The overall goal of the feeding experimentation device is to create an open source device that can measure food intake in a home cage setting in mice. This method can help answer key questions in the feeding and obesity fields, such as whether specific neural circuits can drive different patterns of food intake. The main advantage of this technique is that it is open source and home cage compatible.
It can measure food intake without specialized equipment or caging. We first had the idea for this method when we were weighing food intake in large numbers of mice by hand. This was time consuming and error prone.
Visual demonstration of this method is critical as the fabrication steps can be difficult to learn. Begin by preparing four two pin connector pairs and label both male and female sides A, B, C and D respectively, then remove the red wire from both sides of the connector pair D.Next, prepare one three pin connector pair and label both male and female sides E.Solder female stackable headers with sockets on the top side of the microcontroller. Clip protruding wire from headers on the bottom of the microcontroller, then connect the female stackable headers with sockets on top of the secure digital, or SD, data logging shield.
Leave protruding wires at the bottom of the shield. If they exist, jumper the SCL, SDA, MOSI, MISO and SCK pads on the bottom of the SD shield. If they are not present, disregard this step.
After that, attach male headers onto the Motor Shield with pins protruding from the bottom. Solder the headers onto the Motor Shield. Make sure the VIN jumper is in place above the power block on the Motor Shield.
Insert a three volt lithium cell battery into the SD shield. To assemble the power button, solder the two pin male connector A to C1 using red wire, and A to ground using black wire, as well as B to positive using red wire and B to NO1 using black wire. Heat shrink all connections.
Solder the photointerrupter and a 4.7 K resistor to the breakout board. Clip protruding wires from the back of the photointerrupter breakout board. Attach the male three pin connector E to the back of the breakout board, red wire to PWR, green wire to GND and white wire to SIG, then solder the two pin female connector A to five V and ground pins on the boost board, as well as the black wire from male connector D to the additional GND pin on the boost board.
Next, connect the two pin connector C to the terminals of a BNC jack by placing the red wire to the central pin and black wire to the outside pin. Assemble the Motor Shield by twisting the red and black wires of the female connector B together ane solder to VIN. Finally, solder the following.
One, the black wire of the female connector C to the ground pin next to AREF and the red wire of this connector to pin three. Two, the black wire of the female connector D to the ground pin next to VIN, and three, the green wire of the female connector E to the ground pin next to five V, the red wire of this connector to five V, and the white wire of this connector to pin two. Begin by connecting the FTDI breakout board to the programming pins of the microcontroller and then connect FTDI breakout board to computer via a micro USB cable.
Within the software, click the upload button to send the feeding experimentation device, or FED sketch, to the breakout board. Next, secure the five volt stepper motor onto the 3D printed motor mount with two number six one fourth inch sheet metal screws, then insert the rotating disc into the motor mount and push down to securely attach it to the stepper motor shaft. Twist on the 3D printed food silo to the motor mount, making sure the pellet leveler arm is over the hole in the motor mount.
Next, twist on the newly connected pieces to the top of the printed base, with the stepper motor positioned towards the back of the base and the hole positioned in the front. Cut the five pin connector from the stepper motor wires and strip about two millimeters from the end of each wire, then connect wires from stepper motor to the terminal block connectors on the Motor Shield, red to ground, orange and pink to one motor port and blue and yellow to the other motor port. After that, remove the net from the power button and insert the power button into the hole in the right side of the base.
Secure the button in place with a hex nut. Place the photointerrupter into its 3D printed housing and secure the housing into the FED base with two one inch nylon screws and corresponding nuts. Next, insert the BNC connector into the hole on the left side of the FED base.
Secure in place with nut, then connect a 3.7 volt battery pack to the DC-DC boost converter module via the two pin connection. Screw the boost board into the case using number two one fourth inch steel sheet metal screws, then mount the microcontroller inside of the base with FTDI connections facing the power switch using number four one fourth inch steel sheet metal screws, then stack the Motor Shield and data logging shield on top of the microcontroller. Mount the boost board with the microSD slot pointing down.
Lastly, connect the five connectors, A male to A female, B male to B female, and so forth. Place the battery inside the 3D printed base, slide the front and back covers onto the FED, fill the hopper with pellets and put the lid on the hopper. After assembly is complete, insert an SD card into the data logging shield, power on the FED system with the power push button, and test device functionality.
Manually remove five to 10 pellets from the food well and confirm that replacement pellets are dispensed. Finally, remove the SD card and verify that data was logged properly. After a one week habituation period, the food hopper was removed and replaced with a FED for five days of validation testing.
Pellet retrieval for individual mice show continuous feeding across the validation testing period, with clearly visualized circadian rhythmicity. To quantify the accuracy of FED, each FED system was given 1, 000 pellets for the validation testing period. FED logs 95%of pellets to the SD card.
Once mastered, each FED can be built in approximately two to three hours. After watching this video, you should have a good understanding of how to construct a FED and validate its use. Due to its open source nature, additional capabilities such as operant behavior can be added to the FED to answer additional questions.
