Cornichon homologues (CNIHs) were first described to be necessary for the secretion of growth factors controlling neuronal development and differentiation. More recently, however, they were defined in a different context: as an auxiliary subunit of the ionotropic glutamate receptors of the AMPA subtype (AMPAR), they modulate their biophysics and surface trafficking. In the present study, we have investigated the relative time course of CNIH-2 expression during CNS development compared to that of the AMPAR subunit GluA1. To this end, we chose five time points in rodent ontogeny from E18 until adult stage, selected three brain regions and investigated CNIH mRNA distribution and levels in cryo-sections of rat brain by in situ hybridization. In parallel, we monitored the CNIH and GluA1 protein expression level in total rat brain homogenates. We found that CNIH mRNA and protein were already abundantly present in late embryonic stage, they peaked in the first postnatal week and then decreased towards adulthood.GluA1 protein, however, increased steadily to reach maximum levels in adult stage. Thus, the developmental time course of GluA1 expression contrasts that of its auxiliary subunit CNIH-2. The most striking difference occurs in the early postnatal period, where the process of neuronal migration and patterning is almost completed. This suggests that CNIH might exert additional functions besides modulating GluA properties. Alternatively, the stoichiometry of GluA and its accessory subunit CNIH could vary in development.