Genetic dissection of the zebrafish habenula, a possible switching board for selection of behavioral strategy to cope with fear and anxiety.

The habenula is a part of an evolutionarily highly conserved conduction pathway within the limbic system that connects telencephalic nuclei to the brain stem nuclei such as interpeduncular nucleus(IPN), the ventral tegmental area (VTA), and the raphe.In mammals, the medial habenula receives inputs from the septohippocampal system, and relaying such information to the IPN. In contrast, the lateral habenula receives inputs from the ventral pallidum, a part of the basal ganglia. The physical adjunction of these two habenular nuclei suggests that the habenula may act as an intersection of the neural circuits for controlling emotion and behavior. We have recently elucidated that zebrafish has the equivalent structure as the mammalian habenula. The transgenic zebrafish, in which the neural signal transmission from the lateral subnucleus of the dorsal habenula to the dorsal IPN was selectively impaired, showed extremely enhanced levels of freezing response to presentation of the conditioned aversive stimulus. Our observation supports that the habenula may act as the multimodal switching board for controlling emotional behaviors and/or memory inexperience dependent manners.