Expression of the small GTP-binding protein Rab3A in the adult rat brain.

The ras-related rab genes code for small GTP-binding proteins that are thought to control intracellular membrane trafficking. Some of the rab proteins are localized to the membrane of specific subcellular organelles, and rab3A is associated with small synaptic vesicles. We have studied rab3A mRNA expression in the adult rat brain by in situ hybridization. In the forebrain, rab3A mRNAs were mostly detected in neocortical and limbic areas such as hippocampus, enthorinal cortex, or rhinencephalic nuclei, while no significant labeling was observed in the striatum, in the hypothalamus, or in several thalamic nuclei. Rab3A expression does not directly correspond to any known neurotransmitter expression pattern nor is it completely superimposable to the pattern of expression of other synaptic vesicle proteins. These results show that rab3A is expressed and thus exerts its function in a subset of neurons in the brain.