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L C Katz

Publications and source records attributed to L C Katz.

13 recordsLinked to original sources
PubMed1992

Neuronal domains in developing neocortex.

The mammalian neocortex consists of a mosaic of columnar units whose development is poorly understood. Optical recordings of brain slices labeled with the fluorescent calcium indicator fura-2 revealed that the neonatal rat cortex was partitioned into distinct domains of spontaneously coactive neurons. In tangential slices, these domains were 50 to 120 micrometers in diameter; in coronal slices they spanned several cortical layers and resembled columns found in the adult cortex. In developing somatosensory cortex, domains were smaller than, and distinct from, the barrels, which represent sensory input from a single vibrissa. The neurons within each domain were coupled by gap junctions. Thus, nonsynaptic communication during cortical development defines discrete multicellular patterns that could presage adult functional architecture.

Action Potentials↗
PubMed1992

Development of axonal arbors of layer 4 spiny neurons in cat striate cortex.

Spiny neurons in layer 4 of cat striate cortex are the primary recipients of geniculocortical afferents and provide crucial links to other cortical layers for processing visual information. Using intracellular staining, we examined the development of the local axonal projections of these neurons to determine (1) whether the laminar specificity of their projections emerged specifically or was sculpted from transient exuberant projections and (2) whether the emergence of excitatory connections from layer 4 to layer 2/3 could contribute to the activity-dependent development of clustered horizontal connections of layer 2/3 pyramidal neurons. Differences in the extent of projections to infragranular (layers 5 and 6, which receive sparse projections) versus superficial layers (layers 2/3 and 4, which receive extensive projections) developed specifically from the outset. By postnatal day 15 (P15) projections to infragranular layers matured and were indistinguishable from those in the oldest animal studied (P33). In contrast, projections to superficial layers continued to increase in complexity after P15. Projections within layer 4, which were the most elaborate at all ages studied, reached maturity at about P20, while those to layer 2/3 continued to increase in complexity through P33. No evidence for exuberant projections to any of these cortical layers was observed. At very early postnatal ages (P5) projections to the subplate region were evident. These disappeared by P8-P11, suggesting the presence of transient connections from layer 4 spiny neurons to subplate neurons. Binocular deprivation did not prevent the emergence of projections from layer 4 spiny neurons into layer 2/3 or development of normal laminar differences in projection density. Connections from layer 4 to layer 2/3 emerged after horizontal connections in layer 2/3 were crudely clustered, but in synchrony with the later refinement of clusters. Collaterals from layer 4 cells first crossed into layer 3 at P11, but were extremely short (extending only 50-200 microns beyond the laminar boundary) and uncommon (only 4 of 19 cells). Since by P8 horizontal projections of layer 2/3 pyramidal neurons are already crudely clustered, the emergence of crude clustering is probably independent of layer 4 to layer 2/3 excitatory projections. The proportion of cells projecting to layer 2/3 and the complexity of their arbors both increased in the subsequent weeks, closely matching the timing of both the refinement of crudely clustered horizontal connections and the emergence of visual responsiveness in layer 2/3.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1991

Effects of binocular deprivation on the development of clustered horizontal connections in cat striate cortex.

Intrinsic horizontal axon collaterals in the striate cortex of adult cats specifically link columns having the same preferred orientation; consequently, retrograde tracer injections result in intrinsic labeling that is sharply clustered. We have previously shown that the normal development of this circuitry involves the emergence of crude clusters from an unclustered pattern during the second postnatal week. Crude clusters are later refined to the adult level of specificity by the selective rearrangement of axonal arbors that initially project to incorrect orientation columns. Here we report that depriving animals of patterned visual experience by binocular lid suture prior to natural eye opening had no discernible effect on the emergence of crude clusters. In contrast, cluster refinement was dramatically affected by binocular deprivation. Injections of retrograde tracers in the striate cortex of animals binocularly deprived for greater than 1 month revealed only crude clusters, indicating that horizontal axon collaterals projecting to incorrect orientation columns were retained well past the age when they normally would have been eliminated. Layer 2/3 pyramidal cells from 6-week-old binocularly deprived animals had abnormal distributions of intrinsic horizontal axon collaterals that mirrored the lack of cluster refinement. The radial clustering of their horizontal collaterals was considerably less precise than normal. These cells, nevertheless, developed many of the features of normal mature arbors, including the distal axonal branches not seen in arbors from younger animals with normal visual experience. Together, these results indicate that axonal rearrangements occurred, but with reduced specificity. Thus, binocular deprivation did not simply arrest the development of this orientation-specific circuit at an immature state but limited the accuracy with which axon collaterals were added or eliminated. We suggest that development of this orientation-specific circuitry, like ocular dominance column segregation, may depend on temporal correlation of activity for regulation of axonal rearrangement. The specificity of rearrangement may be degraded in binocularly deprived cats because they do not experience sharply oriented visual stimuli necessary for concurrent activation of same-orientation columns.

