How do neuronal stem cells differentiate into specific types of neurons?

[quantumcarl]

Generally, Brain Plasticity is studied more often in children than adults. Their neurons are still much more flexible to changing roles and functions than those in adults. Its as though they are macro-structured stem-cells with a semi-limited scope of tasks.

Research has shown that the (child's) brain is able to form new connections in response to the environment, such as injury or learning. The formation of these new connections is a measure of the brain’s “plasticity.”

“Through brain imaging, we know that the subject matter, as well as the way it is taught, influences these changes in the brain,” says Michael Posner, UO professor emeritus of psychology and BBMI facility coordinator. “This workshop may help teachers better understand—for good or ill—the consequences of the way they teach.”

http://duckhenge.uoregon.edu/io/article.php?id=278

It would seem obvious that a young set of neurons could adapt to any function with some learning, behaviour modification of the neurons and so on...

But, what about adults? There are many studies that research the deaf, blind, alcoholics, dyslexic and so forth and there are tests designed to observe if the functions that are not being performed properly or not at all can be transfered, by neuroplasticity and neurobehavioural modification, to a fresh set of neurons that, through neuroplasticity, will learn and perform the desired function.

Cognitive Neuroscience Society 11th Annual Meeting
San Francisco, CA
April 19th-21st, 2004
Darves, C., & Neville, H. (2004). Two sides of neural plasticity in the dorsal visual pathway: Evidence from deaf, dyslexic, and control adults [Abstract]. Cognitive Neuroscience Society, 11, 117.
Previous research indicates that dorsal pathway visual functions are highly modifiable, showing both an enhancement in deaf individuals (Armstrong, et al., 2003; Neville & Lawson, 1987) and a deficit in at least some dyslexic individuals (Demb, et al., 1998; Sperling, et al., 2003). In contrast, neither group shows differences in ventral pathway visual functions. However, these studies have used different methodologies to assess dorsal and ventral pathway functions, and no research has yet examined both sides of plasticity (i.e., enhancements and deficits) within the same experimental paradigm. In the present research, dorsal and ventral pathway visual function was compared in deaf (n=17), dyslexic (n=15), and control adults. A dorsal pathway task measured motion detection for single points of moving light traveling from the far (~70°) periphery to the center of vision. Deaf individuals showed enhanced motion detection sensitivity whereas dyslexic individuals showed decreased motion detection sensitivity relative to matched controls. However, the overall enhancement in deaf participants resulted from selective upper visual field advantages, whereas the overall deficit in dyslexic participants resulted from selective lower visual field deficits. A separate ventral pathway test assessed single-point contrast sensitivity for a set of 20 light points presented in the fovea. Results indicated that neither the deaf nor the dyslexic group showed significantly different thresholds relative to controls, and no group or individual approached ceiling performance on this task. Taken together, this research bridges previous reports of selective dorsal pathway plasticity by demonstrating both enhancements and deficits using the same experimental paradigm. NIH#R01DC00128(HJN).

Absract address: http://www.purpled.com/UofO_BDL/Publications/Abstract_Darves_CNS04.pdf

After many years of research into neuroplasticity it is becoming more and more evident that there are certain functions and neurons that retain the adaptability and plasticity that is accepted and observed to reside in a younger person's cognitive makeup.

This is amazing because it shows promise that, without the use of drugs or surgery, certain functions such as hearing, sight and other less obvious faculties can be restored with simple sensory manipulations. There are recent studies into by-passing stroke-damaged areas of the brain as well. Cool eh?

 

[quantumcarl]

Habit and Neuroplasticity

Habit Hides Recovery

Creating a habit is evidence of neuroplasticity. When you do a movement over and over again, all of your neural circuitry and even the connection between your nerve and your muscle that creates the movement are turned into facilitated pathways that fire easily. We all know that when we are learning a new movement, like a dance step, we tend to be fairly “klutzy” about it. However, once we’ve mastered the new dance step, we can be quite graceful. If your child has a “therapy walk” which is different from their normal movement pattern, then you have evidence of brain recovery being hidden by habitual movement. The difference between the medical model and the coaching model is that the coach looks for the best performance level. The “therapy walk“ is an example of best performance. The fact that the child does not use the “therapy walk” all the time is just that they are using HABIT and not expressing their recovered brain function. Their old “sloppy walk” is like a golfer hitting a slice instead of a straight drive down the fairway. Golfers can improve their swing and children can improve their function. Both changes take practice and time.

read the rest of this article @ http://www.tascnetwork.net/habit.asp

There are also cases where children who were born with severe hydroencephally were able to adapt and grow up without anyone realizing the severity of their condition. During the 50s there were two children who's brains were completely mal-shaped because of water pressuring their brains up against the cranium. No one knew about their condition and the children managed to function normally, doing well in english and math at school. When their condition was finally discovered CT scans showed that the morphology of their brains showed no similarity to normal brains. This was a dramatic example of neuroplasticity showing the adaptability of neurons and how their function is not limited to their location, given continuous neuronal-behaviour-modification.

