Parvalbumin-containing interneurons do not innervate granule cells in the olfactory bulb

Combining pre-embedding parvalbumin immunostaining and post-embedding immun ogold detection of GABA in the olfactory bulb, we investigated whether the parvalbumin-containing GABAergic interneurons of the external plexiform lay er exclusively innervate principal cells, or whether they also establish in hibitory synapses upon GABAergic local neurons such as granule cells. Our r esults demonstrate that the parvalbumin-containing cells do not contact GAB Aergic interneurons in the neuropil of the external plexiform layer. On the contrary, their postsynaptic elements were always non-GABAergic principal cells. Although classically it has been accepted that the interneurons of t he external plexiform layer could exert a disinhibitory action upon princip al cells, via inhibition of GABAergic granule cells, we conclude that they exert a feedback inhibitory action directly and exclusively upon principal cells. NeuroReport 12:2553-2556 (C) 2001 Lippincott Williams & Wilkins.