Long-lasting depolarizations in mitral cells of the rat olfactory bulb

We investigated the mechanisms of long-lasting depolarizing potentials (LLD s) generated in mitral cells with whole-cell patch recordings in the rat ol factory bulb slice. LLDs occur spontaneously and are evoked by either ortho dromic stimulation of the olfactory nerve or antidromic stimulation of mitr al and tufted (M/T) cells. LLDs are followed by a long refractory period, l imiting LLD generation to similar to 1 Hz. LLD production does not appear t o involve either intrinsic voltage-activated or metabotropic mechanisms. Th e initiation of LLDs requires activation of non-NMDA but not NMDA receptors . Dual recordings from the apical dendrites and somata of mitral cells show that LLDs are generated in the distal portion of the apical dendrite, most likely in the glomerulus. The rising phase of LLDs shows characteristics o f polyneuronal input, including a high variability and sensitivity to charg e screening. Paired recordings from adjacent mitral cells suggest that LLDs occur synchronously only in cells whose apical dendrites ramify in the sam e glomerulus. These findings suggest that LLDs involve recurrent, intraglom erular dendrodendritic interactions among M/T cells.