Tight junctions in the choroid plexus epithelium. A freeze-fracture study including complementary replicas

Area of Science:

• Cell Biology
• Epithelial Biology
• Neuroscience

Background:

• Tight junctions form a barrier in epithelial tissues.
• The choroid plexus epithelium forms the blood-cerebrospinal fluid barrier.
• Understanding tight junction structure is crucial for barrier function.

Purpose of the Study:

• To investigate the ultrastructure of rat choroid plexus tight junctions.
• To quantify the presence and extent of discontinuities in these junctions.
• To correlate junctional structure with epithelial permeability.

Main Methods:

• Freeze-fracture electron microscopy was used.
• Analysis of both P-face and E-face replicas was performed.
• Complementary replicas were utilized to assess junctional strand continuity.

Main Results:

• Rat choroid plexus tight junctions exhibit numerous discontinuities.
• Approximately 25% of junctional strands were found to be discontinuous.
• Control experiments showed more continuous junctions in the small intestine.

Conclusions:

• Discontinuities (pores) in choroid plexus tight junctions may contribute to high transepithelial conductance.
• These structural findings support the concept of a "leaky" epithelium.
• Artifacts from sample preparation cannot be entirely excluded as an explanation.