Fig. 4. Effect of corticotropin-releasing factor (CRF) antagonist, α-helical CRF^9–41, on nitrous oxide-induced c-Fos expression in the locus ceruleus (LC). Rats were pretreated with intracerebroventricular vehicle (Veh) or CRF antagonist (Ant) and exposed for 60 min to air or nitrous oxide. Bars represent total numbers of c-Fos-positive tyrosine hydroxylase neurons in the LC from three sections (mean ± SD). Nitrous oxide exposure induced remarkable c-Fos immunoreactivity in the LC (Veh/Air vs.  Veh/N²O). Induction of c-Fos immunoreactivity by nitrous oxide exposure was significantly suppressed by pretreatment with CRF antagonist (Veh/N²O vs.  Ant/N²O). *P < 0.0001 versus  vehicle/air, #P < 0.0005 versus  vehicle/N²O, n = 5–7 per group.