About 30% of the world’s population has hypertension due to a recent surge of salt in our diets (1). According to the American Heart Association, the average American eats more than 3,400 milligrams of sodium daily, while the ideal limit is 1,500 mg per day for most adults (2). So, how does your body know when you have ingested salt? Your brain has specialized cells that monitor the amount of sodium (and other ions or substances). Some of these cells are located in the Organum Ventral Lamina Terminus (OVLT). OVLT is one of a few special section of the brain that lacks a complete blood brain barrier that allows substances in the blood to pass more freely from the bloodstream to the brain. So, this section of the brain essentially has the equivalent of “x-ray vision”; it can “see” the particles in the blood, such as salt, and send messages throughout the body to initiate responses. One of these responses may be to increase blood pressure, which is known as salt-sensitive hypertension. Salt-sensitive hypertension refers to an increase in arterial blood pressure to an increase of salt intake.

Figure 1. Rat diagram with optogenetic set-up.

My project utilized a new innovative tool known as optogenetics to inhibit or “turn off” OVLT neurons during dehydration and acute NaCl loads. Optogenetics works by shining a light at different wavelengths at a region of the brain where a light activated or inhibited ion channel was injected via a virally-mediated delivery system. In my experiments, water intake, urine output, and blood pressure (via telemetry) were measured in rats dehydrated overnight or infused with a concentrated NaCl solution with or without the laser on to inhibit OVLT neurons. I found that when these neurons were inhibited, they would decrease the volume of water intake of the rats. Upon further investigation, if OVLT continues to prove to be a major contributor to salt-sensitive hypertension, we hope more methods will be developed and implemented in humans suffering from this disease.

Figure 2. Leica Vibratome used to take serial sections of brain to determine injection location. Credit: Dr. Sean D. Stocker’s Lab, University of Pittsburgh Medical Center

Research is a very rewarding occupation. Although experiments can be long and time sensitive, the outcome is worthwhile. As long as you are careful and perform experiments honestly, any result can be used to learn. Further, I was amazed by the techniques I used to complete my experiments. The science and technology behind them is very interesting and innovative. The use of optogenitics is relatively new and entails complex surgeries and sciences. Unfortunately, with complexity comes consequences, and I have hit some bumps in the road. The technology used on the rats was very fragile and could not be fixed if broken. In addition, since it is not possible to alter salt concentrations without altering other aspects of the rat, we had to test the secondary stimuli to see what affect they had on the rats’ behavior. I am not finished collected data yet for this summer, but the results appear promising. In addition, I still need to test more animals and determine if the injected virus hit OVLT in order to define my conclusions.

Upon arriving, I was most surprised by the dynamic of the lab. All lab members are working on separate projects, but with related goals. Work is mostly independent, yet the goal is interdependent.  Working with a lab team was a fulfilling experience and helped me gain a better understanding of my project. I was able to learn new things and make better sense of my project through communicating with my team members. The best part of my research is the technology and innovation associated with it. One of my favorites is the way we analyzed water intake by applying basic principles of circuits. During experiments, the rats are in cages with metal floor, plastic walls, and water bottles with metal spouts. A wire connected the floor to the spout of the water bottle, creating an incomplete circuit. When the rat takes a drink, it completes the circuit because it is touching both the metal spout and floor. This causes a voltage to occur, which is recorded on a computer application. This data is used to determine when the rats were drinking, and it can approximate water intake because duration of time at the water bottle spout correlates with the amount of water the rats ingested. In contrary, the worst part of my research was the delicacy of the animals. It is very disheartening when the head caps fall off the rats and no longer can be used for experiments. Another incommodious aspect was the time sensitivity of experiments. I have to give the rats time between experiments, so some days were much slower than others. All in all, the positive aspects of research have outweighed the negative, thus far. It has further peaked my interest in a future of biomedical research, and I would recommend anyone interested in the sciences with a love of problem solving to engage in research!

References

1. Choi HY, Park HC, Ha SK. Salt Sensitivity and Hypertension: A Paradigm Shift from Kidney Malfunction to Vascular Endothelial Dysfunction. Electrolytes & Blood Pressure 13:7-16, 2015 [14 July 2017].
2. How Much Sodium Should I Eat Per Day? [Online]. American Heart Association. https://sodiumbreakup.heart.org/how_much_sodium_should_i_eat?utm_source=SRI&utm_medium=HeartOrg&utm_term=Website&utm_content=SodiumAndSalt&utm_campaign=SodiumBreakup [14 July 2017].

Rachel Maile is a junior majoring in Biological Systems Engineering and minoring in Biomedical Engineering at Virginia Polytechnic Institute and State University (Virginia Tech) in Blacksburg, VA. She is a 2017 Undergraduate Summer Research Fellow (UGSRF) working in Dr. Sean D. Stocker’s lab at the University of Pittsburgh Medical Center in Pittsburgh, PA. Rachel’s fellowship is funded by the APS and has enabled her to further her appreciation for research. After graduate, Rachel plans to perform biomedical research, using her engineering background and physiological expertise.