Support for the experiments in awake head-fixed mice

Need help setting up the experiments in awake head-fixed mice? Contact us at mhc-support@neurotar.com for advice on selecting the products and accessories, ensuring their compatibility with other research equipment, using or servicing already purchased devices. But first, take a look at the resources and the frequently asked questions (FAQs) below:

Resources for setting up the experiments in awake head-fixed mice

For selecting the best approach for your research goals, read an overview of approaches for studying the brain functions of non-anesthetized and behaving mice.

An overview of cranial preparations for in vivo imaging and electrophysiology helps to identify the most suitable surgery type. For the surgical implants available from Neurotar, visit the head plates’ page.

The choice of head fixation apparatus follows from the research goals and the choice of cranial preparations. Get oriented with the clamp options available from Neurotar: standard, tilted, Levelt (magnetic), and fUS clamps.

Regardless of the level of your surgical skills, Neurotar’s surgery tutorials (video) for cranial and spinal cord window preparations provide useful tips for optimizing surgical procedures. Due to the tutorials’ sensitive content, we have protected the videos with passwords. No worries, we share the password with all user labs.

Although mousse handling for the Mobile HomeCage follows the standard handling protocols, we recommend reviewing the recommendations for mouse handling in preparation for the experiments in the Mobile HomeCage®.

This page is a must: recommendations for mouse training in preparation for the experiments in the Mobile HomeCage®. We have included tentative timelines for imaging and electrophysiological recordings in awake mice.

Finally, if you are considering testing the Mobile HomeCage® equipment, review the guidelines for the Mobile HomeCage® trials, including the types of trials, their conditions, and a preparation checklist.

FAQ

  • Two-photon microscopy (through cranial window or thinned skull)
  • Electrophysiology in vivo:  patch-clamp, intracellular, extracellular, multi-channel
  • Functional ultrasound (fUS imaging)
  • Optogenetics

High precision tests can be integrated with behavioral monitoring

  • Stable head-fixation of an awake mouse;
  • No general anesthesia during habituation/training or imaging/recording;
  • Efficient stress reduction due to the flat floor and natural cage environment;
  • Natural sensory stimulation (cage floor and walls);
  • Visual stimulation and integration with VR is possible but not required;
  • The mouse controls its own movement;
  • Standard size Mobile HomeCage is compact, compatible with the majority of commercial microscopes;
  • Mobile HomeCage Large is the only head-fixation system that allows using real tangible mazes;
  • The locomotion tracking device (built into the air dispenser) allows monitoring behavior;
  • Cost-efficient.
  • Full-body restraint combined with sucrose or water reward;
  • Air-lifted styrofoam ball (combined with Virtual Reality to compensate for the lack of the sensory input);
  • Linear, circular or cylindrical treadmills (one-dimensional movement only).

These solutions limit the mouse’s control of its movements (granted, this may be desired under certain experimental conditions), and induce significant stress due to unnatural environment.

Alternatives based on the Mobile HomeCage design:

  • AirTrack, primarily a behavioral device. The system is too large for the majority of 2-photon microscopes; stability of head fixation has not been validated for imaging / ephys recordings
  • The Head-fixation apparatus designed by Mark Harnett’s lab (MIT) allows head movement in xy. This marginal improvement must be weight against a significant increase in design complexity and challenges of analyzing the imaging data.

 

Both the standard size Mobile HomeCage and the Mobile HomeCage are designed for mice and occasionally used for juvenile rats (<P20). We are looking for academic partners to continue the work that we have started on adapting the Mobile HomeCage for the research in rats.

The head plates are manufactured from stainless steel and can be reused after soaking overnight in acetone to remove dental cement and cyanoacrylate.

Cranial window implantation surgery (assuming it is done well) does not affect the mouse’s lifespan and health status. We keep the operated animals for up to one year.

We do not recommend implanting a chronic window before P21. Pups must be weaned from their mothers. Acute windows can be done at the neonatal stage. Window implantation in aged animals is feasible; we have operated 10+ months’ old mice for studies on Alzheimer’s disease mouse models.

The most common reason for head plate detachment is poor cleaning of the periosteum from the skull. The grip between the head plate and the skull can be improved in several ways:

  • By carefully removing the periosteum and subsequently drying the skull;
  • By making scratches on the surface of the skull;
  • By priming the skull with a layer of tissue adhesive glue;
  • By using high-quality cement/glue. We use a mixture of Rapid Repair from Panadent and Vetbond or cyanoacrylic glue.

Finally, the loss of a head plate may be caused by insufficient training, and the resulting stress and jerkiness.

