Improved Separation of Odor Responses in Granule Cells of the Olfactory Bulb During Odor Discrimination Learning

Abstract

In the olfactory bulb, olfactory information is translated into ensemble representations by mitral/tufted cells, and these representations change dynamically in a contextdependent manner. In particular, odor representations in mitral/tufted cells display pattern separation during odor discrimination learning. Although granule cells provide major inhibitory input to mitral/tufted cells and play an important role in pattern separation and olfactory learning, the dynamics of odor responses in granule cells during odor discrimination learning remain largely unknown. Here, we studied odor responses in granule cells of the olfactory bulb using fiber photometry recordings in awake behaving mice. We found that odors evoked reliable, excitatory responses in the granule cell population. Intriguingly, during odor discrimination learning, odor responses in granule cells exhibited improved separation and contained information about odor value. In conclusion, we show that granule cells in the olfactory bulb display learning-related plasticity, suggesting that they may mediate pattern separation in mitral/tufted cells.

VIP interneurons regulate olfactory bulb output and contribute to odor detection and discrimination

“…Fiber photometry was performed using a previously described system (Wang et al, 2019(Wang et al, , 2020a(Wang et al, , 2020bWu et al, 2020a). To record fluorescent signals, the beam from a 488-nm laser (OBIS 488LS, Coherent) was reflected by a dichroic mirror (MD498, Thorlabs), focused by an objective lens (10 3, NA: 0.3; Olympus), and then coupled to an optical commutator (Doric Lenses).…”

“…Odor delivery for fiber photometry and in vivo electrophysiology recordings Odors were dissolved in mineral oil at 1% (v/v) dilution. Similar to our previous studies (Wang et al, 2019(Wang et al, , 2020a, eight odors were used: isoamyl acetate, 2-heptanone, phenyl acetate, benzaldehyde, dimethylbutyric acid, n-heptane acid, n-pentanol, and 2-pentanone (Sinopharm Chemical Reagent). Odors were presented by an odor delivery system.…”

Long-range GABAergic projections contribute to cortical feedback control of sensory processing

“…We next investigated the impact of GABAergic feedback stimulation on odor-evoked activity in the GCL. Odor stimulation induced a strong population response in GCL neurons 35 (Fig. 4c ).…”

Long-range GABAergic projections contribute to cortical feedback control of sensory processing

“…We next investigated the impact of GABAergic feedback stimulation on odor-evoked activity in the GCL. Odor stimulation induced a strong population response in GCL neurons (Wang et al, 2020) (Fig. 4c).…”

“…Glutamatergic feedback projections from the AOC target virtually all types of neurons in the OB and induce robust disynaptic inhibition onto MCs and TCs (Boyd et al, 2012; Markopoulos et al, 2012; Mazo et al, 2016; Nissant et al, 2009; Strowbridge, 2009). These reciprocal connections between the OB network and the AOC are important for proper oscillations in the OB (Kay, 2014; Martin et al, 2006), decorrelation of OB output activity (Otazu et al, 2015), inter-hemispheric coordination (Grobman et al, 2018) and modulate odor perception threshold (Soria-Gómez et al, 2014) and odor-association learning (Wang et al, 2020) in a context-dependent manner (Wu et al, 2020). The OB additionally receives external inputs from neuromodulatory systems.…”