 

[Moonbear]

Neuroplasticity in adults is an area of much interest for me. Fascinating, isn't it?

If you're up to it, it would make a good topic for our journal club. There are lots of recent articles on the subject, any of which would be interesting to discuss. Perhaps you'd be willing to choose one and present it? I think it would get a lot of good discussion going. Perhaps even one of the journal articles published by the groups who presented the abstracts you've already listed above would be a good one to choose.

 

[quantumcarl]

Neuroplasticity in adults is an area of much interest for me. Fascinating, isn't it?

If you're up to it, it would make a good topic for our journal club. There are lots of recent articles on the subject, any of which would be interesting to discuss. Perhaps you'd be willing to choose one and present it? I think it would get a lot of good discussion going. Perhaps even one of the journal articles published by the groups who presented the abstracts you've already listed above would be a good one to choose.

It is a fascinating study. The applications are far-reaching and non-invasive. The study of neuroplasticity started with Evoked Potential studies at UBC. I was a pre-teen subject on one of the early tests back in I have no idea what year... must have been 1969 or so.

I know the author of those first papers on Evoked Potential.
She is also the first to have a lab in the US totally devoted to the study and verification of neuroplasticity. That lab was with Jonas Salk at the SALK institute for a period of 17 years. I can get direct, real time comments from the doctor but I should see if she minds being identified here and/or on the internet. ( this paragraph has been edited).

Please direct me to the site of your journal club. Are you in neurosciences or neurobiology or neurophysics? Does your club have a bar and/or a smoking section¿?

 

[Moonbear]

Please direct me to the site of your journal club. Are you in neurosciences or neurobiology or neurophysics? Does your club have a bar and/or a smoking section¿?

I mean the journal club right here on this forum. Look up at the sticky threads at the top of the M&B forum index. We haven't had a volunteer in about a month, so it'd be great if you could present an article, especially on a topic that should stimulate a lot of interest. (If you grab a beer before posting, the club will have a bar; as for smoking, if you must, just keep it on your side of the computer screen. )

 

[quantumcarl]

I mean the journal club right here on this forum. Look up at the sticky threads at the top of the M&B forum index. We haven't had a volunteer in about a month, so it'd be great if you could present an article, especially on a topic that should stimulate a lot of interest. (If you grab a beer before posting, the club will have a bar; as for smoking, if you must, just keep it on your side of the computer screen. )

You may think that there will be interest in this subject yet you are the only other contributor to this thread on the topic. Why would there be any more interest at the Journal Club? I guess we could find that out.. first hand.

I should be able to get there sometime this week after some preparation. Please be warned that my expertise is not neuroscience. However, my close proximity and discussions with America's and, decidedly, the world's top most recognized neuropsychologists, neurobiologists and neurophysicists may provide some entertainment with regard to the study of the neuron and the brain etc...

Thank you for your vote of confidence

 

[neurocomp2003]

i'd be interested but i don't have ink in my printer.

 

[Moonbear]

Please be warned that my expertise is not neuroscience.

No problem, it isn't for a lot of people here. That's the point of our journal club, to help get people who are not neuroscientists more involved and learning how to understand the literature a bit better than you might on your own.

If you introduce a paper for everyone to read along with you, it's much easier to focus the discussion in a way that we can have more to talk about than just generalities and "ooh, isn't that neat." C'mon, pretty please?

 

[eeka chu]

What's more interesting for me about plasticity is the questions it doesn't answer. Neurons take quite a while to physically change and interconnect.

That means there's a big expanse of time in which I'm remembering things and there's no way my neurons could be regrowing to represent those changes as I'm remembering the events. About the only other way neurons have of holding logic is in the synaptic clefts. In effect, the continuity and context of everything I've just said has probably come just from the states of my synaptic junctions as opposed to the structure of my brain.

I also suspect dreams are very closely related to plasticity and the body attempting to cement the memories into more permanent, structural changes. And that when we sleep, we don't 'loose' consciousness, our memories merely stop recording and begin sorting in an altered form of it.

It's quite easy to say that long term memories don't account for our conscious state. That's always the one that comes up when you start talking about cloning and teleportation by quantum entanglement... "It's just a copy of me."

But as you start approaching the shorter and shorter term memory, one might expect that we're probably getting closer and closer to whatever is aware of that memory, just as when one looks at the cache in a computer they're actually looking at the stage just before the processor itself.

Then you can get deep on it... is it the processor that produces the machine's 'consciousness' or the cache? Or... and what I think is far more likely, the whole.

One example of a real world expression of the short term memory might be neurotrophins, and other growth factors, that are expressed as we learn and that then cause the neural structure to reorganise. Perhaps there is some form of more universal 'loop' in either the neural structure or the neurons themselves that can sample and hold an event (just a collection of stimuli coming through the spinal cord say) while neurotrophins are released, a 'delay' on the tail off of the stimulus. Once the new synaptic junctions are formed, that loop might be stopped or detracted from. Loop amplitude and hold time, as well as growth factor release, might be related to things like adrenaline release, allowing scary events to solidify much more rapidly.

