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      A retinoraphe projection regulates serotonergic activity and looming-evoked defensive behaviour

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          Abstract

          Animals promote their survival by avoiding rapidly approaching objects that indicate threats. In mice, looming-evoked defensive responses are triggered by the superior colliculus (SC) which receives direct retinal inputs. However, the specific neural circuits that begin in the retina and mediate this important behaviour remain unclear. Here we identify a subset of retinal ganglion cells (RGCs) that controls mouse looming-evoked defensive responses through axonal collaterals to the dorsal raphe nucleus (DRN) and SC. Looming signals transmitted by DRN-projecting RGCs activate DRN GABAergic neurons that in turn inhibit serotoninergic neurons. Moreover, activation of DRN serotoninergic neurons reduces looming-evoked defensive behaviours. Thus, a dedicated population of RGCs signals rapidly approaching visual threats and their input to the DRN controls a serotonergic self-gating mechanism that regulates innate defensive responses. Our study provides new insights into how the DRN and SC work in concert to extract and translate visual threats into defensive behavioural responses.

          Abstract

          Neural circuits underlying innate fear are only partially understood. Huang et al. identify a subset of retinal ganglion cells that project to both the dorsal raphe nucleus and the superior colliculus, and show that these RGCs mediate looming-evoked defensive behaviours in mice.

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          Most cited references41

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          Rapid innate defensive responses of mice to looming visual stimuli.

          Much of brain science is concerned with understanding the neural circuits that underlie specific behaviors. While the mouse has become a favorite experimental subject, the behaviors of this species are still poorly explored. For example, the mouse retina, like that of other mammals, contains ∼20 different circuits that compute distinct features of the visual scene [1, 2]. By comparison, only a handful of innate visual behaviors are known in this species--the pupil reflex [3], phototaxis [4], the optomotor response [5], and the cliff response [6]--two of which are simple reflexes that require little visual processing. We explored the behavior of mice under a visual display that simulates an approaching object, which causes defensive reactions in some other species [7, 8]. We show that mice respond to this stimulus either by initiating escape within a second or by freezing for an extended period. The probability of these defensive behaviors is strongly dependent on the parameters of the visual stimulus. Directed experiments identify candidate retinal circuits underlying the behavior and lead the way into detailed study of these neural pathways. This response is a new addition to the repertoire of innate defensive behaviors in the mouse that allows the detection and avoidance of aerial predators.
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            Serotonin neurons in the dorsal raphe nucleus encode reward signals

            The dorsal raphe nucleus (DRN) is involved in organizing reward-related behaviours; however, it remains unclear how genetically defined neurons in the DRN of a freely behaving animal respond to various natural rewards. Here we addressed this question using fibre photometry and single-unit recording from serotonin (5-HT) neurons and GABA neurons in the DRN of behaving mice. Rewards including sucrose, food, sex and social interaction rapidly activate 5-HT neurons, but aversive stimuli including quinine and footshock do not. Both expected and unexpected rewards activate 5-HT neurons. After mice learn to wait for sucrose delivery, most 5-HT neurons fire tonically during waiting and then phasically on reward acquisition. Finally, GABA neurons are activated by aversive stimuli but inhibited when mice seek rewards. Thus, DRN 5-HT neurons positively encode a wide range of reward signals during anticipatory and consummatory phases of reward responses. Moreover, GABA neurons play a complementary role in reward processing.
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              Processing of visually evoked innate fear by a non-canonical thalamic pathway

              The ability of animals to respond to life-threatening stimuli is essential for survival. Although vision provides one of the major sensory inputs for detecting threats across animal species, the circuitry underlying defensive responses to visual stimuli remains poorly defined. Here, we investigate the circuitry underlying innate defensive behaviours elicited by predator-like visual stimuli in mice. Our results demonstrate that neurons in the superior colliculus (SC) are essential for a variety of acute and persistent defensive responses to overhead looming stimuli. Optogenetic mapping revealed that SC projections to the lateral posterior nucleus (LP) of the thalamus, a non-canonical polymodal sensory relay, are sufficient to mimic visually evoked fear responses. In vivo electrophysiology experiments identified a di-synaptic circuit from SC through LP to the lateral amygdale (Amg), and lesions of the Amg blocked the full range of visually evoked defensive responses. Our results reveal a novel collicular–thalamic–Amg circuit important for innate defensive responses to visual threats.
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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                31 March 2017
                2017
                : 8
                : 14908
                Affiliations
                [1 ]Guangdong-Hongkong-Macau Institute of CNS Regeneration, Ministry of Education CNS Regeneration Collaborative Joint Laboratory, Jinan University , Guangzhou 510632, China
                [2 ]Guangdong key Laboratory of Brain Function and Diseases, Jinan University , Guangzhou 510632, China
                [3 ]School of Psychology, Nanjing Normal University , Nanjing 210097, China
                [4 ]Psychology Department, School of Medicine, Jinan University , Guangzhou 510632, China
                [5 ]State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences , Wuhan 430071, China
                [6 ]National Institute of Biological Sciences, Zhongguancun Life Science , Park 7 Science Park Road, Beijing 102206, China
                [7 ]School of Veterinary Medicine and Biomedical Sciences, University of Nebraska , Lincoln, Nebraska 68583, USA
                [8 ]Department of Anatomy, School of Basic Medical Sciences, Peking University , Beijing 100191, China
                [9 ]Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center , Omaha, Nebraska 68198, USA
                [10 ]Department of Ophthalmology and State Key Laboratory of Brain and Cognitive Sciences, The University of Hong Kong , Hong Kong, China
                [11 ]Co-innovation Center of Neuroregeneration, Nantong University , Nantong 226001, China
                Author notes
                Author information
                http://orcid.org/0000-0003-3535-6624
                Article
                ncomms14908
                10.1038/ncomms14908
                5381010
                28361990
                07c20856-9a66-47a6-866c-89c97143a39a
                Copyright © 2017, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 19 October 2016
                : 13 February 2017
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