Field of Life Sciences
Achievement
The development of methods that use genetically addressable light-sensitive membraneproteins to unravel neural circuit function

Prof. Gero Miesenböck (Austria)

Born: July 15, 1965 (Age: 57)
Waynflete Professor of Physiology,
Centre for Neural Circuits and Behaviour, University of Oxford

Prof. Karl Deisseroth (USA)

Born: November 18, 1971 (Age: 51)
Professor,Departments of Bioengineering and Psychiatry,and Howard Hughes Medical Institute Stanford University

Previous methods using electrical stimulation and drugs

A new technology that controls neurons freely using lightThe brain is composed of an enormous number of nerve cells,or neurons, which form complex circuits that are used to exchange
information. The reason humans are able to think and move isbecause the neurons responsible for controlling those functions
are activated and thereby transmit information correctly.
Electrical stimulation and the administration of drugs have long
been used to study the neural circuitry that controls behavior,thought, and other functions.
Electrical stimulation is applied by inserting a thin electrodeinto a specific region of the brain and passing an electrical current
through it, which either activates or deactivates neurons in the area
to study how behavior changes. However, this method changes thebehavior not only of the targeted neurons but also any surrounding
cells, which makes it difficult to precisely determine the role of a
specific neuron.
The drug method involves local administration to the brain of adrug that activates or deactivates specific neurons, at which point
subsequent behavioral changes are observed to understand therole of those neurons. However, neural activity moves at a ratemeasurable in milliseconds, so because it takes time for drugs toaffect the targeted neurons, there is a limit to what can be gained
from this method.

The method using light developed by Miesenböck and Deisserothovercomes all the shortcomings of previous methods.
In 2002, Miesenböck developed a new technique that allowed
him to use genetic manipulation to express photo-sensitive proteinsin specific neurons, the activity of which could then be controlled
through exposure to light. Then in 2005, Deisseroth used Chlamydomonas, a type of green algae that contains a photosensitive protein
called channelrhodopsin, to improve this technology and make it
more precise and easier to use, thereby making it possible to apply
in a wide range of research fields.
This technology makes it possible to illuminate and control theactivity of specific neurons in the brain of a living animal using
optical fibers and other equipment, only changing the activity of
the neurons being targeted. Furthermore, this technique allows
neural activity to be freely turned on and off on a time scale ofmilliseconds or microseconds. For example, channelrhodopsin
can be expressed in neurons in mice in the part of the brain called
the amygdala, and they can then be illuminated with light using
an optical fiber. Mice are normally uneasy in open spaces and sothey tend to stay close to walls when they move, but after light isshone on specific neurons, they can temporarily be made to feelless anxious such that they can walk around far from walls without
issue. In this way, the direct causal relationship between neuron
activity and behavior can be made observable.
This light-based technology has revolutionized research in thefield of neuroscience, and it continues to evolve today.

Figure 1: Conventional methods for investigating the role of neurons

Electrical stimulation

Drug administration

Figure 2: The award-winning techniquePhotostimulation

Optical fiber

Clarifying the causal
relationship

Using conventional methods such as electrical stimulation (left) and drug
administration (right) to manipulate neural activity results in other cells near thetargeted neurons also being affected (yellow explosions in figure).

Neural Circuit- Only targeted cells- Quick response

Behavior understoodat the organism level

By expressing photosensitive proteins in specific nerve cells, it is possible tocontrol the activity of target neurons through photostimulation.

Developing the technique – Concepts and principles
Miesenböck was first to come up with the concept behind thetechnique and the principles upon it is based, and he was thefirst to demonstrate its utility. In 2002, Miesenböck took threephotoreceptor genes from the eye of Drosophila, including aphotosensitive protein called rhodopsin, and expressed themin hippocampal neurons of rats, whereupon he demonstrated
that activity in these neurons could be freely controlled byilluminating them with light. This is possible because whenrhodopsin senses light, the cell membrane opens somethingcalled ion channels, proteins that transport ions in and out of acell. The flow of ions in and out of the cell produces an action
potential, the mechanism by which neurons are activated.
Initial experiments were conducted in vitro, but the experiments were repeated in 2005 on living Drosophila. That experiment successfully induced escape behavior in the flies (flyingand flapping wings) by using light to control activity in specificneurons. Moreover, in 2008, the same principles were used toidentify the neural network in male Drosophila responsible forcontrolling courtship behavior.
These results had an immense impact as they demonstrated
that photostimulation could be used to directly research therelationship between neural activity and behavior.

Algae genes open the way to discovering the potentialof the technique
Deisseroth developed a technique for manipulating neural activity
using light by focusing on the protein channelrhodopsin, or ChR2,a microbiological rhodopsin reported to be involved in photoaxis ingreen algae.
ChR2 is a protein that functions as a rhodopsin, which reacts tolight, and as an ion channel, which allows ions to pass through thecell membrane, and one of its properties is the short time between
it being exposed to light and the channel opening. In other words,
using ChR2 has the benefit of making the process simpler because
it involves the introduction of only one gene, and still allows for
precise control of neural activity.
In 2005, Deisseroth demonstrated that photostimulation of ChR2
expressed in cultured hippocampal neurons from rats could affectneuronal activity within milliseconds. He later used the techniqueon live mice and successfully identified the neuronal population that
produces gamma brain waves, and clarified the neural mechanismthat controls social behavior and learning.
A variety of channelrhodopsins with different functions are currently being developed, and the technique is in wide use in everythingfrom pure research to the development of treatments for neurologicaldiseases. Algae genes opened the way to discovering the potential ofthis technique that has revolutionized neuroscience research.

Figure 3: Illustration of one of Miesenböck’s principles
Figure 4: Using the technique with channelrhodopsin (ChR2)

K＋
Ion channel

Na+
Ca2+

K+

Rhodopsin

G protein
Arrestin
3 Drosophila genes
Source : Miesenbock (Neuron 2002)

The structure of rhodopsin changes when exposed to light, activating G proteins andindirectly opening ion channels (green arrow.) When an ion channel is opened, Na +,Ca2+, and K+ move in and out of the cell (red arrows) thereby transmitting information
by inducing a large change in the membrane potential called an action potential.

Na+Ca2+ChR2

Source : Deisseroth (Nat Neurosci 2005)

The structure of ChR2 changes when exposed to light, opening ion channels
contained with the protein itself. When an ion channel is opened, Na+, Ca2+,and K+ move in and out of the cell (red arrows) thereby transmitting information
by inducing a change in the membrane potential called an action potential.