Embryonic and postnatal neurogenesis produce functionally distinct subclasses of dopaminergic neuron

Brief sensory deprivation triggers cell type-specific structural and functional plasticity in olfactory bulb neurons

“…Soma size is a readily-obtainable proxy indicator for DA subtypes: anaxonic DA cells are usually small, while axonbearing DA cells tend to have very large somas. Using previously defined lower (<70 m 2 ) and upper (>99m 2 ) bounds of the OB DA soma size distribution (Galliano et al, 2018), we found that both small/putative anaxonic DA cells and large/putative axon-bearing DA cells from occluded mice display reduced cFos staining relative to their co-embedded control counterparts. Although the smaller sample size of the much rarer large DA cells accentuated variability across staining sets here, this effect was highly significant for both cell types in analyses that specifically account for that variation (small cells: Ctrl mean ± SEM 0.99 ± 0.03, Occl 0.56 ± 0.02; big cells: Ctrl mean ± SEM 1.11 ± 0.11, Occl 0.67 ± 0.07; for both, mixed model ANOVA nested on mouse, p<0.0001).…”

“…2) to show that 24 h naris occlusion strongly and reliably downregulates activity in both subclasses of OB DA interneurons. They also provide evidence for, to date, the fastest activity-dependent TH change observed in this cell class in vivo (Byrne, 2019) Anaxonic DA neurons do not modulate their intrinsic excitably following brief sensory deprivation The vast majority of DA neurons are anaxonic cells (Galliano et al, 2018), which by locally releasing GABA and dopamine in the glomerular layer help to control the overall gain of OSNM/TC transmission (McGann, 2013;Vaaga et al, 2017). Highly plastic, they retain the capability to regenerate throughout life (Bonzano et al, 2016;De Marchis et al, 2007;Galliano et al, 2018;Lledo et al, 2006).…”

“…Previous work from ourselves and others has found that bulbar DA neurons are a heterogeneous population (Chand et al, 2015;Galliano et al, 2018;Kosaka et al, 2019). Two non-overlapping subtypes can be identified by a spectrum of different morphological and functional characteristics, as well as by a binary classifier: the presence or absence of an axon and its key component, the axon initial segment (AIS) (Chand et al, 2015;Galliano et al, 2018). So, does brief unilateral naris occlusion downregulate activity in both axon-bearing and anaxonic DA subtypes?…”

“…This transgenic labelling approach produces red fluorescent tdT-positive glomerular layer cells that are ~75-85% co-labelled for TH ( Fig. 7A; (Byrne, 2019;Galliano et al, 2018;Vaaga et al, 2017)). The remaining tdT-positive/TH-negative nondopaminergic labelled OB neurons in these mice are of the calretinin-expressing OB interneuron class and can be readily identified by their unique physiological properties (Byrne, 2019;Pignatelli et al, 2005;Sanz Diez et al, 2019), so these were excluded from our analyses.…”

“…In our case this was achieved by unilaterally plugging a nostril for just one day, a minimally-invasive manipulation which effectively mimics the sensory disturbance associated with common respiratory infections without damaging the olfactory sensory epithelium (Fokkens et al, 2012). We found that such brief sensory deprivation produced structural and functional plasticity only in axon-bearing dopaminergic (DA) neurons in the bulb's glomerular layer (Chand et al, 2015;Galliano et al, 2018). By targeting excitability in one specialised dopaminergic subpopulation, experience-dependent plasticity in early olfactory networks might act to fine-tune sensory processing in the face of continually fluctuating inputs.…”