A team of Canadian electrical engineers has devised a technique for welding together individual neurons. In the most immediate sense, the laser-based method, which is described in the current Scientific Reports, affords researchers a tool to rapidly construct experimental neural circuits, but it may eventually be employed by doctors needing to rapidly repair damage to nervous tissues.
The problem is that those tissues don't repair themselves very well. Unlike most other cells, neurons aren't capable of dividing, and this limits neurogenesis, especially in adults. Thus, healing in the nervous system is very limited compared to the rest of the body. This is a large part of what makes diseases of and injuries to the nervous system so dire.
"It is of paramount importance to develop a precise means of selectively connecting specific axons to neuron cell body," the current study says. "Such a leap in scientific method will open up doors to unparalleled research frontiers in neurology, cell biology, biochemistry, and electrophysiology."
Being able to quickly connect neurons means being better able to to observe the processes involved in both neurogenesis itself—in which neural stem cells develop into proper specialized neurons—and in the various mechanisms by which neurons degrade and fail following injury or illness.
"Understanding the complex pathophysiological processes and the time frame available in order to prevent conductivity block and axonal death makes it necessary to develop techniques that enable the connection of nerve ends as soon as possible post injury, and maintain the viability of a healthy neural network," the authors continue.
The method developed by the Alberta group is based on femtosecond laser pulses, e.g. those lasting just one millionth of one billionth of a second. The effect of such infinitesimal pulses is so precise that they're already in use in applications such as cell nanosurgery, cell isolation, and cellular and embryo transfection (where nucleic acids are added to cells using light). Removal or ionization of material with femtosecond pulses has the added benefit of not impacting the cells and tissues surrounding a target.
So, one particular utility of femtosecond pulses has to do with their ability to inflict highly precise injuries to cells. This aids in the study of how neurons and axons (the long "tails" of neurons linking them to other neurons) regenerate. It turns out that the opposite effect can be achieved as well: the fusing together of neurons. This is what was demonstrated by the Alberta researchers. While cells have been successfully fused using lasers before, the group argues that this is the first time it's been accomplished using single neurons.
"Precise tuning of the laser parameters allowed us to induce a process called hemifusion at the contact point of two phospholipid membranes," they write. Translated, that means the researchers were able to take two neurons and fuse together only their outside membranes, without disturbing or damaging the stuff inside. So, the neurons remained distinct individual units while also being connected.
"We envisage that femtosecond laser-induced neuronal nanosurgical connection method can potentially provide a scientific leap that will open up new frontiers in the studies of the effects of connecting neurons, right before or after injury," the paper concludes. "The preservation of the viability of the neural network will allow researchers to study new complex pathophysiological processes... This will allow further development of new therapies for neuronal injuries and disease."
Broadly, what we're talking about is stitching together brains and spinal cords at the cellular level: sometimes putting them back together, but not necessarily. We could well be stitching together new things—a few neurons in a dish is a long ways away from the 300 trillion synaptic connections of the human brain, but, hey, you have to start somewhere.