Tufted cell dendrodendritic inhibition in the olfactory bulb is dependent on NMDA receptor activity

Mitral and tufted cells constitute the primary output cells of the olfactor y bulb. While tufted cells are often considered as "displaced" mitral cells , their actual role in olfactory bulb processing has been little explored. We examined dendrodendritic inhibition between tufted cells and interneuron s using whole cell voltage-clamp recording. Dendrodendritic inhibitory post synaptic currents (IPSCs) generated by depolarizing voltage steps in tufted cells were completely blocked by the N-methyl-D-aspartate (NMDA) receptor antagonist D, L-2-amino-5-phosphonopentanoic acid (D,L-AP5), whereas the al pha -amino-3-hdroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor anta gonist 2-3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f] quinoxaline-7-sulfonami de (NBQX) had no effect. Tufted cells in the external plexiform layer (EPL) and in the periglomerular region (PGR) showed similar behavior. These resu lts indicate that NMDA receptor-mediated excitation of interneurons drives inhibition of tufted cells at dendrodendritic synapses as it does in mitral cells. However, the spatial extent of lateral inhibition in tufted cells w as much more limited than in mitral cells. We suggest that the sphere of in fluence of tufted cells, while qualitatively similar to mitral cells, is ce ntered on only one or a few glomeruli.