Because of its putative harmful actions on humans, increased attention has been recently paid to stable and pulsatile magnetic field effects on the structure and functioning of living organisms. Available information regarding the mechanisms of action of magnetic fields on living beings (and on adaptive responses developed by the latter) is rather scarce and fragmentary. Here we have taken advantage of the available information on the physiology and genetics of the visual system of Drosophila to design a test for the study of magnetic field effects on animal motor behaviour.

Drosophila is highly conditioned to orient its behavior according to available visual information. Thus we have developed a test to determine the sensitivity of this fly to the presence of different types of stable or pulsatile magnetic fields (fixed or variable in relation to the animal’s location in the space). We have used a modified version of Buridan’s test, a very well known behavioural paradigm. The classic description of Buridan’s test is supported on three basic characteristics; for its implementation we have developed the following instrumentation: (1) the animal was placed on a circular arena (11.5 cm in diameter). The arena was located inside a larger (15 cm) cylinder widely illuminated. Under these conditions, the animal maintains a strong walking behaviour: the fly walks back and forward between two vertical black stripes, identical in size and shape. Home-made computer programs allowed the determination of animal position, trajectory and speed. When the black stripes were removed, and the arena illuminated faintly, the animals selected resting positions at random. (2) Experimental animals were unable to reach the two black stimuli, because the arena was surrounded by a water pit. Besides, the flies were unable to fly, since their wings were carefully cut under a dissecting microscope. (3) With this experimental design, the evoked behaviour was proved to last for hours, making the test very suitable for quantitative purposes.

Until now we have tested the effects of a fixed magnetic field (24-48 mT) on flies location on the arena and on their performance during Buridan’s test. Preliminary results indicate that fixed magnetic fields (orthogonal to the animal’s trajectory) are able to modify spontaneous location of the flies on the area and their linear trajectories during Buridan’s test performance. Flies move less when a magnetic field is present (females, n = 24; males n = 21; Student’s t test, P < 0.05). The effects are different for males and females. At present, we are checking many different Drosophila mutants in a search for a strain insensitive to these magnetic field signals.

This work was supported by grants from La Caixa, Junta de Andalucía and DGICYT (BFI2002-00936).