Biophysical Effects of Anesthetic Agents on Peripheral Neural Conduction
Advisor: Dr. John Hight
Internship Location: Northwestern's Feinberg School of Medicine
Onsite Mentor: Dr. Claus-Peter Richter
Neural signal propagation drives everything from sensation to movement to higher cognition. When drugs alter that signaling, the effects range from surgical anesthesia to pain relief to neuromodulation therapies. We understand what these drugs do clinically. What remains less clear, particularly in peripheral nerve systems, is exactly how they alter action potential initiation and conduction at a biophysical level. For my Senior Project, I investigate how anesthetics and related pharmacological agents modify neural signal propagation. I conduct this work at the Northwestern University Feinberg School of Medicine within the Department of Otolaryngology, a setting that allows direct observation of peripheral nerve responses under controlled laboratory conditions. The project has two components. First, I build a structured “state of the art” literature synthesis analyzing how specific compounds affect conduction velocity, spike amplitude, refractory periods, and signal fidelity. This review identifies dominant mechanisms, research trends, and unresolved questions in the field. Second, under supervision, I participate in experimental investigation of nerve responses under pharmacological modulation and compare laboratory observations with published models. I expect this project to clarify how anesthetic agents influence neural conduction in ways that connect molecular mechanisms to measurable physiological outcomes. Understanding these mechanisms has implications for surgical anesthesia, pain management, and the development of neural interfaces. By pairing literature analysis with experimental investigation, I aim to strengthen the link between foundational neurophysiology and translational biomedical application.
Project Blog
Post 1: Introduction
I have always been driven by a desire to make impact at scale. Thus, I’ve wanted to work in fields where a single discovery or technology can improve or save millions of lives. That pull has consistently drawn me toward pharmaceuticals, gene editing, and biotechnology. My epiphany about biology came unexpectedly in 10th grade AP Biology, during a stop-motion project on codons. Translating nucleotide sequences into proteins frame by frame made me realize how intricately organized life is, down to individual atoms and molecular interactions. What initially felt mechanical became something almost artistic; biochemistry revealed itself as both functional and beautiful.
Over time, this fascination evolved into a more focused interest in how biological systems can be deliberately altered by medical intervention. Studying neurological and sensory disorders made me curious about what happens at the level of individual neurons when normal signaling is interrupted or purposefully modulated. I became particularly interested in how pharmacological agents, such as anesthetics, affect neural signal propagation beyond their observable clinical effects.
While exploring this area further, I learned about ongoing research at Northwestern University’s Feinberg School of Medicine in otolaryngology and neural stimulation. Conversations with researchers and independent reading showed me that this field offered an opportunity to engage directly with experimental neuroscience while contributing to a broader understanding of how drugs interact with neural tissue.
My Senior Project will examine how anesthetics and other drugs influence neural signal propagation. The first phase involves building a structured “state of the art” review of existing literature, which will support later experimental work during my onsite internship at Feinberg involving nerve studies and pharmacological modulation.
Overall, this project represents a culmination of my interests in neuroscience, pharmacology, and biomedical research. I’m excited to better understand how scientific knowledge is built, tested, and applied beyond the classroom, and I hope that my research in this project will someday contribute to helping millions of people around the world.
Week 1: Senior Research Project Blog - Week 1
I spent this week focused on establishing the foundation for my project on how anesthetics and pharmacological agents influence neural signal propagation. The first step recommended by my mentors was to conduct a systematic review summarizing current research on anesthetic mechanisms, synaptic transmission, and neural conduction. The purpose of this document is to organize the existing research, identify key findings in the field, and determine where important gaps remain.
I reviewed nearly 50 major papers examining how general anesthetics affect neuronal signaling. Many studies show that anesthetics alter neural activity primarily through ion channels embedded in the cell membrane. These compounds often enhance inhibitory signaling while suppressing excitatory transmission, shifting the balance of neural activity toward inhibition. Other studies examine how anesthetics influence neural networks rather than individual neurons alone. Research on propofol-induced unconsciousness suggests that neuronal communication across brain regions becomes disrupted as anesthetic concentration increases. Functional networks fragment, reducing long-range connectivity and contributing to the transition from conscious to unconscious brain states.
The literature also stresses the importance of membrane biophysics and ion channel function. Voltage-gated sodium and potassium channels control the propagation of action potentials along axons, starting at the axon hillock, while calcium channels in the axon terminal regulate neurotransmitter release at synapses. Some anesthetics reduce calcium influx into presynaptic terminals, which weakens synaptic transmission. Because ion channel behavior depends strongly on membrane properties and temperature, these mechanisms connect directly to the thermodynamics component of the broader research project.
