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Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 12 of 12. This is the beginning of the thread.
Posted by SLS on July 25, 2013, at 21:33:15
This sounds right to me. However, this is only one opinion.
- Scott------------------------------------------------
http://bipolarnews.org/?p=1949
The Myth of Neurogenesis in Adult Primates Debunked
July 22, 2013 · Posted in Neurobiology
In a plenary lecture at the Collegium Internationale Neuro-Psychopharmacologicum (CINP) in Istanbul in 2012, Pasco Rakic, professor of neuroanatomy at Yale University, may have debunked a myth of modern medicine, one that we have cited in many previous BNNs. Despite what has been written by famous neuroscientists and published in the most prestigious journals, including Science, Cell, and PNAS, based on data in rodents, Rakic presented evidence that neurogenesis does not occur to any substantial extent in adult primates.
Two decades ago, data in rodents and other species clearly indicated that neurogenesis, the creation of new neurons, occurred in adult animals, especially in the dentate gyrus of the hippocampus. Thousands of papers were written on the subject, and neurogenesis was understood to be possible in adult humans as well. It was even suggested based on data in rodents that the mechanism of action of antidepressants was dependent on neurogenesis. However, Rakic argues that most of the research on neurogenesis was based on faulty data.
Rakic found that while rats do have neurogenesis into adolescence, it diminishes greatly in older adult animals. In primates, neurogenesis in the cortex ends before birth. In the primate dentate gyrus of the hippocampus, there is some postnatal neurogenesis, but it rapidly drops toward zero in the first months of life. Rakic concludes: We are as old as our neuronsor slightly younger.
Why should primates have permanent stores of neurons when rodents and other lower animal species get new ones further into their lifespan? Rakic postulates that for primates, neurons must hold experience-dependent memories necessary for the survival of the species, and turning them over would endanger the permanence of this memory. Whatever the reason, it is disappointing to find out that the revolutionary discovery of adult neurogenesis in rodents so widely presumed to also occur in adult primates and humans may not be correct.
This has clinical implications. If we dont get replacement hippocampal neurons like rats do, it is even more important to protect the billions of neurons that we do have. There are many things that endanger neurons, including inflammation, oxidative stress, high cortisol, poor diet, psychosocial adversity, and episodes of depression and mania. Greater numbers of mood episodes are associated with increasing degrees of cognitive dysfunction because of these many factors. A startling statistic from Denmark by Lars Kessing is that having four or more hospitalizations for depression (either unipolar or bipolar) doubles the risk for a diagnosis of dementia in late life. Thus, it looks like too many episodes hurt the brain.
However, on the positive side, the mood stabilizers (lithium, lamotrigine, valproate, and carbamazepine) and some atypical antipsychotics prevent episodes and increase the neuroprotective factor BDNF, or brain-derived neurotrophic factor, which facilitates synaptogenesis and helps protect neurons. BDNF is produced in selected neurons in the brain and decreases with stress and affective episodes, further endangering neurons. Since many effective treatments both prevent episodes and their associated decreases in BDNF and also directly increase BDNF, they may be having a dual positive benefit. The evidence is best for lithium having neuroprotective effects that can be directly observed in humans. Thus a not unreasonable mantra for patients with recurrent mood disorders is: Prevent Episodes, Protect the Brain.
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Posted by Phillipa on July 25, 2013, at 23:08:40
In reply to Is neurogenesis a myth?, posted by SLS on July 25, 2013, at 21:33:15
It makes sense. Now is there a study that shows that Alzheimers or Dementia is more common in Mental Disorders?
Posted by SLS on July 26, 2013, at 2:44:24
In reply to Is neurogenesis a myth?, posted by SLS on July 25, 2013, at 21:33:15
> In primates, neurogenesis in the cortex ends before birth. In the primate dentate gyrus of the hippocampus, there is some postnatal neurogenesis, but it rapidly drops toward zero in the first months of life.
One might consider that a single neuron can continue to sprout neurites and grow thicker. New connections are made all the time in the absence of neurogenesis. Neuritin, a signaling peptide, can prevent dendrite loss and promote neurite sprouting in the hippocampus. It is thought by some that neuritin has antidepressant properties.
Regarding the statement that recurrent affective episodes can double the risk of Alzheimers, that figure is charitable. I have seen some propose that the risk is tripled. I am not very happy about this. I am headed in that direction, I'm afraid.
- Scott
Posted by linkadge on July 26, 2013, at 10:18:41
In reply to Is neurogenesis a myth?, posted by SLS on July 25, 2013, at 21:33:15
While the idea of new brain cells may or may not be accurate, it is well established that brain does make new connections between existing neurons.
This may also play a part in the neurotrohpic theory of depression.
Linkadge
Posted by linkadge on July 26, 2013, at 10:28:08
In reply to Re: Is neurogenesis a myth? » SLS, posted by SLS on July 26, 2013, at 2:44:24
Feeding mice blueberries (in one study) resulted in enhanced neurogenesis in the hippocampus. Now, perhaps the neurogenesis was misinterpreted. However, the mice fed the blueberries still navigated mazes significantly better than the mice not fed the blueberries. Similar studies occur with mice fed epicatechin. So, there would need to be another mechanism for the enhanced learning.
