Localisation of 3H-GABA in the rat olfactory bulb: an in vivo and in vitro autoradiographic study.

In an attempt to further clarify the localisation of GABAergic elements in the olfactory bulb we have performed, in vivo and in vitro, autoradiographic studies with 3H-GABA (gamma-amino butyric acid) and 3H-DABA (L-2,4 diamino butyric acid). The results have shown a strong labelling with 3H-GABA of the glial cells in all the layers of the olfactory bulb. A high concentration of grains was observed in the periglomerular region. The labelling in the external plexiform layer was uniformly distributed in the neuropile with the strongest activity at the level of the dendritic processes of the granule cells, leaving the mitral cell dendrites and cell bodies almost free of grains. 3H-DABA showed a very similar pattern to 3H-GABA. When olfactory bulb slices were preincubated with beta-alanine the labelling of the glial elements almost disappeared especially at the level of the olfactory nerve layer. The labelling pattern of the other layers of the bulb remained mostly unchanged. This supports the view that a population of periglomerular and granule cells are GABAergic and that beta-alanine competes with GABA uptake sites only in glial cells.