Wednesday, June 13, 2012

The Unsung Scientist, Louis-Antoine Ranvier

To many who read this blog, Notes of Ranvier is a title that probably evokes no thoughts of science or history. There is a backstory to the name, however, and a reason why I chose it as the title.

Notes of Ranvier is meant to be a play on words referring to the nodes of Ranvier, anatomical structures in certain types of neurons that have a myelin sheath. Every neuron has a long projection called an axon that transmits electrical signals to other neurons. Around the axons of some neurons is the myelin sheath, a fatty tissue that insulates the axon like plastic around a copper wire. Electricity can't travel though myelin, so there are even gaps between the sheath where the neuron is exposed and electrical currents can be propagated down the axon. These gaps were discovered by French scientist, Louis-Antoine Ranvier (pronounced rahn-vee-yeh), and thus bear his name as Ranvier's nodes or the nodes of Ranvier.

When you learn about Ranvier's nodes in class, not a lot of attention is paid to how they were discovered or why they have Ranvier's name instead of some other scientist. The treatment of the subject is far more along the lines of, "these exist, this is what they do, moving on." But the question still gnaws, who was Ranvier? How did he find these nodes, and how did he figure out what they do?

Ranvier was a histologist in 19th century France. Histology is the study of organic tissues, employing techniques such as staining and preserving tissues and examining them under a microscope to better understand their anatomy and physiology. When you looked at slides of cells dividing in high school biology, you were performing histology.

While histology and microscopy are so common today that even small children learn how to use microscopes in class, the microscope was renounced by many French scientists and doctors in the 19th century. The dismissal of the microscope was largely related to the dismissal of the cell. Even as late as the 1800's, the theory of the cell being the building block for all living things was still pretty far-fetched to many scholars. This idea known as cell theory, was hotly debated for centuries. But in the latter half of the tumult was Ranvier holed away in his laboratory, with his icepick of a microscope, diligently scratching and scraping on the surface of physiology.

From the time Ranvier was born in 1835 to the peak of his career, histology began to make a sea change in the eyes of French scholars. Histologists were developing newer and more advanced techniques for preserving and staining samples. Ranvier saw the merits of histology for studying anatomy and physiology. In particular, he valued the scrupulousness involved in preparing tissues for histological examination which allowed him to reveal the nodes between myelin sheaths and determine their function.

For a long time it was known that myelin sheaths existed and that they were made up of fatty cells. The cells were and still are called Schwann, after the scientist who identified them. Ranvier wanted to better understand how cells insulated by myelin sheaths were able to exchange nutrients (such as oxygen and ions) with the blood since carmine tissue stains demonstrated that such nutrients could not penetrate through Schwann cells. Closer examination with different chemicals and a more exacting technique revealed the nodes pictured below.
Ranvier's Nodes (e). Image from Barbara, J (2007). Originally from Ranvier, 1878.
Ranvier wasn't finished there. He still wanted to know whether the nodes really were the site for nutrient exchange between the neuron and the capillary. Around the neurons in your body is a small sheet of connective tissue that protects them from mechanical damage. Ranvier destroyed this tissue, and then poured water onto the exposed nerves of living animals. This caused the Schwann cells to swell and expand to cover the nodes. The result? A loss of neuron function and paralysis. Ranvier correctly deduced that the nodes were important for the conduction of signals through neurons.

Ranvier went on to develop some of the first legitimate theories on nerve cell degeneration with his experiments on myelin. Meanwhile, furious debate raged on about the nature of cells and their contributions to the function of the human body. Ranvier, all the while, was only interested in facts and improving his histological techniques. His mentality led to many great discoveries in his life, some of which contributed to our modern understanding of neurophysiology.

He was a man truly deserving of respect and admiration, and his approach to his work should be an inspiration to scientists and science writers alike.

Bracegirdle, B. The History of Histology: A Review of Sources. (1977) Hist. Sci., 15:77-101

Barbara, J. Louis Ranvier (1835-1922): The Contribution of Microscopy to Physiology and the Renewal of French General Anatomy. (2007). Journal of the History of Neurosciences, 16:413-431.