Induction of c-Fos has previously been used to map locations of cells in the central nervous system (CNS) that are activated by ethanol administration. Only a few studies examining a restricted range of CNS areas have identified brain areas activated by nitrous oxide (N(2)O). Because ethanol and N(2)O have overlapping physiological, psychological and behavioral effects, we hypothesized that these drugs act on similar sites in the CNS. To test this hypothesis, we assessed c-Fos-like immunoreactivity in brain slices from male Long-Evans rats that received a 2-h exposure of 0, 20, 40 or 60% N(2)O (n=5 each) immediately prior to sacrifice. N(2)O administration produced significant (P<0.05) dose-related increases of c-Fos expression in several forebrain regions, including the hypothalamic supraoptic and paraventricular nuclei, the thalamic paraventricular nucleus, the amygdala, and in retrosplenial cortex. In the midbrain, N(2)O caused significant dose-related c-Fos expression in the Edinger-Westphal nucleus. Finally, the pontine locus coeruleus, and two medullary regions, the nucleus of the solitary tract and ventrolateral medulla, also showed significant dose-related N(2)O-induced c-Fos expression. Most of the brain areas identified as targets of N(2)O are also activated by ethanol administration. The overlapping pattern of c-Fos induced by ethanol and N(2)O suggests that these drugs may cause comparable central activity by acting on similar neuronal pathways.