ARCHIVED: Fish Neurobiology
Three students working under the guidance of biology faculty member Leah Olson completed a ten-week research project attempting to identify differences in brain structure between two competing species of tube blenny, small fish commonly found in coral reefs. The group was one of seven participating in The Division of Science and Mathematics’ Summer Undergraduate Research Program, now in its sixth year.
Sarah Lawrence first encountered blennies through biology professor Ray Clarke, who has published a series of papers describing the turbulent relationship between roughheads (Acanthemblemaria aspera) and spinyheads (Acanthemblemaria spinosa), named for the branch-like projections jutting from their foreheads. Both prefer higher coral for better access to food, but it is the spinyheads that dominate. Clarke pins this to innate differences in metabolism.
Olson has spent the past three summers, this year accompanied by Meredith Gibbons ’08, Matt Lupoli ’09, and Amina Sariahmed ’08, seeking a physiological explanation for the blennies’ behavior. To test Clarke’s idea, her students conduct experiments comparing the presence of the hormone leptin, a major regulator of energy intake and expenditure by switching on or off appetite, in the two species.
To detect leptin receptors, the brains are first obtained from the fish, prepared so that they can be cut into flimsy slabs of tissue comparable to deli ham, bathed in assays that stain the proteins of interest, mounted on slides and then observed under a microscope. What may appear to be a quick and easy process requires much trial and error, made difficult by the sensitivity of the laboratory procedures and the scale of the brains, each about the size of a sprinkle.
As most leptin research has been done in mammals, and fish neurobiology has focused almost exclusively to goldfish, guppies or zebrafish, each of Olson’s groups face the challenge of treading in new water. “Because there is so little literature out there, we don’t know what to think. It can be really frustrating,” accepts Gibbons. “There’s no reference. You can’t follow a recipe; you just have to make it up as you go along. These projects are more fun, much more personal. You feel like you’ve done it when you get a result here.”
The students also learn that science is more hands-on than how it is presented in a classroom lab component. “We’re working with live animals, so there are some ethical issues,” said Gibbons. To acquire a brain, a fish is chosen and dropped into a bottle of formaldehyde; this fixes the tissue and prepares it for dissection. Each student has come to terms with inevitable killing of the fish. Sariahmed had a tough time at first, but now says, “It makes me more determined so that the animal did not die for no good reason.”
One of the limiting factors for the group was a lack of blennies. They have yet to be bred in captivity, although a university in Florida will soon be making an attempt, so they require Clarke to trek down to the Caribbean, dive into the reef, and pick some out. Until they had a large enough stock, the group practiced the techniques on goldfish and guppies.
“A lot of things we do in the lab require a certain degree of artistic talent” said Sariahmed. “There’s an art to dissection. You can’t go in and rip the animal apart. It’s important to have respect.” To get to the brain, the students must carefully scrape off the skull. Once in hand it is dehydrated and submerged into wax. The artist must return to cut these into blocks, preparing the brain to be sliced and stained.
Once the procedure is complete, everyone braces themselves for the microscope. “This project is like magic for me,” says Olson. “There are so many steps when you’re working blind. You have to just continue through the whole process. But it works fairly regularly, consistently.” Clear staining by Lupoli in the final week showed exactly what she hopes for at the end of each experiment: brown clumps representing leptin receptors. Rather than appearing primarily in the hypothalamus, as is the case in mammals, the team sees staining near the ventricles of the blenny brain, and an area identified by Olson as the optic tectum, where vision is processed.
The question they’re asking now is: If leptin regulates metabolism, what would it have to do with sight? Olson hypothesizes it may “mediate visual appetite responses,” making food stimuli appear more or less appealing as hormone levels fluctuate. She adds, “It is very possible leptin has a different role in fish.”
Despite the difficulties, at the close of the ten weeks each student hoped that it was not the end of their lab experience. As Sariahmed put it, “Three months is nothing. I feel like I’m just getting started.” Lupoli plans to pursue cognitive neuroscience, while Gibbons will continue researching blennies for her senior thesis.
The students became more than fellow scientists in their time together. They had fun discussing what they read in the latest science magazine, planning sleepovers to Gibbons’ air-conditioned apartment and discovering each other’s strengths and weaknesses. Lab coats and microscopes aside, the group also knew how to laugh. There exist very few contexts one can honestly say, “Your brain’s a lot smaller than mine.”
A blenny brain atlas showing the various slides obtained from this research is now accessible on Leah Olson’s .
Joseph Caputo ’07 is a first-year graduate student at Boston University's Center for Science and Medical Journalism.