Table I.
Comparison of Replacement Rates for Neurogenic Populations in Cortex and Dentate Gyrus1
| CB + CR small interneurons in Neocortex2 | Granule Cells in Dentate Gyrus | Notes/references | |
|---|---|---|---|
| (A) Number of Neurons (all cortical neurons or DG granule neurons) | 21,000,000 | 2,170,000 | (Korbo et al., 1990; West and Andersen, 1980) |
| (B) % of Neurons in A belonging to Neurogenic Class | 0.56% | 100% | (Gabbott et al., 1997)3 |
| (C) Number of Neurons in Neurogenic Class | 117,600 cells | 2,170,000 cells | = A*B |
| (D) Volume (Cortical Layer 5/6 or DG Granule Cell Layer) | 152 mm3 | 2.27 mm3 | (Korbo et al., 1990; Gabbott et al., 1997; West and Andersen, 1980)4 |
| (E) Density of Neurogenic Class | 774 cells/ mm3 | 956,000 cells/ mm3 | = C/D |
| (F) Density Ratio of Two Classes | 1 : | 1240 | = E /Edentate gyrus |
| (G) BrdU+ Neuron Density in DG | 850 cells/ mm3 | (Olariu et al., 2005; Dayer et al., 2003)5 | |
| (H) Expected Density for Replacement Rate Equivalent to DG | 0.69 cells/ mm3 | = G/F | |
| (I) Observed Density | 0.78 cells/ mm3 | (Dayer et al., 2005)6 |
The overall neuron density for two neurogenic populations, small calbindin- and calretinin-expressing interneurons in the cortex and granule cells in the dentate gyrus, are calculated from published estimates of neuron numbers and region volumes (rows A–E). The total neuron density in the two populations is compared (F). Finally, the density of new cortical neurons that would produce a replacement ratio equivalent to that of dentate gyrus granule neurons is calculated (H) using the observed density of new neurons in the granule cell layer (G) and compared to the observed density of new cortical neurons (I).
CB, calbindin-expressing; CR, calretinin-expressing
For cortex, % of CB class 7 and CR class 4 interneurons is calculated from % of neurons CB+ and CR+, % of CB+ and CR+ neurons in deep layers, and numbers of CB+ and CR+ classes in deep layers.
For cortex, volume calculated from total volume of 253 mm3 and 60% of cortical depth included in layers 5/6.
After a single BrdU injection, 1072 BrdU+ cells/mm3 x 79% of BrdU+ cells that are NeuN+
3.1 BrdU+/NeuN+ cells/ mm3 in cortex after four BrdU injections, divided by four to estimate the density after one injection.
Table modified from Dayer et al., 2005