August 16, 2006
Human Brain Cells Replicate In Culture And In Mice

Many scientists would like to take human embryonic stem cells (hESC) and find ways to instruct the cells to become whatever cell type that is needed. But restrictions on funding hESC work has slowed that avenue of investigation. Well, scientists at the University of Florida may have found a way to avoid the need for hESC to create neurons or neural progenitor cells for therapeutic purposes.

GAINESVILLE, Fla. -- University of Florida researchers have shown ordinary human brain cells may share the prized qualities of self-renewal and adaptability normally associated with stem cells.

Writing online today (Aug. 16) in Development, scientists from UF's McKnight Brain Institute describe how they used mature human brain cells taken from epilepsy patients to generate new brain tissue in mice.

Furthermore, they can coax these pedestrian human cells to produce large amounts of new brain cells in culture, with one cell theoretically able to begin a cycle of cell division that does not stop until the cells number about 10 to the 16th power.

They can grow large numbers of neurons. But how hard will it be to instruct those neurons to go into the brain and take up positions that replace lost neurons? For example, people with Parkinson's Disease have lost a lot of dopaminergic neurons. But neurons grown in culture aren't helpful unless they can be made to take up residence in those regions of the brain that have lost neurons and then once there the neurons would need to form appropriate connections with other neurons. Still, this is a hopeful result.

"We can theoretically take a single brain cell out of a human being and - with just this one cell - generate enough brain cells to replace every cell of the donor's brain and conceivably those of 50 million other people," said Dennis Steindler, Ph.D., executive director of UF's McKnight Brain Institute. "This is a completely new source of human brain cells that can potentially be used to fight Parkinson's disease, Alzheimer's disease, stroke and a host of other brain disorders. It would probably only take months to get enough material for a human transplant operation."

The findings document for the first time the ability of common human brain cells to morph into different cell types, a previously unknown characteristic, and are the result of the research team's long-term investigations of adult human stem cells and rodent embryonic stem cells.

Some people think that human neurons should not mix with animal neurons. This position reminds me of the Monty Python Catholic family in Yorkshire England who believed every sperm is sacred.

Every sperm is sacred,
Every sperm is great,
If a sperm is wasted,
God gets quite irate.

Let the heathen spill theirs,
On the dusty ground,
God shall make them pay for,
Each sperm that can't be found.

Every sperm is wanted,
Every sperm is good,
Every sperm is needed,
In your neighbourhood.

Every neuron is sacred? Does every neuron contain part of a soul? If you torture a human neuron in lab culture are you torturing a human?

Well, whether or not human neurons are sacred they can grow in mouse brains. They also can grow in culture. Once sperm can be created from regular cells and grown in large numbers in culture dishes will those spem be sacred too?

Human neurons in the brain of a mouse or rat will not make that animal think human thoughts. Their skulls are far too small to provide enough space for enough human neurons to form links that make higher level thought possible.

Share |      Randall Parker, 2006 August 16 09:49 PM  Biotech Stem Cells

Garson Poole said at August 18, 2006 12:14 AM:

Randall Parker makes the following interesting claim, “Human neurons in the brain of a mouse or rat will not make that animal think human thoughts. Their skulls are far too small to provide enough space for enough human neurons to form links that make higher level thought possible.”

It is certainly true that the mouse skull is considerably smaller than the human skull. Also, any brain structure that is created by altering a developing mouse embryo or blastocyst and introducing human neurons will be abnormal. Researchers are thinking about making chimeric mice whose brains are 100% human. It is not clear at this point if such an organism would even be viable. If it does survive then I think there would be major uncertainty about its cognitive capabilities. The relationship between intelligence and brain size is apparently quite complex. Consider the following interesting discussion from the blog of Kevin Kelly:

The smartest animals on land, sea and air (outside of humans) are great apes on land, whales and dolphins in the sea, and parrots and crows in the air. A parrot brain is one thousandth the size of a whale’s. But if you were to test an African grey parrot, a chimpanzee and a bottlenose dolphin behind a suitable screen so that you could not see which animal was taking the test, you would not be able to determine the animal by its intelligence alone. According to Lori Marino, a neuroscientist specializing in large animal brains, the problem solving IQ of parrots, chimps and whales are nearly equivalent, even though the size of their brains vary by a thousand times.

Parrots have a tiny walnut-sized brain compared to humans, yet they display intriguingly powerful cognitive capabilities. The African Grey Parrot, Alex, studied by the scientist Irene Pepperberg is famous for its mastery of language and mathematical concepts. A Science Daily article reports on the parrots understanding of a “numerical concept akin to zero -- an abstract notion that humans don't typically understand until age three or four, and that can significantly challenge learning-disabled children”. A vocabulary of 100 words has been claimed for Alex.

The Sunday Times UK contains the following quote about parrots from Pepperberg:

“Their communication skills are similar to those of a two-year-old child, but their adding and ability with colours and shapes are more like a five or six-year-old,” said Irene Pepperberg, associate professor of psychology at Brandeis University in Waltham, Massachusetts.

Of course, a mouse-sized brain is even smaller than a parrot-sized brain. Also, the structure of an avian brain differs from that of a mammal brain. Further, society currently does not oppose the liquidation of individual parrots despite the cognitive leaps of brethren.

Yet, the material above I think provides evidence that the relationship between brain size and cognition is not well understood in natural animals. It is even less understood in animals created by experimental amalgamation.

In addition, an experiment now that creates a chimeric mouse whose brain contains 100% human neurons is an invitation to massive public backlash. The policy prescribed by the Scottish Council on Human Bioethics is an overreaction and is too restrictive I think. But it illustrates a powerful undercurrent of beliefs that are currently widely held in society and it can not be ignored. This biomedical research area is too important to needlessly alienate the public that ultimately provides funding by performing premature experiments that will mockingly be labeled “Frankensteinian” by detractors.

Randall Parker said at August 18, 2006 6:07 PM:


Interesting observations about parrots. But human neurons require more volume to create intelligence than parrot cells do. I'm guessing light weight has been much more heavily selected for in parrots due to their need to fly.

Now, that brings up an interesting idea: We could build smarter humans brains if we looked at parrot brain genes and figured out how they can generate so much intelligence from such lightweight brains.

How about putting parrot neurons into mice?

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