Corticosterone disrupts spatial working memory during retention testing when highly taxed, which positively correlates with depressive-like behavior in middle-aged, ovariectomized female rats

Abstract

Major Depressive Disorder affects 8.4 % of the U.S. population, particularly women during perimenopause. This study implemented a chronic corticosterone manipulation (CORT, a major rodent stress hormone) using middle-aged, ovariectomized female rats to investigate depressive-like behavior, anxiety-like symptoms, and cognitive ability. CORT (400 μg/ml, in drinking water) was administered for four weeks before behavioral testing began and continued throughout all behavioral assessments. Compared to vehicle-treated rats, CORT significantly intensified depressive-like behaviors: CORT decreased sucrose preference, enhanced immobility on the forced swim test, and decreased sociability on a choice task between a novel conspecific female rat and an inanimate object. Moreover, CORT enhanced anxiety-like behavior on a marble bury task by reducing time investigating tabasco-topped marbles. No effects were observed on novelty suppressed feeding or the elevated plus maze. For spatial working memory using an 8-arm radial arm maze, CORT did not alter acquisition but disrupted performance during retention. CORT enhanced the errors committed during the highest working memory load following a delay and during the last trial requiring the most items to remember; this cognitive metric positively correlated with a composite depressive-like score to reveal that as depressive-like symptoms increased, cognitive performance worsened. This protocol allowed for the inclusion of multiple behavioral assessments without stopping the CORT treatment needed to produce a MDD phenotype and to assess a battery of behaviors. Moreover, that when middle-age was targeted, chronic CORT produced a depressive-like phenotype in ovariectomized females, who also comorbidly expressed aspects of anxiety and cognitive dysfunction.

Keywords: Aging; Anxiety; Chronic stress; Cognition; Corticosterone; Depression; Estrogen; Memory.

Fig. 1.

Study Timeline and Radial Arm Maze (RAWM) Training and Retention Testing. A) For the timeline, all rats were OVX and received 28 days of daily CORT or VEH treatment in drinking water prior to beginning behavioral testing and treatment continued throughout the study. In order of testing, rats completed 12 days of RAWM training and then were tested on sucrose preference (SP), social test, marble bury, novelty suppressed feeding (NSF), elevated plus maze (EPM). four days of RAWM retention assessment, visible platform (BP) and forced swim test (FST). The RAWM had two phases with training occurring over 12 days and then after a few weeks, RAWM retention was assessed B) Total daily errors during 12 days of training and shows that CORT and VEH rats decreased errors as trials progressed and acquired the task similarly. C) Total daily errors made during the four days of RAWM retention testing. CORT and VEH treated rats performed similarly during the first 3 days of retention testing. However, on day 4 of retention testing when a 2-hour delay was introduced between trials 3 and 4, CORT treated rats made significantly more total errors than did VEH treated rats. D) The total errors committed across trials during day 4 retention testing showed that CORT-treated rats made significantly more errors than did VEH treated rats on trial 4. E) The WMC errors committed across trials during day 4 retention testing showed that CORT treated rats made significantly more WMC errors on trial 4 than did VEH. Group sizes were n = 10 for both CORT and VEH treated rats until SP and then n = 9 for VEH. Blocked arrows indicate the delay between assessments. *p< 0.05, ** p < 0.01. VEH = Vehicle (open circles), CORT = Corticosterone (closed triangles).

Fig. 2.