In addition to reviewing the literature, I began outlining experimental directions. The first priority will be establishing a stable experimental environment where neural tissue remains viable in physiological saline such as Ringer’s solution. Once neural activity can be reliably recorded, experiments can begin examining how drugs and other factors influence signal propagation. I have developed a rough draft of the methodology, from Phase 0 to 7, those being Tissue Viability and Baseline Stability, Basic Propagation Characterization, Local Anesthetic Validation, General Anesthetics and Propagation, Ligand-Gated Ion Channel Modulation, Temperature and Thermodynamic Coupling During Drug Application, Frequency-Dependent Propagation and Energy Demand, and finally, Infrared Stimulation Versus Electrical Stimulation.
Next week, when Dr. Claus Peter Richter returns, Dr. Joaquin Cury and I will begin initial validation experiments. We will first measure the compound action potential in an isolated nerve preparation to confirm that the electrodes are properly detecting signal propagation. Lidocaine will then be applied to suppress sodium channel activity and verify that the recorded signals respond appropriately to known anesthetic effects. After validating the recording system, we will test whether the Ringer’s solution we prepare is able to sustain the nerve’s viability for extended periods. Establishing these baseline conditions is essential before more complex experiments examining drug effects and membrane thermodynamics can begin.
Week 2: Senior Project Week 2- Refining Methodology and Experimental Design for Neural Signal Propagation Experiments
This week focused on refining the experimental design for the project and continuing the literature review related to anesthetics, ion channels, and neural signal propagation. While the first week concentrated on building a broad understanding of the field, the goal this week was to translate that background knowledge into a concrete experimental methodology that can be implemented once the lab work begins.
A significant portion of the week involved identifying the specific experimental setup that will be used to measure neural signal propagation. After reviewing common electrophysiology methods used in nerve studies, we determined that the experiments will measure compound action potentials using multiple electrodes placed along an isolated nerve. Using more than one recording electrode will allow us to measure the latency between signals traveling along the nerve. From this delay, it will be possible to calculate conduction velocity and analyze how various compounds influence signal propagation.
Another important decision involved selecting the biological model system. Early experiments will use worm nerves, which are relatively accessible, as they fit well within the budget for large sample size and repeated trials, and thus allow for easier initial testing of the recording setup and experimental conditions. Once the methodology is well established and the system is producing reliable signals, later experiments will transition to lobster nerves. Lobster nerve preparations are commonly used in neurophysiology because they are larger and easier to manipulate experimentally, which can provide clearer electrophysiological recordings and allow for more precise measurements.
In addition to selecting the experimental model, I spent time reviewing physiological solutions that can maintain nerve viability outside the organism. Ringer’s solution will be used to bathe the isolated nerve during experiments, and identifying the correct ionic concentrations is critical. If the solution contains incorrect concentrations of sodium, potassium, calcium, or chloride ions, the nerve may lose excitability or die prematurely. Because of this, I reviewed several protocols describing Ringer’s solutions used in nerve physiology experiments to ensure the formulation we prepare will maintain stable neural activity.
Another focus this week was thinking carefully about experimental reliability and statistical validity. Increasing sample size and repeating trials are essential for ensuring that observed effects are real and not simply noise in the data. For each experimental condition, multiple trials will be conducted so that changes in conduction velocity or signal amplitude can be evaluated with greater confidence.
I also began identifying factors that could unintentionally influence the data. For example, different types of nerve fibers can conduct signals at different speeds depending on whether they are myelinated or unmyelinated. Although the early preparations are likely to involve primarily unmyelinated fibers, this variability still needs to be considered when interpreting results. Other potential issues include excitotoxicity, where excessive stimulation or chemical exposure damages the nerve, and errors in Ringer’s solution preparation that could alter ion concentrations and affect neural activity.
Carefully thinking through these potential confounding factors is important because electrophysiology experiments can be highly sensitive to small environmental changes. Temperature, solution composition, electrode placement, and stimulation intensity can all influence the recorded signals. By identifying these variables in advance, we can design experiments that minimize unwanted variation and produce more reliable measurements.
Next week the focus will shift from planning to validation of the experimental setup. Working with Dr. Joaquin Cury and Dr. Claus Peter Richter, we will begin testing the recording system by measuring compound action potentials in the nerve preparation. Lidocaine will be applied as a control compound to confirm that the electrodes are accurately detecting changes in signal propagation when sodium channels are blocked. Once the recording system is validated, we will continue optimizing the Ringer’s solution and experimental conditions needed to maintain nerve viability for extended periods.
Week 3: Senior Project Week 3- Setting Up Lab Protocol and Beginning Dissections
This week marked the transition into hands-on lab work. Dr. Claus Peter Richter returned from the UK, and we started setting up the actual experimental workflow. Because there is an ongoing replication crisis in academic papers -- i.e. the results of experiments and studies tend to be impossible to replicate -- he provided me with a lab notebook to begin writing out the full protocol in as much detail as possible, to eliminate any human error, unrecorded bias, or anything that would undermine the replicability and therefore the validity of our results. I spent a couple days drafting it, focusing on the step-by-step process for dissection, maintaining the nerve in solution, and eventually recording signals. Writing it out made it clear where things were still vague and needed to be tested in practice. Once I had my method down, I made final preparations for dissection. I prepared a 10% ethanol and 90% Ringer’s solution to anesthetize the worms before dissection. Alongside that, I reviewed worm anatomy so I would have some idea of where the nerve cord sits relative to other structures.
