Abstract
In many sensory systems, different sensory features are transmitted in parallel by several different types of output neurons. In the mouse olfactory bulb, there are only two output neuron types, the mitral and tufted cells (M/T), which receive similar odor inputs, but they are believed to transmit different odor characteristics. How these two neuron types deliver different odor information is unclear. Here, by combining electrophysiology and optogenetics, it is shown that distinct inhibitory networks modulate M/T cell responses differently. Overall strong lateral inhibition was scarce, with most neurons receiving lateral inhibition from a handful of unorganized surrounding glomeruli (~5% on average). However, there was a considerable variability between different neuron types in the strength and frequency of lateral inhibition. Strong lateral inhibition was mostly found in neurons locked to the first half of the respiration cycle. In contrast, weak inhibition arriving from many surrounding glomeruli was relatively more common in neurons locked to the late phase of the respiration cycle. Proximal neurons could receive different levels of inhibition. These results suggest that there is considerable diversity in the way M/T cells process odors so that even neurons that receive the same odor input transmit different odor information to the cortex.
Highlights
In many sensory systems, sensory information is processed locally and transmitted to higher cortical regions in parallel by different cell types
In the mammalian olfactory bulb (OB), mitral and tufted cells (M/T) cells receive their main excitatory input from one glomerulus via their apical dendrite and can receive inhibitory input from several surrounding interneurons in the glomerular, granular and the external plexiform layers[7,8,9,10,11,12,13,14,15,16,17]. These lateral inhibition circuits can modulate M/T cell odor responses so that each cell type carries a different component of the odor stimulus that reflects the response of its main glomerulus and the surrounding glomeruli that responded to the odor
We found that M/T cells can be divided into at least three functional groups based on the amount and strength of lateral inhibition they receive
Summary
Sensory information is processed locally and transmitted to higher cortical regions in parallel by different cell types. Despite extensive research in this field, these parameters are not fully known It is currently unknown how many surrounding glomeruli each M/T cell receives inhibitory inputs from, and whether each of these connections is strong enough to change the neuron’s activity. It remains unclear whether all projection neurons receive lateral inhibition and whether there are differences in the level of lateral inhibition between cell types. To date there is no direct estimation of the amount, frequency and spatial extent of lateral inhibition in the olfactory bulb in-vivo
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