Abstract
Genetic and chemical biology screens of C. elegans have been of enormous benefit in providing fundamental insight into neural function and neuroactive drugs. Recently the exploitation of microfluidic devices has added greater power to this experimental approach providing more discrete and higher throughput phenotypic analysis of neural systems. Here we make a significant addition to this repertoire through the design of a semi-automated microfluidic device, NeuroChip, which has been optimised for selecting worms based on the electrophysiological features of the pharyngeal neural network. We demonstrate this device has the capability to sort mutant from wild-type worms based on high definition extracellular electrophysiological recordings. NeuroChip resolves discrete differences in excitatory, inhibitory and neuromodulatory components of the neural network from individual animals. Worms may be fed into the device consecutively from a reservoir and recovered unharmed. It combines microfluidics with integrated electrode recording for sequential trapping, restraining, recording, releasing and recovering of C. elegans. Thus mutant worms may be selected, recovered and propagated enabling mutagenesis screens based on an electrophysiological phenotype. Drugs may be rapidly applied during the recording thus permitting compound screening. For toxicology, this analysis can provide a precise description of sub-lethal effects on neural function. The chamber has been modified to accommodate L2 larval stages showing applicability for small size nematodes including parasitic species which otherwise are not tractable to this experimental approach. We also combine NeuroChip with optogenetics for targeted interrogation of the function of the neural circuit. NeuroChip thus adds a new tool for exploitation of C. elegans and has applications in neurogenetics, drug discovery and neurotoxicology.
Highlights
Genetic and chemical biology screens on the nematode Caenorhabditis elegans have provided fundamental insight into neural function encompassing key aspects of neurosecretion, synapse formation and regeneration [1,2,3]
Capture of EPG Signals with NeuroChip The pharynx of C. elegans consists of a radial muscle which is divided into three functional parts, the corpus near the mouth of the nematode, the isthmus (I) in the middle, and the terminal bulb (TB) (Fig. 2F) [30,43,44]
An EPG signal corresponds to a single pumping action from these three parts and a typical EPG signal comprises five phases, called e, E, P, R and r. These features can readily be resolved in a conventional microelectrode recording made from a cut head preparation of C. elegans (Fig. 1A) [27]; removing the head from the body of the worm improves the stability of the recording
Summary
Genetic and chemical biology screens on the nematode Caenorhabditis elegans have provided fundamental insight into neural function encompassing key aspects of neurosecretion, synapse formation and regeneration [1,2,3]. We report the development of a device based on this principle which we have called ‘NeuroChip’ because it yields high resolution EPG recordings in which the aforementioned synaptic events can be reliably detected in recordings of low level basal activity and during periods of rapid, stimulated activity It has been optimised for trapping worms in the correct orientation, mimicking the shape of a conventional microelectrode aperture and for rapid drug or chemical application. The device is further configured to allow optogenetic interrogation of the neural network Taken together these features of NeuroChip endow it with the capability to select discrete electrophysiological synaptic and neuromuscular phenotypes from mixed populations of worms, a property commensurate with it performing as a robust platform for genetic and chemical biology screens with potential to deliver new insight into neural function and to facilitate drug discovery
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