Parvalbumin-Expressing Interneurons Linearly Control Olfactory Bulb Output

• PV cells form dense reciprocal connections with most neighboring principal cells
• PV cells show much broader odor-tuning properties compared to mitral or granule cells
• Increase in respiration even without odors is a strong driver of PV cell activity
• Inactivation experiments suggest that PV cells linearly control olfactory bulb output

SummaryIn the olfactory bulb, odor representations by principal mitral cells are modulated by local inhibitory circuits. While dendrodendritic synapses between mitral and granule cells are typically thought to be a major source of this modulation, the contributions of other inhibitory neurons remain unclear. Here we demonstrate the functional properties of olfactory bulb parvalbumin-expressing interneurons (PV cells) and identify their important role in odor coding. Using paired recordings, we find that PV cells form reciprocal connections with the majority of nearby mitral cells, in contrast to the sparse connectivity between mitral and granule cells. In vivo calcium imaging in awake mice reveals that PV cells are broadly tuned to odors. Furthermore, selective PV cell inactivation enhances mitral cell responses in a linear fashion while maintaining mitral cell odor preferences. Thus, dense connections between mitral and PV cells underlie an inhibitory circuit poised to modulate the gain of olfactory bulb output.