A Research For The Neural Circuit And Regulating Mechanism Underlying The Persistence Of Visually Evoked Innate Fear Responses

Adopting adaptive defensive strategies to innate threats is the most critical ability of individuals to avoid predators and ensure survival.Our previous work has found a subcortical pathway,from superior colliculus(SC)via the lateral posterior thalamic nucleus(LP)to amygdala,which can mediates the innate defensive responses evoked by visual predator stimulus.Simulated predators approaching from the air or photogenetic activation of excitatory neurons in the SC can induce a persistent tonic immobility response in mice,while animals have the ability to adapt to repeated predator stimuli,further decreasing the TI duration.However,there are still two questions to be solved: 1)how does the brain maintain and regulate the persistent TI response,and 2)which type of SC-LP projection neurons mediate this behavior.In addition,abnormities in processing fear emotion bring people serious mental disorders and even endanger lives.Studies in our lab also find that the innate fear responses invoked by predator stimulus can be modulated in turn by different anxiety level of animals.Thus,it is important to exame the interaction between fear and anxiety.However,the variations of anxiety measuring paradigms and subjective setting of testing apparatus,individual differences of animals,low dimensional anxiety parameters will confound the study results.Next,using an unsupervised artificial intelligence based hierarchical 3D-motion learning framework,we aim to re-evaluate anxiety-like behaviors with an objective and comprehensive manner.The main work of this paper includes the following three aspects:Tonic immobility is considered an anti-predator defensive behavior that reflects the potential state of innate fear.Although TI is conserved across many species,the neural substrate underlying this behavior remains unclear.In this study,the neural mechanism for maintaining and modulating the TI response to innate fear elicited by a predator stimulus was investigated in mice.With the help of a new neural transmitter probe,optic fiber photometry showed that acetylcholine released in the basolateral complex of the amygdala is involved in the predator stimulus-evoked TI response.Blockage of muscarinic or nicotinic acetylcholine receptors in the basolateral complex of the amygdala significantly suppressed the persistence or adaptation of TIs,respectively.These results reveal a novel role for the acetylcholine system in processing innate fear and may provide new principles of cholinergic treatment for some mental disorders.At present,the neurons projecting from the superficial layer of the SC to the LPare thought to be wide field neurons in the optic layers of SC.The main biomarker used to label these neurons is Ntsr1,and another type of Tac1 positive neurons is also found in optic layer and send projects to the LP.However,the precise downstream loop of these two neurons and their functions in animal innate defensive behaviors are still unclear.In this present study,optogenetic activation of LP terminals from Ntsr1 or Tac1 neurons elicited transient active freezing and persistent TI,respectively.Whereas,only lesion of Tac1 neurons could significantly inhibit the TI responses evoked by optogenetic activation of SC excitatory neurons.Histology showed that Ntsr1 and Tac1 neurons have different efferent subregions of the LP.Only Ntsr1 neurons send projections to the lateral part of LP,which then interacts with visual cortices and further promote arousal in animals.Pupil size enlargement was observed after optogenetic activation the projections of Ntsr1 neurons in the LP,also implicating the rise of arousal.Finally,activation terminals of Ntsr1 or Tac1 wide field neurons increased and decreased the flight behavior evoked by a following looming stimulus.This study separate two subtype wide field neurons in the SC from the anatomy and the function.Various animal models of anxiety have been developed to evaluate anxiety and anxiolytic drugs.However,non-uniform measuring paradigms,various settings of apparatus and individual difference of animals confound study results.In this study,no significant differences between control and stressed mice were found using elevated plus maze and open field test if all tested animals are included in data analysis.To use machine learning approach to analyze elaborate behavioral patterns in all animals,we selected typical subjects in each group as a training set according to classical anxiety parameters.Spontaneous behaviors in these animals were captured by multi-view cameras and decomposed into sub-second modules via Behavior Atlas,and six behavioral features with significant differences between two groups were identified.Combined with low-dimensional embedding and clustering,new features were used to discriminate stressed mice from controls,in both training set and all objects.Our results show Behavior Atlas is a powerful approach to identify new potential biomarkers for effectively eliminating bias in expected and actual values.Our approach can become a complement of classical anxiety measuring paradigms to further evaluate anxiety-like behaviors objectively and comprehensively.