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J Bolz

Publications and source records attributed to J Bolz.

At least 37 records · Page 2Linked to original sources
PubMed1995

The specificity of interactions between the cortex and the thalamus.

The functioning of the adult mammalian cerebral cortex depends critically upon precise interconnections between specific thalamic nuclei and distinct cortical regions. Therefore, one central issue in understanding cortical development is determining the cellular and molecular strategies underlying the specification of thalamocortical projections. We address the role of axon-axon interactions and membrane-bound guidance molecules in the establishment of the development of layer-specific patterns of afferent and efferent cortical connections does not depend upon neuronal activity. We present evidence that activity conveyed by thalamic afferents is required for the elaboration of the columnar specificity of cortical circuits.

Animals↗
PubMed1995

Relationships between dendritic fields and functional architecture in striate cortex of normal and visually deprived cats.

We examined relationships between the pattern of geniculocortical innervation and the dendritic fields of cells in layer 4 of in cat primary visual cortex. Experiments were performed on normal animals and on cats in which the geniculocortical projection was altered by monocular deprivation or by the induction of divergent squint during the critical period. Thalamic afferents providing the input from the contralateral eye were anterogradely labeled by injecting the fluorescent tracer Dil into lamina A of the lateral geniculate nucleus. Intracellular staining with Lucifer yellow in slice preparations allowed simultaneous visualization of the morphology of individual cells and the thalamic afferents. Our results demonstrate that spiny stellate cells close to the upper and lower margin of the geniculocortical input have highly asymmetric dendritic fields, and thereby confine their dendrites to the termination zone of these afferents. This effect was specific for the cell class; it was not observed in pyramidal neurons. These dendritic asymmetries perpendicular to the laminar borders of spiny stellate cells were not altered by monocular deprivation or strabismus. In contrast, visual deprivation strongly influenced the dendritic arbors of spiny stellate cells near the borders between adjacent ocular dominance columns. In normal animals, the dendrites of cells near columnar borders remained preferentially within one column. These dendritic asymmetries became much more pronounced in strabismic animals. Monocular deprivation weakened the influence of the columnar borders on dendritic fields. Spiny stellate cells within the columns of the open eye exhibited a slight tendency to confine their dendrites to these columns. Cells in the columns of the deprived eye showed the opposite effect; they extended their dendrites preferentially into the adjacent columns of the open eye. These results demonstrate that the segregation of geniculocortical afferents into ocular dominance columns and its perturbation by manipulation of the visual input plays an important role in defining the morphology of cortical target cells. Thus, activity-dependent structural changes not only occur at the level of the presynaptic terminals, but also at the level of the postsynaptic target cells, and thereby contribute to build up the functional architecture of the cortex.

Animals↗
PubMed1994

GABAA receptor alpha 1 subunit, an early marker for area specification in developing rat cerebral cortex.

Changes in the expression of neurotransmitter receptors in developing cerebral cortex may be related to the functional maturation of distinct areas. In the present study, we have tested whether GABAA receptor expression in neonatal rats reflects the differentiation of cortical areas. Specifically, the alpha 1 subunit, one of the most prevalent GABAA receptor subunits in adult cerebral cortex, is up-regulated postnatally, suggesting a link with the establishment of inhibitory circuits. Using immunohistochemistry with a subunit-specific antiserum, we observed a striking area- and lamina-specific increase in staining for GABAA receptors containing the alpha 1 subunit (alpha 1-GABAA receptors), from low levels in neonates to an intense and uniform staining in adults. Already at birth, the alpha 1-subunit immunoreactivity selectively demarcated the boundaries of certain cortical areas. In particular, the primary somatosensory (S1) and visual (V1) areas were distinctly delineated with a band of alpha 1-subunit immunoreactivity located in the developing layers III and IV. The staining ended abruptly at the presumptive boundaries of S1 and V1, adjacent areas being unstained at this age. Around postnatal day 3, clusters of alpha 1-subunit positive cells were seen in layers III-IV of S1 and V1 extending their dendrites up to layer I, where they arborized profusely. In addition, the distribution of alpha 1-GABAA receptors in S1 revealed in detail the differentiation of the barrel field during early postnatal development. Although staining was observed in all areas by postnatal day 6, differences in the laminar distribution of alpha 1-GABAA receptors persisted for at least 1 more week. Our results provide evidence for the existence of area-specific boundaries in neocortex of newborn rats before layers III-IV are fully differentiated and innervated by cortical afferents. Furthermore, the area- and lamina-specific maturation of alpha 1-GABAA receptor staining demonstrates the value of this marker for investigating the cytoarchitectonic differentiation of cortical areas during development.

