Science is constantly
churning out new innovations to satisfy unmet clinical needs.
Neurotechnology is a
challenge because of the complexities of the brain such as its heterogeneity,
fragility, inaccessibility, anatomical richness, and the speed with which the
Recently, research in
neurotechnology took up this challenge and came out with some new inventions
that could solve many scientific puzzles. Optogenetics is one of them!
with a toolset of genetically encoded molecules,
opsins that, when
targeted to specific neurons within the brain, control the activity of those
neurons with light.
are a group of proteins that play a role in the molecular basis of different
forms of light- sensing systems including vision, circadian rhythms, phototaxis
go by the name of "rhodopsins", when they are expressed in the rods of retinal
layer of the eye.
are two types of opsins, Type 1 and Type 2,
based on their structure and
function. Research indicates that these two types of opsins evolved separately
and then converged during the process of evolution.
I opsins are present in bacteria and algae are referred to as
bacteriorhodopsin, channelrhodopsin and
halorhodopsin. They take part in phototaxis or photosynthesis.
II opsins are present in eumetazoans (animals excluding sponges) and carry out
various functions such as circadian rhythm, pupil constriction and
photoisomerization or recycling the non-protein component, the chromophore.
II opsins are present in a wide range of simple to complex animals; therefore
they are believed to have originated from a common ancestor that existed about
600 million years ago.
their similar functions, Type I and II opsins have evolved independently.
The story of opsin is that of convergence and also of predictability in
Since the 1970s,
opsins have been the subject of several studies due to their mind-blowing
biophysical properties, and also for the valuable information that they provide
into how various forms of life make use of light as an energy source or sensory
birth of optogenetics offers a number of interesting insights into the array of
factors that started neurotechnological innovation.
are molecules with seven helical
domains. These molecules have the ability to span the lipid membranes of cells
in which they are genetically expressed and respond to light by transporting
ions across the cell membranes.
Opsin found in
bacteria, the bacteriorhodopsin,
successfully been expressed in eukaryotic cell membranes, such as those present
in yeast cells and frog oocyte.
Many laboratories are
discovering new opsins with improved properties such as better light and color
sensitivities and ionic functions.
harboring genes that code for opsins are popular experimental tools
These viruses achieve specificity by restraining their expression to certain
types of neurons.
tools are increasingly being used in famous labs the world over to study to
study the role of neurons in information processing and behavior in various
types of organisms such as C. elegans
zebrafish, mouse, rat, and other forms of primates.
light sources such as conventional mercury, xenon lamps, light-emitting diodes,
scanning lasers, femtosecond lasers, and other common microscopy equipment
suffice for in vitro use.
Guoping Feng, an MIT
professor, has started working on first transgenic mice expressing
channelrhodopsin ChR2 (found in bacteria) in their neurons. Large numbers of
transgenic mice lines are being created to carry out these studies.
In 2009, Ed Boydon,
along with Robert Desimone and Ann Graybiel of the MIT, published the first use
of ChR-2 in the nonhuman primate brain (rhesus macaque) without causing any
these research has revealed the exciting possibility of the potential use of
optical neuron stimulation as a mode for diagnosis and treatment.
However a lot more work is required before it can be unquestioningly
F1000 Biology Reports, DOI:10.3410/B3-11 (open
access at http://f1000.com/reports/b/3/11).