GABA, GABA TRANSPORTERS, GABA(A) RECEPTOR SUBUNITS, AND GAD MESSENGER-RNAS IN THE RAT PARABRACHIAL AND KOLLIKER-FUSE NUCLEI

In the present study, we investigated the key molecules that determine gamma-aminobutyric acid (GABA)ergic signal transduction in the parabr achial/kolliker-Fuse complex (PB/KF) by means of immunocytochemistry a nd in situ hybridization. Our data demonstrate a dense plexus of GABA- immunoreactive (-ir) varicosities throughout the nuclei of the PB and the KF. The number of neurons expressing GAD65 or GAD67 mRNA was fairl y low in the PB, whereas caudally in the KF an accumulation of CAD-exp ressing neurons was observed. The GABA transporter-3 (GAT-3) was detec ted in all parts of the PB/KF, whereas immunolabeling for GAT1 was not observed. All nuclei of the PB and the KF exhibited immunoreactivity for the gamma 2-, alpha 2-, and alpha 3-subunits of the GABA(A) recept or. gamma 2-ir was strong and similar in all PB/KF nuclei. In contrast , alpha 2-labeling was particularly intense in the superior lateral PB , and alpha 3-labeling was most prominent in the external lateral and external medial PB, compared with the remaining nuclei. With respect t o the subcellular localization, we found gamma 2-ir in cell bodies and higher order dendrites, whereas alpha 2- and alpha 3-ir was predomina ntly found in cell bodies. Immunolabeling for the beta 2/3- and the al pha 1-subunit was seen in cell bodies and presumed dendritic profiles. The staining intensity was strongest in the dorsal lateral PB. Most i mportantly, the external lateral PB and the waist area were totally de void of beta 2/3- and alpha 1-ir. Our data suggest that neural process ing in the PB/KF is under a strong GABAergic inhibition that is appare ntly mediated by different types of GABA(A) receptors in functionally different pathways through the PB/KF. (C) 1998 Wiley-Liss, Inc.