Animals↗
PubMed1994

Differentiation of transmitter phenotypes in rat cerebral cortex.

Cortical neurons differ in their neurochemical properties. Projection neurons use excitatory amino acids as transmitters, most local interneurons contain the inhibitory transmitter GABA, and specific subtypes of local circuit neurons express distinct neuropeptides. How this cellular diversity is generated during development is not known. We have been studying the transmitter differentiation of cortical neurons in different in vitro systems using immunohistochemical techniques. Transmitter phenotypes of cortical neurons were examined in slice cultures, i.e. in the absence of extrinsic cortical connections, and in dissociated cortical cell cultures, i.e. in the absence of extrinsic and intrinsic cortical connections. The expression of vasoactive intestinal polypeptide in cortical interneurons occurred normally in slice cultures prepared from neonatal rats between birth and 2 days of age, but was strongly impaired in dissociated cell cultures prepared at the same time. These results suggest that the intact cortical environment present in the slice cultures exerts crucial influences for neuropeptide differentiation. In contrast, the transmitters glutamate and GABA were expressed normally in the appropriate cell types and similar in proportions in dissociated cell cultures prepared from cortices at embryonic day 19. Only cells dissociated during S-phase failed to express glutamate and GABA in vitro. When cells were kept for 24 h after mitosis in a cortical slice preparation in vitro, however, they later expressed their appropriate transmitter phenotypes. Thus, signals from the local cortical environment that act early in the cell cycle are required for the specification of transmitter phenotypes of cortical neurons.

Animals↗
PubMed1994

Cortical circuitry in a dish.

In the mammalian neocortex, local connections as well as projections to and from the cortex are organized in cortical layers. Recent studies have demonstrated that the formation of the patterns of afferent and efferent cortical connections in organotypic co-cultures are similar to those observed in vivo. These findings provide some insights into the cellular strategies that operate during the development of layer-specific cortical connections.

Animals↗
PubMed1993

Formation of specific efferent connections in organotypic slice cultures from rat visual cortex cocultured with lateral geniculate nucleus and superior colliculus.

Cells in the cerebral cortex project to many distant regions in the brain. Each cortical target receives input from a specific population of cells which have a characteristic morphology and which are located in a distinct cortical layer. In an attempt to learn about the mechanisms by which this stereotypic output pattern is generated during development, we have studied the formation of cortical projections in an in vitro system. Slices from developing rat visual cortex were cocultured with slices from the superior colliculus, the major target of cells in layer 5, and the lateral geniculate nucleus, the major target of cells in layer 6. Cortical neurons which established connections with tectal and thalamic explants were retrogradely labelled with fluorescent dyes. It was found that, in vitro, different populations of neurons project to these two targets, and that the laminar position and cellular morphology of the projecting cells were similar to their in vivo counterparts. These specific connections were established when the target explants were placed either next to the white matter or next to the pial side of cortical slice cultures. The axons of cells projecting to ectopic positioned explants reoriented their trajectories and grew through the cortical grey matter directly towards their targets. Thus subcortical targets exert an orienting effect specifically on their innervating cells and attract growing axons of the appropriate cells at a distance. These results suggest that different targets release different molecules that act selectively on specific populations of neurons. Therefore, chemotropic guidance is likely to play a significant role in the development of specific connections between cortical neurons and their target areas.

Animals↗
PubMed1993

Reconstructing cortical connections in a dish.

During development of the cortex, efferent projection neurons located in distinct cortical layers send their axons to different targets, and afferent fibers establish connections with cortical target cells of a particular layer. Recent studies have shown that layer- and cell-specific afferent and efferent cortical connections established in culture are similar to those observed in vivo. The results of these experiments provide evidence for the existence of diffusible and membrane-bound guidance factors for specific sets of axons. Furthermore, they suggest the use of different molecules to navigate axons towards their target, regulate target innervation and mediate target cell recognition.

