In situ hybridization of antisense mRNA oligonucleotides for AMPA, NMDA and metabotropic glutamate receptor subtypes in the rat suprachiasmatic nucleus at different phases of the circadian cycle.

Eleven oligonucleotides directed against mRNA for AMPA, NMDA and metabotropic glutamate receptor subtypes were hybridized to rat coronal brain sections containing the suprachiasmatic nucleus (SCN). These oligonucleotides were hybridized to tissue samples collected at midday and midnight phases of the circadian cycle. Glutamate receptor mRNA for the AMPA subunits GluR1, GluR2 and GluR4, and the NMDA receptor subtype NMDAR1, were heavily expressed in the SCN and surrounding areas. The mRNA for the metabotropic glutamate subunit mGluR1 was only lightly expressed in the SCN. In contrast, mRNA for NMDAR2A, NMDAR2B, NMDAR2C and GluR3 was not detected in the SCN. The mRNA found to be expressed in the rat SCN was similar in samples collected at midday and midnight, suggesting no circadian variation in endogenous SCN glutamate receptors at these two times of the light-dark cycle.