LOCALIZATION OF MESSENGER-RNAS ENCODING 3 GABA TRANSPORTERS IN RAT-BRAIN - AN IN-SITU HYBRIDIZATION STUDY

Localization of the messenger RNAs encoding three gamma-aminobutyric a cid (GABA) transporters, termed GAT-1, GAT-2, and GAT-3, has been carr ied out in rat brain using radiolabeled oligonucleotide probes and in situ hybridization histochemistry. Hybridization signals for GAT-1 mRN A were observed over many regions of the rat brain, including the reti na, olfactory bulb, neocortex, ventral pallidum, hippocampus, and cere bellum. At the microscopic level, this signal appeared to be restricte d to neuronal profiles, and the overall distribution of GAT-1 mRNA clo sely paralleled that seen in other studies with antibodies to GABA. Ar eas containing hybridization signals for GAT-S mRNA included the retin a, olfactory bulb, subfornical organ, hypothalamus, midline thalamus, and brainstem. In some regions, the hybridization signal for GAT-S see med to be preferentially distributed over glial cells, although hybrid ization signals were also observed over neurons, particularly in the r etina and olfactory bulb. Notably, hybridization signal for GAT-S mRNA was absent from the neocortex and cerebellar cortex, and was very wea k in the hippocampus. In contrast to the parenchymal localization obta ined for GAT-I and GAT-3 mRNAs, hybridization signals for GAT-2 mRNA w ere found only over the leptomeninges (pia and arachnoid). The differe ntial distribution of the three GABA transporters described here sugge sts that while each plays a role in GABA uptake, they do so via distin ct cellular populations.