Axon initial segments (AIS) of dentate granule cells (GC) in hippocampus exhibit prominent spines during early development that are associated with microglial contacts. Here, we asked if developmental changes in axon initial segment spines (AISS) could be modified by neonatal maternal separation through stress hormones and microglial activation and examined the potential behavioral consequences. We examined AISS densities at postnatal day (PND) 15 and 50, using Golgi-Cox staining and anatomical analysis. Neuron-microglial interaction was assessed using antibodies against ankyrinG, PSD95 and Iba1, for AIS, AISS and microglia, respectively, in normally reared and neonatal maternally separated (MS) male and female rats. We observed a higher density of AISS in MS groups at both PND15 and PND50 compared to control. Effects were more pronounced in female than in male rats. AIS-associated microglia showed a hyper-ramified morphology and less co-localization with PSD95 in MS compared to normally reared animals at PND 15. An MS-like alteration in microglial morphology and synaptic pruning could be produced ex vivo by vasopressin application in acute hippocampal slices from normally reared animals. MS rats exhibited increased freezing behavior during auditory fear memory testing which, like effects on AISS density, was more pronounced in females than males. Freezing behavior was associated with Fos expression in dorsal and ventral dentate GC. In summary, AIS associated microglial activity is altered by MS. Sex differences in the long-term effects of MS on AISS density are penetrant to a behavioral phenotype of increased stimulus reactivity in adult female subjects.

中文翻译：

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齿状颗粒细胞轴突起始节上的小神经胶质突触修剪：性二形对成年大鼠遭受早期生活压力的恐惧反应的影响

海马中齿状颗粒细胞（GC）的轴突起始节段（AIS）在早期发育过程中表现出突出的棘突，与小胶质细胞接触有关。在这里，我们问是否可以通过应激激素和小胶质细胞激活的新生儿产妇分离来改变轴突初始节段棘（AISS）的发育变化，并研究了潜在的行为后果。我们使用高尔基-科克斯（Golgi-Cox）染色和解剖学分析检查了出生后第15天和第50天的AISS密度。使用抗锚蛋白，PSD95和Iba1的抗体分别评估了正常饲养的和母体分离的（MS）雄性和雌性大鼠的AIS，AISS和小胶质细胞的神经元-小胶质细胞相互作用。与对照组相比，我们在PND15和PND50的MS组中观察到更高的AISS密度。在雌性大鼠中的作用比雄性大鼠中更为明显。与PND 15正常饲养的动物相比，与AIS相关的小胶质细胞在MS中表现出高度分支的形态，与PSD95的共定位较少。通过在急性海马中应用加压素可离体产生小胶质细胞形态和突触修剪的MS样改变。正常饲养动物的切片。MS大鼠在听觉恐惧记忆测试中表现出增强的冰冻行为，这与对AISS密度的影响一样，雌性比雄性更为明显。冷冻行为与背和腹齿状GC中的Fos表达有关。总之，MS改变了AIS相关的小胶质细胞活性。