Updated PubMed. The functions and protein expressions of the blood-brain barrier are changed during brain development after birth. The purpose of the present study was to develop a method to isolate brain capillaries from a single frozen neonatal mouse brain and elucidate the enrichment of brain capillaries by quantitative proteomic analysis. The brain capillary fraction was prepared by the optimized method from a single frozen mouse neonatal brain (postnatal day 7). The brain capillary fractions and brain lysates were digested by trypsin and analyzed by DIA.