Naloxone Effects on Behavior of Inbred Mice with Different Response to Emotional Stress in Open Field Test

Effects of nonspecific opiate receptor antagonist naloxone in doses of 0.1, 0.5, 1.0, 5.0, 10.0 mg/kg on open field behavior and spontaneous motor activity were studied in male BALB/c and С57Bl/6 mice. Differently directed effects of naloxone on behavioral parameters of emotional-stress reaction in BALB/c and С57Bl/6 mice were observed. Naloxone increased motor activity in the open field test in BALB/c mice, but decreased it in С57Bl/6 mice. In the absence of stress, naloxone in the studied dose range did not affect spontaneous motor activity in С57Bl/6 mice, and significantly reduced activity in BALB/c mice in doses 0.5 and 1.0 mg/kg.