Early Odorant Exposure Increases the Number of Mitral and Tufted Cells Associated with a Single Glomerulus

Abstract

The highly specific organization of the olfactory bulb (OB) is well known, but the impact of early odorant experience on its circuit structure is unclear. Olfactory sensory neurons (OSNs) project axons from the olfactory epithelium to the OB, where they form spherical neuropil structures called glomeruli. These glomeruli and the postsynaptic targets of OSNs, including mitral and tufted cells (M/TCs) and juxtaglomerular cells, form glomerular modules, which represent the basic odor-coding units of the OB. Here, we labeled M/TCs within a single glomerular module of the mouse OB and show that odorant exposure that starts prenatally and continues through postnatal day 25 has a major impact on the structure of the glomerular module. We confirm that exposure increases the volume of the activated glomeruli and show that exposure increases M/TC number by Ͼ40% in a glomerulus-specific fashion. Given the role of M/TCs in OB output and in lateral inhibition, increasing the number of M/TCs connected to a single glomerulus may also increase the influence of that glomerulus on the OB network and on OB output. Our results show that early odorant exposure has a profound effect on OB connectivity and thus may affect odorant processing significantly.

Dendritic integration in olfactory bulb granule cells: Thresholds for lateral inhibition and role of active conductances upon simultaneous activation

“…The low threshold spine number seems to match previous observations that 367 uniglomerular stimulation can already fire GCs (Egger, 2008;Schoppa et al, 1998;Geramita et 368 al., 2016). On the other hand, ∼20 MC/TCs belong to a glomerular column, with a slight lower 369 share of TCs (Panhuber et al, 1985;Liu et al, 2016;Royet et al, 1998). The release probability 370 at these inputs is ∼0.5 (Egger et al, 2005) and thus for uniglomerular activation a given GC is 371 unlikely to be fired solely from intracolumnar dendrodendritic inputs, requiring additional 372 activation most likely originating from MC/TC axonal collaterals (Schoppa, 2006a).…”

Lineage does not regulate the connectivity of projection neurons in the mouse olfactory bulb

“…Based on this observation, it seems unlikely that sister M/T cells would have apical dendrites projecting into the same glomerulus. Although improbable, this could still be possible because the soma of M/T cells innervating the same glomerulus may be separated from each out up to 450 µm (for M cells) and 350 µm (for T cells) (Liu et al, 2016). To investigate whether sister M/T cells receive synaptic input from the same glomerulus, we tracked their apical dendrites (Figure 4).…”

Mitf links neuronal activity and long-term homeostatic intrinsic plasticity

“…Interestingly, cell counts showed an increase of glomerular Tbr2+ neurons (t(20)=2.914, p=0.0171, Sidak multiple comparison) in the glomeruli of Mitf mutant mice (Figure 1d,e). An increase in M/T neurons has been shown to occur with increased activity [28,29]. Additionally, analysis of apoptosis showed a twofold increase in cell death in periglomerular cells of Mitf mutant mice (Suppl.…”