Naloxone and vitamin E block stress-induced reduction of locomotor activity and elevation of plasma corticosterone

Normal rats, on being repetitively stressed by being restrained in a tight container for two hours, had higher levels of plasma corticosterone compare d to pre stress values These rats also reacted to the stress by a behaviora l response in which there was marked decrease in locomotor activity assesse d by the open field test (pre stress: 71.3 +/- 2.6 squares crossed versus p ost stress: 14.3 +/- 2.5 squares crossed) by counting the number of squares entered by the rat over 5 minutes. By the 6th to 7th exposures to the repe titive stress, the rats adapted to the stress and had normal plasma cortico sterone levels and locomotor activity scores comparable to the pre stress v alues These responses to stress were completely blocked by the administrati on of 0.32 mu g/100 g BW of naloxone i.p at 10 minutes prior to the stress. In rats fed with rat chow supplemented with 90 mg/kg rat chow or 150 mg/kg rat chow of vitamin E, there was significant reduction of the plasma corti costerone levels and improvement in the locomotor activity. Stress thus caused opioid mediated increase in plasma corticosterone and re duction in locomotor activity which could be blocked by naloxone. These str ess responses probably also involved generation of oxygen free radicals whi ch were scavenged by the vitamin E, thus reducing the effects of repetitive stress on locomotor activity and serum corticosterone levels.