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Chronic unpredictable mild stress (CUMS) is a widely used model to study stress-coping strategies in rodents. Different factors have been shown to influence whether animals adopt passive or active coping responses to CUMS. Individual adaptation and susceptibility to the environment seem to play a critical role in this process. To further investigate this relationship, we examined the effects of CUMS on Carioca high- and low-conditioned freezing rats (CHF and CLF, respectively), bidirectional lines of animals selected for high and low freezing in response to contextual cues that were previously associated with footshocks. For this purpose, the behavior of CHF and CLF animals was evaluated in the contextual fear conditioning, open field, elevated T maze, and forced swimming tests before and after 21 days of CUMS. For all tests, CHF rats were more susceptible to the effects of CUMS compared to CLF. CHF animals exposed to CUMS displayed a reduction in freezing behavior, decreased number of entries and time spent in the center of the open field, greater latencies to become immobile, and increased avoidance and escaping behaviors in the elevated T maze. Overall, these findings support the hypothesis that a heightened susceptibility to the environment exerts a strong influence on coping responses to chronic stress. [ABSTRACT FROM AUTHOR]

• CHF and CLF rats are breeding lines based on contextual fear conditioning. • CHF are more strongly affected by chronic stress than CLF animals. • Shifts in defensive coping strategies occur in CHF rats after chronic stress. • Hypercaloric food has a protective effect over the alterations caused by the stress. • These effects are dependent on innate differences in fear response traits. Stress and eating disorders are closely related and are a topic of major concern due to their burden on human health. Engaging in unhealthy eating habits may come as a result of stress, and it often serves to alleviate the symptoms of anxiety or as a distraction from the stressor itself or self-awareness. However, it can also lead to negative feelings of a person's body figure, guilty, or shame. As diverse as these consequences are in humans, so are the effects of the combined administration of stress and hypercaloric food in animals' models. In this study, we assessed the influence of individual innate behavioral predisposition on the effects of chronic unpredictable mild stress and the dietary supplementation with high-sugar/high-fat food. These conditions were applied to male Carioca low- and high-conditioned freezing (CLF and CHF) rats for 21 days. Behavioral results show that the hypercaloric supplement had a protective effect over the alterations caused by the stress. Notably, it was more strongly observed in CHF rather than CLF animals. As the chronic stress led to an impaired behavior in the contextual fear conditioning and the forced swimming tests in the CLF line, animals fed with the HSHF pellet scored responses similar to their untreated control. On CHF rats, these effects also were seen to a broader extent on the open field test, where the locomotor behavior was also increased. No major effects of the diet were seen in the unstressed groups. Overall, our results show that the influences of both chronic stress and hypercaloric feeding depend on innate differences in fear response traits of male Carioca rats. [ABSTRACT FROM AUTHOR]

Animal models are important tools for studying neuropsychological disorders. Considering their limitations, a more extensive translational research must encompass data that are generated from several models. Therefore, a comprehensive characterization of these models is needed in terms of behavior and neurophysiology. The present study evaluated the behavioral responses of Carioca Low-conditioned Freezing (CLF) rats to haloperidol and methylphenidate. The CLF breeding line is characterized by low freezing defensive responses to contextual cues that are associated with aversive stimuli. CLF rats exhibited a delayed response to haloperidol at lower doses, needing higher doses to reach similar levels of catatonia as control randomly bred animals. Methylphenidate increased freezing responses to conditioned fear and induced motor effects in the open field. Thus, CLF rats differ from controls in their responses to both haloperidol and methylphenidate. Because of the dopamine-related molecular targets of these drugs, we hypothesize that dopaminergic alterations related to those of animal models of hyperactivity and attention disorders might underlie the observed phenotypes of the CLF line of rats. • CLF rats constitute a breeding line based on contextual fear conditioning. • CHF rats have low freezing response in comparison to Control rats. • Methylphenidate increased freezing response and motor activity among CLF rats. • CLF rats exhibited a delayed response to haloperidol at lower doses. • CLF rats might represent an animal model of hyperactivity and attention disorders. [ABSTRACT FROM AUTHOR]

Carioca High- and Low-conditioned Freezing (CHF and CLF, respectively) rats are two bidirectional breeding lines of animals with high and low levels of defensive conditioned freezing response to contextual cues that are associated with an aversive stimulus. In the last decade, various studies have investigated their physiology and response to other external stimuli as a model of trait anxiety. However, the process of the extinction of their characteristic freezing response is not well understood. The present study investigated the acquisition and extinction of a contextual fear conditioning protocol among these animals. The results showed that CLF rats were unable to consolidate aversive memories and thus were unresponsive to extinction. In contrast, CHF rats still exhibited a large freezing response to contextual cues and were susceptible to extinction, reaching levels of freezing that were comparable to control, randomly bred animals. These findings contribute to validating CHF rats as a model of trait anxiety and their usefulness for evaluating exposure protocols to ameliorate excessive levels of context-conditioned fear. [ABSTRACT FROM AUTHOR]

Evidence from clinical and epidemiological studies point towards an association between generalized anxiety disorder (GAD) and alcohol abuse. In the present study we investigated whether a similar relationship could be observed in an animal model of GAD. Specifically, we evaluated the alcohol intake of Carioca High- and Low-conditioned Freezing rats (CHF and CLF, respectively). Sex differences in alcohol drinking behavior were also studied. Male and female rats from randomized crossbreeding populations served as controls (CTL). Free- and forced-choice protocols were used to measure alcohol consumption, and quinine and saccharin were used as taste control solutions. Our results indicate that CHF rats consumed more alcohol than CLF and CTL ones in both the free-choice (6 and 10% concentrations) and the forced-choice (10% concentration) conditions. CHF female rats exhibited the highest amount of alcohol intake in the forced-choice condition. CHF females also consumed more quinine than CHF male rats. Finally, CHF rats exhibited lower saccharin consumption compared to CLF and CTL animals. Altogether, these results support the hypothesis that there is a positive relationship between anxiety and alcohol intake, and provide further evidence for the use of CHF rats as a model of GAD. • CHF and CLF rat are two bidirectional lines that are based on contextual fear conditioning. • CHF rats have a more anxious phenotype than CLF and control rats. • Anxiety and alcohol use disorders often go together. • CHF rats consumed more alcohol than CLF and control rats. • There was a positive association between anxiety and alcohol intake. • CHF and CLF lines can be a useful genetic model for studying anxiety. [ABSTRACT FROM AUTHOR]