Researchers from the University of Dresden have usedembryonic stem cells to grow an intact spinal cord in a petri dish, the team reported this week. Its an enormous achievement in a field that has long viewed neural tissue as the ultimate challenge, and one which could give hope to millions of people suffering fromspinal cord injuries.

Neurons, the cells that form the thinking matrix of your brain and carry its orders to the rest of your body, are very difficult to grow. For a long time growing neurons was thought to be impossible, but then it was discovered that olfactory neurons regrow. This is why you can lose your sense of smell for a few days then slowly regain it; the neuron ends, basically open-ended synapses facing into your nasal cavity, areburned away by corrosive smells, butslowly growback. Intense study followed this discovery, as scientists tried to track down how our olfactory neurons regrow, and others packed them directly into severed spinal cords with real success. In the image above, olfactory neurons have granted a lab rat regains some ability to walk again after being paralyzed (though to be fair, those same researchers are the ones who paralyzed it).

Even if you can grow one, the spinal cord still needs to form connections with an incredible number of body parts.

Now, rather than trying toforceour spinal neurons to act like nasalones, this German teammay have a way of making new ones from scratch. Certain diseases and massive injuries could easily render a spine beyond all hope of repair, but in such a situation a full replacement might still work. Remember, though, that one of the reasons neurons are hard to work with is that they must form complex synaptic connections with other neurons to work properly; just growing the spinal cord is only half the battle, and the patients body still has to accept the new routing hardware and integrate it properly.Still, even just the ability to closelyobserve the growth ofa full spinal cord could move neuronal research forward by leaps and bounds.

This technique worked essentially by letting the stem cells go to work and getting as far out of the way as possible; rather than introducing some novel new growth factor, the researchers basically just created an environment where the spine could grow just like it would in a body. Their setup involved inserting small bubbles of stem cells into a nutrient-rich growth mediumand letting them go from there.Given all the opportunities they required, the cells naturally started coordinating andshuntinggrowth factors around most notably the trio of hedgehog signaling molecules.

The teams diagram shows inserted ESC colonies growing into larger cysts which eventually associate.

The most famous of the three-member band, both for its name and its function, is Sonic Hedgehog, which can stimulate directed neuron growth through itsconcentration gradient. A high concentration of Sonic Hedgehog leads the cord to growmotor neurons tocarry the brains muscular commands, while a lower concentration near the top of the cord will lead to interneurons that wire up the spine itself. This is roughly analogous to growth factors in trees, where the widen the trunk molecule is made at the bottom and ferried up, and the split the trunk into branches molecule is made at the top and ferried down; the two opposing concentration gradients lead to the tree-shaped trees we all know so well, with branches becoming less common toward the bottom, where trunk-width takes priority.

In this case, the stem cells and spinal cord were froma mouse, which allowed for lower cost and ethical considerations, butthe principles of growth and signaling should bethe same. This technique made use of embryonic stem cells (ESCs), which in humans must be collected from fertility clinics and similar, but the ultimate human progenitor cell might not be necessary to further research. As scientists come to understand the mechanics of this breakthrough better, and replicate its results a few more times, it would presumably become possible to begin thisprocesswithinduced stem cells made from adult tissue. If not, this will remain an interesting research tool with little real-world applicabilitydue to the costs and regulatory problemswith ESCs.

Star Trek had a spinal transplant episode but even in the 24th century, its an experimental procedure.

Lab-grown organs are coming far, fast. Somewhere in the world today there are gel baths and petri dishes growing human bladders, eyes, and penises, esophagi, livers, and breasts. Even the quest for lab grown meatfalls under the same basic research umbrella, as scientists use similartechniques to create high quality chicken andbovine skeletal muscle. As with this spinal cord, each of these areas of research is trying to create laboratory conditions that perfectly mimic the body, so cells grow and develop normally.

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Spinal cord has successfully been grown in a lab