Characterization of a thalamic nucleus mediating habenula responses to change in illumination

Abstract

The thalamus mediates diverse brain functions including arousal, perception and memory formation, and is characterized by widespread connectivity. One thalamus projection that is evolutionarily conserved is to the habenula, a regulator of broadly acting neuromodulators. The function of this projection is unknown, as the information transmitted has not been identified. By two-photon calcium imaging of larval zebrafish, we show that change in irradiance triggers dynamic responses in the habenula. Neuroanatomical tracing shows that the dorsal left habenula neuropil, which has the most prominent response to irradiance change and influences irradiance-dependent behavior and raphe response, is innervated by retinorecipient nuclei in the thalamus. Optogenetic stimulation of the thalamus triggers habenula activity, while lesion reduces light-evoked habenula activity. These data establish that the thalamus controls habenula activity following irradiance change, thereby suggesting that the thalamo-habenula projection provides a pathway for visual stimuli to affect neuromodulator release and behavior.