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A reliable protocol for optogenetic studies in the nonhuman primate
A new study, published in the journal Neurophotonics, describes a simple and replicable protocol for carrying out optogenetics studies in monkeys with readily obtainable devices and materials.
For 10 years, optogenetics has been used as a powerful research tool in rodents thanks to the reliable expression of channelrhodopsin-2 (ChR2) in mammalian neurons. In 2009, ChR2 was first expressed in the macaque frontal cortex, opening the door for optogenetics studies in nonhuman primates.
Since then multiple research groups have attempted optogenetics in monkeys because of its advantages over traditional electrical microstimulation or pharmacological methods in spatial and temporal precision, as well as allowing excitation and inhibition.
These experiments have had varied success rates and many researchers struggle to produce reliable expression and output from neural responses in the nonhuman primate brain.
The step-by-step instructions published in this paper includes detailed guidelines on all necessary aspects of a properly designed optogenetics study from virus preparation to stimulation and recording.
The protocol includes two distinct advantages over some other procedures. Firstly, the viral injection can occur “in-chair” or in the operating room (OR). “In-chair” injections are more flexible than injections in the OR and are better for the animal. They can be performed without stereotaxic anaesthesia and sedation whilst in the same position as recording sessions.
Secondly, the group created a tapered optical fibre for light stimulation. Previous studies had reported tissue damage caused by the blunt tips of optical fibres, making long-term recordings difficult. The tapered, smaller-diameter fibres used in this procedure significantly reduces tissue damage and enables repeated experiments in the same area for months.
The methods described in this paper are widely applicable to numerous optogenetics studies in the nonhuman primate, although further design will be necessary to ensure that such experiments can answer the specific experimental goals.
Scientifica’s IVM Single motorised micromanipulator was used by the researchers when developing this protocol. Its stability, precision and software controllable action make it ideal for studies in in vivo tissue by minimising tissue damage. The LinLab software includes the unique “creeper” function, which enables programmable movement at a specified speed.
Dai J, Ozden I, Brooks DI, Wagner F, May T, Agha NS, Brush B, Borton D, Nurmikko AV, Sheinberg DL (2015) Modified toolbox for optogenetics in the nonhuman primate Neurophotonics 2:3 doi: 10.1117/1.NPh.2.3.031202
Image Credit: Steve Ramirez, MIT