Differential effects of chronic predictable and unpredictable stress on neurobehavioral and biochemical responses in rats

The present study was designed to investigate the effects of exposure to chronic predictable and unpredictable stress on neurobehavioral and biochemical responses in rats. Male Wistar rats (200-250g) were exposed to either chronic predictable stress (CPS) i.e. immobilization for 1 hour/day for 14 days or chronic unpredictable stress (CUS) i.e. daily a different, random, novel stressor sequence (immobilization stress for 1h, footshock, cold stress, overnight food and water deprivation and social isolation) for 14 days. Behavioral responses were assessed by the elevated plus maze (EPM) test and biochemical parameters, viz. malondialdehyde (MDA, a marker of oxidative stress) and stable NO metabolites (NOx, marker of nitrosative stress), were measured in brain homogenates of the rats. Exposure to chronic CPS resulted in adaptation to neurobehavioral suppression in the EPM (as observed after acute Restraint stress), which was not seen after CUS. These behavioral changes after CPS and CUS were closely paralleled by alterations in the levels of brain MDA and NOx. These results suggest that CPS and CUS results in differential modulation of the neurobehavioral profile and oxidative/nitrosative stress markers in the brain.