How to choose the best solution for my in vivo optical recording and/or stimulation experiment

Written by Cedric Faure

November 29, 2019

An overview of MCI Neuroscience’s cutting-edge equipment portfolio

 

In vivo recording, imaging and stimulation guide - MCI Neuroscience

Finding the perfect solution for your experimental setup can be daunting. There are many manufacturers and distributors offering a huge variety of equipment with fancy designations (most of the time!), and it can be complicated to compare the features of all the options.

MCI’s portfolio is not an exception to the rule. Each manufacturer has a different approach to naming their equipment. On top of MCI-manufactured products, we collaborate with several suppliers who have their own catalogues, so the outcome on our website can appear complicated. If you are interested in understanding what the so-called “DiveScope®”, “Pryer” or “OASIS Implant” are, do not fear and follow the guide on this tour of our in vivo imaging portfolio!

 

In vivo imaging, recording stimulation - MCI Neuroscience

 

Which range of equipment will be described in this guide?

There are many levels of investigation in the world of neuroscience. Whole-brain imaging, behavioural studies, electrophysiology or microscopy are a few of the ways to answer an interesting question.

At MCI Neuroscience, we have developed experience in the field of neurotechnology addressed to solve problems in basic, pre-clinical and translational research. Our focus is to allow scientists to study neural activity. For this purpose, we have supplied labs with solutions over the years for the stimulation and the recording of neuronal activity through electrical or optical methods. Thus, you will find complete electrophysiology and imaging workstations on our website, as well as services to help you build your bespoke solution.

However, this post is aimed at giving you a comprehensive tour of a crucial part of our offer: our in vivo imaging, recording and stimulation portfolio. From wireless optogenetic stimulation in freely moving animals to complex sub-micron imaging resolution in vivo, we’ve worked towards creating a portfolio that suits most experimental paradigms and funding capacities.

 

What does MCI offer for in vivo imaging, recording and stimulation?

The following technologies are not ranked in terms of complexity of use or quantity of experimental benefits. They all address different questions, overcome specific restrictions and are in some instances complementary to one another. However, to give a structure to this list, I decided to organise them by level of image resolution, from the products not enabling the acquisition of spatial information of the brain region of interest, to technologies giving you access to dendritic spine images in deep tissue. You will find a comparative table at the end of the post summarizing the different strengths and weaknesses of each methods.

 

1. Wireless Optogenetic Stimulation – the “TeleOpto

Scientists have studied animal behaviour for a long time, creating numerous sorts of motor, sensory, nociception, learning or memory assays. The development of optogenetic tools has given these behavioural tasks another level of experimentation: the opportunity to manipulate neural activity simultaneously.  For neuroscientists designing their experiments and willing to learn more about this method, we recommend visiting the Karl Deisseroth lab’s Optogenetics Resource Centre website.

A barrier when using optical stimulation in freely moving animals is the requirement to implant an optical fiber to deliver light. The cable often limits what can be done during the experiment. However, we are offering a solution that allows the animal complete freedom of movement: the Teleopto Wireless Optical Stimulation. This equipment offers a wide range of options:

  • Single or dual illumination of the same area
  • Stimulation in 2 different locations, either simultaneously or independently
  • Different fiber diameters
  • Great selection of LED wavelengths

 

Teleopto for Wireless Optogenetic Stimulation - MCI Neuroscience

This solution will allow you to control neuronal activity without compromising the behavioural aspect of your experiment. However, it won’t give you the opportunity to record neuronal activity. If you are interested in getting this type of information, the instruments described below are better suited.

 

2. Fiber Photometry

Fiber photometry adds the ability to record fluorescent signals in the brain. It is possible to have untethered devices, and the user can detect the activity of neuronal populations in real-time. This method, allowing recordings from subcortical regions, is simple and versatile. Even though it doesn’t allow the user to capture spatial information, it is the perfect technique for chronic recordings of neuronal activity in deep tissue.

Combined with genetically encoded calcium indicators (GECIs) or genetically encoded voltage indicators (GEVIs), fiber photometry allows collection of fluorescence signals from specific cell types or pathways. In addition, some systems allow to combine optogenetic stimulations thanks to the powerful light transmission through the optical fiber.

For detailed explanation of the fiber photometry technique, we have published a dedicated post as a part of our Fundamental Series: deep-tissue optical recording and stimulation in behaving animals. In terms of equipment, we are currently offering two solutions.

