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CSF-brain permeability in the immature sheep fetus: a CSF-brain barrier
Brain Research
|February 1, 1985
Summary
A novel barrier in the immature fetal sheep brain restricts cerebrospinal fluid (CSF) and brain extracellular fluid exchange. This neuroependymal barrier, observed at 60 days gestation, differs from adult brain permeability.
Area of Science:
- Developmental Neuroscience
- Cerebrospinal Fluid Dynamics
- Fetal Physiology
Background:
- The blood-brain barrier and its role in protecting the central nervous system are well-established.
- Understanding the development of barriers between cerebrospinal fluid (CSF) and brain extracellular fluid (ECF) is crucial for fetal brain development.
- Limited information exists on the permeability characteristics of the neuroependyma in the immature fetal brain.
Purpose of the Study:
- To investigate the permeability of the neuroependyma between CSF and brain ECF in fetal sheep at different gestational ages (60 and 125 days).
- To characterize the morphological nature and functional significance of any identified barriers.
- To compare permeability in immature versus more mature fetal brains.
Main Methods:
- Perfusion of radioactive ([3H]inulin, [14C]sucrose, [125I]albumin) and visible (horseradish peroxidase) tracers into the ventricular system of exteriorized fetal sheep.
- Continuous physiological monitoring of anesthetized fetal sheep.
- Analysis of tracer distribution and penetration depth within the neuroependyma and brain tissue.
Main Results:
- A previously undescribed barrier was identified in the immature (60-day) fetal sheep, limiting horseradish peroxidase penetration to the neuroependymal cells.
- In older fetuses (125 days), extracellular penetration of tracers occurred, similar to adult animals.
- Volumes of distribution for sucrose and inulin were smaller in immature brains, suggesting restricted diffusion across the neuroependyma.
Conclusions:
- A specialized membrane barrier exists between CSF and brain ECF in the immature fetal sheep, distinct from adult barriers.
- This barrier appears to narrow, rather than obliterate, the extracellular pathway, suggesting a regulatory role in early development.
- The findings highlight developmental changes in brain barrier function critical for understanding fetal brain maturation.