Jacky Ko

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ERG Dual Mouseholder

An electroretinography (ERG) procedure using mice and stimulus from an Espion ColorDome required the development of a mouse holder. The research group was getting too much noise to clearly see the electrical response of the data that they were collecting. Oxygen delivery and head stabilization were incorporated into the design to minimize the collected noise. The holders were made for two subjects to increase throughput of the experiment.

Design Goals

  • Do not obstruct the eye of the animal.
  • Direct oxygen towards both mice simultaneously.
  • Provide openings for mouth and eye electrodes.
  • Seamlessly incorporate the mouse holder onto the current testing setup on the side of a table with a heating bed.
  • Restrict head movement of two mice facing each other while limiting the distance between them.
  • Deliver anesthesia to the animal during imaging.

Stabilization

The stabilization of the mouse was done in two parts. The first part of the stabilization was done by an excavated area in the holder that was designed to fit the strain of mouse used for the ERG tests. This was created by doing a Boolean subtraction of a mouse mesh from the solid. The mouse mesh was created by 3d scanning a cadaver of a nude mouse. This provided the base mesh which was then cleaned up using the mesh tools that Rhino provides. The mold was scaled up to allow for slight tolerances in mouse sizes within the strain. The second part were small Velcro straps (not shown in images) that when from the flat half semi-circle to the other side of the holder.

Rhino model of ERG holder with a 3d scanned mouse.

Locking Mechanism

The integration of the mouse holder to the bed was done by using a C shape clamping mechanism. The holder could slide onto existing heating beds used for the experiment without moving the bed far from the laboratory table's edge. The use of the mouse holder was designed to be very simple; the scientist would just need to slide the bed on and lock the bed in place with the provided set screw. During the development of the bed, I experimented with a variety of fits for the clamping mechanism to make the holder slide easily onto the heating bed while providing some stability even without the set screw.

ERG holder attached to heating bed via set screws.

Oxygen Delivery and Electrode Placement

Oxygen was provided to the mouse by using a Luer fitting. The hoses at the laboratory fit with the Luer locks to provide leak free fluid connections. The oxygen travels into the bed and is subsequently redirected to each mouse by the shape of the holder. The covering in between the two mice prevented oxygen from escaping up.

Two main electrodes were used for ERG recordings. One electrode was attached to the mouth of each of the mice, the channels that allowed the L shaped electrodes to reach the mouse can be seen on either side of the Luer lock. Eye electrode were allowed to be placed without any obstructions due to the design of the stabilization mechanism.

Top view of ERG holder with a focus on oxygen channel.

Results

There was a dramatic decrease in noise with the new holder. The new ambient noise level is around 2.8x less than without the holder. This was significant for the experiment since ERG readings were then clearly distinguishable from the noise. The pictures below show the noise without external stimulus without the mouse holder and with the mouse holder. The capability of experimenting with two mice simultaneously also increased the throughput by a factor of 2.