Also, the exercise induced enhancement of cognitive function was presumed to be mediated in part by neurogenesis in the hippocampus.
Hmmm. I'd wonder how other researchers would respond.
As a side note, I have a friend with M.S. who overseas for stem cell therapy. The improvement was night and day (he can speak and walk v.s. not so before). So again, I wonder what the mechanisms of this would be? I.e. if injected stem cells can lead to new brain cells.
Linkadge
Posted by SLS on July 26, 2013, at 11:21:39
In reply to Re: Is neurogenesis a myth?, posted by linkadge on July 26, 2013, at 10:18:41
> While the idea of new brain cells may or may not be accurate, it is well established that brain does make new connections between existing neurons.
>
> This may also play a part in the neurotrohpic theory of depression.Look into a peptide called neuritin. Also, note that ketamine treatment produces a thickening of neurites almost immediately.
- Scott
Posted by SLS on July 26, 2013, at 11:45:24
In reply to Re: Is neurogenesis a myth?, posted by linkadge on July 26, 2013, at 10:28:08
> Feeding mice blueberries (in one study) resulted in enhanced neurogenesis in the hippocampus.
Pasco Rakic's contention has been that the results from rodent neurogenesis studies cannot be extrapolated to primates. He has presented the results of his studies that he feels confirms this. According to him, neurogenesis in the hippocampus ceases within the first year postnatally.
> Now, perhaps the neurogenesis was misinterpreted.
That's probably the best explanation. Perhaps the sprouting of neurites into new dendrites and terminals looks like new neurons if one assumes that increased tissue volume equals neurogenesis.
> However, the mice fed the blueberries still navigated mazes significantly better than the mice not fed the blueberries.
What's in blueberries?
> Similar studies occur with mice fed epicatechin. So, there would need to be another mechanism for the enhanced learning.
I'm not familiar with these things.
> Also, the exercise induced enhancement of cognitive function was presumed to be mediated in part by neurogenesis in the hippocampus.Maybe it's hypertrophy rather than hyperplasia.
> Hmmm. I'd wonder how other researchers would respond.
Yes. This guy is rather alone as a dissenter.
> As a side note, I have a friend with M.S. who overseas for stem cell therapy. The improvement was night and day (he can speak and walk v.s. not so before). So again, I wonder what the mechanisms of this would be? I.e. if injected stem cells can lead to new brain cells.Yes. A stem cell is the default progenitor from which specialized cells are formed through the process of differentiation. The same stem cell can become a heart muscle, a neuron, a skin cell, red blood cell, etc., depending upon the signaling in the environment.
- Scott
Posted by linkadge on July 26, 2013, at 18:36:06
In reply to Re: Is neurogenesis a myth?, posted by SLS on July 26, 2013, at 11:45:24
I remember reading about how exercise in humans led to an increased pool of stem cells in a certain area of the brain.
This one is in mice:
http://www.the-aps.org/mm/hp/Audiences/Public-Press/For-the-Press/releases/Archive/08/39.html
exercise and muscle stem cells
http://www.jyi.org/issue/exercise-dailyyour-stem-cells-will-thank-you/
another one in mice:
http://www.skepticblog.org/2010/07/05/neural-stem-cells-and-exercise/
hmm... seems like we need more research in primate brains.
Linkadge
Posted by Phillipa on July 26, 2013, at 19:04:57
In reply to Re: Is neurogenesis a myth?, posted by linkadge on July 26, 2013, at 18:36:06
Exercise is the ticket. Phillipa
Posted by linkadge on July 26, 2013, at 19:58:06
In reply to Re: Is neurogenesis a myth?, posted by Phillipa on July 26, 2013, at 19:04:57
Lithium induces stem cell production in human umbilical vein endothelial cells
http://www.nature.com/cr/journal/v21/n10/full/cr2011108a.html
Again, not sure how it all links together.
Linkadge
Posted by Lamdage22 on July 29, 2013, at 11:54:26
In reply to Re: Is neurogenesis a myth? » SLS, posted by SLS on July 26, 2013, at 2:44:24
"Neuritin, a signaling peptide, can prevent dendrite loss and promote neurite sprouting in the hippocampus. It is thought by some that neuritin has antidepressant properties."
Where do i get it and does it have any of the psych-med common side effects?
Posted by SLS on July 29, 2013, at 13:04:25
In reply to Re: Is neurogenesis a myth?, posted by Lamdage22 on July 29, 2013, at 11:54:26
> "Neuritin, a signaling peptide, can prevent dendrite loss and promote neurite sprouting in the hippocampus. It is thought by some that neuritin has antidepressant properties."
>
> Where do i get it and does it have any of the psych-med common side effects?To the best of my knowledge, neuritin is not being developed as a drug for use in humans at this time. Neuritin is a naturally occurring substance in the body.
- Scott
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