Fig. 5.
Induced knockout of microglial P2Y12 receptors enhances innate fear responses and c-fos expression. a Representative immunostaining images showing P2Y12R loss in most (85.9 ± 2.5%, n = 6 mice) of Cd11b + microglia cells after tamoxifen treatment in the adult P2Y12f/f:CX3CR1CreER/+ mice (Induced KO). b Representative images of microglial process chemotaxis 6 min after laser burn injury in vivo in induced microglial P2Y12R KO cortex (P2Y12f/f:ROSAtdTomato/+:CX3CR1CreER/+) and control (ROSAtdTomato/+:CX3CR1CreER/+) mice. c Intensity changes within the area surrounding the laser burn core (white ring area in panel B) after local injury. (n = 3 mice for each group. ***p < 0.001, two-way ANOVA.) d The induced P2Y12R KO mice (n = 18) showed decreased open arm time and entries in the EPM, compared with WT mice (n = 21). e The adult-induced KO mice (n = 20) showed less lighted side exploration time and stepped out less times from the dark enclosure in the light/dark box test, compared with WT mice (n = 19). The WT control in D-E were the same in Fig. 2 since the experiments were run together. f Quantification of c-fos+ cells in the ventral hippocampal CA1 region indicates equivalent c-fos expression levels in WT and induced KO animals prior to EPM exposure (naive state, n = 5 images from 2 mice for each group). Enhanced c-fos activation occurs in the induced KO group after performing in the EPM, when compared to WT controls (n = 7 images from 3 mice for each group). g 24 h after fear conditioning training, the adult-induced KO mice showed similar freezing responses to the training context and paired auditory tone stimulus as the WT control mice (n = 17 for the control, n = 13 for the induced KO group). **p < 0.01, ***p < 0.001, t-test or U-test. All data are presented as the mean ± SEM