Mice Vapor Control

Senior Design Day Presentation

Project Background

The opioid crisis has been a continuing societal and public health problem in the United States, and the Hnasko research lab is interested in studying the phases of opioid addiction using mice. There are two current methods of drug delivery used in addiction studies, the intravenous self-administration (IVSA) approach and the full vapor immersion approach, which limit the inferences researchers can make to human addiction.

The Hnasko Lab aims to correct the limitations of the existing methods by creating the volitional vapor inhalation (VVI) approach through this project. The researchers want us to build a vapor delivery system where the

mouse will voluntarily receive drug vapor by inserting its nose in a small hole (called a nose poke) and triggering a sensor. The vapor will flow through the nose poke so that the mouse can inhale it. Using this method, the mice will easily be able to voluntarily receive the drug without stress from a catheter and without the researchers being present to administer the drug. Additionally, no drug vapor will settle on the mice’s fur because the vapor will be sucked to the exhaust immediately after it flows by the mouse’s nose, which will allow mice receiving the drug to be socially interactive with other mice.

With the VVI method, the Hnasko lab can more realistically model in the mice the different phases of the development of drug addiction: drug intake, escalation of drug intake, withdrawals during abstinence, and relapse. Once these phases are modeled with the mice, the researchers can study the role that different brain regions and specific cell types within these brain regions play in the behavior of the mice.

Project Objectives

Our team was tasked to realize this VVI approach by designing a vapor delivery system that allows mice to voluntarily receive drug vapor without being immersed in the drug.

The key components of our project are:

• Airtight chamber

• Automatic mouse door

• Vaporizer and vacuum exhaust

• Two vapor delivery ports

• Removable waste pan and grid floor

• Integrated pellet dispenser, LED, and speaker

• MED PC interface through which to control chamber components and collect data

High Priority:

• Automatically detect mouse’s nose and deliver vapor to it

• Minimize drug flow into operant chamber

• Allow no leakage of drug vapor outside of the system for safety of lab personnel

• Integrate chamber with the existing mouse home chamber

• Incorporate components such as pellet dispenser, grid floor, and removable waste tray

Medium Priority:

• Integrate the control with Med PC software (current control interface)

• Track drugging frequency and duration

• Install speakers and LEDs for other behavioral cues

WOW Priority:

• Measure volume of drug inhaled by mouse

Final Design Description

The main components of the final design are highlighted in the figure above. The video on the right is an animation of the design. The foundation of the design is a laser-cut acrylic chamber that is made airtight using acrylic glue, silicone sealant, rubber gaskets, and clamps. One of the key components attached to the chamber is an automated mouse door that will allow mice to enter one at a time, while also ensuring the chamber will remain airtight during each vapor cycle. Another key component is the pair of nose pokes on the far side of the chamber that will detect the mouse's nose with a photobeam sensor and automatically administer the drug to the mouse via the nose hole. The nose poke also has a nozzle connected to an vacuum exhaust system which constantly pulls air out of the chamber to ensure no drug vapor drifts out of the nose poke into the rest of the chamber. This necessitates the combination of a pressure gauge and relief valve. The pressure gauge and relief valve combination serves the purpose of regulating the negative pressure inside the chamber by allowing air to enter the chamber when the pressure inside the chamber dips below a certain threshold, and enabling researchers to constantly monitor the air pressure. This method avoids the need of a complex air intake and regulation system, while still ensuring mice will always have fresh air to breathe and not be submitted to very low pressures caused by the vacuum exhaust. The other two components that are highlighted in the figure are a speaker that will deliver behavioral cues to the mice and a pellet receptacle that will deliver food pellets as a reward if the mouse completes certain tasks.

The figure above shows the control logic of the vapor delivery system throughout the course of the experiment. The Hnasko lab has a preexisting system called the mouse sorter which houses the mice and allows one mouse to exit at a time. The exiting mouse will then be allowed to scurry into the vapor chamber through the open mouse door.

1. Before the start of the experiment, the mouse door will be in the open position. The vacuum

exhaust will be on and remain on for the duration of the experiment.

2. When a mouse enters the chamber and inserts its nose in the nose poke, it will break the

photobeam sensor which triggers two components instantaneously.

• The mouse door shuts and seals.

• The vaporizer turns on and vapor flows through the nose poke hole to be inhaled by the

mouse.

• The vacuum connection on the other side of the nose poke will immediately vent

out the un-inhaled vapor.

3. When the mouse removes its nose from the nose poke, the photobeam sensor will trigger the

vaporizer to turn off. The mouse door will remain closed.

• Since the vacuum will be continuously venting air from the chamber, the pressure inside

may begin to drop below atmospheric pressure. When that happens, the relief valve will

open and allow outside air to enter the chamber and restore the pressure.

4. The mouse door will remain closed for a period of time set by the researchers. During

this period, the mouse may choose to intake the vapor additional times using the same above

process. The mouse may also receive food pellets from the pellet dispenser, and the researchers

may also choose to utilize the speaker and the LED lights for audio and visual cues.

5. After the set amount of time has passed, the mouse door will open and the mouse is free to

return to the mouse sorter.

Testing and Performance

The chamber was constructed from laser cut acrylic pieces and was made airtight using acrylic solvent to bond the walls and silicone sealant to fill any gaps. The front removable door has a rubber gasket around the edges which is compressed by four latches. In order to test for air leaks, we covered possible leak points with soapy water and used a bike pump to pump air into the chamber. Bubbles formed at the locations of the leaks, which we then filled with silicone sealant. Using this leak testing method, we were able to make the chamber walls, front removable door, and mouse door airtight. The only source of potential air leaks is through the pellet dispenser, which is a low risk air leak.

After assembly, the chamber and vapor system were tested in the sponsor's lab. Each component was set up to be controlled with the lab's existing software: Med-PC. In order to test the vapor system, we shined a laser pointer in front of the nose poke while triggering the vaporizer. Whenever vapor flowed into the chamber, the laser line would become visible. We found that, as desired, the majority of the vapor flowed through the nose poke directly to the vacuum exhaust. While a minimal amount of vapor entered the chamber, this is not an operational issue because in practice the mouse's nose will be inserted in the nose poke hole and inhaling vapor. The important result is that the vapor is being properly transferred to, and exhausted from the chamber.

For more details on key components, tests and performance, see final design section.

Executive summary