Effects of Semax in the Rat Models of Acute Stress

Acute stress exposure triggers a cascade of neurochemicalreactions, leading, specifically, to behavior changes and increasedpain tolerance in humans and animals. ACTH/MSH-like peptides playan important role in regulating the organism's response to stressfulexposures. The aim of the present study was to assess the effectsof the heptapeptide Semax, a synthetic ACTH(4-10) analog,in various models of acute stress. The effect of intraperitonealSemax administration at doses of 0.05 and 0.5 mg/kg on changes inbehavior and pain sensitivity of Wistar rats was investigated inmodels of inescapable intermittent footshock stress and forced cold-waterswim stress. To assess the involvement of the endogenous opioidsystem in the effects of stress, there was studied an impact of thepreadministration with the opioid receptor antagonist Naloxone (1 mg/kg).The stressors used led to an increase in the pain threshold in thepaw-pressure test, which indicates the development of stress-inducedanalgesia (SIA). In addition, rats exposed to stress showed decreasedexploratory behavior and increased anxiety-like behavior in thehole board test. Both Semax and Naloxone attenuated SIA in the modelof inescapable footshock stress, but did not affect pain thresholdvalues in the model of forced cold-water swim stress. Both drugsdid not affect rat behavior in the above models of acute stress.It can be concluded that Semax attenuates the opioid form of SIA,but does not affect behavior changes in rats exposed to acute stress.