08/17/2005
Strange Fliers
How long has it been since you saw a G-rated movie? If you haven’t seen “March of the Penguins”, you’re missing a movie with everything – a passionate love story with sex, violence, tragedy, fulfillment, stark realism, spectacular scenery and a moving narration by Morgan Freeman. The Emperor penguin is at once a most stately, yet ridiculous looking bird that becomes an agile, streamlined creature in the sea, its favorite habitat. Why did the penguin choose to hang around as Antarctica drifted to its current position, with one of the coldest, inhospitable climates on Earth? I could go on about the penguin’s hard and inspiring life but don’t want to spoil the story if you haven’t yet seen this wonderful movie about a bird that can’t fly.
Let’s turn to a creature that can fly. The fruit fly is a favorite of scientists, the subject of a huge number of papers published over the past century or so. When I saw mention of the results of one fruit fly study in the September 2005 issue of Discover, I couldn’t help thinking of chickens. One of the houses we rented in Mechanicsburg, Pennsylvania, when I was a child, had a chicken coop and we used it. My mother would select a chicken for dinner and, wielding a hatchet, would chop off its head.
I found this a distressing sight, a bloody, headless chicken flopping around on the ground for some time after losing its head. I had to be convinced that the chicken really wasn’t alive and that its movements were some kind of reflexive muscular thing. I preferred that my mother just buy a “dressed” chicken, all set to be stuck in the oven or to be chopped up to make fried chicken. Later, in my first year of marriage, a chicken almost led to divorce.
My pregnant wife sent me to a farmers market in Cleveland to pick up some produce and a chicken. I dutifully found a nice, plump “dressed” specimen and proudly presented it to my wife. It was then that I found the term “dressed” did not mean the same thing in Cleveland as it did in Pennsylvania. In Cleveland, it meant that the chicken’s feathers were removed but not the inner contents! My wife was not happy to learn of this regional difference as she went to put the foul in the oven. A tearful and disgusted trip to the laundry area to properly “dress” the chicken followed; she has not trusted my shopping since that time.
But I digress. Back to fruit flies and the work of Gero Miesenb ck and graduate student Susana Lima at Yale, published in the August 8 issue of the journal Cell. Parkinson’s disease is a prime example of a disease involving the loss of control over one’s motor skills. In Parkinson’s, the dopamine receptors don’t do their job and one well-known treatment is L- dopa, which works for a limited time in many cases. Fruit flies also have dopamine neurons, which stimulate walking and control the path that a fruit fly follows.
What the Yale researchers have done is to genetically engineer so-called “phototriggers” for different sets of fruit fly neurons. They have engineered these phototriggers to affect not only dopamine neurons but also neurons in the “giant fiber” system in the fruit fly. When giant fiber neurons are stimulated, the escape response is activated – there’s beating of the wings, jumping and flight. You know these neurons do their job very quickly if you try to catch or swat a pesky fly. Normally, if researchers want to try to study individual neurons or small groups of neurons, they wire up electrodes in contact with the neurons. Apply a voltage to the electrode to prod the neuron into action. By observing what action occurs, you can trace it back to that neuron.
It’s obvious that wiring electrodes to neurons in a fly must be a delicate and difficult task. Here’s where Miesenbock and Lima’s phototriggers provide a distinct advantage. Their phototriggers respond to light, no electrodes required. When they illuminate their giant fiber phototriggers with laser light, the fruit fly flaps its wings, jumps and/or flies away. Blind flies respond in the same manner. The laser light penetrates through the cuticle, or skin, of the fly to reach the phototrigger. If the photriggers are associated with the dopamine neurons, the researchers can stimlate walking and control the path the fly takes. (I’m not sure whether the dopamine neurons respond in a blind fly.)
So, what Lima and her professor can do is shine the laser light on the genetically engineered flies and control what they do, at least most of the time (60-80%). Some might see this as a disturbing step towards mind control but what if there’s no mind to control? Here’s what reminded me of my mother and the chicken. It seems that flies can be kept “alive” up to a day if kept moist – without their heads! So, what happens if you shine laser light on a headless fruit fly that’s been in the hands of the Yale researchers? It jumps, walks around and even flies away! The implications for science fiction movie scenarios are endless!
How do they do it? Something called an ion channel is one player. Ion channels play an important role in our bodies and let certain charged ions pass through them. Lima and Miesenbock managed to genetically engineer ion channels not normally attached to the selected neurons. When a compound known as ATP, a compound found in all plant and animal cells, latches onto one of these ion channels it causes the neuron to fire and do its thing. The Yale scientists made a “cage”, another compound that traps ATP. They inject the caged ATP into the fruit fly.
One analogy is to call the ion channel the lock, the ATP the key and the cage the trigger. When light of the right wavelength hits the cage, the cage opens up and releases the ATP. (It’s the photons that open the cage, hence the term “phototrigger”.) The ATP keys onto the ion channel and activates the neuron. The fruit fly flies, walks, jumps, whatever that neuron controls.
I gathered the above details from various Web sites, notably the Yale University, University of Minnesota and Scientific American Web sites and the abstract of the paper on the Cell site. (Sorry, I wasn’t willing to pay the $30 necessary to get the full text!)
The use of light, instead of electrodes to activate neurons and observe the results directly seems likely to open up a new field of endeavor in the area of studying the control of neuron activity and resulting motion. Down the distant road is the hope that such studies might help those with motion problems as in Parkinson’s patients or in paraplegics.
Thanks to the generosity of our Editor, Brian Trumbore, I had the opportunity to move around the course at Baltusrol last week at the PGA. Actually, with the extreme heat and humidity, this 77- year-old had no desire for much movement but did share with Brian a few hours early Saturday morning sitting at the signature 4th hole until the Tiger and Couples twosomes had passed through. Fortunately we did not have any falling branches, as happened the day before on the 4th, sending one fellow to the hospital with a broken leg.
In this world of cellphones and other audio devices (banned from the course), it was impressive how utterly silent the hundreds of spectators were while Tiger and the others were putting. At the 4th, while we were there, there were none of those exasperating loud cries of “You’re the man!” or “Get in the hole!”
Allen F. Bortrum
Addendum: Regular readers will know that I’ve shamelessly taken every opportunity to mention my hole-in-one some years ago. In the interest of full disclosure, I’m compelled to reveal my experience at the 4th hole at Baltusrol. I don’t belong to a country club and when a Baltusrol member called one night years ago to ask if I wanted to join his group the next morning, it took me a microsecond to answer in the affirmative. That night I couldn’t sleep, thinking of the 4th and the water to be cleared. It turned out to be my most embarrassing golfing experience. I dumped several balls in the water, finally shanking a shot that skirted the side of the pond and carded a 13! However, I now share something with Tiger – we both have hit drives into the water on the 4th! (If you missed it, his was on Friday and the big tree branch fell after he hit his shot from the drop area.)
|