Long-term Recovery of the Rat Vomeronasal System after Nerve Transection

The vomeronasal system in adult animals has the capacity to produce new receptor cells continuously. When the vomeronasal nerve bundles in rodents are transected, or the accessory olfactory bulb (AOB) is removed, vomeronasal receptor cells degenerate and immediately start to regenerate receptor cells. To investigate in further detail the changes to the vomeronasal system during the long recovery period following nerve transection, we conducted an immunocytochemical analysis of the AOB using anti-NCAM (neural cell adhesion molecule), anti-Gi2 α, and antisynaptophysin (SYN) antibodies, together with electron microscopy of the vomeronasal organ (VNO) in rats. On day 200 after nerve transection, NCAM, Gi2 α and SYN immunoreactivity (ir) was observed within the vomeronasal nerve layer (VNL) and/or glomerular layer (GL) in the AOB of four of ten rats, but the immunoreactive areas were smaller than those in control sections (positive group). The remaining six rats showed no ir for NCAM, Gi2 α, or SYN within the VNL and/or GL in the AOB (negative group). The percentage of receptor cells with microvilli relative to the total number of receptor cells contacting the luminal surface of the VNO was calculated, showing no difference evident when comparing the positive and negative groups; that is, the microvilli of receptor cells were observed whether or not there were connections between the VNO and the AOB. These results suggest that regeneration of the VNO and AOB occurs independently.