Light-gated cation channels such as the blue light-activated depolarizing Channelrhodopsin-2 (ChR2), allow optical activation of individual neurons of live and behaving C. elegans at the millisecond time-scale in a non-invasive manner (Nagel et al., 2005, Zhang et al., 2007, Liewald et al., 2008). This optogenetics approach paves the way for further functional dissection of peptide signalling pathways or individual neuronal networks in a detail that is not possible in higher organisms. The huge advantage is that we can specifically stimulate the sensory input neurons, while other potentially contributing neurons are kept silent. The sensory PVD neurons that envelop the nematode with highly branched dendritic arbors are involved in harsh touch nociception. Expression and activation of ChR2 in PVD results in a forward escape movement and sometimes a reversal. These results are in line with the fact that the PVD neurons make synaptic contacts with the locomotory command interneurons PVC and AVA that regulate forward and backward movement, respectively. Using electrophysiology, we will assess the physiology of the PVD cells, as well as the downstream interneurons in response to photoactivation, while the involvement of different ion channels, receptors or neurotransmitters will be assessed by RNAi. We are also investigating the
flp-15 and
nlp-38 neuropeptidergic signalling pathways by optogenetics. Neuropeptide release can be triggered by photo-activating the respective neurons in an acute fashion while effects on behaviour can be observed at the same time. This way, we can correlate neuropeptide action with acute behavioural changes or effects, about which very limited knowledge is currently available in any system. References Liewald JF, Brauner M, Stephens GJ, Bouhours M, Schultheis C, Zhen M, and Gottschalk A (2008) Optogenetic analysis of synaptic function. Nat Methods, 5, 895-902. Nagel G, Brauner M, Liewald JF, Adeishvili N, Bamberg E, and Gottschalk A (2005) Light activation of channelrhodopsin-2 in excitable cells of Caenorhabditis elegans triggers rapid behavioral responses. Curr Biol, 15, 2279-2284. Zhang F, Wang LP, Brauner M, Liewald JF, Kay K, Watzke N, Wood PG, Bamberg E, Nagel G, Gottschalk A, and Deisseroth K (2007) Multimodal fast optical interrogation of neural circuitry. Nature, 446, 633-639.