Synaptic transmission between dendrites in the olfactory bulb is thoug
ht to play a major role in the processing of olfactory information. Gl
utamate released from mitral cell dendrites excites the dendrites of g
ranule cells, which in turn mediate GABAergic dendrodendritic inhibiti
on back onto mitral dendrites. We examined the mechanisms governing re
ciprocal dendritic transmission in rat olfactory bulb slices. We find
that NMDA receptors play a critical role in this dendrodendritic inhib
ition. As with axenic synapses, the dendritic release of fast neurotra
nsmitters relies on N- and P/Q-type calcium channels. The magnitude of
dendrodendritic transmission is directly proportional to dendritic ca
lcium influx. Furthermore, recordings from pairs of mitral cells show
that dendrodendritic synapses can mediate lateral inhibition independe
ntly of axonal action potentials.