In Vivo: Naloxone (2.0 mg/kg with constant infusion of 1.7 mg/kg/h) causes a significant improvement in neurobehavioral outcome which persists up to 4 weeks postinjury in rat. Naloxone treatment causes a modest and nonsignificant increase in mean arterial blood pressure (MAP). Naloxone (0.4 mg/kg) causes memory facilitation and antagonizes the amnestic effect of ACTH and epinephrine in rat. Naloxone treatment diminishes the strength of the initial tetanus in a dose-related manner in cats. Naloxone (5 or 10 mg/kg, i.v.) causes subsequent doses of morphine to produce less PTP depression but has no effect on maximal twitch depression.