WordNet records no synonym and no antonym for blood-brain barrier. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a mechanism that creates a barrier between brain tissues and circulating blood; serves to protect the central nervous system
“the brain was protected from the large molecules of the virus by the blood-brain barrier”
Synonyms, antonyms and the broader and narrower relations for blood-brain barrier come from Princeton University’s WordNet. Full sources and licences.