Thursday, October 6, 2011
Learning neuroscience from a virus
Back in college, the shortest theorem proof I sat through in class (I was a math major) was the following: "Suppose the topological manifold is a chunk of cheese. Put a mouse on one of the cells and wait until the mouse has eaten all of the cheese." The cells, in that context, weren't biological cells, but rather topological ones. Believe me, it was a real proof and, once you worked out the details, it held.
So now suppose that instead of cheese you have a brain, and instead of topological cells you have neurons. What would the mouse be?
The nervous system processes information through a network across neurons. Neurons communicate exchanging signals (either chemical or electrical) through synapses. These network exchanges across neurons can be reconstructed with the use of chemical tracers, which allow researchers to visualize the activity of a specific neuron with its neighbors. However, chemical tracers have limits: not all of them can trace the "output" signal from a neuron, and not all of them are able to cross synapses. A study recently published in PNAS  presents a new way to trace neural circuits, using... guess what? Yes, you've guessed it: a virus. Pretend the brain is a chunk of cheese and let the virus "eat it all up." Well, okay, in principle.
With the disclaimer that neuroscience is not my field (but I'm always fascinated by any creative use of viruses), let me give you my two-cent-worth understanding of what was done.
The authors genetically modified VSV, the vesicular stomatitis virus, enabling it to travel back and forth across synapses. They placed a fluorescent reporter upstream of the viral proteins, and then they injected it into a mouse model. The virus used the communication network established by the neurons to infect the brain tissue. Basically, the path of infection followed the neural network in the mouse brain. Pretty cool how these pesky little viruses come in handy!
 Beier, K., Saunders, A., Oldenburg, I., Miyamichi, K., Akhtar, N., Luo, L., Whelan, S., Sabatini, B., & Cepko, C. (2011). From the Cover: Anterograde or retrograde transsynaptic labeling of CNS neurons with vesicular stomatitis virus vectors Proceedings of the National Academy of Sciences, 108 (37), 15414-15419 DOI: 10.1073/pnas.1110854108