Habituation consists of acclimation, handling, and training. For detailed instructions, visit https://www.neurotar.com/mouse-training-for-mobile-homecage/

Sources of sound or smell and reward/reinforcement systems (positive and negative) can be mounted on the MHC bridge or on the head fixation clamp. Some sensory stimuli, e.g. novel objects with distinct surface structure, colors, patterns and smell, can be positioned directly into the carbon cage (either attached to the wall or placed on the floor) as long as they do not impede the movement.

It is feasible to implement various reward systems in the MHC, e.g. a sucrose lick port for positive reinforcement or an air-puff tube for negative reinforcement. The bridge and clamp have screw holes for such applications. We are actively collaborating with other companies and laboratories to create standardized solutions. Please let us know your specific requirements, we’ll be happy to work with you on a customized solution.

Water and food may be delivered to the head-fixed mouse either manually or via automated tubes/feeding ports.

We recommend a 25x  water immersion objective with high NA (e.g., 1.05). The maximum imaging depth typically achievable is 700-900 micrometers.

Z-stacks can be acquired in a stable manner with micrometer-scale precision. Please note that, while the skull is immobilized by fixing it through the metal headplate to MHC’s head fixation frame, the living brain always has some degree of freedom to move inside the skull. Thus, lateral displacements of 1,3-1,5 micrometers can be expected; however, these displacements are elastic (e.g., cells/organelles will return to exactly the same position on the image, without a continuous cumulative “drift”).

Both intra- (whole-cell) and extracellular (cell-attached, field, single unit) recordings have been performed in the MHC. We and other MHC users have performed blind patch-clamping in both whole-cell and juxtacellular modes, holding the cells for up to one hour in awake behaving mice. Electrical noise is no greater than with standard patch-clamping in a brain slice setup. Also, 16-channel silicon probes and glass electrodes have been used by several research groups and produced extremely stable, high-quality recordings.

MHC has been used with a wide variety of manipulators (including Luigs&Neumann, Narishige, Scientifica, Sutter, Sensapex etc). Our own setup consists of the 3-axis Sensapex manipulator mounted on top of a Narishige manual 3-axis manipulator. In collaboration with micromanipulator providers, we have developed a number of adapters designed for mounting the manipulators directly on the MHC bridge (please contact us for more information).

All dorsal structures are accessible for optical imaging in the MHC; for electrophysiological recordings, any brain region can be accessed (if the recording electrode is made sufficiently long and inserted at a feasible angle using specified stereotaxic coordinates).

MHC is designed to ensure maximal compatibility with all commercially-available microscopes provided by Bruker, Femtonix, Leica, Neurolabware, Nikon, Olympus, Scientifica, Sutter, Thorlab, Zeiss and other vendors. A variety of xy-translation stages have been used with MHC, including Prior’s z-deck and other models capable of carrying the weight of MHC with other accessories, e.g. micromanipulators or reward systems. We will work with you to ensure that all critical dimensions/clearances are measured prior to purchasing MHC (e.g., vertical distance between the objective and xy-stage, horizontal distance between the objective axis and the microscope frame, etc).

Sutter MOM, and the latest systems from Neurolabware and Femtonics can accommodate the MHC-L without any modifications to the device or the carbon cage. MHC-L can also be adapted for Scientifica’s Vivoscope, ThorLab’s Bergamo and Bruker’s Ultima. Please contact mhc-support@neurotar.com for further help.

The MHC can operate either with a standard laboratory source of compressed air, or with a stand-alone air pump (turbine). The recommended air flow rate is 100-120 liters per minute. The air pressure requirements are less critical (typically, 0.1-0.2 bar pressure is sufficient). Should your laboratory air supply be insufficient, we can recommend a third-party air pump model that we and many of other MHC users have been using successfully.

The MHC is designed from aircraft-grade aluminium alloy and carbon fiber to be maximally silent and vibration-free. Acoustic noise produced by the MHC is essentially whisper-level, comparable to a typical laboratory background noise at 35-40dB. When an air pump is used, the overall noise can be somewhat higher but not to the level of being stressful. To minimize the acoustic noise, please use our noise reduction unit or place the air source farther away from the Mobile HomeCage using a longer air hose.

There are no special temperature and humidity requirements. The MHC kit (standard delivery) comes in a cardboard box with a foam insert. MHC is a robust device that does not require cleaning on a regular basis. Please note that pouring a solution into the MHC might block the air holes. It is, however, easy to open, wash and reassemble the MHC. Please contact us should you require further advice. Carbon cages should not be kept in places where room temperature exceeds 30 degrees Celsius.

One year standard warranty for all metal parts; 6 months warranty for all other parts.