This guest post was written by Sloka Iyengar, Ph.D., a neuroscientist who studies animal models of epilepsy. This is her depiction of her first experiment with a rat brain.
I was in the animal lab sweating bullets. Today was the day of my first-ever animal experiment and I was anxious to say the least. I’m an animal lover and when I thought of animals, I recalled my days working in an animal shelter. Between graduating from pharmacy school in India and starting graduate school in South Carolina, I worked for a year at a shelter for stray animals while applying to graduate schools in the U.S. As an administrator at the shelter, I cared for dogs that had suffered horrible injuries and accidents, had maggots, and had experienced extreme cruelty. I also had in my charge a few cats and kittens, owls, vultures, hawks, kites, snakes and even monkeys (this was India after all). I would feed the stray puppies and kittens (and take some of them home with me), make sure that the pharmacy was stocked with proper medicines and tools, and organize events to raise awareness about animal cruelty. I even had the opportunity to help out during surgeries, which was something I loved. The year passed, and I had to depart for grad school. Leaving the shelter with ‘my’ animals was one of the hardest things I have ever done. I remember my last day at the shelter and I had tears streaming down my face; I promised myself I would never get emotionally attached to another animal ever again! Of course, this vow didn’t last long.
So, here I was in South Carolina getting my degree in biomedical sciences. I spent the first year taking the required courses in biochemistry, molecular biology and physiology. I was particularly fascinated by the brain and disorders of the nervous system. I remembered studying drugs for neurological disorders as a pharmacy student, and while studying their mechanisms of action, there seemed to be gaping holes in what we understood about the brain. In graduate school, we were required to do at least two rotations (each six weeks-long) before settling on a lab in which to do our dissertation work. I did my first rotation in a lab that was studying the effect of diabetes on the brain using neuronal cultures. It was cool stuff, and I was hooked!
My second rotation was with Dr. M who used electrophysiology to study brain circuits. Electrophysiology is a technique by which you can record neuronal activity from brain cells, and his work sounded awesome! I was very excited about working with him, but a bit scared too, because I knew I would have to conduct experiments with rats. I had come to graduate school with very little experience working with research animals. Given that I had worked with animals in the past in a completely different setting, I wasn’t sure how I would do. Would I freak out? Would I be able to ‘sacrifice’ the rats? I told Dr. M I was a bit hesitant to use animals. He was very kind and understanding. At the end of the six weeks, I could stay in his lab or move on to another lab.
After a few days of reading, and establishing our line of inquiry, we studied how the hippocampus affects epilepsy. The hippocampus is a part of the brain important for learning and memory and for epileptic seizures as well. Back in the 1920s, a guy named Henry Gustav Molaison, also known as ‘Patient HM,’ developed epilepsy after falling off a bike. Because his seizures originated from the hippocampus, he didn’t respond well to medication and his physicians suggested taking out the hippocampus in a so-called ‘resection’ surgery. His seizures stopped, but he unfortunately developed a severe, specific type of amnesia called anterograde amnesia, where he had an inability to form new memories. Reading about Patient HM’s experience gave me insight into how incredibly complex seizure disorders can be, and the role the hippocampus plays not only in seizures, but also in memory. From then on, I knew I wanted to learn more about this amazing part of the brain.
Fast forward to the day of the actual experiment with rat models of epilepsy. I hadn’t slept well in a few days and was anxious when I thought of the ordeal that lay ahead. Dr. M and I had been through the process a few times already and I told myself that I was as prepared as I would ever be. We were back up in the lab with a lab rat. First, Dr. M showed me how to anesthetize the rat. We used an inhalation anesthetic, isoflurane, which Dr. M added to a bell jar before placing the rat inside. In a minute or so, the rat was deeply anesthetized; the way to check for that is to sharply pinch the rat’s paw. If the rat doesn’t respond to pain, you can be reasonably sure it won’t be awake or feel pain when euthanized. The procedure itself only took a few seconds. To me though, it seemed to take ages. I felt that participating in surgeries at the shelter really prepared me for this process in the lab. Once the rat was euthanized, the surgery to remove the brain from the skull was quite straightforward. The dissection needs to be done as quickly as possible and it makes one appreciate the need to have ‘good hands’ to do bench science. As an avid embroiderer, I felt prepared and empowered, I have to say. The first cut was made around the base of the skull after which a few more strategically placed cuts exposed the brain. A tiny spatula was used to get the brain free from the dura – it was crucial that the dura be cut and not pulled to minimize any mechanical shear effects on the brain, as that might lead to sick and dying neurons. Once the brain was prepared, it was adhered to a platform. This entire assembly was put in an ice-cold solution so that the metabolic process that might kill neurons could be slowed down. Although all this was a bit daunting, I couldn’t help but feel an intense excitement for what might come next. I had never seen anything like this before! After affixing a blade onto a machine called the vibratome, the slicing started in the next few minutes and we had brain slices floating in a solution. In the skull, the brain is bathed in a solution called the artificial cerebrospinal fluid. What Dr. M and I had prepared in anticipation of this experiment was artificial cerebrospinal fluid – which was basically a mixture of salts in the correct proportion in water.
After letting the brain slices rest for a bit, Dr. M showed me how to record electrical activity. He placed a slice in the recording chamber, positioned a stimulating electrode in the axons and a recording electrode amidst the dendrites. He gave a stimulus pulse and there was a downward trajectory response on the computer screen. It was the most beautiful thing I had ever seen! Here was a way to quantify neuronal activity!
The brain is an organ that is quite different from say, the heart or the lungs. If you were to look at the structure of the heart, you could observe that its job is to pump blood to different parts of the body. Similarly, looking at the lungs you can tell its job is to exchange oxygen and CO2. Looking at the brain does not tell anything about how it operates. Instead, we must understand its functions. Brain cells, or neurons, communicate with each other using electrical signals, and the brain is made up of billions of neurons. The electrical signal from each neuron is too tiny to detect. Given the unique alignment of neurons in the hippocampus, the electrical activity when measured from outside the neurons do not cancel each other out, but rather add up to give a signal known as a ‘field potential’. In a way, the field potential response is similar to an EEG recording as the signals you see are from the population of neurons, not individual ones. The field response that I was seeing now was such a beautiful sight! The blob of neurons and glia that makes us who we are is such a mystery, and I felt humbled that I was getting a chance to study it. On that first day, I even recorded a few slices myself.
Finding the work fascinating and productive, I decided to stay in Dr. M’s lab to study synaptic plasticity in epilepsy. Working with rats never got easy, but our procedures were always humane and painless.
Animal research is an important component of biomedical research. Countless people make up research teams. Given the nature of the work, it is no surprise that emotions can run high. And of course, these reactions are understandable and concerns are valid. It is important to note though, that in my experience, animal research is strictly monitored and regulated, and there are committees and agencies in place to make sure that no animal undergoes undue or unnecessary pain. In the 10 years that I did preclinical (animal) research, I never encountered anyone who didn’t treat animals with respect and kindness.
For neurological disorders like epilepsy, preclinical research paves the way for better treatments and hopefully, one day, a cure. Working with lab animals, studying, and writing about the brain, is a privilege and one, I hope, I never take for granted.
About the Author
Sloka Iyengar, Ph.D. is a neuroscientist and studies animal models of epilepsy to understand what causes neuronal circuits to generate seizures. She has worked with adults and children with epilepsy as a clinical researcher. Sloka is also a science writer, who has written numerous articles explaining neuroscience to non-scientists. She coordinates activities in the New York area for science outreach and has visited Capitol Hill to advocate for increased funding for basic neuroscience research.