Ex Vivo Functional Characterization of Mouse Olfactory Bulb Projection Neurons Reveals a Heterogeneous Continuum

Area of Science:

• Neuroscience
• Olfactory System Research
• Cellular Electrophysiology

Background:

• Mitral cells (MCs) and tufted cells (TCs) are key olfactory bulb projection neurons.
• Traditionally classified by size and location, recent in vivo studies suggest parallel channel functions.
• Ex vivo studies often group them as mitral/tufted, potentially overlooking heterogeneity.

Purpose of the Study:

• To reconcile in vivo and ex vivo findings on olfactory bulb projection neurons.
• To investigate if soma size can classify these neurons based on physiological properties.
• To understand the functional heterogeneity within mitral cells and tufted cells.

Main Methods:

• Immunohistochemistry in adult mice.
• Whole-cell patch-clamp electrophysiology on fixed and acute brain slices.
• Analysis of passive and intrinsic firing properties.

Main Results:

• No clear electrophysiological separation between mitral cells and tufted cells was found.
• A heterogeneous continuum of properties was observed, with three loosely clustered subgroups.
• Tufted cells in the EPL and putative tufted/mitral cells in the ML showed distinct groupings.

Conclusions:

• Olfactory bulb projection neurons exhibit significant functional heterogeneity.
• A soma size-based classification is insufficient to distinguish mitral cells and tufted cells.
• This heterogeneity may be crucial for decoding complex olfactory information in the olfactory bulb.