Extracellular space parameters in the rat neocortex and subcortical white matter during postnatal development...

Area of Science:

• Neuroscience
• Developmental Biology
• Biophysics

Background:

• Brain development involves significant changes in tissue microstructure.
• Understanding diffusion parameters is crucial for comprehending substance transport in the brain.

Purpose of the Study:

• To characterize extracellular space volume fraction, tortuosity, and tetramethylammonium uptake in the developing rat brain.
• To correlate diffusion parameters with cytoarchitectonic development.

Main Methods:

• In vivo measurement of tetramethylammonium concentration-time profiles using ion-selective microelectrodes.
• Analysis of diffusion parameters in somatosensory neocortex gray matter and subcortical white matter from postnatal days 2-120.
• Correlation of diffusion data with histological analysis of rapidly frozen brain tissue.

Main Results:

• Extracellular space volume fraction was highest in newborns and decreased significantly by adulthood, with distinct developmental timelines across cortical layers and white matter.
• Adult extracellular space volume fraction ranged from 0.19 to 0.23 in cortical layers and 0.20 in white matter.
• Tortuosity (1.51-1.65) and nonspecific cellular uptake (3.3-6.3 x 10(-3)/s) showed no significant age-related variations.

Conclusions:

• The developing brain exhibits a larger extracellular space that diminishes with maturation, influencing the dilution of neuroactive substances.
• Constant tortuosity indicates that diffusion of small molecules is not hindered in the developing brain compared to the adult brain.
• The large neonatal extracellular space may play protective roles against anoxia and seizures and is integral to developmental processes.