The neuroplastic effect of olfactory training to the recovery of olfactory system in mouse model

Abstract

Background: Several studies have reported the benefits of olfactory training (OT) in the olfactory nervous system of mouse models. Therefore, in this study we performed next-generation sequencing to evaluate the effects of OT on mRNA sequencing in the olfactory area.

Methods: Mice in each group were administered 300 mg of 3-methylindole per kilogram of mouse weight. The olfactory function was evaluated by a food-finding test once a week. The olfactory neuroepithelium was harvested for histologic examination and protein analysis. Subsequently, data analysis, gene ontology and pathway analysis, quantitative real-time polymerase chain reaction of mRNA, and Western blot analysis were conducted.

Results: Mice were divided into 4 groups according to treatment. Control, anosmia, training, and steroid group mice resumed food finding. Olfactory Maker Protein, olfr1507, ADCY3, and GNAL mRNA expression was higher in the olfactory neuroepithelium of OT than anosmia group mice. In total, 26,364 mRNAs were analyzed. Comparison of the results of OT vs anosmia revealed that ADCY8,10, GFAP, NGF, NGFR, GFAP, and BDNF mRNAs were upregulated in the gene ontology.

Conclusion: OT improved olfactory function, as indicated by the food-finding test. OT improved the olfactory recovery time to stimulate olfactory nerve regeneration. OT may initially stimulate the olfactory receptor, followed by neurogenesis. Steroid therapy and OT operated under completely different mechanisms in the upregulated gene study. These results indicate that OT may be one of the future modalities for treating olfactory impairment.

Keywords: olfaction; olfactory disorders; quality of life.

Figure 1

Olfactory‐trained mice found food significantly faster than the anosmia and steroid groups in FFT 3. Almost all mice showed recovery of olfaction at FFT 4. ^* p < 0.05. FFT = food‐finding test.

Figure 2

OMP, Olfr1507, ADCY3, and GNAL mRNA levels in olfactory neuroepithelium were evaluated using real‐time polymerase chain reaction. OMP, Olfr1507, ADCY3, and GNAL mRNA levels were significant higher in the 2‐week olfactory training group than the anosmia group (control vs training in OMP, p = 0.004; anosmia vs training in Olfr1507, p = 0.030; anosmia vs training in ADCY3, p = 0.023; control vs training, p = 0.024; anosmia vs training in GNAL, p = 0.015). ^* p < 0.05. ADCY3 = adenylyl cyclase 3; GNAL = guanine nucleotide‐binding protein G(olf) subunit alpha; Olfr1507 = olfactory receptor 1507; OMP = olfactory marker protein.

Figure 3

OMP, Olfr1507, ADCY3, and GNAL mRNA levels in the olfactory neuroepithelium were evaluated using real‐time polymerase chain reaction. ADCY3 and GNAL mRNA levels were higher in the olfactory training group than in the anosmia group at 3 weeks after olfactory training (control vs training in ADCY3, p = 0.009; control vs training in GNAL, p = 0.002). ^* p < 0.05. ADCY3 = adenylyl cyclase 3; GNAL = guanine nucleotide‐binding protein G(olf) subunit alpha; Olfr1507 = olfactory receptor 1507; OMP = olfactory marker protein.

Figure 4

Scatterplots showing differentially expressed mRNAs. (A) Olfactory training group at 2 weeks. (B) Olfactory training group at 3 weeks. Red: expression level of y value is higher than expression level of x value; green: expression level of y value is lower than expression level of x value.

Figure 5

Gene ontology analysis and Venn diagram analysis of mRNA expression. (A) Anosmia group, (B) olfactory training group, and (C) steroid group after 2 weeks of olfactory training (fold change, 1.5; log2 normalized read counts of ≥4 were selected).

Figure 6

Gene ontology analysis and Venn diagram analysis of mRNA expression. (A) anosmia group, (B) olfactory training group, and (C) steroid group after 3 weeks of olfactory training (fold change, 1.5; log2 normalized read counts of ≥4 were selected).

Figure 7

Western blot analysis was performed to detect protein expression of OMP and Olfr1507 in the olfactory training group compared with the anosmia group. Olfr1507 = olfactory receptor 1507; OMP = olfactory marker protein.