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The development of induced cerebrocortical microgyria in the rat
G D Rosen1, D M Press, G F Sherman
1Dyslexia Research Laboratory, Beth Israel Hospital, Boston, MA 02215.
Abstract:
Placement of a freezing probe on the skull of neonatal rats produces four-layered microgyria, complete with a lamina dissecans and microsulcus. We studied the developmental course of this induced microgyria under light microscopy by examining changes in neurons, glia, and macrophages following a focal freezing insult on the day of birth (postnatal day [P]0). The destruction of neurons and glia induced by the freezing probe extends through the cortical plate and occasionally through the subplate, but the pial membrane appears undamaged and radial glial cells, while damaged, are not eliminated. Reactive astrocytes and macrophages arrive in the damaged area within 24 hours of the injury, and repair of the damaged tissue peaks within the first week. Damaged radial glial fibers regrow, and supragranular neurons migrate through this damaged area, also within the first week. The newly formed supragranular layer overlies the cell-free area. The damaged cortex begins to assume its adult-like microgyric appearance from P5 to P10. On P15 and P32, long glial fibers, resembling radial glia, are present and are immunoreactive for glial fibrillary acidic protein and radial glial fiber antibodies (vimentin and Rat-401). No such fibers appear at this age in the non-microgyric areas or in normal brains. We conclude that microgyria formation may be the consequence of brain repair mechanisms occurring during neuronal migration to the neocortex, and that it appears to preserve primitive features characteristic of the developing cortex.
Insights
Induced microgyria in neonatal rats results from brain repair mechanisms during neuronal migration. This process preserves primitive cortical features and involves glial cell regrowth and astrocyte/macrophage activity.
Area of Science:
- Neuroscience
- Developmental Biology
- Pathology
Background:
- Neonatal brain injury can lead to structural abnormalities.
- Microgyria is a developmental disorder characterized by an abnormally small and convoluted cerebral cortex.
Purpose of the Study:
- To investigate the cellular and developmental changes during the formation of induced microgyria in neonatal rats.
- To understand the role of glial cells and immune responses in microgyria development.
Main Methods:
- Induction of microgyria using a freezing probe on postnatal day 0 in rat pups.
- Light microscopy examination of neuronal, glial, and macrophage changes over time.
- Immunohistochemical analysis for glial fibrillary acidic protein, vimentin, and Rat-401.
Main Results:
- Focal freezing injury caused neuronal and glial destruction but spared the pial membrane.
- Reactive astrocytes and macrophages infiltrated the injury site within 24 hours.
- Radial glial fibers regrew, and supragranular neurons migrated, forming a new layer over the damaged area.
- The microgyric appearance developed between postnatal days 5-10, with persistent glial fibers resembling radial glia observed at later stages.
Conclusions:
- Microgyria formation is linked to brain repair processes during neocortical development.
- The observed repair mechanisms may preserve primitive developmental features of the cortex.
- Long-term presence of radial glia-like fibers in microgyric areas suggests altered cortical organization.