Effect of Cold Stress on Neurobehavioral and Physiological Parameters in Rats

Abstract

Objective: Cold stress is an important current issue and implementing control strategies to limit its sometimes harmful effects is crucial. Cold is a common stressor that can occur in our work and our occupational or leisure time activities every day. There are substantial studies on the effects of chronic stress on memory and behavior, although, the cognitive changes and anxiety disorders that can occur after exposure to chronic intermittent cold stress are not completely characterized. Therefore, the present study was undertaken with an aim to investigate the effects of chronic intermittent cold stress on body weight, food intake and working memory, and to elucidate cold stress related anxiety disorders using cognitive and behavioral test batteries. Methods: We generated a cold stress model by exposing rats to chronic intermittent cold stress for 5 consecutive days and in order to test for the potential presence of sex differences, a comparable number of male and female rats were tested in the current study. Then, we measured the body weights, food intake and the adrenal glands weight. Working memory and recognition memory were assessed using the Y maze and the Novel Object Recognition (NOR) tasks. While, sex differences in the effects of chronic stress on behavior were evaluated by the elevated plus maze (EPM), open field maze (OF), and Marble burying (MB) tests. Results: We found that 2 h exposure to cold (4°C) resulted in an increase in the relative weight of the adrenal glands in male rats. Given the same chronic stress 5 days of cold exposure (2 h per day), increased weight gain in male rats, while females showed decreased food intake and no change in body weight. Both sexes successfully performed the Y maze and object recognition (OR) tasks, indicating intact spatial working memory performance and object recognition abilities in both male and female rats. In addition, we have shown that stress caused an increase in the level of anxiety in male rats. In contrast, the behavior of the female rats was not affected by cold exposure. Conclusion: Overall, the current results provide preliminary evidence that chronic intermittent cold stress model may not be an efficient stressor to female rats. Females exhibit resilience to cold exposure that causes an increase in the level of anxiety in male rats, which demonstrates that they are affected differently by stress and the gender is an important consideration in experimental design.

Keywords: anxiety-like behavior; body weight; chronic intermittent cold stress; food intake; sex difference; working memory.

FIGURE 1

Variation in adrenal weight relative to body weight (mg/100 g of body weight) of control and stressed rats of both sexes. In males, cold stress significantly increased relative adrenal weight in the stressed group compared to the control group. In females, exposure too cold for 5 days had no effect on adrenal glands weight. Adrenal glands weight is expressed in (mg) per 100 g of body weight. Data are represented as mean ± SEM (n = 5) for each sex. Effect of stress: ^∗∗P = 0.001.

FIGURE 2

Effect of cold stress on corticosterone levels in male and female rats. Corticosterone was significantly higher in male rats exposed to cold stress compared to their controls. Chronic intermittent cold stress had no significant effect on the corticosterone levels determined in female rats. Data are represented as mean ± SEM (n = 5) for each sex. Effect of stress: ^∗P < 0.05.

FIGURE 3

Body weight changes observed in control and stressed rats of both sexes. Cold stress increases body weight gain in male rats (A) but does not affect female’s body weight (B). Weight gain is expressed in grams. Data are represented as mean ± SEM (n = 5). (A) Male rats: Effect of stress: ***p < 0.001; Effect of the day: ****p < 0.0001; Bonfferoni’s post hoc test showed no significant interaction between stress and day on body weight gain (p = 0.9393). (B) Female rats: Effect of stress: ns p > 0.05; Effect of the day: ns p > 0.05 (ns: not significant).

FIGURE 4

Variation in food intake in control and stressed rats of both sexes. Male rats are not affected by chronic intermittent cold stress until the 14th day (post stress), represented by a decrease in food intake (A). In female rats, cold exposure leads to a significant decrease in food intake (B). Food intake is expressed in grams (g). Data are represented as mean ± SEM (n = 5). (A) Male rats: Effect of stress: ns p > 0.05. Effect of the day: **P < 0.01. (n = 5). (B) Female rats: Effect of stress: *p < 0.05. Effect of the day: ns p > 0.05 (ns: not significant).

FIGURE 5

Behavioral evaluation of spatial working memory disorders in male and female rats in a Y-maze spontaneous alternation test (% alternation). In both sexes cold stress had no effect on spatial working memory assessed in Y maze test. Each value represents the mean ± SEM (n = 5); Effect of stress: ns p > 0.05 (ns: not significant).

FIGURE 6

Behavioral evaluation of recognition memory disorders in male rats in a Novel object recognition test (Recognition index%). Cold stress had no significant effect on the recognition performance assessed in an object recognition test in male and female rats. Each value represents the mean ± SEM; Effect of stress: ns p > 0.05 (ns: not significant) (n = 5).

FIGURE 7

Behavioral evaluation of anxiety-like behavior in male and female rats in an Elevated plus Maze. The behavior of the animals was recorded by a videotracking system. In male rats, chronic intermittent cold stress causes an increase in the time spent in closed arms (B), with a decrease in the time spent in the center (E). It also leads to a decrease in the number of entries in the open arms. Cold exposure had no significant effect on the various variables measured during this test in female rats. (A) Time spent in open arms; (B) time spent in closed arms; (C) number of entries in open arms; (D) number of entries in closed arms; (E) time spent in the center. Each histogram represents the mean ± SEM; effect of stress: ^∗ns p < 0.05, ns: (not significant) p > 0.05 (n = 5).

FIGURE 8

Behavioral evaluation of anxiety-like behavior in male and female rats in an open field test (OF). The behavior of the animals was recorded by a videotracking system. In male rats, exposure to cold leads to an increase in the time spent in the peripheral zone (A) associated with a decrease in the time spent in the central zone (B) and a decrease in the number of entries in the central zone (D). In female rats, intermittent cold stress had no significant effect on the various variables measured during this test. (A) time spent in the peripheral zone; (B) time spent in the central zone; (C) number of entries to the peripheral zone; (D) number of entries to the central zone. Each histogram represents the mean ± SEM. Effect of stress: ^∗p < 0.05 (n = 5), ns p > 0.05 (ns: not significant) (n = 5).

FIGURE 9

Evaluation of the burying behavior in Marbel Burying test (MB) for 20 min of recording in male and female rats. The cold stress studied leads to an increase in the latency time (A), as well as an increase in the number of buried marbles (B) in male rats. In female rats, exposure to cold had no detectable effect on latency time (A) and number of buried marbles (B) between the two groups of rats. Each histogram represents the mean ± SEM. Effect of stress: ^∗p < 0.05, ^∗∗p < 0.01, ns p > 0.05 (n = 5).