The Effect Of Early Life Stress On Looming Evoked Innate Fear Behavior

Early life stress,also known as early life adversity or adverse childhood experiences.A large number of epidemiological researches have demonstrated that early life stress is a high-risk factor for adult mental disorders,such as depression,anxiety and schizophrenia.On the other hand,among patients with mental illness,compared to other individuals,those who exposed to early life stress had higher odds of self-injury,suicide or suicide ideation,accidental death,showing innate fear emotion processing disorder.The relationship between early life stress and innate fear processing disorder or dysfunction,and its underlying neural circuits and mechanism,are very interesting questions which still remain largely unknow.Solving these questions has important implications for understanding metal illness development,as well as for seeking early diagnosis and treatment strategies.Maintaining accurate innate fear response to predator or dangerous stimuli is critical for individual survival and species reproduction.In recent years,the paradigm of looming evoked innate defensive behaviors mimicking responses to aerial predators have been used to study neuronal mechanism underlying innate fear behaviors.Experiments across species show that looming induces animals to flight,avoidance,or freezing according to environmental cues.Our study used mice as model animal to study the effect of early life stress on looming evoked innate fear behavior.In rodent studies,the underlying neural mechanism of looming evoked innate defensive behavior,including types of neurons,brain regions,neural circuits,from retinal input to defensive behavior output,was gradually dissected by scientists,using neuronal manipulation techniques such as optogenetics and chemogenetics.However,it remains to be studied that whether looming evoked innate fear behavior is affected by early life stress and the underlying neural mechanisms,and the characteristics of retinal ganglion cells responding to the looming approach.Based on the above research backgrounds and crucial questions,our study mainly completes three parts of work.Firstly,we investigated the effects of different stages of early life stress on the innate defensive behavior of mice at different developmental stages.Mice live for about2 years and have different behavioral characteristics at different developmental stages.We found that looming evoked flight to nest innate defensive behavior was built up at postnatal day 20 to 24.We used two different stages of social deprivation to induce early life stress,that is,early social deprivation(ESD,postnatal day 1 to 12)and late social deprivation(LSD,postnatal day 10 to 20).Then we tested looming evoked innate defensive behavior on postnatal day 22,30 and 60.We found that LSD impaired looming evoked innate defensive behavior in both adult male and female mice,while ESD did not.Then,we revealed that oxytocin signaling mediated LSD induced looming evoked innate defensive behavior deficit in adult mice.Clinical studies have shown that individuals who exposed to early life stress have lower levels of endogenous oxytocin signaling in adulthood.In mice,oxytocin is mainly synthesized by the paraventricular nucleus(PVN)and the supraoptic nucleus(SON)of hypothalamus.Oxytocin neurons extensively project to the brain and involve in various behaviors regulation,such as social interaction,rewarding,addiction,fear,learning and memory,eating and drinking,etc.Consistent with human clinical studies,animal studies show that oxytocin signaling is impaired to varying degrees in individuals who experienced early life stress,such as the number of oxytocin neurons decreases,or the expression of oxytocin receptors in some brain regions decreases.We found that no significant changes in the number of oxytocin neurons and secretion level of oxytocin in the brain of LSD mice,while the expression of oxytocin receptor m RNA level in the Superior Colliculus(SC)was significantly reduced.SC is a key brain region mediating looming evoked innate defensive behavior.We found that specific knockout of its oxytocin receptor mimics behavior deficits in LSD mice.Furthermore,using calcium imaging and chemogenetics,we demonstrated that oxytocin signaling bidirectionally regulate looming evoked innate defensive behavior in mice.Finally,we describe the characteristics of the retinal ganglion cell(RGC)associated with looming response.Previous studies have shown that the Kcnip2⁺OFF-transient RGCs is essential for mediating looming response in mice.Experiment by our colleagues has shown that Calretinin⁺RGCs are also involved in looming response.Our preliminary experimental results suggested that SC projecting Calretinin⁺RGCs respond to both ON and OFF light stimuli.Kcnip2⁺and Calretinin⁺RGCs belong to?RGCs,they have large cell body and dendrite area,can be recognized by SMI-32antibody.However,it has been suggested that SMI-32 labels more than one morphological RGC type,and due to the thick cover of SMI-32⁺neurofilaments,the morphology of SMI-32⁺RGCs in the central retinal region is obscured and rarely described.In order to clarify these questions,the distribution and morphological characteristics of SMI-32⁺RGCs in the whole retina were described in detail using immunostaining and intracellular neurobiotin injections.We found that SMI-32⁺RGCs were evenly distributed throughout the retina.We describe the morphological characteristics of SMI-32⁺RGCs in the central,middle,and peripheral retinal regions,and found that SMI-32⁺RGCs can be classified into five clusters.In addition,more than 90%of SMI-32⁺RGCs presented parvalbumin positive.