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Postnatal Neurogenesis in the Developing Dentate Gyrus

Dentate gyrus figureThe image grid below shows specimens that were injected with ³H-thymidine on four consecutive days: birth (P0), P1, P2, and P3.  One specimen survived to P10 (left column), another to P20 (middle column), and another to P40 (right column).  These specimens are representative of others in their respective age groups.  All images are of sagittal sections from the most medial (Level 1, row 1) to far lateral (Level 12, row 12).   The diagram to the right is my attempt to explain how the interlocked pyramidal layer (orange) in Ammon’s horn and the granular layer (green) in the dentate gyrus appear in the various cuts through the hippocampus (Ammon’s horn and the dentate gyrus).  The top drawing shows how the hippocampus extends in a curved pattern around the thalamus, from just posterior to the septum (septal end), extending laterally and downward into the cortical temporal lobe (temporal end).  Note that Levels 1 – 4 only cut through the dorsal hippocampus overlying the thalamus; Levels 5 – 7 cut the dorsal and ventral parts of the hippocampus in separate parts of the slices; Levels 8-12 show the merged parts of the lateral hippocampus.
This series is especially helpful in differentiating the positions of the prenatal granule cells (approximately 15% of the population) from the postnatal granule cells.  Three neurogenetic gradients visible only in the PRENATAL granule cells–probably best seen in the P10 survival group where prenatal cells are a greater proportion of the population:

  1. Prenatal granule cells are the “pioneers” that outline the superficial limits of the granular layer.
  2. The external limb of the granular layer has a more robust representation of prenatal granule cells than the internal limb.
  3. The septal and temporal ends of the granular layer are almost completely composed of prenatal granule cells.

What these images show is that the prenatal population of granule cells may have different properties from the postnatal population.  Their generation and positioning may play a critical role in shaping the mature dentate gyrus as it characteristically wraps around the CA4 field of Ammon’s horn pyramidal layer.

Click on the link below to download a pdf file of the illustration on the right.

Dentate gyrus figure

1 P10 L1 hippocampus

1 P10 L1 hippocampus PDF

2 P20 L1 hippocampus

2 P20 L1 hippocampus PDF

3 P40 L1 hippocampus

3 P40 L1 hippocampus PDF

4 P10 L2 hippocampus

4 P10 L2 hippocampus PDF

5 P20 L2 hippocampus

5 P20 L2 hippocampus PDF

6 P40 L2 hippocampus

6 P40 L2 hippocampus PDF

7 P10 L3 hippocampus

7 P10 L3 hippocampus PDF

8 P20 L3 hippocampus

8 P20 L3 hippocampus PDF

9 P40 L3 hippocampus

9 P40 L3 hippocampus PDF

10 P10 L4 hippocampus

10 P10 L4 hippocampus PDF

11 P20 L4 hippocampus

11 P20 L4 hippocampus PDF

12 P40 L4 hippocampus

12 P40 L4 hippocampus PDF

13 P10 L5 hippocampus

13 P10 L5 hippocampus PDF

14 P20 L5 hippocampus

14 P20 L5 hippocampus PDF

15 P40 L5 hippocampus

15 P40 L5 hippocampus PDF

16 P10 L6 hippocampus

16 P10 L6 hippocampus PDF

17 P20 L6 hippocampus

17 P20 L6 hippocampus PDF

18 P40 L6 hippocampus

18 P40 L6 hippocampus PDF

19 P10 L7 hippocampus

19 P10 L7 hippocampus PDF

20 P20 L7 hippocampus

20 P20 L7 hippocampus PDF

21 P40 L7 hippocampus

21 P40 L7 hippocampus PDF

22 P10 L8 hippocampus

22 P10 L8 hippocampus PDF

23 P20 L8 hippocampus

23 P20 L8 hippocampus PDF

24 P40 L8 hippocampus

24 P40 L8 hippocampus PDF

25 P10 L9 hippocampus

25 P10 L9 hippocampus PDF

26 P20 L9 hippocampus

26 P20 L9 hippocampus PDF

27 P40 L9 hippocampus

27 P40 L9 hippocampus PDF

28 P10 L10 hippocampus

28 P10 L10 hippocampus PDF

29 P20 L10 hippocampus

29 P20 L10 hippocampus PDF

30 P40 L10 hippocampus

30 P40 L10 hippocampus PDF

31 P10 L11 hippocampus

31 P10 L11 hippocampus PDF

32 P20 L11 hippocampus

32 P20 L11 hippocampus PDF

33 P40 L11 hippocampus

33 P40 L11 hippocampus PDF

34 P10 L12 hippocampus

34 P10 L12 hippocampus PDF

35 P20 L12 hippocampus

35 P20 L12 hippocampus PDF

36 P40 L12 hippocampus

36 P40 L12 hippocampus PDF