ONTOGENY OF NMDA R1 SUBUNIT PROTEIN EXPRESSION IN 5 REGIONS OF RAT-BRAIN

A polyclonal antiserum to a fusion protein corresponding to a region o f the NMDA R1 (NR1) subunit (amino acids 656-811) was produced and aff inity purified. A quantitative immunoblotting technique was developed using the fusion protein as a standard. By employing this method, onto genic studies (day 2-42) of the density of NR1 protein were carried ou t in several regions of rat brain. The results showed that in all five of the brain regions examined [olfactory bulb (Ob), cortex (Cx), hipp ocampus (Hp), midbrain (Mb) and cerebellum (Cb)], levels of NR1 protei n are low at birth and increase with similar patterns having a sharp r ise within the first 3 weeks after birth. Levels increased 2.0 to 4.5- fold from postnatal day 2 to postnatal day 42. Although the general pa tterns of developmental expression are similar, large differences in t he absolute amounts of NR1 protein among the five brain regions were o bserved. The maximal levels (pmol of fusion protein equivalent/mg +/- S.E.) of NR1 subunit attained during development in the five regions a re: Hp 2.0 +/- 0.37 > Cx 1.4 +/- 0.11 > Ob 1.3 +/- 0.2 > Mb 1.0 +/- 0. 10 > Cb 0.57 +/- 0.13. The temporal patterns of expression of NR1 prot ein are similar to results from studies examining the expression of NR 1 mRNA. Furthermore, the absolute numbers obtained from our studies ar e close to those found using [H-3]MK-801 binding suggesting that many of the NR1 subunits expressed in the brain exist in an active form.