Differential distribution of N-methyl-D-aspartate receptor-2 subunit messenger RNA in the rat superior olivary...

The distribution of N-methyl-D-aspartate receptor subunit messenger RNA was examined in the superior olivary complex of the rat using in situ hybridization methods. Non-radioactive methods showed N-methyl-D-aspartate receptor-1 and N-methyl-D-aspartate receptor-2A, -2B and -2C subunit expression to be abundant in principal cells of all major superior olivary complex regions, with N-methyl-D-aspartate receptor-1 expression higher than N-methyl-D-aspartate receptor-2. After auto-radiographic in situ hybridization, counting silver grains over cells was used to quantitate and compare levels of expression of the N-methyl-D-aspartate receptor-2 subunits. N-Methyl-D-aspartate receptor-2A, -2B and -2C expression was detected over cells in the lateral and medial superior olive, the medial, lateral and ventral nucleus of the trapezoid body, and the superior paraolivary nucleus. N-Methyl-D-aspartate receptor-2D expression was only observed in the lateral superior olive, lateral nucleus of the trapezoid body and ventral nucleus of the trapezoid body. Three distinct patterns of labeling were observed. The lateral superior olive and ventral nucleus of the trapezoid body showed higher expression of N-methyl-D-aspartate receptor-2A and -2C than other subunits; the medial nucleus of the trapezoid body showed higher N-methyl-D-aspartate receptor-2B expression than other subunits; and the medial superior olive, superior paraolivary nucleus and ventral nucleus of the trapezoid body showed relatively equivalent expression of N-methyl-D-aspartate receptor-2A, -2B and -2C subunits. N-Methyl-D-aspartate receptor-2D had the lowest expression, with levels greater than background in only the lateral superior olive, ventral nucleus of the trapezoid body and lateral nucleus of the trapezoid body. Immunocytochemistry using antibodies to N-methyl-D-aspartate receptor-2A, -2B and -2C showed immunolabeling consistent with in situ hybridization results. These results show diversity in expression of N-methyl-D-aspartate receptor-2 subunits in different superior olivary complex regions and would predict pharmacological differences.