DISTRIBUTION OF NON-NMDA GLUTAMATE-RECEPTOR MESSENGER-RNAS IN THE DEVELOPING RAT COCHLEA

In situ hybridization was used to document the distribution of mRNA en coding six subunit isoforms of non-N-methyl D-aspartic acid (NMDA) glu tamate receptors (GluR1, GluR2, GluR3, GluR4, GluR5 and GluR6) in the inner ears of embryonic, postnatal and adult rats. GluR2 and GluR3 exp ression in the spiral ganglion appeared well before birth, and reached adult levels several days before the onset of function in the cochlea . In the spiral limbus, expression of GluR2 and GluR3 mRNA reached ver y high levels at around the time of birth, then declined after a few d ays. Low levels of GluR1, GluR4 and GluR6 expression were detected in various tissues of the cochlea during development. In the adult cochle a, GluR expression was limited to GluR2 and GluR3 mRNAs in the spiral ganglion neurons and GluR2 mRNA in fibrocytes of the spiral limbus, a non-neural tissue. The ontogenetic expression of additional GluR subun it genes and their appearance in different cochlear tissues could refl ect different roles for these genes during development, or less precis e regulation of gene expression within the GluR family. In particular, the very high levels of GluR gene expression in the spiral limbus dur ing the perinatal period support a non-neural function, perhaps as cel l surface receptors during tissue differentiation. (C) 1995 Wiley-Liss , Inc.