 

a. TeleFipho for Wireless Fiber Photometry

TeleFipho for Wireless Fiber Photometry, developed and produced by our partner Teleopto, is the first commercially available wireless fiber photometry system. One restriction of the traditional fiber photometry systems is the requirement to have the optical cable attached to the head of the animal. Under certain circumstances, it can limit the movement of the animal when interacting with its environment. It can also cause some artefacts in the recordings, such as ghost movement due to the optical fiber swaying even if the animal stops moving.

Even though the power output is too low for optogenetic stimulation, TeleFipho solves all the issues associated to tethered experiments by placing all the system components on the headstage. Thus, this simple equipment provides the user with an inexpensive tool to record fluorescence from GCaMP and GFP-like indicators while performing the usual behavioural assays.

 

TeleFipho for Wireless Fiber Photometry - MCI Neuroscience

 
 

b. FiberOptoMeter III for Fiber Photometry

More conventional in its design than the TeleFipho for Wireless Fiber Photometry, the FiberOptoMeter III for Fiber Photometry comes with an optical fiber connected to the main unit. However, this system offers more versatility.

One can combine different wavelengths through the same optical fiber. Thus, the user can perform dual-band excitation, allowing for near simultaneous measurement of neuronal activity and optogenetic stimulation. Short flashes of high-power light in various wavelengths provide the user with the possibility to stimulate a great range of opsins (ChR2, ArchT…). Concurrently, the photomultiplier tube (PMT) detects the light emitted by Ca2+ indicators (GCaMP, RCaMP, OGB1…) and fluorescent proteins (tdTomato, mCherry, eGFP, YFP…). This combination allows the user not only to measure physiological signals from cell populations in freely moving animals, but also to manipulate the activity of neuronal network.

 

FiberOptoMeter III for Optogenetic Stimulation and Neural Activity Recording in Freely Moving Animals - MCI Neuroscience

 
 

3. Optical Fiberscope – the “OASIS Implant

In principle, optical fiberscopes offer a relatively similar approach to neuronal activity recording and manipulation than fiber photometry systems. However, the main difference lies in the complexity of the optical components. The system is designed to not only detect overall fluorescence from a region of interest, but to image deep-tissue with a few micrometres resolution. To achieve this, optical fiberscopes integrate fiber-optic bundles, enabling the user to obtain spatial information. A lot of the fiber photometry benefits and restrictions also apply to the optical fiberscope. The imaging fiber is directly connected to the detection hardware, making the animal tethered to the main unit during the experiment. Conversely, the user can still perform simultaneous calcium imaging and optogenetic stimulation in freely moving animals with excellent spatial resolution. As an example, the optical fiberscope allows for simultaneous optogenetic stimulation and calcium imaging of distinct neuronal populations.

For in-depth analysis of the optical fiberscope, please refer to our Fundamental Series: deep-tissue optical recording and stimulation in behaving animals.

The OASIS Implant by Mightex Systems is a ground-breaking optical fiberscope for simultaneous illumination and imaging of neuronal networks in the deep-brain, cortex and multiple other brain or spinal cord regions. By using flexible imaging fibers instead of miniature microscopes – such as miniscopes – mounted on the animal’s head, the OASIS Implant accomplishes to maximise the microscope performance and optimise the behaviour. A few key benefits are:

  • A unique scalable and reconfigurable imaging platform, compatible with multiple light sources and therefore multiple wavelengths, allowing simultaneous multiwavelength illumination.
  • A universal C-Mount camera adaptor compatible with various cameras such as high-end sCMOS ones.
  • Patterned illumination for cellular-resolution optogenetics when coupled to Mightex’s digital mirror device (DMD) technology: the Polygon.
  • Compact and light headmount (as little as 0.7g, which is up to 3X lighter than miniscope alternatives).
  • Rotative Adaptive Mechanism (ROAM) to provide the animal with unconstrained fiber rotation and movement.
  • Bifurcated imaging fiber to allow the investigation of 2 brain regions simultaneously.

