Comparative Effects of Anti-Inflammatory Therapies on Olfactory Bulb Histopathology and Olfactory Function in a Rat Model of Experimental Allergic Rhinitis

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Purpose: This study aimed to evaluate histopathological changes in the olfactory bulb and nasal mucosa, as well as olfactory outcomes, following treatment modalities in an rat model of experimental AR. Methods: This experimental study included 49 female Sprague-Dawley rats, randomly allocated into seven groups (n = 7 per group). Allergic rhinitis was induced by ovalbumin sensitization and intranasal challenge. Study groups included negative and positive controls, and treatment groups receiving methylprednisolone, montelukast, levocetirizine, olopatadine, or fluticasone propionate between days 21 and 34. The primary outcome was histopathological evaluation of inflammatory and structural changes in the nasal mucosa and olfactory bulb at day 34. The secondary outcome was assessment of olfactory function using the food-finding latency test. Results: All animals completed the study without mortality. Compared with the positive control group, all treatment modalities resulted in significant improvement in nasal mucosal histopathology, including vascular dilatation, goblet cell hyperplasia, inflammatory cell infiltration, plasma cell infiltration, mast cell infiltration, eosinophil infiltration, chondrocyte hypertrophy, and ciliary loss. Similarly, significant improvements were observed in most olfactory bulb parameters, including glomerular layer thickness, glomerular diameter, glomerular organization, neuronal degeneration, vascular congestion, perivascular edema, and microglial activation. No significant superiority was observed among treatment groups in histopathological outcomes. In olfactory testing, a significant reduction in food-finding latency at day 28 compared with day 21 was observed only in the methylprednisolone and olopatadine groups (p = 0.038 and p = 0.027). By day 34, significant reductions in food-finding latency compared with day 21 were observed within all treatment groups (p < 0.001 for methylprednisolone, olopatadine, and fluticasone propionate; p = 0.005 for levocetirizine; p = 0.026 for montelukast). Conclusion: All treatment modalities improved olfactory mucosal and olfactory bulb histopathological parameters, with no clear superiority. Notably, methylprednisolone and olopatadine provided early improvement in olfactory function, highlighting their therapeutic potential.

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