Animals↗
PubMed1992

Relationships between dendritic morphology and cytochrome oxidase compartments in monkey striate cortex.

In primate striate cortex, staining for the mitochondrial enzyme cytochrome oxidase reveals a regular pattern of intense staining, the blobs, which are surrounded by the lighter stained interblob regions. Neurons in both compartments exhibit profound functional differences: blob cells have color selective, unoriented receptive fields, whereas interblob cells are usually not color selective and have oriented receptive fields. Neuroanatomical tracing studies have shown that blob and interblob cells receive different inputs and participate in different projections. It is not known, however, whether this compartmental organization is also reflected in the dendritic morphology of individual cells. We therefore combined intracellular staining with cytochrome oxidase histochemistry to study the relationship between cell morphology and blob pattern in layers 2 and 3 of macaque striate cortex. Single cells were injected with the fluorescent dye lucifer yellow in lightly fixed tangential sections. Adjacent sections were reacted for cytochrome oxidase to reveal the blobs. The spatial relationship between stained cells and the pattern of the blobs were subsequently determined by aligning the sections by using radially running blood vessels as landmarks. Our results show that pyramidal cells located in blob and interblob regions do not differ in their soma size, spine density, and basal dendritic field structure. This indicates that the characteristic functional properties of the neurons in both compartments do not depend on the morphology of their dendritic trees. Since the elongation of the dendritic fields of blob and interblob cells was also found to be similar, we conclude that cortical orientation selectivity is not generated through elongated dendritic fields. We found several cells with dendrites freely crossing the borders between blob and interblob regions. These cells might correspond to cells with "mixed" receptive field properties, e.g., color selective oriented cells, which in physiological studies were found at the transition from blob to interblob regions. However, there were also a number of cells that respected the borders. A quantitative analysis of the dendritic fields revealed that 67% of the cells located close to the borders have a tendency to confine their dendrites to only one compartment. Thus the pattern of basal dendrites of these cells might be shaped by the parcellation of the striate cortex in blob and interblob regions. These dendritic field asymmetries may help to maintain the segregation at the single cell level into different processing channels in monkey striate cortex.

Animals↗
PubMed1992

Formation and preservation of cortical layers in slice cultures.

During cortical development, neurons generated at the same time in the ventricular zone migrate out into the cortical plate and form a cortical layer (Berry and Eayrs, 1963, Nature 197:984-985; Berry and Rogers, 1965, J. Anat. 99:691-709). We have been studying both the formation and maintenance of cortical layers in slice cultures from rat cortex. The bromodeoxyuridine (BrdU) method was used to label cortical neurons on their birthday in vivo. When slice cultures were prepared from animals at different embryonic and postnatal ages, all cortical layers that have already been established in vivo remained preserved for several weeks in vitro. In slice cultures prepared during migration in the cortex, cells continued to migrate towards the pial side of the cortical slice, however, migration ceased after about 1 week in culture. Thus, cortical cells reached their final laminar position only in slice cultures from postnatal animals, whereas in embryonic slice, migrating cells became scattered throughout the cortex. Previous studies demonstrated that radial glia fibers are the major substrate for migrating neurons (Rakic, 1972, J. Comp. Neurol. 145:61-84; Hatten and Mason, 1990, Experientia 46:907-916). Using antibodies directed against the intermediate filament Vimentin, radial glial cells were detected in all slice cultures where cell migration did occur. Comparable to the glia development in vivo, radial glial fibers disappeared and astrocytes containing the glia fibrillary-associated protein (GFAP) differentiated in slice cultures from postnatal cortex, after the neurons have completed their migration. In contrast, radial glial cells were detected over the whole culture period, and very few astrocytes differentiated in embryonic slices, where cortical neurons failed to finish their migration. The results of this study indicate that the local environment is sufficient to sustain the layered organization of the cortex and support the migration of cortical neurons. In addition, our results reveal a close relationship between cell migration and the developmental status of glial cells.

Aging↗
PubMed1992

Formation of specific afferent connections in organotypic slice cultures from rat visual cortex cocultured with lateral geniculate nucleus.

