Heterogeneity of bulbar dopaminergic cells
Thu-P1-021
Presented by: Ailie G McWhinnie
Dopaminergic (DA) neurons in the murine olfactory bulb (OB) control the gain of the first olfactory synapse. They are known for adult neurogenesis, but recent work found that a subset of them cannot regenerate. These, unlike the anaxonic DA cells born throughout life, have an axon. Further differences in soma size, dendritic branching, excitability, odour tuning and plasticity suggest different roles in the OB.
Their connectivity is still unknown, so we began studying this using rabies tracing. By timing the floxed starter virus injection in a DAT-Cre mouse – embryo lateral ventricles, or adult rostral migratory stream – and waiting respectively 6 or 2 months before delivering rabies to the OB, we attempted to differentially trace the two subtypes. To validate, we checked DA identity of starter cells (cells infected by starter and rabies virus) by staining for tyrosine hydroxylase and used soma area as a proxy for subtype classification (axon-bearing cells >=100μm2).
Embryonic-injected brains (n=6) showed a mixed traced population of axon-bearing and anaxonic DA cells. Although there was a soma size difference between embryonic- and adult-injected brains (means 69.7μm2 and 48.5μm2 respectively, p=0.0002), this was due to high variability in embryonic-injected brains (range 8 - 198μm2, SD = 33.19) rather than consistently larger cell sizes. This indicated that anaxonic cells born in the embryo had survived the six-month window between starter and rabies injection, contrasting previous findings of their short lifespan.
If a mixed population has been traced, the pre-synaptic partners will nonetheless enlighten general DA connectivity in the OB which is thus far undefined. This could guide future physiological approaches to connectivity in the future, in which subtypes can be more clearly defined.
Funding: PDN-Wolfson College PhD Studentship (AGM), BBSRC and ERC (MSG), Royal Society, Isaac Newton Trust, Wellcome Trust and University of Cambridge (EG).
Their connectivity is still unknown, so we began studying this using rabies tracing. By timing the floxed starter virus injection in a DAT-Cre mouse – embryo lateral ventricles, or adult rostral migratory stream – and waiting respectively 6 or 2 months before delivering rabies to the OB, we attempted to differentially trace the two subtypes. To validate, we checked DA identity of starter cells (cells infected by starter and rabies virus) by staining for tyrosine hydroxylase and used soma area as a proxy for subtype classification (axon-bearing cells >=100μm2).
Embryonic-injected brains (n=6) showed a mixed traced population of axon-bearing and anaxonic DA cells. Although there was a soma size difference between embryonic- and adult-injected brains (means 69.7μm2 and 48.5μm2 respectively, p=0.0002), this was due to high variability in embryonic-injected brains (range 8 - 198μm2, SD = 33.19) rather than consistently larger cell sizes. This indicated that anaxonic cells born in the embryo had survived the six-month window between starter and rabies injection, contrasting previous findings of their short lifespan.
If a mixed population has been traced, the pre-synaptic partners will nonetheless enlighten general DA connectivity in the OB which is thus far undefined. This could guide future physiological approaches to connectivity in the future, in which subtypes can be more clearly defined.
Funding: PDN-Wolfson College PhD Studentship (AGM), BBSRC and ERC (MSG), Royal Society, Isaac Newton Trust, Wellcome Trust and University of Cambridge (EG).