Limits...
Adult neurogenesis and specific replacement of interneuron subtypes in the mouse main olfactory bulb.

Bagley J, LaRocca G, Jimenez DA, Urban NN - BMC Neurosci (2007)

Bottom Line: New neurons are generated in the adult brain from stem cells found in the subventricular zone (SVZ).Neuronal populations in these layers undergo turnover throughout life, but whether all neuronal subtypes found in these areas are replaced and when neurons begin to express subtype-specific markers is not known.We also show that many neurons in the glomerular layer do not express NeuN, but are readily and specifically labeled by the fluorescent nissl stain Neurotrace.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Science, Carnegie Mellon University, Pittsburgh, PA 15213, USA. bagleyjo@ninds.nih.gov

ABSTRACT

Background: New neurons are generated in the adult brain from stem cells found in the subventricular zone (SVZ). These cells proliferate in the SVZ, generating neuroblasts which then migrate to the main olfactory bulb (MOB), ending their migration in the glomerular layer (GLL) and the granule cell layer (GCL) of the MOB. Neuronal populations in these layers undergo turnover throughout life, but whether all neuronal subtypes found in these areas are replaced and when neurons begin to express subtype-specific markers is not known.

Results: Here we use BrdU injections and immunohistochemistry against (calretinin, calbindin, N-copein, tyrosine hydroxylase and GABA) and show that adult-generated neurons express markers of all major subtypes of neurons in the GLL and GCL. Moreover, the fractions of new neurons that express subtype-specific markers at 40 and 75 days post BrdU injection are very similar to the fractions of all neurons expressing these markers. We also show that many neurons in the glomerular layer do not express NeuN, but are readily and specifically labeled by the fluorescent nissl stain Neurotrace.

Conclusion: The expression of neuronal subtype-specific markers by new neurons in the GLL and GCL changes rapidly during the period from 14-40 days after BrdU injection before reaching adult levels. This period may represent a critical window for cell fate specification similar to that observed for neuronal survival.

Show MeSH
Adult born neurons express the neuron specific marker NT in the SVZ and proximal RMS 12 hours after the final BrdU injection. 40× images of sagittal sections through the olfactory bulb of SVZ showing BrdU (red) and NT (green). Co-localization is seen within the SVZ (A) and the proximal RMS (B). Scale bars, 37 μm. NT, NeuroTrace; SVZ, sub-ventricular zone; RMS, rostral migratory stream, BrdU, bromodeoxyuridine.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2238759&req=5

Figure 5: Adult born neurons express the neuron specific marker NT in the SVZ and proximal RMS 12 hours after the final BrdU injection. 40× images of sagittal sections through the olfactory bulb of SVZ showing BrdU (red) and NT (green). Co-localization is seen within the SVZ (A) and the proximal RMS (B). Scale bars, 37 μm. NT, NeuroTrace; SVZ, sub-ventricular zone; RMS, rostral migratory stream, BrdU, bromodeoxyuridine.

Mentions: NeuN is a marker of adult neurons that has been used previously to identify BrdU positive cells as neurons (as opposed to glia) [27]. However, certain cell types, notably cerebellar Purkinje cells and olfactory bulb mitral cells do not consistently stain for NeuN [27]. In initial studies, we observed that relatively few GLL cells seemed to express NeuN, consistent with a recent report [28]. Thus we compared the staining of NeuN and another potentially neuron-specific marker, the fluorescent Nissl stain Neuro Trace (NT). NT and NeuN both showed the same robust labeling in the GCL, but in the GLL many cells that were labeled by NT were not stained for NeuN, indicating that NeuN does not label all PG neurons (Fig. 5). Of the cells stained by NT, greater than 95% in the GCL and only 15% in the GLL also express NeuN. In contrast, all NeuN positive cells express NT. Based on these observations we further tested NT as a candidate label for the total population of neurons within the GCL and GLL of the MOB. Sections were stained with NT and for the glial marker S-100B to determine how specific NT staining was for neurons vs glia. We found that only about 2% (14/640) of NT labeled cells in the glomerular layer were also positive for S-100B. This is comparable to the fraction of NeuN positive cells that were identified as being S-100B positive in this same layer in tissue from the same animals (4/640). Similar fractional overlap was found for the granule cell layer (13/640 for NT and 1/640 for NeuN).


