A 2-hit model of early life stress and later life restraint stress: Susceptibility or resilience to anxiety and alcohol drinking?

Early life stress adversely influences neurodevelopment and has profound long-term effects on brain function and behavior. Here we measure endogenous stress hormone and determine locomotor, anxiogenic, and operant binge drinking behavior of rats exposed to a 2-hit model of maternal deprivation (MD) stress in infancy followed by acute (ARS) or chronic restraint stress (CRS) paradigms during adolescence/adulthood to determine resiliency or susceptibility to the second stress exposure. Adolescents (n=40) exhibited higher baseline corticosterone (CORT) levels than adults (n=40) and with CRS exposure, showed significantly elevated circulating CORT irrespective of MD exposure status. In adults, MD females had lower baseline CORT levels than controls, whereas MD and control male CORT were indistinguishable. For behavior, N=40 was used in total. In the open field, locomotion was significantly decreased upon ARS, with MD having a significant sustained impact on ambulatory measures with CRS. When tested for anxiety-like behavior on an elevated zero maze, ARS interacted with MD to induce protracted and more profound anxiogenic behavior. Upon CRS, MD anxiogenic behavior was reversed to baseline levels whereas controls, especially males, exceeded baseline levels to spend significantly more time in the open arms of the EZM. Finally, in testing for binge drinking behavior, MD rats lever-pressed significantly more for 10% ethanol on an operant apparatus and exhibited a 3-fold greater drinking baseline than controls. Binge drinking behavior was further elevated with ARS, but quickly returned to the MD baseline even prior to reaching CRS. By contrast, controls had much lower baseline but significantly elevated binge drinking behavior by 3–5-fold in response to ARS which remained elevated through CRS, stabilizing at MD baseline levels. Sex differences were most evident in controls where males exhibited accelerated binge drinking behavior at consistently higher rates than females until Day 21 of CRS where their binge drinking behaviors were similar. There was also a main effect of alcohol binge behavior for MD males, and not females. This study illustrates that, depending on the biobehavioral output, males and females differ in reactivity to stressors where MD stress may confer sex-dependent resilience to subsequent stressors, and males are differently impacted than females.