Effects of Semax in the Rat Models of Acute Stress

Acute stress exposure triggers a cascade of neurochemical reactions, leading, specifically, to behavior changes and increased pain tolerance in humans and animals. ACTH/MSH-like peptides play an important role in regulating the organism’s response to stressful exposures. The aim of the present study was to assess the effects of the heptapeptide Semax, a synthetic ACTH 4–10 analog, in various models of acute stress. The effect of intraperitoneal Semax administration at doses of 0.05 and 0.5 mg/kg on changes in behavior and pain sensitivity of Wistar rats was investigated in models of inescapable intermittent footshock stress and forced cold-water swim stress. To assess the involvement of the endogenous opioid system in the effects of stress, there was studied an impact of the preadministration with the opioid receptor antagonist Naloxone (1 mg/kg). The stressors used led to an increase in the pain threshold in the paw-pressure test, which indicates the development of stress-induced analgesia (SIA). In addition, rats exposed to stress showed decreased exploratory behavior and increased anxiety-like behavior in the hole board test. Both Semax and Naloxone attenuated SIA in the model of inescapable footshock stress, but did not affect pain threshold values in the model of forced cold-water swim stress. Both drugs did 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.