Regeneration of vomeronasal nerves into the main olfactory bulb in the mouse.

After surgical section of the vomeronasal nerves the neurosensory cells in the vomeronasal epithelium die. Electron microscopy has been used to demonstrate that their axons, and synaptic terminals in the accessory olfactory bulb degenerate and are removed by phagocytic astroglia. The vacated postsynaptic sites in the accessory bulb persist, and are not re-innervated, either by vomeronasal or olfactory axons, as long as 150 days post-operatively. However, new neurosensory cells which are produced in the vomeronasal epithelium after vomeronasal nerve section do form axons. Light and electron microscope autoradiography of axonally transported material has been used to show that some of these axons grow back into the cranial cavity and form glomeruli in the main olfactory bulb, in regions where it is damaged or de-afferented. The regenerated vomeronasal glomeruli contain synapses between vomeronasal nerve terminals and dendrites of main bulb neurons.