The effects of various types of steroids on the nicotinic acetylcholine (ACh) receptor (nAChR)-mediated responses were investigated in superior cervical ganglionic neurons acutely dissociated from rats using nystatin perforated patch recording. ACh induced a peak followed by a gradual decrease in the inward current at a holding potential of -40 mV. Nicotine, but not muscarine, mimicked ACh. Hydrocortisone at a concentration of >10(-6) M reversibly suppressed both the peak and steady-state nicotine-induced currents (Inic) in a noncompetitive manner. The inhibition of Inic by hydrocortisone did not show any voltage dependency and persisted in the presence of either cyclic AMP modulators, forskolin and 3-isobutyl-1-methylxanthine, or a protein kinase A inhibitor, N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89). Beta-estradiol, androsterone, aldosterone, and 17alpha-estradiol mimicked hydrocortisone in its inhibitory action on ACh-induced currents (I(ACh)). The potency for the inhibitory actions on I(ACh) was as follows: androsterone > beta-estradiol > hydrocortisone > or = aldosterone = 17alpha-estradiol. Cholesterol had no effect on the I(ACh). In conclusion, the structural characteristics of a steroid are thus considered to be necessary to block nicotinic I(ACh) in rat superior cervical ganglionic cells, whereas the cholesterol side chain might disturb the inhibitory action of the steroid skeleton on nAChRs.