Optogenetics with the FlyPad
My name is Spencer and I just finished my freshman year at Dalhousie University in Halifax, Canada (yes, where the maple syrup and igloos are). I’ll be studying Neuroscience and Immunology there for the next three years.
I’m originally from Vancouver but ended up all the way on the other coast to study in Halifax. Having relatives in Florida and a lot of friends on the west coast, I’ve visited the US quite a bit but have never lived here. I am thrilled to be in Ann Arbor this summer interning with Backyard Brains!
In the two weeks I’ve been here I’ve already had some awesome experiences. I love the food here, playing basketball at local outdoor courts, and the trees and streams that make the city vivacious. It takes me 20 minutes to bike to work, which might sound worse than what I get to look at each day:
Isn’t summer a great time? Sun, flowers, ripe fruit, and…those pesky fruit flies are all over them… Fruit flies may be tiny and annoying, but they happen to be one of the most important model organisms for the past 100 years. In spite of over a century of research, the feeding behavior of fruit flies, specifically the Drosophila melanogaster, has not been fully understood. Knowing how animals feed gives us insight into things like how they learn, reproduce, and physically function. Unfortunately, the Drosophila is so small and moves so quickly that its rapid sips of food cannot be caught with the human eye.
That’s why Dr. Pavel Itskov helped create a device called the flyPAD (proboscis activity detector) to measure how often the flies take sips of food with an accuracy of 100 samples per second. The flyPAD is so accurate because it uses capacitive sensors, the same type of technology iPads use to track touch responses. With food on one electrode and a fly on the other, the number and duration of sips the fly takes can be recorded and studied. I got my hands on one of these new gadgets this summer to study what natural foods Drosophila prefer to eat, what nutrients they require, and see if I can alter their food preference with neural stimulation.
To see what natural foods my flies prefer to eat, I will offer them a variety of commonly liked and disliked foods to see which ones they visit and eat from more. I am interested to see if the food choice preferences they make are based on the macronutrients (proteins, carbohydrates, fats) which are crucial to their diet. I will deprive flies of specific nutrients to see if, when offered those again, they spend more time eating to regain those nutrients. One application of this is to test the dietary requirements for reproduction. An example of this is to see if adult female flies eat more protein than males since they produce eggs and if virgin flies (which don’t make eggs) eat little protein. I am still doing research into more of such hypotheses to test, as well as the effect which ripe or rotten fruit has on their eating.
After figuring out what foods my flies like, would it be possible to override their decision-making abilities and alter what they perceive as tasting good or bad? Well, I will be putting this question to the test with optogenetics – a tool which can activate neurons with light stimulation.
I visited a local fly lab at the University of Michigan to order genetically modified flieswith the opsin ReaChR in their gr5a and gr66a neurons. These neurons control the flies’ gustatory reception – what they perceive as tasting sweet (gr5a) and bitter (gr66a). Through stimulation of ReaChR with light at certain frequencies, I should be able to activate these taste responses to give the flies virtual taste realities. If a fly loves banana but I activate its bitter taste receptors each time it tries to eat it, they should learn to stay away from banana. Likewise, I will try to make them love eating the foods they once abhorred through stimulation of their ‘sweet’ neurons. I am excited to see how Drosophila learn and remember, by measuring if their food choice preferences can be changed after multiple days of stimulation.
How powerful is optogenetics? Can I alter the free will of what Drosophila choose to eat? This is what I aim to discover in the upcoming weeks! Stay tuned.