18 Jul 2008
optics.org speaks to researchers trying to get to grips with how lasers influence neuron growth.
Researchers are one step closer to understanding how lasers can be used to repair and grow neurons thanks to work being carried out by biologists and physicists at St Andrews University, UK (Optics Express 16 10507).
David Carnegie and his colleagues used optical line traps to initiate and guide the growth of neurons and hope that one day the technique could be used to repair the human nervous system after spinal trauma, for example.
It is known that light fields, such as Gaussian beams and optical line traps, can exert mechanical forces on cellular systems and affect the direction of growth of neurons. However, the mechanism that underlies this phenomenon is still poorly understood.
"Before optical line traps can be used to repair neurons, we have to understand the mechanism by which the light field is affecting their growth," Carnegie told optics.org. "In contrast to previous studies, our research has shown similar levels of growth regardless of the direction of intensity variations along an optical line trap. This leads us to suggest another mechanism for neuronal growth."
During growth, neurons send out filopodia – thin spike-like protrusions that can form from the growth cone, along which the cells tend to grow. Carnegie and his colleagues observed that these filopodia aligned themselves with the major axis of the line trap, which leads the extending growth cone to subsequently align and grow along the line trap.
"We believe that the laser light is creating a torque on the filopodia and pulling them in the direction of the laser," said Carnegie. "To explain this effect, we have developed a theoretical model to describe the optical torques experienced by the filopodia."
This work was carried out on very simple cells. The group plans to test its theory on primary cells, taken from animals, and hope to eventually use the technique to form a synapse – a junction through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.
"There is still a lot of work to be done before the mechanism of neuron growth using lasers is understood," said Carnegie. "There are other possibilities such as a temperature effect or perhaps we are interfering with a chemical process."
Nadya Anscombe is a freelance journalist based in Bristol, UK.