Neurexophilin-3 (NXPH3) is a neuropeptide-like secreted glycoprotein in the neurexophilin family (1, 2). The 252 amino acid (aa) NXPH3 precursor contains a 22 aa signal peptide, plus a 230 aa proprecursor that is likely cleaved at a basic motif, producing a 76 aa propeptide and a 154 aa mature protein (1). Mature rat NXPH3 shares 99%, 95% and 92% aa identity with mouse, human and bovine NXPH3, respectively. It contains motifs that are conserved among all neurexophilins, including three potential N-glycosylation sites in the N-terminal portion and six cysteines in the C-terminal portion (1). NXPH3 is expressed selectively in subplate-derived neurons in the cortex, granule cells in the vestibulocerebellum, and Cajal-Retzius cells during development (3). NXPH1 is the neurexophilin most similar to NXPH3, sharing 69% aa identity within the mature region. Expression of NXPH1 and NXPH3 does not appear to overlap, with NXPH1 expression occurring mainly by cells that resemble inhibitory interneurons (2 - 4). Both are tightly bound extracellular ligands of alpha -neurexins, synaptic transmembrane molecules that are essential for calcium-triggered neurotransmitter release (1, 5, 6). Genetic deletion of NXPH1 and/or NXPH3 produces no anatomical effect, although mice lacking NXPH3 show specific defects in motor coordination (3, 4). Of the other known neurexophilins, NXPH2 is not expressed in rodents, and NXPH4 does not bind alpha -neurexins (1, 5).