The development of the cerebral cortex involves the specification of intrinsic circuitry and extrinsic connections, the pattern of inputs and outputs. To investigate the development of a major afferent input to the cortex, we studied the formation of thalamocortical connections in an organotypic culture system. Slices from the lateral thalamus of young rats were cocultured with slices from the visual cortex. Thalamocortical projections in vitro were examined anatomically with fluorescent dyes and physiologically with electrophysiological and optical recording techniques. Axons emerged from thalamic explants radially in all directions. The outgrowth of thalamic fibers and the course of the axonal trajectories were not influenced by the presence of the cocultured cortex. Only those thalamic axons that happened to grow toward the cortical slices invaded their target tissue. Thalamocortical projection cell in vitro had the characteristic morphology of thalamic relay neurons. Cells with the morphology of interneurons were present in thalamic explants, but these neurons did not project to the cocultured cortex. Thalamocortical axons in vitro terminated in their appropriate cortical target layer, formed axonal arbors, and made functional synaptic contacts. Such specific connections between thalamic neurons and their cortical target cells were established regardless of whether thalamocortical axons invaded the cortex from the white matter side or from the pial surface. These results suggest that thalamic projection neurons have an innate mechanism that allows them to recognize their cortical target cells. Thus, intrinsic factors play a significant role in the laminar specification of cortical connections during development.

Afferent Pathways↗
PubMed1991

Cortical barrelfields in organotypic slice cultures from rat somatosensory cortex.

We are attempting to determine the factors that influence both the formation and maintenance of barrels in the rodent somatosensory cortex. Cytochrome oxidase histochemistry and Nissl staining were used to identify the presence of barrels in slice cultures of rat cortex. Barrels were observed in sagittally cut slices, in cortical layer IV, from animals aged postnatal day 5-10 that were cultured for at least 10 days. No differences were observed in the barrel pattern from animals at different postnatal ages, or from cortex that was cultured for different lengths of time. In contrast, cortical barrels in tangentially cut sections from similarly aged animals were clearly visible after one day in culture, but they disappeared after two days in culture. These results suggest that intact connections within cortical columns are sufficient to sustain the functional architecture of the somatosensory cortex in vitro.

Animals↗
PubMed1991

Ultrastructural organization of slice cultures from rat visual cortex.

We have been studying the fine structural organization of slice cultures prepared from the visual cortex of 6-day-old rats and cultured for 2 weeks using a roller culture technique. Neurons in culture exhibited the characteristic cytological differences between perikarya, axons and dendrites. Neuronal and glial processes formed a dense neuropil with minimal extracellular spaces, and within the neuropil there were numerous synaptic contacts. Both morphological types of cortical synapses, type I (asymmetrical) and type II (symmetrical) could be readily identified in slice cultures. The pattern of synaptic connections in culture was remarkably similar to that observed in normal cerebral cortex; asymmetrical synapses were usually found in contact with dendritic spines, less frequently with dendritic shafts, and never on perikarya, whereas symmetrical synapses were found mostly on perikarya, occasionally on dendritic shafts but never on dendritic spines. Synaptic morphology appeared mature after 2 weeks in vitro and did not show the immature features observed at the time of culture preparation. Taken together with our previous light microscopic studies, these results indicate that cortical slice cultures are organotypically organized and serve as a useful model to study mechanisms of cortical development and plasticity.

Animals↗
PubMed1991

Functional specificity of a long-range horizontal connection in cat visual cortex: a cross-correlation study.

Anatomical investigations of the visual cortex revealed a regular set of interlaminar connections and long-range horizontal connections. An important component of the intrinsic cortical circuit is the projection from layer 5 to layer 6 over long horizontal distances. Previous work has shown that when layer 5 is locally inactivated, layer 6 cells lose their response in a segment of their receptive fields corresponding to the blocked area in layer 5. It has therefore been proposed that the long receptive fields characteristic of layer 6 cells might be generated by concatenating layer 5 cells with similar orientation preferences. In the present study, we used cross-correlation analysis to examine both source and target cells of the interlaminar connection from layer 5 to layer 6. We found correlated firing between cells separated by up to 4.2 mm, the longest horizontal distance studied. The occurrence of correlated firing depended on the functional properties and on the topographic position of the cells in layer 5 and layer 6. Interactions were only observed if the cells had matching orientation tuning and similar eye preference and if the layer 5 cells lay within the summation area of the layer 6 cells. Both simple and complex cells in layer 6 fired in synchrony with layer 5 cells. In layer 5, mainly standard complex cells, but very few special complex cells, participated in correlated firing with layer 6 cells. These results suggest that cells in layer 6 receive their input from cooriented, coaxially aligned standard complex cells in layer 5. This topographic arrangement and the length summation properties of standard complex cells in layer 5 are well suited to generate long receptive fields in layer 6. Thus, our experiments provide evidence for the functional specialization of a particular component of cortical circuitry.

