Here's another development in science that seems to have been taken from science fiction. Chemists at LMU Munich in collaboration with colleagues from Berkeley and Bordeaux have shown that it is possible to inhibit pain sensitive neurons using an agent that acts as a photosensitive switch.

The pain switch is a chemical compound called QAQ that is made up of active analogs of lidocaine, a well-known anesthetic. Lidocaine blocks the ability of the nerve cells to feel pain by inhibiting the action of receptors found in specific nerve cells.

"The molecule is made up of two functional parts, each containing a quaternary ammonium, which are connected by a nitrogen double bond (N=N)," explains the report. "This bridge forms the switch, as its conformation can be altered by light. Irradiation with light of a specific wavelength causes the molecule to flip from a bent to an extended form; exposure to light of a different color reverses the effect."

Researchers Richard H. Kramer and Dirk Trauner synthesized QAQ, which can be controlled by light. QAQ has the same mechanism to enter pain-sensing neurons but the researchers were able to alter QAQ by exposure to light with a wavelength of 500nm. The molecule switches between two conformations in response to light waves. Ultraviolet light turns the pain suppressing effect on while green light turns it off. The researchers tested the molecule in the retina of living rats.

The new method has been developed as a tool for neurobiological studies for pain research. Actual treatments of patients using the molecule are still a long a way off. The team still has to find an alternative to QAQ that can respond to red light of longer wavelength which can easily pass through human skin.