Microbial light-activatable proton pumps as neuronal inhibitors to functionally dissect neuronal networks in C. elegans

• Published in: PloS one 2012-07, Vol.7 (7), p.e40937-e40937
• Main Authors: Husson, Steven J, Liewald, Jana F, Schultheis, Christian, Stirman, Jeffrey N, Lu, Hang, Gottschalk, Alexander
• Format: Article
• Language: English
• Subjects: Animal behavior; Animals; Archaeal Proteins - pharmacology; Arches; Ashes; Behavior; Biochemistry; Bioengineering; Biology; Caenorhabditis elegans; Caenorhabditis elegans - drug effects; Caenorhabditis elegans - physiology; Caenorhabditis elegans - radiation effects; Cholinergic Neurons - drug effects; Cholinergic Neurons - physiology; Dopamine; Electrophysiology; Fungal Proteins - pharmacology; Halorhodopsins - pharmacology; Illumination; Inhibition; Interdisciplinary aspects; Interneurons; Life sciences; Light; Locomotion - drug effects; Membrane proteins; Microorganisms; Motor Neurons - drug effects; Motor Neurons - physiology; Muscle Cells - drug effects; Muscle Cells - physiology; Muscle Cells - radiation effects; Nematodes; Nerve Net - drug effects; Nerve Net - physiology; Nerve Net - radiation effects; Nervous system; Neural networks; Neurons; Neurons - drug effects; Neurons - physiology; Neurons - radiation effects; Nociception - drug effects; Optogenetics; Proton Pumps - pharmacology; Proton Pumps - radiation effects; Protons; Pumps; Rodents; Roundworms; Sensory neurons; Signal Transduction - drug effects; Signaling; Touch - drug effects; Worms
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0040937

Essentially any behavior in simple and complex animals depends on neuronal network function. Currently, the best-defined system to study neuronal circuits is the nematode Caenorhabditis elegans, as the connectivity of its 302 neurons is exactly known. Individual neurons can be activated by photostimulation of Channelrhodopsin-2 (ChR2) using blue light, allowing to directly probe the importance of a particular neuron for the respective behavioral output of the network under study. In analogy, other excitable cells can be inhibited by expressing Halorhodopsin from Natronomonas pharaonis (NpHR) and subsequent illumination with yellow light. However, inhibiting C. elegans neurons using NpHR is difficult. Recently, proton pumps from various sources were established as valuable alternative hyperpolarizers. Here we show that archaerhodopsin-3 (Arch) from Halorubrum sodomense and a proton pump from the fungus Leptosphaeria maculans (Mac) can be utilized to effectively inhibit excitable cells in C. elegans. Arch is the most powerful hyperpolarizer when illuminated with yellow or green light while the action spectrum of Mac is more blue-shifted, as analyzed by light-evoked behaviors and electrophysiology. This allows these tools to be combined in various ways with ChR2 to analyze different subsets of neurons within a circuit. We exemplify this by means of the polymodal aversive sensory ASH neurons, and the downstream command interneurons to which ASH neurons signal to trigger a reversal followed by a directional turn. Photostimulating ASH and subsequently inhibiting command interneurons using two-color illumination of different body segments, allows investigating temporal aspects of signaling downstream of ASH.