Aging↗
PubMed1991

Control of postsynaptic Ca2+ influx in developing neocortex by excitatory and inhibitory neurotransmitters.

We assessed the pathways by which excitatory and inhibitory neurotransmitters elicit postsynaptic changes in [Ca2+]i in brain slices of developing rat and cat neocortex, using fura 2. Glutamate, NMDA, and quisqualate transiently elevated [Ca2%]i in all neurons. While the quisqualate response relied exclusively on voltage-gated Ca2+ channels, almost all of the NMDA-induced Ca2+ influx was via the NMDA ionophore itself, rather than through voltage-gated Ca2+ channels. Glutamate itself altered [Ca2+]i almost exclusively via the NMDA receptor. Furthermore, synaptically induced Ca2+ entry relied almost completely on NMDA receptor activation, even with low-frequency stimulation. The inhibitory neurotransmitter GABA also increased [Ca2+]i, probably via voltage-sensitive Ca2+ channels, whereas the neuromodulator acetylcholine caused Ca2+ release from intracellular stores via a muscarinic receptor. Low concentrations of these agonists produced nonperiodic [Ca2+]i oscillations, which were temporally correlated in neighbouring cells. Optical recording with Ca2(+)-sensitive indicators may thus permit the visualization of functional networks in developing cortical circuits.

Acetylcholine↗
PubMed1990

Green fluorescent latex microspheres: a new retrograde tracer.

The properties of a new fluorescent retrograde neuronal tracer, green fluorescent latex microspheres ("beads"), are described. Green beads, like the red beads that have been in use for several years, are readily transported by neurons in the mammalian central nervous system. After survival times ranging from 24 h to over one month they produce a distinct granular green fluorescence in the neuronal cytoplasm that is highly resistant to fading, when viewed using fluorescein filter sets. Green and red beads are transported with similar efficacy; cells labelled with either one or both tracers are easily distinguished. When injected into the brain, green beads, like red beads, show only minimal diffusion from the injection site. Because these two tracers differ only in their fluorescence, they should be ideal for double-labelling studies in a wide variety of systems and in developmental studies in which long-term retention of labels is required.

Animals↗
PubMed1990

Cell surface molecules containing N-acetylgalactosamine are associated with basket cells and neurogliaform cells in cat visual cortex.

In the cerebral cortex, the plant lectin Vicia villosa (VVA) selectively stains the surfaces of nonpyramidal neurons. This lectin binds specifically to alpha- and beta-linked N-acetylgalactosamine (GalNac). VVA-reactive carbohydrate is highly concentrated in layer 4 of the primary visual cortex of the cat, where it is associated exclusively with GABAergic local circuit neurons. We have studied this neuronal subset with intracellular electrophysiological recording and dye marking to identify the particular cell types expressing surface GalNac. Five different types of local circuit neurons were stained intracellularly (N = 45), but only 2 types, the columnar basket and large neurogliaform cells, were also labeled by the lectin (N = 19/45). Lectin negative types included small basket, chandelier, and large bitufted cells (26/45). Spiny stellate and pyramidal neurons were also lectin negative. Electrophysiological recordings revealed differences in the duration of action potentials in smooth versus spiny stellates but no differences between lectin-positive or -negative types. A biochemical analysis of cortical glycoproteins by SDS-PAGE and lectin blotting revealed multiple bands containing GalNac enriched in membrane fractions. These carbohydrate-containing molecules may be part of a biochemical mechanism for linking together cells with common functional properties.

Acetylgalactosamine↗
PubMed1990

Emergence and refinement of clustered horizontal connections in cat striate cortex.

