Microglia are the immune cells of the CNS and play an important role in synaptic maturation and plasticity. During neurodevelopment a large number of synapses are engulfed by microglia and are eliminated in a process termed synaptic pruning. The remaining synapses are strengthened, forming mature neuronal circuits. Studies have shown that disrupted microglial function results in altered synaptic development, and this may contribute to deficits in cognition and behaviour associated with autism spectrum disorders (ASDs). This project will use the newly generated Csf1r∆FIRE/∆FIRE mouse model which selectively lacks brain microglia to investigate the effects of microglia depletion on synaptic development and plasticity. Quantification of structural properties such as synaptic density, dendritic morphology and spine density will be carried out. Synaptic activity will also be measured to investigate the effect of microglia on synaptic plasticity. Lastly changes in behaviour typical of ASD will be assessed