Structural inhomogeneity in the neuropil of lamina II/III in rabbit visual cortex

Schmolke, Cordula; Schleicher, Axel

doi:10.1007/bf00250565

Cited by 9 publications

(14 citation statements)

References 23 publications

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“…From an earlier stereological study of the upper half of lamina II/III at the ultrastructural level it is known that the volume fraction of extracellular space is about 30% larger in the neuropil between bundles, than in the compartments of dendrite bundles (Schmolke and Schleicher 1989). Together with the data of the present study which has revealed that the relative amount of neuropil between bundles in the lower half of lamina II/III is higher than that in the upper half of lamina II/III (cf.…”

Section: Extracellular Spacementioning

confidence: 99%

“…This contradiction can only be explained by taking into account the effect of tortuosity upon electrical conductivity, which is contrary to that of the size of extracellular space. The fact that the neuropil between bundles mainly consists of submicroscopically small cell processes running in all directions, whereas the dendrite bundles comprise a large proportion of thick, vertically oriented cell processes (Schmolke and Schleicher 1989), might indicate that the degree of tortuosity of the extracellular space is higher in the neuropil between bundles than in the dendrite bundles. If this assumption is true, the tortuosity of extracellular space would be higher in the lower than in the upper half of lamina II/III.…”

Section: Extracellular Spacementioning

confidence: 99%

“…Apart from these changes of dendritic structures, a decrease in synaptic density as well as in the area fraction of axon terminals was reported as a sign of aging in ultrastructural studies of human frontal and rat parietal cortex (Huttenlocher 1979;Adams and Jones 1982). In an earlier study of the rabbit visual cortex it was shown that synapses and axon terminals as well as dendrites of the kind found to be reduced in aged mice, rats and humans as cited above, are predominantly localised in the neuropil betwen bundles (Schmolke and Schleicher 1989). It remains to be investigated at the ultrastructural level whether or not the reduction of the volume fraction of neuropil between bundles in aged rabbits, observed in the present study, is also due to a loss of oblique and horizontal branches of pyramidal cell dendrites and thin unmyelinated axons terminating in this neuropil compartment, and which role plays glial architecture.…”

Section: Correlation With Structural Changesmentioning

confidence: 99%

“…From an earlier ultrastructural stereological study (Schmolke and Schleicher 1989) it is known that the proportion of thin unmyelinated axons and axon terminals is higher in the neuropil between bundles than in dendrite bundles. Therefore, the neuropil between bundles might be the compartment that reflects the intensity of neuronal connectivity in the respective cortical lamina.…”

Section: Correlation With Functional Changesmentioning

confidence: 99%

“…Because of this pattern of organisation, the neuropil in laminae IV and II/III is not a homogeneous mass of cell processes filling the spaces between perikarya and blood vessels, but can be subdivided into three compartments: (a) dendrite bundles, (b) bundles of myelinated axons and (c) neuropil between bundles. From ultrastructural investigations (Schmolke 1987;Schmolke and Schleicher 1989) it is known that these compartments differ with respect to their composition as well as to their stereological characteristics. The compartment of dendrite bundles comprises volume fractions of about 50% of thick apical dendrites and 50% of thin processes that can only be delineated with the electron microscope.…”

Section: Introductionmentioning

confidence: 99%

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Tissue compartments in laminae II?V of rabbit visual cortex ? three-dimensional arrangement, size and developmental changes

Schmolke

1996

Anat Embryol

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The neuropil in laminae II/III and IV of the mature rabbit visual cortex is subdivided into (a) dendrite bundles consisting of apical dendrites of pyramidal cells and associated axons and glial processes, (b) bundles of myelinated axons ascending vertically from the white matter up to lamina IV and (c) neuropil between bundles comprising mainly thin unmyelinated axons, small dendrites and associated glial processes. In this investigation the three-dimensional structure of these compartments was analysed. In addition, the volume fractions of the three neuropil compartments, perikarya and blood vessels in the different laminae and their quantitative changes from the late fetal period up to young adulthood and in a group of aged animals were determined. Serial 1-micron epoxy sections were analysed. Dendrite bundles are more numerous and more intensively intertwined in lamina II/III than in lamina IV. At 28 days after conception the tissue in laminae II-V consists of approximately equal amounts, i.e. between 40 and 50%, of perikarya and neuropil. The volume fraction of blood vessels is about 4% and does not change much during development. During the first 16 days after birth the volume fraction of the neuropil increases to more than 70%, and conversely the volume fraction of nerve cells decreases to about 20%. Later, significant changes are seen only when the volume fractions of the three neuropil compartments are considered separately. The volume fraction of the neuropil between bundles increases throughout all laminae investigated, whereas the volume fraction of dendrite bundles is found to decrease. After 1 month, in lamina IV further increase of the neuropil between bundles is less marked, because here the bundles of myelinated axons become visible as an additional compartment. In young adult animals, the volume fractions of dendrite bundles are about 28% in the upper half, 16% in the lower half of lamina II/III and 7% in lamina IV. The neuropil between bundles comprises about 52% in the upper half, 65% in the lower half of lamina II/III and 62% in lamina IV. In lamina IV 14% is occupied by bundles of myelinated axons. In aged animals, the volume fraction of the neuropil between bundles decreases significantly in all laminae investigated. From previous ultrastructural studies, the extracellular space is known to be about 30% larger in the neuropil between bundles than in the dendrite bundles. Moreover, due to the prevalence of thin cell processes, the degree of tortuosity is larger in the neuropil between bundles than in the dendrite bundles. The present results together with these previous data are an indication of lamina-specific differences in the structure of the extracellular space. This may help to explain the electrical conductivity in the respective laminae of the cerebral cortex. The time course of postnatal changes of the neuropil compartments coincides with fundamental steps of structural and functional maturation of the rabbit visual cortex that are documented in the literature, and thus may be a vali...

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Section: Extracellular Spacementioning

confidence: 99%

Section: Extracellular Spacementioning

confidence: 99%