An anonymous reader quotes a report from IEEE Spectrum: In April, Guoping Feng and colleagues at MIT, along with [Karl Deisseroth, a neuroscientist and bioengineer at Stanford University] demonstrated a minimally invasive optogenetic system that required drilling a small hole in the skull, then being able to control opsin-expressing neurons six millimeters deep into the brain using blue light. This approach used of a type of opsin that slowly activates neurons in a step-wise manner. In the most recent study [published in the journal Nature Biotechnology], Deisseroth and colleagues sought to instead enable both deep and fast optogenetics without surgery. The Stanford team expressed in the brain cells of mice a powerful new opsin called ChRmine (pronounced like the deep-red color “carmine”), discovered by Deisseroth’s group last year in a marine organism. Then, they shined a red light outside the skull and were able to activate neural circuits in the midbrain and brainstem at depths of up to 7 millimeters. With the technique, the scientists turned on and off brain circuits with millisecond precision. “It really worked well, far better than we even expected might be possible,” says Deisseroth.
The team then tested the effectiveness of the system. In one instance, they used light to quickly and precisely stop seizures in epileptic mice, and in another to turn on serotonin-producing neurons to promote social behavior in mice. Most optogenetic techniques involve injecting viruses with an opsin gene of choice directly into the brain with a needle. To avoid this, the Stanford team used a type of PHP virus developed at CalTech that can be injected in the blood. The virus then crosses the blood-brain barrier to deliver its payload, an opsin gene, to brain cells. In this case, even the delivery of the gene is noninvasive — no needle penetrates the brain. Deisseroth’s team is now testing the non-invasive technique in fish and collaborating with others to apply it to non-human primates. They’re also working with the Seattle-based Allen Institute to develop mouse lines bred with ChRmine in their cells.
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