試験管のなかで脳の生成 - 科学は何をもたらす
イギリスとスイスの研究者が、試験管のなかで脳のミニチュア版を
生み出すのに成功した。4ミリほどの大きさだが、人間の脳と同じような
機能分化が認められ、それは精神病などの原理解明とその治療に画期的な
道を開くことになるであろう、というような話である。
私はこうした科学の進歩にたいし素直に肯定する気にはなれない。
科学者性善説のようなものがつねに当然視されているが、それは現実の人間世界の状況を反映していないからである。
科学者は「真理の探究」を職業にしているから、だれもが発見していないもの、発明していないものを求めるのは当然である。そしてそれは名誉も伴い、初めての人にはノーベル賞が待っているのである。
しかし、人間社会は科学の発明を、殺戮手段にも同時に使う存在である。究極のものはなんであれ、威力は高い。鉄砲よりも機関銃、機関銃よりも大砲である。
核の構造解明は、恐ろしいエネルギーの爆発手段を人類にもたらした。原子力の平和利用と称して、世界中で原子力発電所は増大し続けている。しかし、使用済み核燃料を安全なものにする知識を物理学は提供できないでいる。だから地下深くにそれらを保存しなければならないのだが、それが安全なものになるのには10万年もかかるのである。世界中でその施設が動いているのはフィンランドだけである。
遺伝子組み換えはいまや通常に多くの食糧生産に利用されている。しかし、組み換えが悪い意図で用いられることも十分人間社会では可能である。
科学者は、ますます神の領域に侵入していっている。そしてそれらの成果は善用もされるが悪用もされ続けてきている。はてしないこの繰り返しの結末は一体人類に何をもたらしてくれるのだろうか。だれもそれにたいしては責任をもっていない。いまあるままの状況を前に進むだけである。
「進歩」は人間にしか持ち合わせていない能力である。しかし、それを持ち合わせていない動物にくらべ、「悪」も比べ物にならないくらいでかいのである。
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Miniature brains grown in test tubes – a new path for neuroscience?
Lab-grown 'organoids' resembling embryo brains could be used for modelling diseases and testing drugs
Alok Jha, science correspondent
The Guardian, Wednesday 28 August 2013 18.00 BST
Stem cell scientists at Edinburgh and the Institute of Molecular Biotechnology in Vienna grew this organoid, or tiny 'brain', which measures just 4mm across. Photograph: Madeline A Lancaster/PA
Scientists have grown miniature human brains in test tubes, creating a "tool" that will allow them to watch how the organs develop in the womb and, they hope, increase their understanding of neurological and mental problems.
Just a few millimetres across, the "cerebral organoids" are built up of layers of brain cells with defined regions that resemble those seen in immature, embryonic brains.
The scientists say the organoids will be useful for biologists who want to analyse how conditions such as schizophrenia or autism occur in the brain. Though these are usually diagnosed in older people some of the underlying defects occur during the brain's early development.
The organoids are also expected to be useful in the development and testing of drugs. At present this is done using laboratory animals or isolated human cells; the new organoids could allow pharmacologists to test drugs in more human-like settings.
Scientists have previously made models of other human organs in the lab, including eyes, pituitary glands and livers.
In the latest work researchers at the Institute of Molecular Biotechnology in Vienna started with stem cells and grew them into brain cells in a nourishing gel-like matrix that recreated conditions similar to those inside the human womb. After several months the cells had formed spheres measuring about 3mm-4mm in diameter.
"The cerebral organoids display discrete regions that resemble different areas of the early developing human brain. These include the dorsal cortex identity – the dorsal cortex is the largest part of the human brain. They also include regions representing the ventral forebrain and even the immature retina," said Madeline Lancaster, who was first author of the paper published in Nature, on Wednesday.
Jürgen Knoblich, who was part of the team that created the organoids, said that tests on the brain cells in the structures showed that they were functional.
"Previous models were pieces of small tissue that aggregated to a decent size but there was no success, so far, in generating something that would resemble the cortex in a particular stage of development."
To show how effective the organoids could be in illuminating brain disorders, Knoblich and Lancaster teamed up with neurologists from Edinburgh University to grow brain tissue that modelled the developmental disease microcephaly, a condition where the brain grows to a much smaller size than normal, leading to mental disability.
"When I looked at the organoids derived from the microcephaly patient cells, the immediate thing I noticed was that [their] overall size was much smaller than the organoids derived from control, healthy cells," said Lancaster.
The reason, she said, was that brain stem cells normally undergo many rounds of cell division before finally turning into brain cells. But in microcephaly patients, the stem cells begin turning into brain cells too early, leading to a depletion in the overall number of brain cells.
Zameel Cader, a consultant neurologist at the John Radcliffe Hospital in Oxford, said: "This is a fascinating and exciting piece of research extending the possibilities of stem-cell technologies for understanding brain development, disease mechanistics and therapy discovery, as well as hopes for regenerative medicine."
He said the organoid was "audacious and the similarities with some of the features of a human brain really quite astounding".
Cader said one similar feature was "the fact that a considerable degree of the brain complexity and patterning is [being] encoded and which could arise from the DNA of the starting stem cells without additional external manipulations".
Paul Matthews, a professor of clinical neuroscience at Imperial College London, said that what made the observations so exciting was that cells from the patient with microcephaly developed into an abnormal organoid with features analogous to many of those existing in the patient. "The investigators then showed that these abnormal features could be 'cured' by replacing the defective gene."
Knoblich said that the team's goals included growing larger organoids and modelling more brain diseases.
At the moment the structures did not grow larger than a few millimetres in the culture dishes because nutrients and oxygen could not reach into the centre of the organoids as they grew. To grow much bigger the organoids would need to be equipped with a blood supply of some kind that could feed their centres.
He added that the organoids were unlikely to reach the complexity required to model cognition or any other higher brain function, and the intention of the research was not to grow replacement brain parts or an entire brain in culture.
"I have to be pessimistic about this. The ultimate complexity of the brain will not allow any replacement of structures," he said. "In the adult brain all the parts are intimately integrated with other areas of the brain. It would be very hard to repair defects with this."
