USING VERTICAL MIGRATION OF LARVAL ZEBRAFISH TO STUDY NON-IMAGE-FORMING LIGHT PROCESSING: OPSIN, NEURAL CIRCUITS AND NEUROMODULATORS

Abstract

Non-image forming (NIF) light perception can acutely modulates locomotion, mood and cognition. These effects are thought to be mediated by specialized light detection systems that are sensitive to short-wavelength light, while most of the functional neural circuits are less known. This thesis uses the light-evoked vertical migration of larval zebrafish, combined with whole brain two-photon calcium imaging, to identify neural circuits underlying the acute effect of NIF. Administration of a melanopsin antagonist causes a loss of vertical migration. Additionally, red light fails to drive climbing to the water surface, in contrast to blue light. Calcium imaging reveals that the habenula and pretectum show a strong response to blue but not to red light, suggesting that they participate in NIF processing. Lipophilic tracing indicates that the habenula is directly innervated by an pre-tectal nucleus, AF-4. Habenula lesion impairs this behaviour. The habenula regulates serotonergic neurons in the raphe, and pharmacological and genetic disruptions of serotonin changes vertical migration. Hence, NIF light information appears to influence behaviour by a circuit involving the habenula, which links the pretectum to neuromodulator release.