Absence of N-methyl-D-aspartate receptors on ovine cerebral microvessels

Radioreceptor methods were used to quantitate the N-methyl-D-aspartate (NMDA) receptor-complex of ovine cerebral microvessels and cerebral gray matter. Specific binding of D[³H]2-amino-5-phosphonopentanoate and [³H]1-[1-(2-thienyl)cyclohexyl]piperidine, ligands for the NMDA primary acceptor site and ionophore, respectively, was found in cerebral gray matter but was not detectable in membranes prepared from brain microvessels enriched in capillaries. Sigma receptors, another locus of action for phencyclidine congeners, were also not present on microvessels but were found in cortical homogenates. On the other hand, cerebral microvessels and gray matter contained significant numbers of β-adrenoceptors. Our results indicate the NMDA receptors and NMDA antagonists are unlikely to regulate the function of the cerebral microvasculature.