Thursday, February 21, 2013

Birthing new neurons at night

By now it's well established that adults can grow new neurons.

Growing Neurons (source)
But how, when and why these neurons grow is currently under investigation. A 2008 paper attempts to answer the 'when' of neurogenesis. They labeled (PH3) cells in the mouse hippocampus (dentate gyrus to be specific), and counted how many cells were currently going through mitosis at different times of day. They found that during the dark phase, more cells were PH3-positive, indicating that more cells were growing at night.

They also tested whether neurogenesis was modulated by exercise. And it was. Mice who had access to a running wheel in their cage grew about the same number of cells during the night, but grew more cells during the day. So much so that the difference between night and day disappeared.

Tamai et al.,, 2008 Figs 1B and 2D
This figure shows the light-dark cycle (Zeitgeber time) and the number of 'growing' cells. B shows the pattern for control mice, and D shows the pattern for the running mice. Notice that the y axes are scaled differently.

So exercise helped new cells grow, but without exercise more cells grew during the night time. Now all this use of the phrase 'night time' might make you think that this neural growth is happening during sleep.

After a long night of wheel running, Jasper succumbs to a restful days sleep. (source)

But it's not. Mice are nocturnal. They sleep during the day and are wide awake at night. The paper shows that almost all the running that occurs on the running wheel happens at night. So the enhanced cell growth is happening when the mice are active. Why exercising at night causes cells to grow during the day is interesting, but the authors offer no mechanism for why that might be happening.

© TheCellularScale
Tamai S, Sanada K, & Fukada Y (2008). Time-of-day-dependent enhancement of adult neurogenesis in the hippocampus. PloS one, 3 (12) PMID: 19048107


  1. Max
    Thank you! As always, interesting post! I am learning so much from your blog.
    Wondering what type of cells are (re)produced through neurogenesis and in which regions of the brain their are located?

  2. Glad you find it interesting! Great question about where and which type of cells get generated during neurogenesis. The ones I talk about here are from the subgranular zone of the dentate gyrus (which is a part of the hippocampus. The other place showing neurogenesis clearly is the subventricular zone. The new cells in the dentate gyrus become granule cells (as far as I know), but I'm not sure what kind of cells are generated at the SVZ.