Impact of chronic intermittent challenges in stressor-susceptible and resilient strains of mice

Background Stressors promote altered neurochemical functioning that may be of adaptive value. The sustained elevations of neurochemical activity elicited by chronic stressors may exact excessive demands on biological systems (allostatic load), thereby rendering the organism more vulnerable to pathology, but such effects may be dependent on individual characteristics. Methods Stressor reactive BALB/cByJ mice and the relatively resilient C57BL/6ByJ mice were exposed to a variety of psychogenic and neurogenic stressors, twice a day over 60 days. The resultant neurochemical and behavioral changes in these strains was assessed relative to the effects of acute stressors. Results Acute restraint elicited more pronounced and more widespread variations of norepinephrine and serotonin utilization in BALB/cByJ than in C57BL/6ByJ mice. Following the chronic stressor, BALB/cByJ mice showed marked behavioral alterations thought to be indicative of depression- and anxiety-like states. The chronic stressor was also associated with moderation of amine utilization in the C57BL/6ByJ mice, whereas such an outcome was less prominent or entirely absent in BALB/cByJ mice. Conclusions The sustained increase of amine activity in the BALB/cByJ, coupled with the marked depressionogenic-anxiogenic characteristics of this strain, may provide a useful preparation to assess the impact of chronic stressors on the development of behavioral and physical pathology.