Olfactory marker protein immunohistochemistry and the anterograde transport of horseradish peroxidase as indices of damage to the olfactory epithelium

The present study compared the relative effectiveness of wheatgerm agglutinin--horseradish peroxidase (WGA--HRP) and olfactory marker protein (OMP) in detecting the presence of intact olfactory axons in glomeruli of the main olfactory bulb (MOB) in the rat. The olfactory epithelium was damaged by i.p. injections of the toxin 3-methyl indole and, after 5 or 6 days, the olfactory sac was injected with a 1% WGA--HRP solution. No anterograde labeling was observed in the dorsal and ventromedial quadrants of the MOB in the WGA--HRP material. However, in the same cases OMP immunostaining was observed throughout the MOB. In other rats the rostral olfactory epithelium was aspirated unilaterally and after 3, 11 and 16 days the olfactory sacs were injected with WGA--HRP and rats were perfused 1 day later. In these cases WGA--HRP reaction product was absent in the dorsolateral quadrant of the MOB on the aspirated side in all animals, but OMP immunostaining could be detected in the 4 and 12 day survival animals but not in the 17 day survival rat. These findings indicate that anterograde transport of WGA--HRP accurately reflects the presence of intact axons en route to the MOB. In contrast, OMP immunostaining persists in axon terminals severed from their parent cell body for at least 12 days and is a less useful marker of intact olfactory axons in experiments using short survival times.