Animals↗
PubMed1990

Morphological types of projection neurons in layer 5 of cat visual cortex.

Pyramidal cells in layer 5 of the visual cortex have multiple cortical and subcortical projection sites. Previous studies found that many cells possess bifurcating axons and innervate more than one cortical or subcortical target, but cells projecting to both cortical and subcortical targets were not observed. The present study examines the morphology of cells in cat visual cortex projecting to the superior colliculus, the main subcortical target of layer 5, and cells in layer 5 projecting to cortical areas 18 and 19. The neurons that give rise to these different projections were retrogradely labelled and intracellularly stained in living brain slices. Our results show that cells within each projection group have several morphological features in common. All corticotectal cells have a long apical dendrite forming a large terminal tuft in layer 1. Their cell bodies are medium sized to large, and their basal dendrites form a dense and symmetrical dendritic field. Corticocortical cells in layer 5 have a very different morphology: their apical dendrites are short and they never reach higher than layers 2/3. Their cells bodies are small to medium sized and they have fewer basal dendrites than corticotectal cells. Thus there are two morphologically distinct projection systems in layer 5, one projecting to cortical and the other one to subcortical targets, suggesting that these two systems transmit different information from the visual cortex. Among the corticotectal cells with the largest cell bodies we found some cells whose basal and apical dendrites were almost devoid of spines. Spiny and spinefree corticotectal cells also have different intrinsic axon collaterals and therefore play different roles in the cortical circuitry. While many spiny corticotectal cells have axon collaterals that project to layer 6, spinefree corticotectal cells have fewer axon collaterals and these do not arborize in layer 6. We suggest that the two morphological types of corticotectal cells might be related to functional differences known to exist among these cells. We discuss how the presence or absence of spines affects the integration of the synaptic input and how this might be related to the cells' functional properties.

Animals↗
PubMed1990

Formation of target-specific neuronal projections in organotypic slice cultures from rat visual cortex.

A characteristic feature of the mammalian cortex is that projection neurons located in distinct cortical layers send their axons to different targets. In visual cortex, cells in layers 2 and 3 project to other cortical areas, whereas cells in layers 5 and 6 project to subcortical targets such as the lateral geniculate nucleus. The proper development of these projections is crucial for correct functioning of the visual system. Here we show that specific connections are established in an organotypic culture system in which rat visual cortex slices are co-cultured with another slice of the visual cortex or with a thalamic slice. The laminar origin and cellular morphology in vitro of cortical projections to other cortical regions or to subcortical targets are remarkably similar to those seen in vivo. In addition, axons of projecting cells are not restricted to particular pathways, but appear instead to grow directly towards their appropriate target. These observations raise the possibility that chemotropic attraction from the target areas may play an important part in the development of the cortical projection pattern.

Afferent Pathways↗
PubMed1990

Non-Hebbian synapses in rat visual cortex.

In the mammalian CNS, long term potentiation can be induced by repeatedly pairing presynaptic stimulation with postsynaptic depolarization of a single cell, similar to a model proposed by Hebb, that synaptic strengthening occurs as a result of correlated pre- and postsynaptic activity. However, our experiments indicate that the Hebbian rule is not strictly valid in the cortex. Double intracellular recordings showed that synaptic reinforcement is not confined to the depolarized postsynaptic neuron, but is also observed in adjacent but not coactivated neurons. The enhancement and its spread is stimulus-specific, it occurs only for fibres stimulated during the pairing procedure. During development, this spread might lead to a characteristic organizing principle of the cortex, the clustering of cells with similar functional properties.

Animals↗