小鼠条件性恐惧模型的建立和品系敏感性研究

目的在敏感品系上建立稳定可靠的小鼠条件性恐惧模型。方法采用给予30 s声音刺激(85 dB,5000 Hz),后2 s伴随给予不可逃避的足底电击(0.6 mA,持续2 s),声音-电击共配对5次,每次间隔2 min的方法建立小鼠条件性恐惧模型,在ICR、DBA/2(简称DBA)和C57BL/6J(简称C57)3种品系小鼠上评价场景恐惧和声音线索恐惧获得和表达的行为特点,以确定敏感品系鼠;分别于条件性恐惧训练第2,7,14,21和28天对C57小鼠场景恐惧和声音线索恐惧进行检测,以评价该品系小鼠条件性恐惧的自然消退特点;采用30 s声音+30 s间隔+10次消退训练的模式进行声音线索恐惧消退训练,并于24 h后进行消退保持测试,以评价该品系小鼠消退训练和保持的特点。结果声音-电击配对5次可成功诱导C57小鼠形成场景恐惧和声音线索恐惧,DBA小鼠可诱导形成声音线索恐惧但无法形成场景恐惧,ICR小鼠场景恐惧和声音线索恐惧均未诱导成功,确定C57小鼠为敏感品系鼠。C57小鼠呈现时间依赖的恐惧反应自然消退,其中场景恐惧在训练后第7天僵住百分率消退至(25±12)%,声音线索恐惧训练后第28天僵住百分率维持在(48±22)%;C57小鼠经10轮30 s声音消退训练,僵住时间百分率由(55±30)%消退至(32±27)%,但24 h后消退保持测试时僵住时间百分率又回升至(47±35)%。结论以敏感品系C57小鼠为研究对象,建立了恐惧获得、表达、自然消退、消退训练和消退保持各阶段恐惧行为检测的实验方法,成功建立小鼠条件性恐惧模型。

Establishment of fear conditioning model in mice and study on mouse strain variation

OBJECTIVE To establish a mouse fear conditioning model in sensitive strains.METHODS Different strains of mice in model groups,ie,ICR,DBA/2(DBA)and C57 BL/6 J(C57)mice,were placed in the foot shock box(context A)for 2 min before 5 trails of sound(30 s,85 dB)-shock(2 s,0.6 mA)presentation(2 min intervals).Control mice were subjected to the same procedure without shock.Twenty-four hours later,different strains of mice were re-placed in the same shock box(context A)or a new context(context B)to test the expression of contextual(5 min)and cued fear(30 s tone presentation),respectively.To evaluate the time-dependent extinction characteristics of C57 mice,contextual fear and cued fear behaviors were re-tested at D7,D14,D21 and D28,respectively.As an extinction training procedure,C57 mice were subjected to 10 extinction trails with 30 s sound presentation and 30 s intervals in context B.Twenty-four hours later,extinction retention test was performed in the same context for 30 s with sound on.Freezing behavior was recorded by the computer(MED Associates),and the percentage of freezing time was calculated as an index of fear behavior.RESULTS Both contextual and cued fear behaviors were successfully induced by five-trails of sound-shock presentation in C57 mice.ICR mice were not sensitive in either fear type,whereas DBA mice were sensitive in cued fear conditioning.C57 mice exhibited time-dependent extinction in both contextual and cued fear.The percentage of freezing time in the contextual fear test decreased from to(25±12)%at D7,whereas that of the cued fear test decreased from(48±22)%at D28.Results from extinction training indicated that 10 trails of extinction decreased the percentage of freezing time from(55±30)%to(32±27)%,increased it to(47±35)%in the retention test 24 h later.CONCLUSION The present study demonstrates that C57 is a sensitive strain in studying fear conditioning behavior,anda workable mouse fear conditioning model has been established.