Abstract
Electrical measurements from large populations of animals would help reveal fundamental properties of the nervous system and neurological diseases. Small invertebrates are ideal for these large-scale studies; however, patch-clamp electrophysiology in microscopic animals typically requires low-throughput and invasive dissections. To overcome these limitations, we present nano-SPEARs: suspended electrodes integrated into a scalable microfluidic device. Using this technology, we have made the first extracellular recordings of body-wall muscle electrophysiology inside an intact roundworm, Caenorhabditis elegans. We can also use nano-SPEARs to record from multiple animals in parallel and even from other species, such as Hydra littoralis. Furthermore, we use nano-SPEARs to establish the first electrophysiological phenotypes for C. elegans models for Amyotrophic Lateral Sclerosis and Parkinson’s disease, and show a partial rescue of the Parkinson’s phenotype through drug treatment. These results demonstrate that nano-SPEARs provide the core technology for microchips that enable scalable, in vivo studies of neurobiology and neurological diseases.
Highlights
As an alternative to single-cell measurements, one can use suction pipettes or microfluidic channels to record the ensemble electrical activity from the group of cells that compose the C. elegans pharynx[20,21]
We found that when we immobilized C. elegans inside the microfluidic chamber, individual muscle cells wrap around a nano-SPEAR that we manufactured to be roughly 25 times smaller than a single muscle cell (4 μm wide, 3 μm long, 100 nm thick) (Fig. 1d)
As further confirmation that nano-SPEARs record electrophysiological activity from the body-wall muscles we found that egl-19(n582) and shk-1(ok1581) loss-of-function mutant worms show longer putative spike waveforms as compared to wild type (WT) worms, which is consistent with previously reported patch-clamp electrophysiology data for body-wall muscle APs7,33,34 (Fig. 3d–f, Supplementary Fig. 5)
Summary
As an alternative to single-cell measurements, one can use suction pipettes or microfluidic channels to record the ensemble electrical activity from the group of cells that compose the C. elegans pharynx (the organ responsible for feeding)[20,21]. To create a platform for scalable, cellular-resolution electrophysiology in intact small animals, we invented a new electrode geometry that we call nanoscale suspended electrode arrays (nano-SPEARs) (Fig. 1a–d; Supplementary Fig. 1) These electrodes—designed to be smaller than an individual cell—are suspended above the surface of a microfluidic chamber. The concept of nano-SPEAR electrophysiology was inspired by recent experiments showing that high-aspect-ratio nano- and micro-structures brought into contact with cultured cells can develop an electrical coupling sufficient to record APs26–31 Based on these results we believed that nano-SPEARs would provide a less-invasive and scalable alternative to patchclamp electrophysiology in small organisms like C. elegans. Micro-movements of the muscle cells themselves did not correlate with our recordings (Fig. 2c, Supplementary Fig. 3, Movie 3) These observations combined with confocal images showing nano-SPEARs engulfed by body-wall muscles (Fig. 1d) suggest that nano-SPEARs record extracellular electrophysiological activity from the body-wall muscles
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