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When a maternal rat nurtures her pups, she relies on adequate resources to provide optimal care for her offspring. Accordingly, limited environmental resources may result in atypical maternal care, disrupting various developmental outcomes. In the current study, maternal Long-Evans rats were randomly assigned to either a standard resource (SR) group, provided with four cups of bedding and two paper towels for nesting material or a limited resource (LR) group, provided with a quarter of the bedding and nesting material provided for the SR group. Offspring were monitored at various developmental phases throughout the study. After weaning, pups were housed in same-sex dyads in environments with SRs for continued observations. Subsequent behavioral tests revealed a sex × resource interaction in play behavior on PND 28; specifically, LR reduced play attacks in males while LR increased play attacks in females. A sex × resource interaction was also observed in anxiety-related responses in the open field task with an increase in thigmotaxis in LR females and, in the social interaction task, females exhibited more external rears oriented away from the social target. Focusing on morphological variables, tail length measurements of LR males and females were shorter on PND 9, 16, and 21; however, differences in tail length were no longer present at PND 35. Following the behavioral assessments, animals were perfused at 56 days of age and subsequent immunohistochemical assays indicated increased glucocorticoid receptors in the lateral habenula of LR offspring and higher c-Fos immunoreactivity in the basolateral amygdala of SR offspring. Further, when tail vertebrae and tail tendons were assessed via micro-CT and hydroxyproline assays, results indicated increased trabecular separation, decreased bone volume fraction, and decreased connectivity density in bones, along with reduced collagen concentration in tendons in the LR animals. In sum, although the restricted resources only persisted for a brief duration, the effects appear to be far-reaching and pervasive in this early life stress animal model.

Both social and physical stimuli contribute to the complexity of an animal’s environment, influencing biobehavioral responses to subsequent challenges. In the current study, male Long-Evans rats were randomly assigned to an isolate (ISO), social control (SC) or social enriched (SE) group (n = 8 per group). The SC and SE conditions were group housed with the SE group exposed to physical enrichment stimuli that were natural as opposed to manufactured (e.g., hollowed out log instead of plastic hiding place). On three occasions during their 40-day enriched environment exposure, night/dark phase videos were obtained for 1 h during the early part of the dark phase. During this time, the SE animals exhibited significantly more social grooming with no differences between the SE and SC in the frequency of play or self-grooming bouts. Subsequently, all animals were assessed in social interaction and problem-solving escape tasks during the last week of the enriched environment exposure. SE rats exhibited increased digging bouts toward the restrained conspecific in the social interaction task whereas the other groups exhibited more escape responses. In the problem-solving task, SE animals exhibited a decreased latency to cross the barrier to escape from the predator odor (i.e., cat urine and fur). Neural analyses indicated increased oxytocin-immunoreactive (OT-ir) tissue in the SE supraoptic and paraventricular nuclei of the hypothalamus compared to the other groups. Interestingly, blood samples indicated lower peripheral corticosterone (CORT) and higher OT levels in the ISO animals when compared to the SC and SE animals, an effect retrospectively attributed to separation anxiety in the SE and SC animals in preparation for histology procedures. When the behavioral, neural and endocrine data were visualized as a multifaceted dataset via a multidimensional scaling analysis, however, an association between social enrichment and higher OT involvement was observed in the SE animals, as well as heightened stress responsivity in the ISO and SC groups. In sum, the SE animals exhibited a facilitation of social responses, problem-solving ability and OT immunoreactive responsiveness. These findings provide new information about the influences of both physical and social stimuli in dynamic and enriched environments.

Emotional resilience enhances an animal's ability to maintain physiological allostasis and adaptive responses in the midst of challenges ranging from cognitive uncertainty to chronic stress. In the current study, neurobiological factors related to strategic responses to uncertainty produced by prediction errors were investigated by initially profiling male rats as passive, active or flexible copers (n = 12 each group) and assigning to either a contingency-trained or non-contingency trained group. Animals were subsequently trained in a spatial learning task so that problem solving strategies in the final probe task, as well-various biomarkers of brain activation and plasticity in brain areas associated with cognition and emotional regulation, could be assessed. Additionally, fecal samples were collected to further determine markers of stress responsivity and emotional resilience. Results indicated that contingency-trained rats exhibited more adaptive responses in the probe trial (e.g., fewer interrupted grooming sequences and more targeted search strategies) than the noncontingent-trained rats; additionally, increased DHEA/CORT ratios were observed in the contingent-trained animals. Diminished activation of the habenula (i.e., fos-immunoreactivity) was correlated with resilience factors such as increased levels of DHEA metabolites during cognitive training. Of the three coping profiles, flexible copers exhibited enhanced neuroplasticity (i.e., increased dentate gyrus doublecortin-immunoreactivity) compared to the more consistently responding active and passive copers. Thus, in the current study, contingency training via effort-based reward (EBR) training, enhanced by a flexible coping style, provided neurobiological resilience and adaptive responses to prediction errors in the final probe trial. These findings have implications for psychiatric illnesses that are influenced by altered stress responses and decision-making abilities (e.g., depression).