 

OASIS Implant for targeted optogenetic stimulation and imaging in freely moving animals - MCI Neuroscience

 
 

 4. Two-photon deep-tissue in vivo imaging – the “Pryer Endoscopic Objective

Two-photon microscopy has revolutionised the ability to image neural activity in the brain of a living animal. Compared to single photon microscopy, this technique allows for targeting fluorophores and opsins in deep tissue. Moreover, the two-photon technique provides some key advantages:

  • High spatial resolution allowing sub-cellular imaging (e.g. dendritic spines)
  • Deep tissue penetration (800-1000 μm) and less scattering
  • Efficient light detection
  • Reduced phototoxicity and photobleaching

 

MCI Pryer for sub-cellular resolution deep-tissue imaging in vivo - MCI Neuroscience

 

As powerful as it is, the imaging depth of a stand-alone two-photon microscope has limits (typically around the 1mm depth below the surface). To overcome these limitations, MCI Neuroscience has decided to aim for a unique approach with our own endoscopic objective: the MCI Pryer. This state-of-the-art objective allows for deeper in vivo tissue access thanks to its 5.87mm tip. Combined with the objective working distance, the MCI Pryer gives the user the capacity to image at a depth up to 6mm.

We further offer two magnifications, a 70x and a 30x, allowing for respectively 0.5 and 0.8 μm resolution. For easier integration in your already existing imaging workstation, the MCI Pryer is compatible with any fluorescence microscope. With a high transmission ranging from the visible to the infrared region (400-1100nm), the MCI Pryer can be used not only on two-photon but also on confocal microscopes.

 

MCI Pryer vs GRIN Lens resolution

An alternative technique used to image deeper is to couple the two-photon microscope with a gradient index (GRIN) lens. Implanted in the tissue, the GRIN lens allows the user to record from deep areas through conventional objectives. However, this technique comes with its own limitations. Imaging through GRIN lens introduces some image distortion, spherical and chromatic aberration. On the other hand, the MCI Pryer is an actual compound objective, providing improved quality imaging compared to a GRIN lens.

 

MCI Pryer vs GRIN Lens spherical aberration

Working with a multi-photon implies some constraints regarding the behaviour of the animal. It is designed for head-fixed applications, whether the animal is anaesthetised or awake. However, the development of virtual reality solutions simulating natural environment allows for studying simple behaviour paradigms while imaging subcellular processes. If you are interested in this kind of simulator, please visit the website of our partner Phenosys.

 

 5. Multi-channel deep-tissue in vivo imaging – the “DiveScope®

For neuroscientists, the quest to observe activity in deep tissue layers is not restricted to the brain. Observing brain activity with simultaneous imaging of other tissues and/or organs (e.g. spinal cord, uterus, gut or pancreas) can answer interesting questions.

The constraints linked to the depth of the recording and the angle of access to these tissues make it challenging to perform recordings with conventional microscopes. Using our experience in micromanipulation, we developed a small easy to handle epifluorescence microscope. Mounted on our highly reliable micromanipulators, this microscope – named the “DiveScope®” – can be positioned at any angle and moved in all directions with tenth of nanometres precision. Its small diameter (2 to 3 mm depending on the model) allows minimally invasive image acquisition in vivo and in real time with sub-cellular spatial resolution.

Additionally, the DiveScope® can be combined with a second imaging device – whether it is a second DiveScope®, or any type of microscope with or without the MCI Pryer – to perform imaging in multiple areas simultaneously. For example, one could record from the intestinal mucosa while performing calcium imaging in the spinal cord; therefore, simultaneously studying multiple areas of the gut-brain axis.

 

DiveScope for Multi-channel deep-tissue in vivo imaging - MCI Neuroscience

 

MCI in vivo imaging, recording and stimulation in a nutshell

All currently available solutions for in vivo optogenetic stimulation and imaging have their own strengths and limitations. Your choice will depend on your application. You can find a summary table at the end of this post.

 

Teleopto for behavioural tasks - MCI Neuroscience

 

Fiber Photometry for neural activity recording in freely moving animals - MCI Neuroscience

 

OASIS Implant for targeted optogenetic stimulation and calcium imaging - MCI Neuroscience

 

  • The MCI Pryer, coupled to a two-photon microscope, provides deep brain tissue imaging in head-fixed animals with subcellular resolution.

MCI Pryer for high resolution deep tissue imaging - MCI Neuroscience

 

  • The DiveScope® combines multiple channels to record from various regions of the body simultaneously and in real-time.

DiveScope for simultaneous multi-region imaging - MCI Neuroscience

 

At MCI, we believe that this unique portfolio gives you access to a wide range of solutions, adapted to most experimental protocols and every budget. However, if you are interested in alternative technologies, please get in touch. We would be glad to help and might already have a solution we are working on to fulfil your requirements.

 

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