Background Studies have shown that benzo(a)pyrene (BaP) exhibits neurotoxicity and can induce cognitive dysfunction. Olfactory dysfunction is an early marker of mild cognitive impairment; however, the mechanism by which BaP exposure causes this impairment is still unclear. Objective To investigate the effects of BaP exposure on olfactory function in mice. Methods Thirty 5-month-old male C57BL/6 mice were randomly assigned to five groups (n=6 per group): blank control, solvent control (olive oil), and low, medium and high doses (0.72, 1.44, and 2.89 mg·kg⁻¹, respectively). Following one week of acclimatization, BaP was administered intranasally every other day. Behavioral changes were assessed using the buried food test and Morris water maze (MWM). Olfactory bulb tissues were subsequently harvested for analysis. Hematoxylin-eosin (HE) staining was used to evaluate pathological changes, while immunofluorescence and quantitative polymerase chain reaction (qPCR) were employed to examine the expression and distribution of protein and mRNA expressions and distributions of olfactory marker protein (OMP), membrane-spanning 4-pass A1 (MS4A1), trace amine-associated receptor1 (TAAR1). Results The buried food test revealed that BaP exposure significantly prolonged the time taken to find food in a dose-dependent manner (F=56.753, P< 0.01). MWM results showed significant main effects for both time (F=128.5, P<0.01) and dose (F=3.889, P<0.05), with a significant interaction effect between them (F=2.128, P<0.05). HE staining showed that in the 2.89 mg·kg⁻¹ group, although granule remained abundant, mitral cell layer neurons exhibited structural atrophy and deep staining. Immunofluorescence demonstrated a decreased distribution of OMP, MS4A1, and TAAR1 in the olfactory nerve layer and glomerular layers in the 2.89 mg·kg⁻¹ group compared with the blank control group (F=11.590, P<0.01; F=12.807, P<0.01; F=7.436, P<0.01). Furthermore, mRNA expression levels of OMP, MS4A1, and TAAR1 in the 2.89 mg·kg⁻¹ group were also significantly downregulated compared to the control group (F=6.720, P<0.01; F=16.931, P<0.01; F=48.060, P<0.01). Conclusion BaP exposure leads to olfactory dysfunction in mice by inducing pathological damage to mitral cells and reducing the expression of key olfactory receptors and markers in the olfactory bulb.

Background Studies have shown that benzo(a)pyrene (BaP) exhibits neurotoxicity and can induce cognitive dysfunction. Olfactory dysfunction is an early marker of mild cognitive impairment; however, the mechanism by which BaP exposure causes this impairment is still unclear. Objective To investigate the effects of BaP exposure on olfactory function in mice. Methods Thirty 5-month-old male C57BL/6 mice were randomly assigned to five groups (n=6 per group): blank control, solvent control (olive oil), and low, medium and high doses (0.72, 1.44, and 2.89 mg·kg⁻¹, respectively). Following one week of acclimatization, BaP was administered intranasally every other day. Behavioral changes were assessed using the buried food test and Morris water maze (MWM). Olfactory bulb tissues were subsequently harvested for analysis. Hematoxylin-eosin (HE) staining was used to evaluate pathological changes, while immunofluorescence and quantitative polymerase chain reaction (qPCR) were employed to examine the expression and distribution of protein and mRNA expressions and distributions of olfactory marker protein (OMP), membrane-spanning 4-pass A1 (MS4A1), trace amine-associated receptor1 (TAAR1). Results The buried food test revealed that BaP exposure significantly prolonged the time taken to find food in a dose-dependent manner (F=56.753, P< 0.01). MWM results showed significant main effects for both time (F=128.5, P<0.01) and dose (F=3.889, P<0.05), with a significant interaction effect between them (F=2.128, P<0.05). HE staining showed that in the 2.89 mg·kg⁻¹ group, although granule remained abundant, mitral cell layer neurons exhibited structural atrophy and deep staining. Immunofluorescence demonstrated a decreased distribution of OMP, MS4A1, and TAAR1 in the olfactory nerve layer and glomerular layers in the 2.89 mg·kg⁻¹ group compared with the blank control group (F=11.590, P<0.01; F=12.807, P<0.01; F=7.436, P<0.01). Furthermore, mRNA expression levels of OMP, MS4A1, and TAAR1 in the 2.89 mg·kg⁻¹ group were also significantly downregulated compared to the control group (F=6.720, P<0.01; F=16.931, P<0.01; F=48.060, P<0.01). Conclusion BaP exposure leads to olfactory dysfunction in mice by inducing pathological damage to mitral cells and reducing the expression of key olfactory receptors and markers in the olfactory bulb.