This article details a method for recording neuronal responses in live Drosophila flies using electrophysiological techniques. The procedure involves mounting the fly, positioning electrodes, and delivering odorants to study sensory neuron activity.
Mount a live Drosophila fly in a tube with its head exposed, antennae adhered to sticky tape, and secured by a holding rod.
Keep the preparation under a constant flow of humidified air to prevent desiccation.
Insert the reference electrode through the clypeus, a supporting structure protecting the mouthparts, to reach the circulatory system.
Place the recording electrode near the sensillum, the insect's sensory organ.
Insert the electrode into the base of the sensillum.
Record signals with specific spikes to confirm the correct electrode positioning near the olfactory receptor neurons.
Connect a cartridge containing the test odorant to the delivery tube.
Position the tube aiming at the fly's antenna, adjusting the height and distance from the electrodes.
Using the software, set the odor flow rate and dosage amount, then release the odorant.
Now, record electrical signals to capture the fly's neuronal response to the odorant.
To take recordings, insert the reference electrode into the clypeus using a swift and smooth motion. Place it just below the cuticle where it will be in contact with the hemolymph. Next, slowly lower the recording electrode until it enters the same plane of view as the target sensillum. Then, insert the recording electrode into the sensillar base.
Before proceeding, ensure that there is a high signal-to-noise ratio, with identifiable spikes from at4A and at4C neurons. The at4A neuron should fire no faster than 20 hertz.
Now, connect the cartridge to the odorant delivery tube. In this case, a palmitoleic acid cartridge is attached. Next, use the micromanipulator to maneuver the cartridge towards the prep while aiming it to the head. Position the cartridge tip pointing directly at the antenna from a distance of about 4 millimeters. The cartridge must also be about 1 millimeter above the slide.
The cartridge might be closely bordered by the electrodes and the slide. It should ideally be at least four millimeters from either electrode. For stimulation, set the odorant flow controller to 500-millisecond bursts and use a 500-milliliter per minute flow rate. For each stimulus burst, record the electrical activity for 10 seconds.
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