CHARACTERIZATION OF NMDA RECEPTOR SUBUNIT-SPECIFIC ANTIBODIES - DISTRIBUTION OF NR2A AND NR2B RECEPTOR SUBUNITS IN RAT-BRAIN AND ONTOGENIC PROFILE IN THE CEREBELLUM

Selective antisera for NMDA receptor subunits NR2A and NR2B have been developed. Each antiserum identifies a single band on an immunoblot at similar to 175 kDa that appears to be the appropriate subunit of the NMDA receptor, Using these antisera the relative densities of the subu nits in eight areas of adult rat brain have been determined. The NR2A subunit was found to be at its highest level in hippocampus and cerebr al cortex, to be at intermediate levels in striatum, olfactory tubercl e, midbrain, olfactory bulb, and cerebellum, and to be at lowest level s in the pons-medulla. The NR2B subunit was found to be expressed at i ts highest levels in the olfactory tubercle, hippocampus, olfactory bu lb, and cerebral cortex, Intermediate levels were expressed in striatu m and midbrain, and low levels were detected in the pons-medulla. No s ignal for NR2B was found in the cerebellum, These regional distributio ns were compared with that for [H-3]MK-801 binding sites, It was found that although the distribution of the NR2A subunit corresponds well w ith radioligand binding, the distribution of the NR2B subunit does not . The ontogenic profiles of NR2A and NR2B subunits in the rat cerebell um were also determined, Just following birth [postnatal day (P) 2] NR 2A subunits are undetectable, whereas NR2B subunits are expressed at a mounts easily measurable, Beginning at about P12 the levels of NR2A ri se rapidly to reach adult levels by P22, At the same time (P12), level s of NR2B protein begin to decline rapidly to reach undetectable level s by 22 days after birth. The results suggest that NMDA receptors are likely to be composed of different subunits in different parts of the brain and that even in the same tissue the receptors are likely to sho w different properties at various times during development due to alte rations in the subunit composition of the receptor.