Abstract
Non-invasive recording in untethered animals is arguably the ultimate step in the analysis of neuronal function, but such recordings remain elusive. To address this problem, we devised a system that tracks neuron-sized fluorescent targets in real time. The system can be used to create virtual environments by optogenetic activation of sensory neurons, or to image activity in identified neurons at high magnification. By recording activity in neurons of freely moving C. elegans, we tested the long-standing hypothesis that forward and reverse locomotion are generated by distinct neuronal circuits. Surprisingly, we found motor neurons that are active during both types of locomotion, suggesting a new model of locomotion control in C. elegans. These results emphasize the importance of recording neuronal activity in freely moving animals and significantly expand the potential of imaging techniques by providing a mean to stabilize fluorescent targets.
Highlights
The ability to record the activity of particular neurons noninvasively in untethered, freely moving animals would greatly accelerate studies of the neuronal basis of behavior, but such recordings remain generally elusive
Noninvasive recordings have been made in freely moving zebrafish larvae by means of an activity-dependent bioluminescent probe that is transgenically expressed in target neurons and monitored by a wide-field photodetector [2]
The new system represents a significant advance over previous approaches in four key respects. It is compatible with the high performance microscope objectives (636, 1.4 NA) required to resolve minute, densely packed neurons
Summary
The ability to record the activity of particular neurons noninvasively in untethered, freely moving animals would greatly accelerate studies of the neuronal basis of behavior, but such recordings remain generally elusive. Noninvasive recordings have been made in freely moving zebrafish larvae by means of an activity-dependent bioluminescent probe that is transgenically expressed in target neurons and monitored by a wide-field photodetector [2]. To record from identified neurons in untethered animals it is usually necessary to genetically target an optical probe to known subsets of neurons Such recordings have been achieved from groups of neurons, or spatially isolated single neurons, in freely moving Caenorhabditis elegans. This was done by periodically recentering the target in the field of view either manually [3] or by means of image processing software that controlled a motorized stage [4], an approach developed more than a decade ago for behavioral tracking experiments [5]. The image processing approach is not a general method for recording from neurons of interest in freely moving C. elegans and other model organisms
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