A Novel Microsurgery Technique Reveals Distributed Sources of Convulsive Signals in a C. elegans Epilepsy Model

Alice Liu working at wet bench

Students

Faculty

Wilf Family Term Assistant Professor of Bioengineering

Project Summary

Caenorhabditis elegans, a 1 mm long roundworm, has long been a useful model for understanding neural circuits. With a fully mapped connectome, characteristic rhythmic movement, and genetic accessibility, the nematode has driven scientific advancement in understanding the mechanisms underlying animal locomotion. Laser microsurgery has long been a powerful tool for creating specific cellular or circuit lesions in C. elegans (Fang-Yen et al., 2012). However, traditional methods do not allow for ablations of large or deep structures in animals older than L2 larvae. Thus, for my project, I studied whether a modified infrared laser system for single-cell heat shock can precisely and robustly damage the worm’s circuit elements.

First, we wanted to know whether adult C. elegans motor neurons can be ablated via locally elevated temperature. We found that a pulse length of 0.8 milliseconds reliably ablated the target neuron, but not its neighboring neurons. At this dosage, we found that a targeted neuron was killed almost every time. By contrast, neurons 2.5 micrometers from the target were killed about half the time, and neurons > 5 micrometers from the target were almost never removed. We proceeded to ask whether we can precisely cut the nerve cords of the adult worm. Using trains of 10-20 pulses, each of length 2 milliseconds, we were able to effectively cut the nerve cords in all worms.

We recently used this system to study the nature of rhythm generation within the circuit for forward locomotion (Fouad et al., 2017) and are now approaching unanswered questions about a C. elegans model of epilepsy. In particular, we asked whether the frequent “convulsions” suffered by worms with a mutation in a certain receptor channel arise from one neuronal source or multiple locations in the network. We found that after severing the ventral nerve cord and recording worms’ body shape or muscle activity, seizure-like convulsions occurred independently anterior and posterior to the cut. This finding also served as functional evidence of the effectiveness of our modified infrared laser system for cutting the main nerve cords.

From my research experience thus far, I learned that scientific research is a long and arduous process. However, I love how the experiments, theories, patterns, and connections offer me a way to break things down into their fundamental parts. Having once regarded scientific research as an esoteric field, I am glad to have discovered that it is a means to satisfy my curiosity of the world.