Functional Neurogenesis

Yesterday I was taking pictures of 1-day-old neurons, which was irritating me for several reasons. First, at this age they’re small, irregular and uglier than the mature neurons I’m used to examining. Second, very immature neurons are located amongst a mess of proliferating cells and fellow young neurons so it becomes hard to discern one cell from the next.

One positive thing that came out of looking at these very immature neurons was that I got the chance to see several examples of pyknotic (dying) cells. Older, adult-born neurons also die, particularly after an experience (see here and here), but it’s infrequent and hard to visualize. However, a relatively large proportion of new neurons die within a few days of their birth making them easier to find – the cluster of cells shown below is an example that caught my attention.

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Two recent papers have attracted a lot of media attention because they draw direct links between adult neurogenesis and behavioral disorders: Noonan et al. showed that rats lacking adult neurogenesis (stopped with irradiation) are more susceptible to cocaine addiction. Jin et al. showed that mice lacking adult neurogenesis (using a transgenic model) suffer greater infarct size and have more severe motor deficits after stroke.

While the papers themselves have important implications, what caught my attention was the angle taken by press releases: both articles studied the effects of reducing neurogenesis but the media focused on potential benefits of increasing neurogenesis. See speculation that antidepressants, by increasing neurogenesis, might be stroke-protective here. And, from Science Daily:

While the research specifically focused on what happens when neurogenesis is blocked, the scientists said the results suggest that increasing adult neurogenesis might be a potential way to combat drug addiction and relapse.

It may very well be the case that increasing neurogenesis is good in the same way decreasing neurogenesis is bad but it shouldn’t be assumed – maybe we have all the neurogenesis we need and, while completely arresting neurogenesis could be harmful, increasing neurogenesis beyond normal levels is just redundant. Read the rest of this entry »