Sucrose Preference (SP) Timeline and Outcome. A) A modified SP protocol was implemented that used a ten day 2-bottle choice during single housing without food or drink deprivation. Initially, rats were given access to 2% sucrose or water for 3 days during acclimation, and then were changed to 1% sucrose and water for the following 7 days. CORT was administered in both bottles for rats exposed to CRT. The final 3 days of 1% SP were the test days and averages from the 3 days were used. B) During the 3-day 1% SP testing period, CORT treated rats showed a significantly lower SP index compared to VEH rats to reveal that CORT-treated rats drank less 1% sucrose than did VEH-treated rats. C) During 1% SP testing, CORT and VEH treated rats consumed similar volumes of fluid (1% sucrose and RO water) per day. D) During the 3-day 2% sucrose acclimation period, CORT treated rats showed a significantly lower SP index compared to VEH rats. E) During 2% SP acclimation, CORT treated rats consumed significantly less total fluid (2% sucrose and RO water) compared to VEH rats to suggest that the lower 2% SP Index could be confounded by total volume drank and reveals that CORT-treated rats may respond to the introduction of novel drinks differently than VEH-treated rats ***p< 0.001, VEH = Vehicle, CORT = Corticosterone.

Fig. 3.

Forced Swim Test (FST). Compared to VEH-treated rats, CORT-treated rats spent significantly more time being immobile (A) and climbing (B) For time spent swimming (C) CORT- and VEH-treated rats spent similar amounts of time swimming. *p< 0.05, VEH = Vehicle, CORT = Corticosterone.

Fig. 4.

Social Tests. A) Sociability involves assessing whether a test rat prefers to spend time with a novel conspecific (R1) or a novel, inanimate object (O). The rat scan see, hear and smell each other, but are unable to physically interact. B) During sociability testing, CORT and VEH-treated rats showed statistically similar sociability indexes. C) During sociability testing, VEH-treated rats spent significantly more time in the chamber with R1 compared to the chamber with the object. In contrast, CORT-treated rats showed no chamber preference. D) Social novelty involves assessing whether a test rat prefers to spend time with the conspecific (R1) from the sociability assessment (R1) or a novel, conspecific (R2). CORT and VEH treated rats showed statistically similar social novelty indexes (E), which was also supported by time spent in the two side compartments (F). Individual animals represented by circles (VEH) and solid triangles (CORT). *p< 0.05, VEH = Vehicle, CORT = Corticosterone. C = Center chamber.

Fig. 5.

Assessments of Anxiety-Profile using Marble Investigation, NSF, and EPM. A) For Mable Investigation, CORT-treated rats spent less time investigating marbles compared to VEH treated rats. B No differences were observed in time to investigate the first marble. VEH- and CORT-treated rats were similar in the time spent burying marbles (C), grooming (D), and being immobile (E). In NSF, the latency to approach the food in the center of the OF was statistically similar (F), and the amount of food consumed within the home cage after NSF was completed was also statistically similar (G). In the EPM, no difference was found in the anxiety index (H), nor did groups differ in the total entries made (I). Individual animals represented by circles (VEH) and solid triangles (CORT). *p< 0.05, VEH = Vehicle, CORT = Corticosterone.

Fig. 6.

Pearson Correlations Performed on the Composite Scores for Depressive-Like and Anxiety-Like Behavior with RAWM Performance. A) The three depressive-like measures (immobility in the FST, SP index, sociability index) were transformed into z-scores, adjusted as appropriate by multiplying by −1 to ensure that the higher score corresponded with greater depressive-like behavior. Then the z-scores were summed to create a single composite score and correlated with working memory correct (WMC) errors committed on the retention testing Day 4, Trial 4 to reveal a significant positive correlation. The greater the depressive score, rats committed more WMC errors. B) The three anxiety-like measures (anxiety index on EPM, time investigating marbles on Marble Bury, and latency to approach food in NSF) were similarly calculated into a composite z-score and correlated with WMC errors committed on retention test day 4, trial 4, but no significant correlation was observed. VEH = White Circles, CORT = Black Triangles.

Fig. 7.

Effects of CORT on Body Weight Gain, Adrenal and Thymus Weights. A) CORT-treated rats gained significantly less body weight compared to VEH-treated rats, which was most pronounced during week 5. B) CORT-treated rats significantly atrophied adrenal weights and thymus weights at euthanasia compared to VEH treated rats. VEH = Vehicle, CORT = Corticosterone. Circles = VEH, triangles = CORT. *p< 0.05, **p< 0.01, ***p< 0.001.