Pyramidal cells in layer 2/3 of adult cat striate cortex have long, intrinsic horizontal axon collaterals within both layer 2/3 and layer 5. These collaterals form periodic "clusters" of finer axon branches that link columns of similar orientation selectivity. We have investigated the sequence of events and possible mechanisms underlying the development of these clustered intrinsic horizontal connections using a combination of neuronal tracers and intracellular staining. Small injections of fluorescent latex microspheres made during the first postnatal week (at P4-6), when examined in tangential sections, produced an even, unclustered distribution of retrogradely labeled cells up to 2 mm from the injection site. At P8, retrograde labeling extended over a larger area and clustering was discernible, primarily among the most distant labeled cells. At both P6 and P8, labeling was similar in layers 2/3 and 5, indicating that the transition from clustered to unclustered connections occurred simultaneously for cells in superficial and deep laminae. By the end of the second postnatal week (P12-15), retrogradely labeled cells were far more clustered both within and beyond the extent of P6 label; the density of labeled cells was high throughout the labeled region, but much higher within clusters. The periodicity of these nascent clusters was similar to that in the adult. Despite obvious clustering, the pattern of retrograde label observed following injections at 2-3 weeks (P12-21) differed markedly from the adult, in that the regions between clusters contained many labeled cells. Over the next 3 weeks, the connections were refined, so that by the sixth postnatal week (P36-38), regions between clusters contained very few retrogradely labeled cells and the overall pattern of retrograde label was indistinguishable from that in adults. Despite differences in postmigratory ages of neurons from the superficial and deep laminae, clustering of retrogradely labeled cells from these 2 populations was similar at all ages. Experiments in which 2-3 weeks elapsed between the time microsphere injections were made and animals were killed demonstrated that neither the initial formation of crude clusters nor their refinement was due to cell death. Instead, cluster refinement resulted from specific process elimination. When a red microsphere injection at P15 was followed by a green microsphere injection at exactly the same location on P29, the earlier injection resulted in crude clustering, as expected. Virtually all of the cells double-labeled by the later injection were within the densest clusters of label from the early injection.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Local circuits and ocular dominance columns in monkey striate cortex.

The relationships between ocular dominance columns and intrinsic cortical circuitry were examined in brain slices prepared from the striate cortex of macaques. Ocular dominance columns in layer 4C beta were visualized in vitro following anterograde transport of rhodamine injected into the lateral geniculate nucleus in vivo. The axonal and dendritic arborizations of individual layer 4C beta cells were revealed by intracellular fluorescent dye injections. Both qualitative observations and quantitative analysis showed that the dendrites of cells close to borders remained preferentially, although not absolutely, in the "home" column (the column containing the cell body). Thus, the segregated pattern of afferent input appears to have considerable influence on the pattern of dendritic arbors. Similarly, while axon collaterals within layer 4C beta could cross into the adjacent column, their limited lateral spread produced arbors that remained primarily within the home column. The terminal arbors of collaterals that travelled from layer 4C beta to layer 3 had a larger lateral spread, and the termination pattern appeared to be independent of column borders. Thus, our observations indicate that, while the course of many layer 4C beta dendrites appears to be guided by columnar boundaries as defined by geniculate afferents, there exist morphological substrates for intercolumnar interactions even between 4C beta cells. Intercolumnar interactions are seen more commonly in layer 3, however, where larger, denser axon arbors originating from 4C beta cells can freely cross ocular dominance column boundaries.

Animals↗
PubMed1988

Relationships between segregated afferents and postsynaptic neurones in the optic tectum of three-eyed frogs.

In 3-eyed frogs, afferents from 2 eyes converge on an optic tectum that normally receives input from only 1 eye. This produces an interdigitating series of stripes, resembling the ocular dominance columns in cats and monkeys. The consequences of this induced striping on the behavior of tectal dendrites was investigated in an in vitro preparation of the tectum. Stripes were labeled by anterograde transport of a fluorescent dye (rhodamine) and postsynaptic tectal cells labeled by intracellular injections of Lucifer yellow. The same types of cells were present in both normal and striped tecta, but dendritic arbors were altered in 2 ways. In normal tecta, dendrites were most frequently biased in a rostral direction. In striped tecta, dendrites were more frequently unbiased: fewer arbors had a strong rostral bias. The second effect of stripes was on the behaviors of individual dendrites of certain cell types. Some cells, primarily those with small, highly branched arbors, had dendrites that abruptly terminated at the borders between stripes. Other cells, with larger arbors, maintained "clumps" of dendrites in both eye's stripes. While these cells had portions of their dendritic arbor in more than one stripe, each individual dendrite was restricted to a single stripe. However, the processes of many cells, especially those with extensive, medial-laterally oriented dendrites, did not respect stripe boundaries in any obvious fashion. At the border between 2 stripes, there is an abrupt discontinuity in the patterns of activity in afferent axons. The dendritic alterations seen in striped tecta suggest that correlated activity can, in some cells, modulate the spatial arrangement of dendrites, such that an individual dendrite preferentially arborizes within such areas, but not between them. These cells as a whole can accommodate uncorrelated inputs, if these are segregated onto separate dendrites. This implies that local interactions between presynaptic terminals and postsynaptic dendrites, rather than action potentials in the postsynaptic cells, may furnish important signals for the modulation of dendritic arbor shape.

