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Neuronal integration in the adult mouse olfactory bulb is a non-selective addition process.

ABSTRACT: Adult neurogenesis in the olfactory bulb (OB) is considered as a competition in which neurons scramble during a critical selection period for integration and survival. Moreover, newborn neurons are thought to replace pre-existing ones that die. Despite indirect evidence supporting this model, systematic in vivo observations are still scarce. We used two-photon in vivo imaging to study neuronal integration and survival. We show that loss of new neurons in the OB after arrival at terminal positions occurs only at low levels. Moreover, long-term observations showed that no substantial cell death occurred at later stages. Neuronal death was induced by standard doses of thymidine analogs, but disappeared when low doses were used. Finally, we demonstrate that the OB grows throughout life. This shows that neuronal selection during OB-neurogenesis does not occur after neurons reached stable positions. Moreover, this suggests that OB neurogenesis does not represent neuronal turnover but lifelong neuronal addition.

SUBMITTER: Platel JC

PROVIDER: S-EPMC6634973 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Neuronal integration in the adult mouse olfactory bulb is a non-selective addition process.

Platel Jean-Claude JC Angelova Alexandra A Bugeon Stephane S Wallace Jenelle J Ganay Thibault T Chudotvorova Ilona I Deloulme Jean-Christophe JC Béclin Christophe C Tiveron Marie-Catherine MC Coré Nathalie N Murthy Venkatesh N VN Cremer Harold H

eLife 20190711

Adult neurogenesis in the olfactory bulb (OB) is considered as a competition in which neurons scramble during a critical selection period for integration and survival. Moreover, newborn neurons are thought to replace pre-existing ones that die. Despite indirect evidence supporting this model, systematic in vivo observations are still scarce. We used two-photon in vivo imaging to study neuronal integration and survival. We show that loss of new neurons in the OB after arrival at terminal position ...[more]

PMID: 31294694

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Project description:Neurogenesis in the adult brain is largely restricted to the subependymal zone (SVZ) of the lateral ventricle, olfactory bulb (OB) and the dentate subgranular zone, and survival of adult-born cells in the OB is influenced by factors including sensory experience. We examined, in mice, whether survival of adult-born cells is also regulated by the rate of precursor proliferation in the SVZ. Precursor proliferation was decreased by depleting the SVZ of dopamine after lesioning dopamine neurons in the substantia nigra compacta with 6-hydroxydopamine. Subsequently, we examined the effect of reduced SVZ proliferation on the generation, migration and survival of neuroblasts and mature adult-born cells in the SVZ, rostral migratory stream (RMS) and OB. Proliferating cells in the SVZ, measured by 5-bromo-2-deoxyuridine (BrdU) injected 2 hours prior to death or by immunoreactivity against Ki67, were reduced by 47% or 36%, respectively, 7 days after dopamine depletion, and by 29% or 31% 42 days after dopamine depletion, compared to sham-treated animals. Neuroblast generation in the SVZ and their migration along the RMS were not affected, neither 7 nor 42 days after the 6-hydroxydopamine injection, since the number of doublecortin-immunoreactive neuroblasts in the SVZ and RMS, as well as the number of neuronal nuclei-immunoreactive cells in the OB, were stable compared to control. However, survival analysis 15 days after 6-hydroxydopamine and 6 days after BrdU injections showed that the number of BrdU+ cells in the SVZ was 70% higher. Also, 42 days after 6-hydroxydopamine and 30 days after BrdU injections, we found an 82% increase in co-labeled BrdU+/?-aminobutyric acid-immunoreactive cell bodies in the granular cell layer, while double-labeled BrdU+/tyrosine hydroxylase-immunoreactive cell bodies in the glomerular layer increased by 148%. We conclude that the number of OB interneurons following reduced SVZ proliferation is maintained through an increased survival of adult-born precursor cells, neuroblasts and interneurons.

Project description:In this study, we demonstrate that insulin is produced not only in the mammalian pancreas but also in adult neuronal cells derived from hippocampus and olfactory bulb. Paracrine Wnt3 plays an essential role in promoting the active expression of insulin in both hippocampus and olfactory bulb-derived neural stem cells. Our analysis indicates that the balance between Wnt3, which triggers the expression of insulin via NeuroD1 transcription factor, and IGFBP-4, which inhibits the original Wnt3 action, is regulated depending on the diabetic status. We also show that adult neural progenitors derived from diabetic animals retain the ability to give rise to insulin-producing cells and that grafting neuronal progenitors into the pancreas of diabetic animals reduces glucose levels. This study provides an example of a simple and direct use of adult stem cells from one organ to another, without introducing additional inductive genes. In this study, we demonstrate that insulin is produced not only in the mammalian pancreas but also in adult neuronal cells derived from hippocampus and olfactory bulb. Paracrine Wnt3 plays an essential role in promoting the active expression of insulin in both hippocampus and olfactory bulb-derived neural stem cells. Our analysis indicates that the balance between Wnt3, which triggers the expression of insulin via NeuroD1 transcription factor, and IGFBP-4, which inhibits the original Wnt3 action, is regulated depending on the diabetic status. We also show that adult neural progenitors derived from diabetic animals retain the ability to give rise to insulin-producing cells and that grafting neuronal progenitors into the pancreas of diabetic animals reduces glucose levels. This study provides an example of a simple and direct use of adult stem cells from one organ to another, without introducing additional inductive genes. Total four different samples, gene expressions in hippocampal derived neural stem cells (HPC NSC), that in Olfactory bulb-derived neural stem cells (OB NSC), that in neurons derived from the HPC NSCs (HPC Neu) and that in neurons derived from the OB NSCs (OB Neu) were independently analyzed. Three independent experiments were performed to prepare each cell sample, and the extracted total RNAs from each cell source were mixed to apply following microarray analysis (Four independent RNA sample; HPC NSC, OB NSC, HPC Neu and OB Neu).

Dataset Information

Neuronal integration in the adult mouse olfactory bulb is a non-selective addition process.

Publications

Neuronal integration in the adult mouse olfactory bulb is a non-selective addition process.

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