The Mechanism Of PBLA^Calb1 Neurons In Regulating Anxiety-and Depression-Like Behavior And Its Role In Melatonin-ameliorated Anxiety And Depression

【Background】Different emotional preferences,such as those of optimism and pessimism,frequently appear in our daily lives,especially in times of uncertainty.When faced with ambiguous situations,optimistic people tend to be enthusiastic and keep trying with good expectations.However,pessimists always negatively distort interpretations of ambiguous information and display extensive avoidance,which is especially evident in anxiety and depression.Inaddition to genetics,the above-mentioned reward generalization and fear generalization are also affected by the external environment and individual experience.Excessive fear generalization and impaired reward generalization are closely related to many psychiatric disorders,such as a large number of avoidance behaviors triggered by the generalization of multiple fears,are particularly evident in anxiety and depression.However,the neural circuit mechanism for reward generalization and its role in anxiety anddepression remain elusive.Melatonin（N-acetyl-5-methoxytryptamine）is mainly secreted by the pineal gland,acts through G protein-coupled receptors M1 and M2.In addition to antioxidant and antiinflammatory effects,whether and how melatonin modulates anxiety and depression-like behaviours are still unclear.【Objective】1.Dissect the monosynaptic neural circuit between IL and pBLA and clarify its role in reward generalization.2.To explore the changes of IL–pBLA monosynaptic circuit in pathological anxiety and depression and investigate its role in anti-anxiety and anti-depression.3.To explore whether and how melatonin modulates pathological anxiety and depression.【Methods】The transsynaptic tracer technology of anterograde and retrograde were used to display the IL–pBLA circuit structure connection.Electrophysiological recording and optogenetics were combined to detect IL–pBLA monosynaptic functional connectivity.c-Fos staining and in vivo optical fiber recording system（GCAMP6）were used to detect IL–pBLA activation.Optogenetic and chemogenetic technology were used to regulate the IL–pBLA circuit.A go/go-task behavioral paradigm was created to detect reward generalization and aversive generalization in mice.By establishing a chronic unpredictable mild stress mouse model,using the elevated plus maze and open field experiments,avoidance behavior was detected to evaluate the anxiety level and moving ability,and tail suspension test and sucrose preference test were used to detect depression-like behaviors of mice.Intraperitoneal injection of melatonin was used to detect changes in anxiety-and depression-like phenotypes of CUMS mice.Chemogenetic were used to selectively inhibit pBLA,and the changes of anxiety and depression-like phenotypes in CUMS mice administered melatonin were detected to determine whether pBLA mediates melatonin’s anti-anxiety and antidepression phenotypes.【Results】1.Excitatory monosynaptic connections exist between IL–pBLA^Calb1 circuit.2.The degree of reward generalization is positively correlated with the activation level of IL–pBLA^Calb1 neural circuit.3.Optogenetic or chemogenetic activation of IL–pBLA^Calb1 circuit enhances reward generalization;Optogenetic or chemogenetic inhibition of IL–pBLA^Calb1 circuit reduces reward generalization.4.CUMS mice exhibit anxiety-and depression-like behavioral phenotypes,accompanied by IL–pBLA^Calb1 circuit inhibition.5.Activation of IL–pBLA^Calb1 circuit significantly ameliorates anxiety and depressionlike behavioral phenotypes in CUMS mice.6.Administration of melatonin significantly ameliorates anxiety-and depression-like behavioral phenotypes in CUMS mice,accompanied by activation of pBLA^Calb1 neurons.7.Chemogenetic inhibition of pBLA^Calb1 neurons,abrogates the anxiolytic and antidepressant-like effects of melatonin.【Conclusion】1.Excitatory monosynaptic neural circuit of IL–pBLA^Calb1 regulates reward generalization and exerts anxiolytic and antidepressant effects.2.Melatonin exerts anxiolytic and antidepressant effects by activating pBLA^Calb1 neurons.