Brains in a Test Tube

The fastest, most intricate computer ever built is a primitive machine compared with the human brain. One human brain cell, for example, may be "wired" to as many as 60,000 other cells. In an effort to unravel and understand the complexities of the brain, scientists in a number of laboratories are literally reconstructing the living brain tissue of lower animals in test tubes.

Pioneered by Biologists Aaron Moscona of the University of Chicago and Malcolm Steinberg of Princeton, the technique is deceptively simple. After taking tissue from the fetus of, say, an unborn mouse, researchers coax the individual cells apart with the help of enzymes and then put the separated cells into a growth-sustaining solution. Carefully incubated, the mix soon displays extraordinary activity. The cells begin to join and organize themselves into a pattern resembling the original tissue.

Last summer Neurobiologist Nicholas Seeds of the University of Colorado Medical Center reported that he had not only been able to reassemble brain cells from mice, but that the reconstructed tissue continued to develop in a normal way. Now, in the Proceedings of the National Academy of Sciences, Seeds and a colleague, Albert E. Vatter, disclose that the cells in the test tube mature and form synapses, the vital cell-to-cell connections that transmit messages through the brain and the rest of the nervous system. The material also appears to develop the myelin "insulation" that covers part of the cell in order to protect the messages from interference by other nearby cells.

Harvard's Richard Sidman, who was the first to apply the reassembly technique to brain cells, is now experimenting with a special variety of laboratory-produced mice called "reelers." A genetically caused "wiring" defect in the cerebellum and cerebral cortex of the reelers' brains impairs their coordination so completely that they stagger like drunks whenever they try to walk. Remarkably, when the brain tissue was taken from fetuses that had just developed the defect, Sidman's cells reorganized themselves in the same curious pattern.

If researchers can ever learn to intercept the genetic command that orders brain cells to link up in a particular way, they may eventually be able to substitute commands of their own. That, in turn, might enable them some day to prevent wiring defects in mice and possibly even in higher mammals, including man.

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