On Wednesday afternoon, 100 red wriggler worms arrived. Thursday was my first attempt at dissection. It did not go well. I damaged the nerve and surrounding blood vessels pretty quickly and at one point realized I had the specimen oriented incorrectly, which made it much harder to identify what I was doing. Most of the process was trial and error.
That said, I did start getting more comfortable with the tools. Using forceps and scissors with any level of precision under the microscope is harder than expected, especially when trying to isolate something small and fragile like a nerve. Even just pinning the specimen properly takes practice.
Friday I was in Virginia for Science Olympiad state competition, so I was not in the lab, but the earlier part of the week was still useful. The main takeaway is that dissection is going to take repetition before it becomes consistent. Right now the focus is just getting to the point where I can reliably isolate the nerve without destroying it.
Next week, the goal is to improve dissection technique and start getting clean nerve samples that can actually be used for recording.
Week 4: Senior Project Week 4 - Continuing Dissections
This week I continued to work on removing intact worm nerves. On Monday, I started by helping a med student in my bay with creating the PBS solution out of Monobasic and Dibasic solution. For the rest of the week, I focused on being able to remove all of the worm’s internal organs besides the nerve without damaging the latter. It was a complicated process, but I have gotten the hang of it. Additionally, me and Claus were able to properly locate the Medial Giant Fiber consistently, as well as sometimes locate the intact Lateral Giant Fibers. Two Lateral Giant Fibers and one Medial Giant Fiber make up the worm’s ventral nerve chord. I took photos of the microscopic view using Xiaodong's Nikon SMZ1270i. The images are below.
Next week, I look forward to starting the stimulation of the nerve and measuring the compound action potential, as well as exploring further into the thermodynamics of the fluid membrane.
Week 4: Senior Project Week 4.5- Embedding
I am writing this on the week after spring break, but, being the diligent researcher I am, I still performed lots of research over spring break. Last week, me, Jen, and Claus spent a lot of time prepping and performing the embedding and microscopic sectioning for the samples. The worms intestines were removed in order to verify the presence of the ventral nerve chord in the anatomically correct spot. Next, we had whole worms dehydrated and embedded with the following process- 25% acetone 15 minutes, 50% acetone 15 minutes, 75% acetone 15 minutes, 90% acetone 15 minutes, 100% pure acetone 15 minutes, 100% pure acetone 20 minutes, 1:7 plastic to acetone 1 hour, 1:1 1 hour, 7:1 1 hour, pure plastic 1 hour. They were then sliced in 10 micron slices by the ultratome in order to gain cross sections to locate the ventral nerve chord, and location was performed under Phase Contrast, Darkfield, Brightfield, and DIC. Next in the process is segments of the nerve chord itself, which was dissected out by cutting again on the dorsal side, removing intestines, pinning down top skin to the side, and cutting off excess skin around the nerve chord, followed by sectioning the isolated nerve chord into 3 sections and preserving them in formaldehyde. They will soon be embedded and examined in the 10 micron cross sections. Next week will also contain some stimulation and the first recordings of our CAPs.
Week 6: Senior Project Week 6: Second Trial of Embedding and Sectioning
This week, I started the second round of embedding the worms for sectioning. This time, we will be cutting a full worm into 5 parts and a full isolated worm nerve into 8 parts. This is in order to give us insight into how the nerve chord narrows as you travel in the posterior direction in order to evaluate the best places to stimulate and to record for the next round of stimulation. We preserved the samples in Eppendorf's filled with Paraformaldehyde, or PFA, and then proceeded to dehydrate the samples along with another batch of human cochlea. The process is as follows: 25% acetone 15 minutes, 50% acetone 15 minutes, 75% acetone 15 minutes, 90% acetone 15 minutes, 100% pure acetone 15 minutes, 100% pure acetone 20 minutes, 1:7 plastic to acetone 1 hour, 1:1 1 hour, 7:1 1 hour, pure plastic 1 hour. We will then slice them in 10 micron slices by the ultratome in order to gain cross sections to analyze the width changes along the course of the nerve from caudal to cranial.
Week 7: Senior Project Week 7- Simulation
This week, we did more stimulation. This time, I took better notes in my notebook in order to better input the data into my analysis code (specifically, the gain on the iso-80 and the valhalla). We also used different methods to get rid of the background noise picked up by the recording electrode, such as purposefully flipping the polarity of the graph for every other average captured. Our conclusions from this week revealed to us that the narrowing of the nerve chord as you approach the posterior end might be a serious problem for our experiment. There is a certain distance needed to differentiate the actual measured compound action potential response from the general stimulation artifact. However, with that distance, if we stimulate from the head, where there are more nerves (due to the ganglion), and measure at the tail end, the nerve fibers begin to branch away from the main ventral nerve chord as you progress posteriorly, leaving only a few at the area of recording towards the tail end.