The Activity-regulated cytoskeletal associated protein (Arc) is an effector immediate early gene and has been shown to be involved in synaptic plasticity related events. Rats were exposed to a novel environment for five minutes and then sacrificed immediately, or after 15 or 30 minutes. The figure shows confocal laser microscope images taken at 60X. From left to right are z-projections of dorsal striatal medium spiny neurons expressing arc and preproenkephalin (PPE) mRNA as well as a nuclear counterstain. PPE is a phenotypic marker for the striatopallidal neurons of the indirect pathway. The nuclear stain is green, arc is red, and PPE is blue.