Loss of the Habenula Intrinsic Neuromodulator Kisspeptin1 Affects Learning in Larval Zebrafish Charlotte Lupton, Mohini Sengupta, Ruey-Kuang Cheng, Joanne Chia, Vatsala Thirumalai, Suresh Jesuthasan eNeuro 8 May 2017, 4 (3) ENEURO.0326-16.2017; DOI: 10.1523/ENEURO.0326-16.2017
Learning how to actively avoid a predictable threat involves two steps: recognizing the cue that predicts upcoming punishment and learning a behavioral response that will lead to avoidance. In zebrafish, ventral habenula (vHb) neurons have been proposed to participate in both steps by encoding the expected aversiveness of a stimulus. vHb neurons increase their firing rate as expectation of punishment grows but reduce their activity as avoidance learning occurs. This leads to changes in the activity of raphe neurons, which are downstream of the vHb, during learning. How vHb activity is regulated is not known. Here, we ask whether the neuromodulator Kisspeptin1, which is expressed in the ventral habenula together with its receptor, could be involved. Kiss1 mutants were generated with CRISPR/Cas9 using guide RNAs targeted to the signal sequence. Mutants, which have a stop codon upstream of the active Kisspeptin1 peptide, have a deficiency in learning to avoid a shock that is predicted by light. Electrophysiology indicates that Kisspeptin1 has a concentration-dependent effect on vHb neurons: depolarizing at low concentrations and hyperpolarizing at high concentrations. Two-photon calcium imaging shows that mutants have reduced raphe response to shock. These data are consistent with the hypothesis that Kisspeptin1 modulates habenula neurons as the fish learns to cope with a threat. Learning a behavioral strategy to overcome a stressor may thus be accompanied by physiological change in the habenula, mediated by intrinsic neuromodulation.
We thank Satoshi Ogawa and Ishwar Parhar (Brain Research Institute, Monash) for the antibodies to Kisspeptin1 and the kisspeptin receptor. We also thank Caroline Kibat (IMCB) for performing the antibody label and associated imaging and Samuel James (University of Oxford) for help with the behavioral assay. CL was funded by the A*Star Graduate Academy, under the ARAP scheme. MS was supported by Senior Research Fellowship from Council of Scientific and Industrial Research. JC was funded by the National University of Singapore Graduate School. This work was supported by core funding from Institute for Molecular and Cell Biology and a Lee Kong Chian School of Medicine, Nanyang Technological University MOE Start-Up Grant to SJ; core funding from National Centre for Biological Sciences; Intermediate Fellowship from Wellcome Trust-DBT India Alliance; and grant funding from the Department of Biotechnology to VT.