Growth associated protein 43 (GAP43) is very abundant in the nervous system and is found concentrated in the axons and synapses of neurons. It was discovered as one of three proteins which becomes greatly upregulated during the regeneration of toad optic nerve following nerve section. Upregulation of this protein in other situations is frequently seen as indicative of ongoing CNS remodeling. GAP43 antibodies are therefore useful for identifying synapses and axons and monitoring neuronal plasticity. Mouse select image at left for larger view.