colliculus.

Animals↗