Verlag des Forschungszentrums Jülich
JUEL-4095
In the present study we investigated the development of the cerebral cortex of the newborn rat. In
order to obtain information concerning the basic organization and neuronal differentiation, we used
histological and morphometrical methods to analyze the cortical structure. The studies were
performed under physiological and experimentally altered conditions.
Four principal types of neurons can be distinguished in the early developing neocortex, namely
Cajal-Retzius cells, immature and bifurcated pyramidal cells, as well as subplate cells. Each cell type
was analyzed morphometrically and three-dimensionally reconstructed. The shape and size of the
immature pyramidal cells suggests, that these cells represent the migrating neurons. The bifurcated
pyramidal cells are more differentiated, they establish their connectivity. Cajal-Retzius- and subplate
cells have a differentiated dendritic system and could integrate synaptic information over a broad
spatial territory. Cajal-Retzius and subplate cells might function together as an early transient
network, creating a scaffold on which the cortex itself is constructed.
In the second part of the study, an animal model was established to enable the examination of
altered physiological conditions on brain structure and architecture. The physiological
concentrations of the neurotransmitters glutamate and GABA were changed by means of ethylenevinyl
acetate (EVA) copolymers, which enable long-term controlled release of substances. The
influence of muscimol (a GABAA receptor agonist), bicuculline, (a GABAA receptor antagonist)
and MK801 (an NMDA receptor antagonist) on the migratory process and normal brain
development was investigated.
Reiprich, Petra
Neuroanatomie des Cortex cerebri der neugeborenen Ratte
128 S., 2003
Neuronal migration is a fundamental event in the construction of the mammalian brain during
ontogeny. Forming the six layered cortex requires the movement of postmitotic neurons from their
sites of origin to their final laminar positions. This migration is essential for normal brain
development and depends on the orchestration of many extra- and intracellular signals. Alterations
in the mechanisms that underlie the migratory process lead to abnormal laminar organization and
loss of function in the developing neocortex.
The resulting severe changes in cortical architecture were detected by means of histological and
immuncytochemical methods.
Besides disorders in laminar organization affecting all cortical layers, we identified malformations of
cortical layer I. Furthermore heterotopic cells that could be identified as neurons were found in
lamina I.
Our observations suggest, that GABA and glutamate play an essential role in directed neuronal
migration during the ontogeny of the cerebral cortex.
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