In contrast, sleep deprivation produced a significant (about 30%) decrease in the Bma x both of 6 (measured by [3H]DADLE binding) and/x receptors (measured by [3H]DAGO binding). As for D 1 receptors also, these changes in opioid receptors were found to be localized in limbic areas, while they were absent in the striatum and in the mesencephalon. No changes in K receptors were observed after sleep deprivation (Fadda et al., 1991, 1992).