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Comment by superkuh | Hacker News Reader

Yeah, at least one of the things they report is irrelevant.

>Impaired hippocampal neurogenesis, decreased oligodendrocytes and myelin loss in subcortical white matter were evident at 1 week

I can forgive them for not knowing that the great "Do adults humans have neurogenesis in the dentate gyrus of the hippocampus (or EC)" debate has been pretty much ended. We don't. Adult humans don't make new neurons. Humans aren't like other mammals. So... I'm not sure how much the "impared hippocampal neurogenesis" bit applies. Our hippocampal neurogenesis is already impaired. Unless you're pre-pubescent.

ref: "Transcriptomic taxonomy and neurogenic trajectories of adult human, macaque, and pig hippocampal and entorhinal cells" Franjic et al., 2022 https://www.cell.com/neuron/pdf/S0896-6273(21)00866-7.pdf

laymen ref: https://neurocritic.blogspot.com/2022/02/the-ongoing-debate-...

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wow, I remember learning the opposite in my neurobiology class several years ago, but your source checks out.

one question though: what about that study that measured carbon-14 levels in the brains of people born before atomic bomb testing? [0]

I don't doubt you're correct re: neurogenesis, I'm just confused how different studies saw different things.

0. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4394608/

Does this mean BDNF in adult humans does not actually promote neurogenesis?

adults humans can have neurogenesis in specific regions https://www.frontiersin.org/articles/10.3389/fncel.2018.0044... but the most salient thing, which is very potent is synaptogenesis, e.g magnesium l-threonate giving multiple IQ points.

Your linked paper talks about how the "adult mammalian brain can produce new neurons". That isn't controversial. What used to be controversial, but isn't anymore, is that adult humans brains don't produce new neurons. Not in the dentate gyrus, not in the entorhinal cortex between the hippocampus and cortex, not even in the olfactory bulb. Your linked paper does not have any human studies of neurogenesis, only BDNF serum levels and assumptions about what that means from mouse models. But mouse, even ape models, don't translate re: neurogenesis.

Like everyone else, yourself included, I used to think that THC's main anti-depressant effect was mediated through increasing survival of new neurons during their granual cell to neuron journey in the dentate. But nope. Adult humans don't have new neurons.

https://www.jneurosci.org/content/41/12/2541 Looks like there is evidence. Also are you claiming there are no stem-cells/MSCs in the brain? I have read multiples papers about drugs that specialize unspecialized cells into olygoendrocytes (a microglia) in the human brain. I don't see why epigenetics wouldn't allow unspecialized cells to become neurons vs glial cells. Finally if I recall correctly, some glial cells might not act like neurons but still release neurotransmitters. More importantly, humans should preserve their neurons by actively fighting apoptosis, e.g. by taking skq1. And as said previously, synaptothrophics exists and are very potent. Finally, hypermnesics are a thing. BTW children are generally happiers/more emotional than adults. One might wonder wether this is related to neuron/synapse density

I'll give that paper it's claim, that "DCX+ dentate granule cells are a dynamic cell population that undergoes progressive maturation" but I don't see new evidence from that paper suggesting they actually make it through the complex, multi-step, evolution of granule cells to neurons. There are a lot of stops and pitfalls on the way. The evidence from the 2022 paper I linked at the start of this thread shows the gene expression profiles of adult human dentate granule cells are very different from other mammals.

Yes. It's really upset a giant amount of papers and proposed mechanisms of actions all across human neuroscience.

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