The age-related decline in gonadal steroids is associated with changes in mood and memory function. It appears that normal physiological concentrations of the steroids are required for adequate synaptic plasticity. However, the effects of high levels of androgens subsequent to misuse of anabolic androgenic steroids (AAS) are largely unknown. In this study, rats were given i.m. nandrolone as a single dose or daily for 14 days and the effects on synaptic components in hippocampal synaptoneurosomes were measured 24h after the last injection. Western blot analysis revealed that a single injection of AAS increased phosphorylation of the NMDA receptor subunits NR2A and NR2B and ERK1/2, while the levels of phosphorylated CaMKIIalpha were unaltered. No changes were seen in other synaptic proteins tested, i.e., BDNF, Arc, TUC-4, and beta-tubulin III. Daily administration of nandrolone for 2 weeks did not affect the content of any of the proteins tested. From this in vivo study, it is concluded that important synaptic components respond to a single high dose of nandrolone, an effect that may influence synapse function.