In order to study stress, you need a good way to measure it. A common method to measure how “stressed out” an organism is at a particular time is to measure the concentration of “stress hormones” in their blood. In reptiles we measure corticosterone (CORT), which is similar to cortisol in humans and fish. Our lab uses an ELISA (enzyme-linked immunosorbent assay) to determine the concentration of CORT in our samples. These kits are commercially produced for a variety of hormones and make it very convenient to do so, though it takes a solid day of lab work. Jenny, Chris, and I have each been running a number of CORT assays in the last months in order to work through our samples from last summer. One of the lab’s undergrads, Mark H, is also learning this technique to run some of his own samples.
Although these kits are pretty straightforward, you can’t help but be paranoid about doing it right. A mistake costs you not only the precious samples you are running but also the cost of the kit (which is not insignificant!). Because of this, we make sure any newcomers to the kit are trained up and very comfortable with the assay before we turn them loose.
After the day of lab work, the completed plate looks something like this (above). This plate is then placed in a micro-pate reader, which reads the absorbance of each well at various wavelengths. The result is a spreadsheet of numbers, which ultimately lets you determine the concentration of CORT in each of your samples. It’s always a little nerve-wracking at the end of the day when you walk away with just a flash drive, but the data usually turns out just fine!
The next step: data analysis!