Refining optogenetic methods to map synaptic connections in the brain

August 19, 2016

Turning on and off neural circuits

Optogenetics is a technique that combines genetics and optics to control neuronal activity, which is based on the discovery of light-sensitive membrane channels within pond algae that control movement in response to light. When genes that produce one such light-sensitive membrane channel, called channelrhodopsin (ChR), are inserted into neurons and subsequently exposed to light, they regulate the flow of ions across cell membranes, increasing the neuron's activity. This allows scientists to discretely control neuronal activity by using pulses of light to activate specific populations of neurons.

Optogenetics is leveraged for mapping connections in the brain by stimulating individual neurons with light and recording the responses of nearby neurons with an electrode. In this manner, scientists ask whether stimulation of a putative presynaptic neuron causes a response in the putative postsynaptic neuron being monitored by the electrode. When ChRs are inserted into neurons using genetic techniques, however, their expression occurs throughout the entire surface of the neuron, from dendrites, the parts of the neuron that receive information, to the axon, the part of the neuron that sends information. The fact that ChR expression is not restricted to one particular domain of the neuron limits the information researchers can collect and interpret about synaptic connectivity, since it can be difficult to determine whether ChR stimulation was generated in a protein located in that neuron's cell body, or in the axon terminal or in the dendrites of other cells that happen to be passing through the light-stimulated area.

In their August publication in eLIFE, MPFI researchers, Christopher A. Baker, Ph.D. and McLean Bolton, Ph.D., described how they optimize optogenetic methods for mapping neural circuits in the brain. Their improved method uses optical techniques to confine light stimulation to a defined disc-like shape deep within living tissue, combined with a genetic approach for spatial restriction of ChR expression to the cell body and proximal dendrites of neurons. The spatially restricted ChR expression allows unmasking of synaptic connections from neurons whose cell bodies lie close to the dendrites of the postsynaptic cell that would have been occluded by direct activation of ChR on its dendrites. Moreover, it ensures that when light stimulation is applied to a particular cell, any recorded responses can reliably be assigned to the activity of that cell and not to the stimulation of axons or dendrites of other cells that happen to be passing within the disc of light stimulation. This method is a reliable way to rapidly evaluate synaptic connectivity with single neuron resolution and also offers enhanced specificity for other experiments involving optogenetic manipulations.

Future directions

According to Dr. Bolton, their goal is to construct precise maps revealing the functional connectivity of synapses, without the loss of information that limits the current optogenetics method. Evaluating neural circuits through optical stimulation promises to reveal much about how the nervous system functions, how it is modified by experience, and how it is disturbed in animal models of neurologic or psychiatric disease. "This optimized method is straightforward and easy to implement with standard two-photon microscopy, opening up many possibilities in research not only at MPFI but also for the entire field of neuroscience", said Dr. Bolton.
-end-


About Max Planck Florida Institute for Neuroscience


The Max Planck Florida Institute for Neuroscience (Jupiter, Florida, USA) specializes in the development and application of novel technologies for probing the structure, function, and development of neural circuits. It is the first research institute of the Max Planck Society in the United States.

Max Planck Florida Institute for Neuroscience

Related Neurons Articles from Brightsurf:

Paying attention to the neurons behind our alertness
The neurons of layer 6 - the deepest layer of the cortex - were examined by researchers from the Okinawa Institute of Science and Technology Graduate University to uncover how they react to sensory stimulation in different behavioral states.

Trying to listen to the signal from neurons
Toyohashi University of Technology has developed a coaxial cable-inspired needle-electrode.

A mechanical way to stimulate neurons
Magnetic nanodiscs can be activated by an external magnetic field, providing a research tool for studying neural responses.

Extraordinary regeneration of neurons in zebrafish
Biologists from the University of Bayreuth have discovered a uniquely rapid form of regeneration in injured neurons and their function in the central nervous system of zebrafish.

Dopamine neurons mull over your options
Researchers at the University of Tsukuba have found that dopamine neurons in the brain can represent the decision-making process when making economic choices.

Neurons thrive even when malnourished
When animal, insect or human embryos grow in a malnourished environment, their developing nervous systems get first pick of any available nutrients so that new neurons can be made.

The first 3D map of the heart's neurons
An interdisciplinary research team establishes a new technological pipeline to build a 3D map of the neurons in the heart, revealing foundational insight into their role in heart attacks and other cardiac conditions.

Mapping the neurons of the rat heart in 3D
A team of researchers has developed a virtual 3D heart, digitally showcasing the heart's unique network of neurons for the first time.

How to put neurons into cages
Football-shaped microscale cages have been created using special laser technologies.

A molecule that directs neurons
A research team coordinated by the University of Trento studied a mass of brain cells, the habenula, linked to disorders like autism, schizophrenia and depression.

Read More: Neurons News and Neurons Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.