Kirrel3 is a synaptic cell adhesion protein necessary for the formation of a specific type of synapse in the hippocampus, a brain region that is important for learning and memory. Kirrel3 is expressed on both sides of the synapse and mediates cell adhesion likely by holding the synaptic membranes together. Previously the Megan William's lab found that germline Kirrel3 knock-out mice are missing these specific synapses in the hippocampus. These mice also have an increase in neuronal activity in the hippocampus most likely due to the loss of synapses. Interestingly, mice that express Kirrel3 during development continue to express it after a synapse is formed. However, it is unknown if Kirrel3 is needed to hold the synapse together after development. I hypothesize that Kirrel3 is necessary in maintaining mature synapses and if knocked out, there will be a significant change in the structure of these synapses. I will test this by knocking out Kirrel3 in adult neurons after synapse formation is complete using Kirrel3 conditional mice. Then I will use confocal microscopy to image, analyze, and compare the morphology of the synapses. This investigation of Kirrel3 in adult mice will bring us closer to understanding the mechanical role of Kirrel3 in synaptic formation and neuronal connectivity. Moreover, understanding the function of Kirrel3 may be clinically beneficial as variations in Kirrel3 are associated with neurodevelopmental disorders like autism and learning disabilities.