Fractalkine Signaling and Microglia Functions in the Developing Brain

Figure 3

Fractalkine/CX3CR1 signaling controls the recruitment of microglia and the functional maturation of thalamocortical synapses. (a) Drawing of the sensory system of vibrissae in rodents and link between the distribution of vibrissae and that of barrels in layer 4 somatosensory cortex. Adapted from [59]. ((b) and (c)) Microglia (green) distribution in the layer 4 of the somatosensory cortex during postnatal development in Cx3cr1^+/eGFP (b) and Cx3cr1^eGFP/eGFP (c) mice. At P5, microglial cells are exclusively located outside of the barrel centers which contain thalamocortical synapses (red, staining of thalamocortical axons). At P7, microglial cells start to invade the barrel centers in Cx3cr1^+/eGFP mice and this invasion is delayed in Cx3cr1^eGFP/eGFP mice. At P9, microglial cell distribution is similar for the two genotypes. Scale bar, 100 µm. (d) Relative change in the synaptic currents resulting of the activation of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-D-aspartate) postsynaptic receptors expressed at thalamocortical synapses between P5 and P9 in Cx3cr1^+/eGFP and Cx3cr1^eGFP/eGFP mice. Note that the AMPA/NMDA ratio increases between P5 and P9 in Cx3cr1^+/eGFP but not in Cx3cr1^eGFP/eGFP mice. ((b) and (c)) Adapted from [48].