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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.

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Adult born neurons express GABA and NC. 40× images of sagittal sections with arrowheads indicating double positive cells for BrdU (red) and the subtypes GABA and NC (green). Scale bars, 37 μm. (A and B) BrdU co-labels with GABA in the GLL (A) and the GCL (B). (C and D) BrdU co-labels with NC in the GCL (C) and TH (D) in the GLL. NC, N-copine; GLL, glomerular layer; GCL, granule cell layer.
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Figure 3: Adult born neurons express GABA and NC. 40× images of sagittal sections with arrowheads indicating double positive cells for BrdU (red) and the subtypes GABA and NC (green). Scale bars, 37 μm. (A and B) BrdU co-labels with GABA in the GLL (A) and the GCL (B). (C and D) BrdU co-labels with NC in the GCL (C) and TH (D) in the GLL. NC, N-copine; GLL, glomerular layer; GCL, granule cell layer.

Mentions: The expression patterns of each of the subtype markers are distinctive while new neurons observed 40 days after BrdU injection reside fairly uniformly throughout the GLL and GCL. Thus, we tested whether the new neurons may represent a variety of immunohistochemically-defined neuronal subtypes or whether a few subtypes are selectively replaced by new neurons. To assess this quantitatively, we determined the fraction of BrdU-positive cells that co-expressed each of the immunohistochemical markers described above. Adult mice (7–9 weeks old, additional file 1) were injected with BrdU and then perfused 40 days after the final BrdU injection. Sections were stained for BrdU and one other marker (see table 1). We identified BrdU positive cells in the GLL and then determined the number and percentage of these cells that were also positive for CR (28 of 123 cells; 23 ± 2%), CB (22 of 169 cells; 14 ± 3%), TH (34 of 149 cells; 23 ± 4%), GABA (129 of 215 cells; 60 ± 2%), and NC (11 of 99 cells; 12 ± 2% (Fig. 2, 3 and 4). The ssame analysis was performed on the BrdU positive neurons in the GCL (Fig. 2, 3 and 4), except that, as stated above, TH-positive cells were not analyzed. The numbers and percentages of GCL neurons expressing the different markers are as follows: CR (302 of 3502 cells; 9 ± 1%), CB (69 of 4127 cells; 2 ± 0%), GABA (319 of 504 cells; 62 ± 6%), and NC (50 of 229 cells; 22 ± 2%).


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 GABA and NC. 40× images of sagittal sections with arrowheads indicating double positive cells for BrdU (red) and the subtypes GABA and NC (green). Scale bars, 37 μm. (A and B) BrdU co-labels with GABA in the GLL (A) and the GCL (B). (C and D) BrdU co-labels with NC in the GCL (C) and TH (D) in the GLL. NC, N-copine; GLL, glomerular layer; GCL, granule cell layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Adult born neurons express GABA and NC. 40× images of sagittal sections with arrowheads indicating double positive cells for BrdU (red) and the subtypes GABA and NC (green). Scale bars, 37 μm. (A and B) BrdU co-labels with GABA in the GLL (A) and the GCL (B). (C and D) BrdU co-labels with NC in the GCL (C) and TH (D) in the GLL. NC, N-copine; GLL, glomerular layer; GCL, granule cell layer.
Mentions: The expression patterns of each of the subtype markers are distinctive while new neurons observed 40 days after BrdU injection reside fairly uniformly throughout the GLL and GCL. Thus, we tested whether the new neurons may represent a variety of immunohistochemically-defined neuronal subtypes or whether a few subtypes are selectively replaced by new neurons. To assess this quantitatively, we determined the fraction of BrdU-positive cells that co-expressed each of the immunohistochemical markers described above. Adult mice (7–9 weeks old, additional file 1) were injected with BrdU and then perfused 40 days after the final BrdU injection. Sections were stained for BrdU and one other marker (see table 1). We identified BrdU positive cells in the GLL and then determined the number and percentage of these cells that were also positive for CR (28 of 123 cells; 23 ± 2%), CB (22 of 169 cells; 14 ± 3%), TH (34 of 149 cells; 23 ± 4%), GABA (129 of 215 cells; 60 ± 2%), and NC (11 of 99 cells; 12 ± 2% (Fig. 2, 3 and 4). The ssame analysis was performed on the BrdU positive neurons in the GCL (Fig. 2, 3 and 4), except that, as stated above, TH-positive cells were not analyzed. The numbers and percentages of GCL neurons expressing the different markers are as follows: CR (302 of 3502 cells; 9 ± 1%), CB (69 of 4127 cells; 2 ± 0%), GABA (319 of 504 cells; 62 ± 6%), and NC (50 of 229 cells; 22 ± 2%).

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