Probing Disease Processes
The scale of microfluidic channels—tens to hundreds of microns—lends itself to the study of whole organisms, if that organism is a nematode, and specifically, C. elegans, which is a commonly used model organism to study development, physiology, and disease processes.
Work published by a team of researchers at McMaster University has shown that worms contained in microchannels and exposed to an alternating current (AC) electric field can be immobilized. Similarly, the introduction of a direct current (DC) electric field stimulus results in directed movement of the worms along the microfluidic channel, quite predictably toward the negative end of the channel.
Bhagwati Gupta, Ph.D., associate professor of biology, explains how the team is using a combination of AC and DC electrical fields as a control mechanism to confine and manipulate worms, a technique called microfluidic electrotaxis. They are applying this technique to study movement-related disorders, such as Parkinson disease, exposing the worms to neurotoxic stimuli and screening compound libraries to identify potential drug candidates.
The facts that C. elegans will move in a predictable manner in response to an electric field, that this movement is controlled by neurons, and that neuronal defects can disrupt normal electrotaxis, make this a valuable strategy for studying the neural basis of behavior.
Furthermore, “neuronal circuits are fairly well understood in worms, allowing us to focus on specific kinds of neuronal activity and degeneration involved in movement,” says Dr. Gupta.
Parkinson disease is caused by a loss of cells that produce the neurotransmitter dopamine. C. elegans has only eight dopamine-producing cells, and only six of those appear to be involved in signaling in the brain, making this a relatively simple biological system. Techniques are in development to knock out the dopamine-producing activity of individual cells, says Dr. Gupta, but at present, one of the challenges is that the introduction of neurotoxins or the use of gene-knockdown approaches affects all of these cells.
The group at McMaster is employing microfluidic technology to study the effects of neurotoxins on dopamine function and the movement of individual organisms.
“Our assay system is up to 10 times more sensitive than conventional C. elegans assays,” he says. One aspect of their research is to understand which cells actually perceive the electrical field stimulus. Are they the dopamine-producing cells themselves or another cell type that then signals the dopamine-producing cells to release the neurotransmitter?
“We are now developing different kinds of microfluidic devices to look at neuronal activity at the single-cell level,” says Dr. Gupta. The goal is to enable faster and more accurate measurements—at the millisecond level—to improve the sensitivity of detecting neuronal responses.
Another area of technology development is focused on identifying better and less costly imaging options. Additional challenges include the need for more automation to minimize the amount of hands-on time still needed to prepare the worms and load them into the microchannels, as well as improved electrical sensors and detectors that would be less costly yet as powerful as conventional CCD cameras and could be mounted on the microfluidic devices.
New types of software are also needed that can integrate tasks and data collection across a series of linked microfluidic chips, each of which performs one or more dedicated tasks.