In situ hybridization analysis of flip/flop splice variants of AMPA-type glutamate receptor subunits in the rat parabrachial and Kölliker-Fuse nuclei.

The aim of the present study was to analyze the occurrence and distribution of flip/flop splice variants of AMPA-type glutamate receptors (GluRA-D) in the rat parabrachial and Kölliker-Fuse nuclei (PB/KF). We performed in situ hybridization experiments on sections through different rostro-caudal levels of the PB/KF and analyzed the subunit expression semiquantitatively by means of grain counts for each probe in eight PB nuclei and in the KF. Our experiments revealed that the splice variants of the AMPA receptor subunit mRNAs are expressed differentially in the distinct nuclei of the PB/KF. The flip splice variants were predominantly expressed (GluRB-D flip) while the flop splice variants (GluRA flop and C flop) were expressed considerably weaker. Within the PB/KF, several nuclei expressed transcripts of GluRB flip (superior, central, dorsal, external, and ventral lateral PB, waist area, medial PB, KF) and GluRC flip (internal, superior, central, dorsal, external, and ventral lateral PB, waist area, KF). GluRB transcripts were not found in neurons of the internal lateral PB and in only 50% of the neurons in the KF. A more restricted expression in the PB/KF was observed for the GluRD flip (internal lateral PB), GluRA flop (medial PB, KF) and GluRC flop mRNA (superior lateral PB, KF). The present data demonstrate that the nuclei of the PB/KF show a differential expression of AMPA receptor subunits. This suggests that the anatomically and functionally distinct nuclei might make use of AMPA-type glutamate receptors with different physiological properties and ion selectivities.