Oscillations, bursting, and resonance have been linked to synchronization of neuronal activity and to the emergence of brain rhythms. Using simultaneous whole-cell recording from pairs of juxtaglomerular (JG) olfactory bulb neurons, we were the first to discover that membrane potential oscillations and spontaneous bursting activity are highly correlated in external tufted (ET) cells associated with the same glomeruli. This synchronous activity occurs at theta frequency (2-7 Hz), the same frequency that characterizes investigative sniffing in rodents. Synchronous ET cell bursting may play an important role in olfactory coding and in regulating the induction of synaptic plasticity at the first input stage of the main olfactory bulb. We have further found that synchronous activity among bursting neurons persists in the presence of blockers of fast glutamatergic and GABAergic synaptic transmission. These findings suggest that synchrony could be mediated by slowly acting neurotransmitters and/or by non-synaptic interactions such as gap junctions that interconnect ET cells. Synchronously active ET cells could, in turn, via synaptic interactions synchronize other JG neurons, as well as mitral cells, the major output neurons of the olfactory bulb. This project will assess the functional roles of synaptic and non-synaptic interactions in establishing synchronous activity among electrophysiologically and morphologically characterized JG neurons. Further, it will investigate the functional significance of synchronous bursting by analyzing short-term facilitation of excitatory postsynaptic potentials that are evoked by ET cell bursts in periglomerular and short axon cells of the same glomerulus. This would support the idea that glomerular interneurons that are postsynaptic to ET cells, may act as coincident input detectors, firing optimally upon receiving synchronous bursting input. Taken together, these experiments will provide important, new insight into the intrinsic synaptic organization of the glomeruli and the role of glomerular circuitry in olfactory coding.
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