Adult neurogenesis and specific replacement of interneuron subtypes in the mouse main olfactory bulb.

Bagley J, LaRocca G, Jimenez DA, Urban NN - BMC Neurosci (2007)

Adult born neurons express the neuron specific marker NT in the SVZ and proximal RMS 12 hours after the final BrdU injection. 40× images of sagittal sections through the olfactory bulb of SVZ showing BrdU (red) and NT (green). Co-localization is seen within the SVZ (A) and the proximal RMS (B). Scale bars, 37 μm. NT, NeuroTrace; SVZ, sub-ventricular zone; RMS, rostral migratory stream, BrdU, bromodeoxyuridine.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2238759&req=5

Figure 5: Adult born neurons express the neuron specific marker NT in the SVZ and proximal RMS 12 hours after the final BrdU injection. 40× images of sagittal sections through the olfactory bulb of SVZ showing BrdU (red) and NT (green). Co-localization is seen within the SVZ (A) and the proximal RMS (B). Scale bars, 37 μm. NT, NeuroTrace; SVZ, sub-ventricular zone; RMS, rostral migratory stream, BrdU, bromodeoxyuridine.
Mentions: NeuN is a marker of adult neurons that has been used previously to identify BrdU positive cells as neurons (as opposed to glia) [27]. However, certain cell types, notably cerebellar Purkinje cells and olfactory bulb mitral cells do not consistently stain for NeuN [27]. In initial studies, we observed that relatively few GLL cells seemed to express NeuN, consistent with a recent report [28]. Thus we compared the staining of NeuN and another potentially neuron-specific marker, the fluorescent Nissl stain Neuro Trace (NT). NT and NeuN both showed the same robust labeling in the GCL, but in the GLL many cells that were labeled by NT were not stained for NeuN, indicating that NeuN does not label all PG neurons (Fig. 5). Of the cells stained by NT, greater than 95% in the GCL and only 15% in the GLL also express NeuN. In contrast, all NeuN positive cells express NT. Based on these observations we further tested NT as a candidate label for the total population of neurons within the GCL and GLL of the MOB. Sections were stained with NT and for the glial marker S-100B to determine how specific NT staining was for neurons vs glia. We found that only about 2% (14/640) of NT labeled cells in the glomerular layer were also positive for S-100B. This is comparable to the fraction of NeuN positive cells that were identified as being S-100B positive in this same layer in tissue from the same animals (4/640). Similar fractional overlap was found for the granule cell layer (13/640 for NT and 1/640 for NeuN).

Bottom Line: New neurons are generated in the adult brain from stem cells found in the subventricular zone (SVZ).Neuronal populations in these layers undergo turnover throughout life, but whether all neuronal subtypes found in these areas are replaced and when neurons begin to express subtype-specific markers is not known.We also show that many neurons in the glomerular layer do not express NeuN, but are readily and specifically labeled by the fluorescent nissl stain Neurotrace.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Science, Carnegie Mellon University, Pittsburgh, PA 15213, USA. bagleyjo@ninds.nih.gov

ABSTRACT

Background: New neurons are generated in the adult brain from stem cells found in the subventricular zone (SVZ). These cells proliferate in the SVZ, generating neuroblasts which then migrate to the main olfactory bulb (MOB), ending their migration in the glomerular layer (GLL) and the granule cell layer (GCL) of the MOB. Neuronal populations in these layers undergo turnover throughout life, but whether all neuronal subtypes found in these areas are replaced and when neurons begin to express subtype-specific markers is not known.

Results: Here we use BrdU injections and immunohistochemistry against (calretinin, calbindin, N-copein, tyrosine hydroxylase and GABA) and show that adult-generated neurons express markers of all major subtypes of neurons in the GLL and GCL. Moreover, the fractions of new neurons that express subtype-specific markers at 40 and 75 days post BrdU injection are very similar to the fractions of all neurons expressing these markers. We also show that many neurons in the glomerular layer do not express NeuN, but are readily and specifically labeled by the fluorescent nissl stain Neurotrace.

Conclusion: The expression of neuronal subtype-specific markers by new neurons in the GLL and GCL changes rapidly during the period from 14-40 days after BrdU injection before reaching adult levels. This period may represent a critical window for cell fate specification similar to that observed for neuronal survival.

Show MeSH