Low-cost, open-source device for simultaneously subjecting rodents to different circadian cycles of light, food, and temperature

Abstract

Exposure of experimental rodents to controlled cycles of light, food, and temperature is important when investigating alterations in circadian cycles that profoundly influence health and disease. However, applying such stimuli simultaneously is difficult in practice. We aimed to design, build, test, and open-source describe a simple device that subjects a conventional mouse cage to independent cycles of physiologically relevant environmental variables. The device is based on a box enclosing the rodent cage to modify the light, feeding, and temperature environments. The device provides temperature-controlled air conditioning (heating or cooling) by a Peltier module and includes programmable feeding and illumination. All functions are set by a user-friendly front panel for independent cycle programming. Bench testing with a model simulating the CO₂ production of mice in the cage showed: a) suitable air renewal (by measuring actual ambient CO₂), b) controlled realistic illumination at the mouse enclosure (measured by a photometer), c) stable temperature control, and d) correct cycling of light, feeding, and temperature. The cost of all the supplies (retail purchased by e-commerce) was <300 US$. Detailed technical information is open-source provided, allowing for any user to reliably reproduce or modify the device. This approach can considerably facilitate circadian research since using one of the described low-cost devices for any mouse group with a given light-food-temperature paradigm allows for all the experiments to be performed simultaneously, thereby requiring no changes in the light/temperature of a general-use laboratory.

Keywords: animal research; circadian alteration; experimental model; intermittent fasting; light cycle; open-source hardware; temperature cycle.

FIGURE 1

Diagram of the device. (A) A conventional mouse cage with a water bottle (WB) is enclosed inside an opaque and thermal isolation box. Warm-white LEDs and a temperature sensor (TS) are placed inside the box. An air-conditioning (A/C) Peltier-based module is placed through the box wall, allowing heat (Q) to flow (red arrows) from the box to the room and vice versa when acting as a cooler or heater, respectively. An on/off feeder allows for controlling food availability. A fan and an orifice in the box walls allow continuous airflow (V′) for air renewal (green arrows). (B) A microcontroller drives the cycling of A/C, feeder, and light based on the box and the room temperature (measured by a temperature sensor (TS)) and according to the settings established by the user. Signals from/to the box in red color. See the text for a detailed explanation.

FIGURE 2

(A) Diagram of unmounted pieces of the on/off feeder. 1: internal cylinder to contain the conventional mice chop. One lateral part is made with stainless steel bars and the other lateral part is 3D-printed PLA (internal) and stainless steel (external, not seen in the figure). 2: External cylinder with a window. 3: Piece to be connected to the internal cylinder. 4: 3D-printed cap. 5: the place for a rotating motor. When the pieces are mounted (by displacing them from left to right), the internal cylinder can rotate inside the external one, allowing the mice (in front of the window of the external cylinder) to access the chop when the internal cylinder presents its lateral side with bars or preventing chop access when presenting the stainless-steel wall. (B) Two examples of the selectable illumination patterns applied to mice. The user can select whether the light pattern is constant (black) or progressive thus mimicking natural solar light (blue). The daytime of light on and off, and the illuminance amplitude in lux (250 and 200 lux, respectively, in the examples) can also be set by the user.

FIGURE 3

(A) General view of the setting, showing the box to enclose the mouse cage, the control unit, the external part of the Peltier-based air conditioning (A/C) unit, the fan for introducing room air into the box, and the wall orifice used for passing the electrical lines that also serves as the outlet of the air renewal system (green arrows represent the airflow). (B) Internal top view of the box showing the conventional mouse cage incorporating the on/off feeder (1), the internal blowers of the air conditioning unit (2), the illumination LEDs (3), the temperature sensor (4), the entrance for the air renewal from the fan (placed at the external side of the wall) (5), and the orifice used for passing electrical lines and used as the air outlet (6). (C) Detail of the front panel of the control unit. (D) Feeder perspective as seen by the mice, with the window open (top) and closed (bottom) making food available and unavailable to them, respectively.

FIGURE 4

(A) Example of raw temperatures recorded in the box (red line) and the room (blue line) when the device was normally working for 48 h for box temperature set to cycle between 18°C and 32°C. (B) Change in CO₂ concentration inside the box when a continuous flow of CO₂ mimicking the production by 5 mice (10 mL·min^-1) was injected into the mouse cage at min 3. CO₂ concentration increases by less than the safe threshold of 500 ppm above the room air value.