Combined vs. Singular Chronic Predictable Stress: Behavioral and Neurobiological Outcomes

Author

Claudia Grace Ford, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2025

Degree Name

Master of Arts

Department

Psychology

First Advisor

Hylin, Michael

Abstract

Stress is pervasive across species, and while acute stressors allow for the healthy adaptability of an organism, chronic stressors lead to worsened overall health and long-term prognosis. The current study examined the effects of combined chronic predictable early life stress models of maternal separation (MS) and limited bedding/nesting (LBN) during adolescence. Subjects were subjected to one of four early environmental manipulations (MS alone, LBN alone, MS & LBN combined, and standard rearing). Groups were further analyzed with respect to gender and each experimental group used 4-5 different liters from virgin dams to avoid non-specific effects due to liter. Pups were weighed at 3 post-natal time points (PND9, PND21, PND44) and their average weights per group were compared. The pups were tested upon reaching adolescence (PND35) on the elevated plus maze (EPM) and open field task (OF) for anxiety-like behavior (PND36), as well as in the Morris water maze (MWM) for spatial learning and memory (PND37-43). It was expected that the combined stressed subjects would display the most significant increase in anxiety-like behavior that would occur in addition to increased learning and memory deficits in the MWM. In the MWM, it was expected that the combined stress subjects would have longer latencies to the platform for both the training trials, as well as in the reversal trials. For the probe trial, these subjects were expected to have longer overall paths to the annulus, indicating worse memory for the initial platform location. Following the completion of behavioral testing, subjects were euthanized and adrenal and brain weights were taken. Similar what has been conventionally found following chronic stress, adrenal weights for the combined stress subjects were expected to be higher on average than the other three groups. It was anticipated that brain weights would not vary significantly. Following histological preparation, the hippocampus was analyzed for overall cell loss and microglial activity. It was anticipated that there would be no significant changes in the overall hippocampal volumes, but there would be increases in microglial cell in the hippocampal subareas (CA1/2, CA3, and dentate gyrus) in subjects exposed to combined early life stress models. Generally, the subjects in the combined experimental manipulation were expected to demonstrate significant behavioral impairments and histopathological changes. The findings of the current study did not support the hypotheses made prior. Notably, the group that received the MS manipulation alone demonstrated learning impairments in the MWM, and their behavioral deficits corresponded to an increased amount of microglial cell counts in the CA3 and DG areas.