19 February 2008 ICFO in El País

Prof. Pablo Loza

Research by Prof. Pablo
Loza\'s group on neuron
guiding by laser light is
the topic of a feature in
the national newspaper.
A laser beam capable of \"orienting\" the termination of a neuron and guiding its growth. This discovery of Pablo Loza\'s group, with potential applications in the reconstruction of damaged zones of the brain, is the topic of an article by Mónica Ferrado in El País. The research has the patronage of Cellex Foundation and is done in collaboration with Eduardo Soriano’s team, at the Institut de Recerca Biomèdica.

Prof. Pablo Loza\'s group has placed the focus of the laser beam of a “multiphoton microscope” in the proximity of neurons, discovering that in this condition their terminations (the axones) grow in the direction of the focus. The multiphoton or “non-linear microscope” is a device that produces very focused and short laser pulses of infrared light, with a duration of a few femtoseconds: \"If the Mediterranean was a second, a femtosecond would be a swimming pool for children”, Loza explains. This allows to concentrate in a point of the space (the focus) a power of hundreds of Kilo-Watts for every impulse. In these conditions special “non-linear” optical effects appear. Pablo Loza\'s group has built one of the best microscopes of this type available at the moment.

Previous studies have revealed that a light beam pointed towards the termination of a PC12 (a cancerous cell that is used as a model of a neurons) can operate like an “optical tweezer” and stretch the termination in the desired direction. Nevertheless, Loza\'s microscope has obtained this effect for the first time with neurons. The focused beam doesn\'t point directly to the axon (something that would kill it), but in proximity of it. The extremities of the termination (filaments called “filopodias”) explore constantly their environment and when they identify a \"desirable\" zone they “catch” the substrate and stretch the axon towards that zone. For reasons still unknown, the light focus turns out to be \"attractive\" to them.

One explanation might be that the neuron contains opsines (proteins sensitive to the light). Another one, that the beam modifies the chemical conditions of the substrate. The third one, that the pulse produces small acoustic waves (“The neuron is orientated towards the sound as a person walking by is attracted by the music of a party”, Loza explains. A short-term objective is to cut axones of worms of the earth (nematodos) and then orientate their growth with the beam. In the long term, it is possible to think of applying this technology to the wide range of diseases that imply neuronal damage and reduced connectivity in a region of the brain.