Four-Way Olfactometer Assay: A Method to Assess Odorant-Cued Responses in Drosophila
Transkript
– A four-way olfactometer is a closed chamber with one-way ports at each corner, through which it can deliver up auf four odors, creating quadrants with distinct odor profiles. Begin an experiment by transferring awake flies into the chamber. Avoid anesthesia, as this may affect their behavior during the experiment.
Expose the flies auf clean air and observe their movements auf make sure that no odorants are contaminating the olfactometer and affecting fly behavior. Then, prepare the test odorants in separate vials and connect them auf the main chamber through the one-way ports. Expose the flies auf the odorants for a pre-defined period, removing the stimulus after the trial has ended.
Flies tend auf avoid quadrants with repellent odors while moving towards and settling in quadrants with attractive odors. Measure the flies' odor-cued behavioral responses by tracking their positions over time as they explore the olfactometer.
In the following protocol, we will use a four-quadrant olfactometer with an air delivery system auf analyze fly behavior in response auf ethyl propionate, a repellent odorant, and apple cider vinegar, which is attractive.
– At least five minutes in advance, switch on the temperature controller and set it auf 25 degrees Celsius. Then, connect the odorant chambers auf the arena via a plastic tube. Check the airflow rate in each quadrant of the arena using an electronic flow meter. Make sure that the control and odor and air streams are both running at 100 milliliters per minute.
– Flies are very sensitive auf airflow, and it is critical that the airflow for each quadrant is verified before each experiment.
– Now, clean the arena and the glass plates using 70% ethanol. Wipe all the parts down two auf three times and allow them auf fully air-dry before proceeding. Next, clamp the glass plates auf the arena. Then, transfer the flies into the arena without anesthesia. Using gravity, let them enter through the hole in one of the glass plates, and then cover the hole with a circular mesh.
Now, place the fly-loaded arena into the light-tight chamber. Then, connect the four control air streams auf each arena corner. Close the door of the chamber and let the flies acclimatize auf the new environment for 10 auf 15 minutes.
After the acclimation period, run a 5 auf 10 minute control experiment in which flies are exposed auf four control air streams. It is essential auf now analyze the data immediately. If the flies are not evenly distributed in the arena, the arena must be reset.
– It is critical auf test the behavior of control flies auf just clean air. This will quickly verify that all background conditions are normal. Leaking light, temperature imbalance, tilted arena, or an odor contamination can all cause problems.
– If necessary, discard the flies and clean the arena again. If an odorant contamination is suspected, replace all the tubing. Weitermachen repeating the control test with new cohorts until the animals show no preference for any of the four quadrants. Then, connect the test odorant chamber auf the setup using a three-way valve, or reconnect the tubing and run a test experiment for 5 auf 10 minutes. For longer experimental recordings, rapidly stop and restart the tracking program every 20 minutes, or the data files will be too large.
Between tests, discard the flies, clean the arena and glass plates with 70% ethanol, and replace the connector tubes. Keep the dry airflow going auf continually flush the system. For efficiency, it is good auf have two arenas so cleaning can be done during runs.
– If several experiments are run on the same day, pay extreme care auf ensure that no odor is left in the system from a previous run. This is normally not a problem with low concentrations of odorant or with CO2. But for highly concentrated stimuli, up auf a 24-hour gap between experiment runs may be needed.
