Miesenböck says one of the most difficult parts of the experiment was deciding which particular nerve cells to target with the remote control system. "To ascertain that the system actually worked, it wasn't clear how we could measure activation in the neurons in moving, freely behaving organisms," he explains.
The breakthrough, he says, came when they decided to target a small set of nerve cells in the fly called the giant fiber system. The giant fiber system controls very specific, stereotypical movements such as escape movements, jumping, and the beginnings of flight. If the flies engaged in these behaviors after the giant fiber neurons had been outfitted and "operated" with the remote control, Miesenböck and Lima reasoned, they could be sure that their system was working.
After genetically engineering the flies to express the ion channel in the giant fiber system cells and using the tiniest of injections to place the caged ATP inside the flies, the researchers shone a ultraviolet-wavelength laser in brief, millisecond pulses at the flies trapped inside a glass-domed arena. On command, the flies began a series of escape movements--extending their legs, jumping, and opening and rapidly flapping their wings.
The laser-triggered remote controls in the giant fiber system worked about 63 percent of the time, while remote controls placed in other nerve cells that were targets of the giant fiber system worked 82 percent of the time, the researchers concluded. Lima and Misenböck also equipped another set of nerve cells called dopaminergic neurons with the remote controls, boosting the