A New Surgical Approach to the Study of Vomeronasal System Regeneration

Abstract

We observed OMP reactivity of vomeronasal nerve terminals in the accessory olfactory bulb at several time points after vomeronasal nerve transection. A rapid reduction in OMP positive nerve terminals within the accessory olfactory bulb was observed 6 days after surgery and no OMP positive terminals were present in any of the animals examined at 20 and 60 days. Interestingly, in some animals examined on day 120, OMP positive nerve terminals were observed in the accessory olfactory bulb. But, the size and distribution of these terminals was reduced compared with those in control animals. In addition, we observed the expression of OMP reactivity in the vomeronasal epithelium after surgery. In control animals, OMP positive neurons were present throughout the vomeronasal epithelium. A reduction in the number of OMP positive neurons was observed in the vomeronasal epithelium at 6 days after surgery. By 20 and 60 days, there were no OMP positive neurons present in the epithelium. At 120 days after surgery, OMP positive neurons were observed in some animals while others showed no signs of recovery. Interestingly, in those animals where recovery was observed, OMP positive nerve terminals were also observed in the accessory olfactory bulb. We also examined the olfactory epithelium and the main olfactory bulb after surgery. OMP positive glomeruli in the main olfactory bulb were present at all recovery times (in controls and 6, 20, 60 and 120 days after surgery). There was little or no damage to olfactory bulb connections. OMP positive neurons in the olfactory epithelium at the same time points in recovery showed no changes following the vomeronasal nerve transection procedure. These results are consistent with the intact olfactory nerve terminals observed in the main olfactory bulb. In the present study, we observed a complete reduction of OMP positive neurons in the vomeronasal epithelium and terminals within the accessory olfactory bulbs after surgery. This finding suggested that this new approach to cut the vomeronasal nerve was very effective. We confirmed the reduction of OMP reactivity in the accessory olfactory bulbs of all animals examined at 20 and 60 days after surgery. The number of mice in each group was >15, so we are confident that our surgery performed a complete transection of the vomeronasal nerves. An additional advantage of this method is that there was minimal or no damage to the olfactory system, including the olfactory epithelium and main olfactory bulb. Our findings suggest that this new surgical method is effective in making a complete and selective transection of the vomeronasal nerves. Using this new surgical method, we can observe regeneration and recovery in the vomeronasal system. In some animals we observed recovery of OMP reactivity in the accessory olfactory bulb. Interestingly, where epithelial recovery was observed on one side but not the other, recovery of OMP positive nerve terminals in the accessory olfactory bulb was observed only on that same side. These findings suggest that recovery of the vomeronasal epithelium may require successful retargeting of nerve terminals in the accessory olfactory bulb. Retargeting of the vomeronasal nerves to the accessory olfactory bulb may depend on several factors, for example, tissue damage within the surgery area, the position of the cutting blades and postoperative bleeding. Tissue damage and gliosis within the surgery area