Also called BBB · blood brain barrier
The blood–brain barrier (BBB) is formed by tight junctions between the endothelial cells lining cerebral capillaries. It restricts the passage of most large molecules — including most peptides — from blood into brain tissue. BBB permeability is a key determinant of whether a cognitive or neuroprotective peptide can act centrally. Semax and selank are studied in part because of reported CNS activity despite the barrier.
Research use only. This definition is an educational reference, not medical advice or dosing guidance.