Because overexpression of Rac1 can induce the formation of dendritic spines, IQGAP1 can bind to Rac1 as a junction (integrating receptor signals) and a node (diversifying signals to multiple out-puts), improve dendritic spine collapse, adjust dendritic morphology, reshape actin cytoskeleton, affect synapse formation, adjust the sensitivity of reward pathways, change neuronal plasticity, and then affect the formation of morphine dependence (29). Here, RAC1 is linked to morphine dependence.