Here we describe how to tether a fly in an olfactory magnetic-tether (OMT) apparatus. We describe how to align the rare-earth magnets and odor ports, and how to set mass flow rates for both the stimulus delivery and vacuum suction to achieve optimal odor tracking.
Introduction
The OMT is an adaptation of a magnetic tether system [1] designed to incorporate a “virtual plume simulator”. The following protocols will explain how to properly tether flies (Part 1) and provide strategies for setting up the magnets (Part 2) and mass-flow regulated odor delivery system (Part3). The information described here is optimized for this particular system and may vary for components with other technical specifications.
Part 1: Tethering flies
The steps for tethering described here are similar to many previous studies [2] but adapted for use in an OMT [3]. Proper tethering is crucial to ensure robust and repeatable experimental trials. The importance of careful tethering can not be overstated.
Part 2: Aligning the magnets
Aligning the magnets (Rare-earth-magnets.com) properly is necessary for the fly to achieve a smooth 360 degree range of motion. Follow these steps to properly align the magnets.
Part 3: Odor Delivery
Representative Results:
When these steps are followed correctly two things should be observed. First, under constant rotating visual stimuli a tethered fly placed in the OMT should rotate smoothly 360 degrees in the yaw axis. “Jerky” turns (called saccades) are characteristic of spontaneous turning behavior in the absence of constant visual stimuli. If flies can apparently not rotate smoothly, improper gluing (see Part 1) and misaligned magnets may be to blame (see Part 2). Second, when the odor is turned on, the fly should head in the direction of the odor. When the odor is turned off, the fly should saccade spontaneously with no preference for any single position in the arena. If flies do not actively track the odor plume, the position of the odor port, the air flow rate and/or the vacuum flow rate may need adjustment (see Part 3).
Tethering flies and eliciting stable odor tracking in this arena is relatively straightforward. It requires practice, patience and trial and error. Many parts of this arena could be further optimized or substituted to yield variations in experimental potential. For example, newer versions of the vacuum chamber are much smaller and allow more space below the arena. Also, the strength and type of rare-earth magnets can be varied slightly and additional odor ports could be added to increase the number of odor types and/or concentrations utilized in experiments. We note that any variations in equipment will require tailored optimization. As described here, the OMTA allows users to test the effect of visual cues on odor localization. A wide variety of visual stimuli can be presented with the LED panel system and when coupled with the versatility and expandability of the odor delivery system the system offers the potential to explore visuo-olfactory integration at many levels. This system also adds to the increasing number of quantitative behavioral assays for Drosophila, particularly for characterizing the behavior of flying adults.
Funding provided by the National Science Foundation (M.F.).
Material Name | Type | Company | Catalogue Number | Comment |
---|---|---|---|---|
Cooling Stage | Teca | LHP-300CP | ||
Brass Cooling Block | Custom Machined | ~4 x 8 x 2cm | ||
Sarcophagus | Custom Machined | Contact us for details | ||
UV-Activated Glue | Kemxert corp | KOA300 | 1oz bottle lasts years | |
Panel System | Caltech | http://www.dickinson.caltech.edu/panels | [4] | |
Minutien Pins | Fine Science Tools | 26002-20 | ||
Lower Ring Magnets | Rare-earth-magnets.com | NSN0615 | 5 – 0.75″o.d. x 0.375″ i.d. x 0.125″ | |
Upper Rod Magnet | Rare-earth-magnets.com | NSN0750 | 0.125″ x 1″ | |
V-Jewel Bearing | Small Parts | VJ-0469-01 | ||
MFC-4 Flow Regulators | Sable Systems International | |||
Gas Multiplexer | Sable Systems International | |||
Teflon Tubing | Small Parts | STT-20-C | ||
20 Gauge Hypodermic Tubes | Small Parts | HTX-20R-06 | ||
Glass Tubing | 4mm o.d. | |||
Vacuum Flow Regulator | Cole Parmer | EW-32464-52 |