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Fruit flies fly while scalped, exposing their brain cells for science

Hats off to Caltech researchers, who found that scalping fruit flies allowed them to record the insects' brain activity for the first time while they were actually flying - or at least trying to. (The Nature Neuroscience abstract here.)

Scientists love fruit flies because they're so simple, yet revealing. Some 70% of their genes are found, in one form or another, in humans, while 80% of the genes known to be associated with human disease occur in the fly.

But working with the little nose-divers can drive one nuts. In an accompanying Caltech news release, lead researcher Gaby Maimon states the obvious: "[I]nsects are really, really tiny, which means it is very difficult to record from their brain during active behaviors such as flight."

Oh, and another small detail: A fly's brain cells aren't sitting on the outside of its head, convenient though this would have been for neurobiologists. Still, where there's a will - and a scalpel - there's a way: By slicing off a patch of the hard cuticle covering the brain, "we were able to target our electrodes onto genetically marked neurons," the study's senior author, Michael Dickinson, explained. The scientists essentially lassoed the little buzzing broncos, then blew air puffs at them to get them to flap their wings.

Indeed, if you've got a steady hand and a lot of patience, the sky's the limit. Stanford Medical School researchers in the lab of David Schneider, PhD, showed a penchant for micromanipulation when, just over a year ago, they demonstrated that fruit flies' immune systems responded differently to bacterial infections depending on whether the flies were snoozing or cruising when infected:

Working with jerry-rigged, light-bulb-laden shoeboxes to manipulate the flies’ daily cycle and with syringes small enough to inject measured amounts of germs into the wee winged ones, the investigators have shown that the insects’ immune response waxes and wanes with the diurnal oscillations called circadian rhythms... This enabled the researchers to infect two sets of flies (from “nighttime” or “daytime” shoeboxes) in a single experimental session. [U]sing syringes fashioned from glass capillary tubes heated and then stretched so that they were extremely thin, but still hollow. . . [lead investigator Mimi Shirasu-Hiza] spent hours on end in a dark room lit only by a red bulb (red light doesn’t seem to perturb the daily rhythms of the flies) while injecting, one by one, multiple hundreds of tiny, week-old male flies (half of them sleeping, the other half awake) per session with precise volumes of solutions containing different pathogenic bacteria.

And she survived to tell the story. But writer's cramp can be a job hazard of the fruit-fly inoculation trade, as evidenced by a more recent Stanford study (also in Schneider's lab) that used the flies to probe the effects of caloric restriction on immune response to bacterial infection. That required injecting so many tiny flies with a special syringe that, as lead investigator Janelle Ayres put it, “at one point, my hand got stuck in injecting position and I had trouble unfolding it.”

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