Animals↗
PubMed1987

Local circuitry of identified projection neurons in cat visual cortex brain slices.

The relationship between pyramidal cell morphology and efferent target was investigated in layer 6 of cat primary visual cortex (area 17). Layer 6 has 2 projections, one to the lateral geniculate nucleus (LGN) and another to the visual claustrum. The cells of origin of each projection were identified by retrograde transport of fluorescent latex microspheres. The labeled cells were visualized in brain slices prepared from area 17, using an epifluorescence compound microscope modified for intracellular recording. Individual retrogradely labeled cells were penetrated and intracellularly stained with Lucifer yellow to visualize the patterns of axons and dendrites associated with each projection. The neurons that give rise to the 2 projections had very different patterns of dendrites and local axonal collaterals, but the patterns within each group were highly stereotyped. The differences between their axonal collaterals were particularly dramatic. Claustrum projecting cells had fine, horizontally directed collaterals that arborized exclusively in layer 6 and lower layer 5. Most LGN projecting cells had virtually no horizontal arborization in layer 6. Instead, they sent widespread collaterals vertically, which arborized extensively in layer 4. The apical dendrites of the 2 groups also differed markedly. Claustrum projecting cells had apical dendrites reaching to layer 1, with branches in layer 5 only, while LGN projecting cells never had an apical dendrite reaching higher than layer 3, with side branches in layers 5 and 4. Therefore, each efferent target must receive inputs from neurons whose synaptic connections within area 17 are significantly different from those of neurons projecting to other targets. This further suggests that distinct visual response properties should be associated with each projection. In addition to the claustrum and LGN projecting cells, about 20% of layer 6 pyramidal neurons lacked an efferent axon. Morphologically, most resembled LGN projecting neurons, but a few had characteristics of claustrum projecting cells. These neurons may represent cells that either failed to make an efferent connection or cells that lost an efferent axon during development. Their frequency suggests that such intrinsic, presumably excitatory, neurons may play a significant role in cortical processing.

Animals↗
PubMed1981

Auditory responses in the zebra finch's motor system for song.

Vocal learning in songbirds is critically dependent on auditory information. Intracellular electrophysiological recordings, combined with horseradish peroxidase staining of single cells has revealed neurons within one central nervous system vocal control nucleus, hyperstriatum ventrale, pars caudale (HVc) that show responses to auditory stimuli. Auditory and non-auditory neurons fall into distinct morphological classes, based on soma size, dendritic field structure, and efferent projections. The neurons described may play a role in conveying auditory information into the vocal control system.

Acoustic Stimulation↗
PubMedDate not supplied

Neural development. FESN Study Group.

The FESN-sponsored follow-up meeting on neural development highlighted progress toward understanding several central issues in developmental neurobiology with particular emphasis on investigation into the mechanisms of cell fate determination. In systems as diverse as the HSN neurons of C. elegans, the photoreceptor cells of the Drosophila eye, the wide range of cell types within the vertebrate retina and the neurons of the cerebral cortex, hindbrain and spinal cord, the importance of environment in the determination and maintenance of cell fate was clearly established. Advances in cell marking techniques, including fluorescent dye and retroviral tagging, have enabled the fates of cells in normal and heterotypic environments to be followed and have demonstrated the initial plasticity of the progenitor cell population in many systems. The recent establishment of in vitro systems for studying neural development should further define the precise nature and identity of the environmental signals that act to establish and maintain cell fate. Of course, establishment of cell identity is only the initial phase in the formation of the mature nervous system. Once the fate of individual cells is determined, migration of cells to appropriate locations, extension of axons to appropriate targets and refinement of neuronal circuitry must occur. Both the definition of genes that influence these processes in nematodes and recent advances in imaging techniques that provide a means of observing these later, dynamic processes in 'living' brain slices promise to significantly advance understanding of the complexities of development of functional nervous systems.

Animals↗