All interesting thought experiments for my pink goo to work on. I expect that the term consciousness is due for some expansion and redefinition.

 

[Moonbear]

What's more interesting for me about plasticity is the questions it doesn't answer. Neurons take quite a while to physically change and interconnect.

Well, the unanswered questions are of course the reason many of us have become scientists in the first place. That's what's so fascinating, to realize what questions have not yet been answered and to start trying to find answers to them.

I also find the process whereby the change is occurring to be much more interesting than just that it happens. I work on a neural system that takes a month or longer to change...twice a year, every year, for the entire adult reproductive life of the animals (this would be seasonal reproduction I'm talking about). We've made a lot of progress in determining what changes between seasons, but not how it changes during that transitionary period between seasons. So, I definitely share your enthusiasm on this subject.

 

[quantumcarl]

What's more interesting for me about plasticity is the questions it doesn't answer. Neurons take quite a while to physically change and interconnect.

That means there's a big expanse of time in which I'm remembering things and there's no way my neurons could be regrowing to represent those changes as I'm remembering the events. About the only other way neurons have of holding logic is in the synaptic clefts. In effect, the continuity and context of everything I've just said has probably come just from the states of my synaptic junctions as opposed to the structure of my brain.

It could be that the structure is in place for neuroplasticity to take place. It may not be so much the structure that has to change as it may be that the use and function of the structure changes.

FMRI imaging tracks the volume of oxygenated blood utilization by actively "firing" neurons. The neurons begin long before the blood gets there to support the function, but they require a large amount. This may indicate that neuroplasticiy involves developing delivery systems (extra venules and arteioles for more volume) for iron and oxygen rich blood to groups of neurons that are being modified (or that are plastic) to a specific new function by the presentation of specifically designed or sought-out stimuli.

It is obvious that time is a factor in neuroplasticity. Learning conservatory level concert piano is a 10 year long affair. Learning to be a scientist in most areas takes even longer. Note how long some stroke or head trauma patients need to begin to learn to walk and/or talk again.

To initiate a benefit of neruoplasticity specific neurons require behavioural modification using specific tools that evoke their potential. The behavioural/structural modification of any organ's structure requires discipline, commitment, time and perseverence, among many other skill sets.

As I understand it "connectivity" between neurons is already established... the structure has been built according to genetic code and environmental influences. This would include the function and chemical potentials of the synapses. It is the part and function of the facilitator to specifically encourage the modification of the utilization of that structure or parts thereof. That facilitator can and does often include the actual subject in question.

 

[somasimple]

As I understand it "connectivity" between neurons is already established... the structure has been built according to genetic code and environmental influences.

Not really, each new thought, each new action create a new neural program and thus plasticity is just the key of constant brain maturation. We are connecting around 1000 synapses/sec and creating 1000 new neurons/hour and destroy quite the same quantity. This role is devoted to glia cells.

There are neurons able to migrate within the brain.

 

[quantumcarl]

Not really, each new thought, each new action create a new neural program and thus plasticity is just the key of constant brain maturation. We are connecting around 1000 synapses/sec and creating 1000 new neurons/hour and destroy quite the same quantity. This role is devoted to glia cells.

There are neurons able to migrate within the brain.

Cool!
It sounds like plasticity extends to a point where neurons adapt to take on a number of functions including motility. This is why I used the analogy of a stem cell to illustrate neuroplasticity. So there is some differentiation among neurons?

 

[quantumcarl]

To answer my own question there are some very in-depth studies on neuronal cell differentiation... here's one from Harvard.

The establishment of neuronal identities in the developing nerve cord
Stefan Thor, Assistant Professor
Department of Neurobiology,
Harvard Medical School
Email: Stefan Thor

The long-range goal of Dr. Thor's work is to understand the molecular genetic mechanisms that control establishment of motor neuron identities. His laboratory uses Drosophila as its primary model, and although the fly has a relatively simple nervous system it still features about 100 distinct types of cells that can be classified as neurons, glia, or interneurons. Recent experiments have focused on LIM homeodomain proteins, a family of transcription factors that are expressed in discrete subsets of developing neurons throughout the animal kingdom.

Dr. Thor's experiments indicate that three LIM-HD genes, islet (isl), lim3, and apterous act in a combinatorial code to specify motor neuron subtype identity. By attaching markers to mutant versions the genes, he has found that they control two basic hallmarks of neuronal identity - they guide axons toward target cells and specify which neurotransmitters are turned on. Additional genes are probably required to establish the ultimate, unique identity of neurons, and current research focuses on identifying them.

From: http://www.hms.harvard.edu/armenise/old_site/4a_cell.htm

Also:

Neural stem cells proliferate in vitro and form neurospheres in the presence of epidermal growth factor (EGF), and are capable of differentiating into both neurons and glia when exposed to a substrate.

Apparently there are specific stem-cells to neuronal development.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9624622&dopt=Abstract