The results of the inanimate object approach experiments may also be considered in this context from a broader perspective, because contact with objects can be regarded as a behavioral response to environmental change. The environmental changes in these tests may have exposed the mice to stressful situations in which they had to evoke behavioral responses. We speculate that Lrrtm1 is necessary for some versatile perception or executive functions required for the appropriate behavioral responses. We also identified other behavioral abnormalities through our behavioral analysis. One was a social discrimination performance defect in the SD test. Because the test was conducted soon after the training session, the increased response to the familiar mice may indicate impairment of social perception, disturbance of shortterm Epoxomicin chemical information memory formation, or altered emotional status. However, the possibility of the latter two abnormalities may be low, considering that the other behavioral tests did not show abnormalities closely related to these two. The other suggestive abnormality is the spatial memory deficit shown in the MWM test. Although we cannot exclude the influence of altered adaptive response in the training process, the longer distance swum by KO mice was limited to the first day , and the other parameters��latency in approach to the goal, and no movement time��were not significantly altered in the MWM test . We therefore considered that a spatial memory deficit did exist in the Lrrtm1 KO analysis. On the whole, the behavioral abnormalities in Lrrtm1 KO mice could be summarized as indicating impaired cognitive function. The morphological analysis revealed altered synaptic density and morphology in the Lrrtm1 KO hippocampus. The decrement in synapse density may represent the absence of Lrrtm1 synaptogenic TGF-beta inhibitor activity . The longer spines are considered to indicate an abnormality related to postsynaptic differentiation. YFP-tagged Lrrtm1 is known to localize to excitatory synapses in cultured hippocampal neurons and can induce postsynaptic differentiation upon being subjected to an artificial clustering stimulus .