Odour adaptation allows organisms to acclimate to their environment whilst remaining sensitive to changes in the odour landscape. The neural mechanisms underlying odour adaptation and whether this occurs in the olfactory bulb has not been thoroughly explored. Input to the olfactory bulb is provided by olfactory receptor neurons, which arrange themselves into functional units (glomeruli) based upon the receptor they express, and transmit sensory information to a pool of output neurons, the mitral/tufted cells. Olfactory receptor neurons receive feedback inhibition onto their axon terminals from periglomerular cells, while mitral/tufted cells are subject to feedback, feedforward and lateral inhibition via the dendrodendritic connections they form with periglomerular cells and deeply situated granule cells. 

We used two-photon imaging to measure the glomerular activity of olfactory receptor neurons, mitral/tufted cells and periglomerular cells in anaesthetised mice, in response to 3s and 60s odour stimuli across concentrations spanning five orders of magnitude. We find that both the extent and the rate of adaptation varies widely across dorsal glomeruli (n=14, 125 glomeruli). Fast and slow adaptation was observed; slower adapting responses had time constants of seconds to over a minute (34.6% of observed responses), whereas fast adapting responses with time constants 10 s after odour presentation (45.9% of observed responses from 48 glomeruli, n=5). In contrast, olfactory receptor neuron terminals and periglomerular responses were more homogenous and responses generally terminated at odour offset (with only 16.6% [73 glomeruli, n=7] and 8.3% [11 glomeruli, n=2] of responses exhibiting odour after-effects, respectively). We can provide a comprehensive view of odour adaptation across the different circuit components of the olfactory bulb; experiments exploring the role of inhibition are ongoing.