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Effects of glucocorticoid on cyclic nucleotide-gated channels of olfactory receptor neurons.

OBJECTIVE
Cyclic adenosine monophosphate (cAMP) and cyclic nucleotide-gated (CNG) channels play an important role in olfactory perception. The purpose of this study was to explore the effect of glucocorticoid on the CNG channels of olfactory receptor neurons (ORNs).


METHODS
For in vivo studies, rats were injected with dexamethasone 1 mg/kg body weight intraperitoneally once or once a day for 2 weeks. After 24 hours or 2 weeks, the difference in CNGA2 (the principal subunit of CNG channels) messenger ribonucleic acid (mRNA) in the ORNs was detected. For in vitro studies, the ORN membrane was extracted and incubated with 0.1 or 1 mg/mL dexamethasone for 5 or 30 minutes, respectively, and then the concentrations of cAMP were measured. For all experiments, normal saline was used as the control.


RESULTS
For in vivo studies, compared with the normal saline group, CNGA2 mRNA could be upregulated in the 2-week group (p < .01) but not in the 24-hour group (p > .05). For in vitro studies, dexamethasone of both 0.1 and 1 mg/mL raised the concentration of cAMP in the ORNs at 5 and 30 minutes, respectively (p < .05), and the concentration of cAMP was higher in the 1 mg/mL groups than in the 0.1 mg/mL groups (p < .05). However, there was no significant difference between the 5-minute and 30-minute groups with either concentration.


CONCLUSIONS
Glucocorticoid enhanced both the mRNA expression of CNG channels and the production of cAMP, which might be a possible pathway for treating olfactory disorders. The effect of glucocorticoid was dose-dependent.