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| Local Circuit Function in the Olfactory Bulb |
| Ben Strowbridge Case Western Reserve Univ, Cleveland, OH, United States |
The olfactory bulb serves as a relay region for sensory information transduced by receptor neurons in the nose and ultimately routed to a variety of cortical areas. While the molecular organization of different olfactory sensory inputs in this region has been well described, understanding how synaptic inputs interact to generate an efficient output code for specific odors remains challenging. Unlike principal cells, which receive glutamatergic input from one class of sensory neuron, GABAergic interneurons, like granule cells, integrate excitatory inputs from many different sensory modules. And unlike most CNS neurons, granule cells lack an axon and instead generate postsynaptic output onto principal cells via reciprocal dendrodendritic synapses that were first described by Gordon Shepherd and colleagues in the 1960s. Through their dendritic connections with mitral and other principal cells, GABAergic granule cells sculpt the output of the olfactory bulb and facilitate odor discrimination. Less is known about how granule cell interneurons are activated during sensory processing. Our group recently reported the first paired intracellular recordings of dendrodendritic excitation between glutamatergic mitral cells and granule cell dendrites. Surprisingly, we also found both spontaneous and evoked excitatory postsynaptic potentials in granule cells that are far larger and faster than dendrodendritic inputs, suggesting that granule cells may be excited by two distinct glutamatergic local circuits. Using computational simulations, we show that the large, non-dendrodendritic EPSPs more reliably encode the duration of principal cell discharges than dendrodendritic EPSPs. Together these excitatory pathways determine much of the timing of the local inhibitory synaptic responses that shape the output of the olfactory bulb. |