Distinct patterns of brain Fos expression in Carioca High- and Low-conditioned Freezing Rats

An animal model of trait anxiety: Carioca high freezing rats as a model of generalized anxiety disorder

Despite being one of the main components of anxiety and playing a pivotal role in how an individual perceives and copes with anxiogenic situations or responds to a given treatment, trait anxiety is paradoxically omitted in most animal models of anxiety. This is problematic and particularly more concerning in models that are used to screen drugs and other treatments for specific anxiety disorders and to investigate their neurobiological mechanisms. Our group has been engaged in the search for specific anxiety-related traits in animal models of anxiety. We developed two new lines of rats with strong phenotypic divergence for high (Carioca High-conditioned Freezing [CHF]) and low (Carioca Low-conditioned Freezing [CLF]) trait anxiety as expressed in the contextual fear conditioning paradigm. Here, we summarize key behavioral, pharmacological, physiological, and neurobiological differences in one these lines, the CHF rat line, relative to randomized-cross controls and discuss how far they represent a valid and reliable animal model of generalized anxiety disorder and so high trait anxiety.

Non-human contributions to personality neuroscience: From fish through primates - a concluding editorial overview

This special issue attempts to integrate personality, psychopathology, and neuroscience as means to improve understanding of specific traits and trait structures in humans. The key strategy is to dive into comparative research using a range of species to provide simple models. This strategy has, as its foundation, the fact that the most basic functions, and their supporting neural systems, are highly conserved in evolution. The papers collected in the issue show that, from fish, through rats, to primates, the homologies in brain systems and underlying functions (despite species-specific forms of expression) allow simpler cases to provide insights into the neurobiology behind more complex ones including human. Our introductory editorial paper to this special issue took a bottom-up approach, starting with the genetics of conserved brain systems and working up to cognition. Here, we deconstruct the different aspects of personality, progressing from more complex ones in primates to least complex in fish. With the primate section, we summarize papers that discuss the factors that contribute to sociability in primates and how they apply to healthy and pathological human personality traits. In the rat section, the focus is driven by psychopathology and the way that "high" strains selected for extreme behaviors can illuminate the neurobiology of motivated responses to environmental cues. The section on fish summarizes papers that look into the most fundamental emotional reactions to the environment that are governed by primitive and conserved brain structures. This raises metatheoretical questions on the nature of traits and to a section that asks "which animals have personalities." We believe that the issue as a whole provides a nuanced answer to this question and shines a new, comparative, light on the interpretation of personality structure and the effects on it of evolution.

Systemic Chronic Treatment with Cannabidiol in Carioca High- and Low-Conditioned Freezing Rats in the Neuropathic Pain Model: Evaluation of Pain Sensitivity

Studies have shown high comorbidity of anxiety disorder and chronic pain; generalized anxiety disorder (GAD) and neuropathic pain are among these pathologies. Cannabidiol (CBD) has been considered a promising treatment for these conditions. This study investigated whether chronic systemic treatment with CBD alters pain in high- (CHF) and low-freezing (CLF) Carioca rats (GAD model) and control rats (CTL) submitted to chronic neuropathic pain. The rats were evaluated in the sensory aspects (von Frey, acetone, and hot plate tests) before the chronic constriction injury of the ischiatic nerve (CCI) or not (SHAM) and on days 13 and 23 after surgery. Chronic treatment with CBD (5 mg/kg daily) was used for ten days, starting the 14th day after surgery. The open field test on the 22nd also evaluated locomotion and anxiety-like behavior. CBD treatment had an anti-allodynic effect on the mechanical and thermal threshold in all lineages; however, these effects were lower in the CHF and CLF lineages. Considering emotional evaluation, we observed an anxiolytic effect in CTL+CCI and CHF+CCI after CBD treatment and increased mobility in CLF+SHAM rats. These results suggest that the CBD mechanical anti-allodynic and emotional effects can depend on anxiety level.

Pharmacological and Physiological Correlates of the Bidirectional Fear Phenotype of the Carioca Rats and Other Bidirectionally Selected Lines

The Carioca rat lines originated from the selective bidirectional breeding of mates displaying extreme defense responses to contextual conditioned fear. After three generations, two distinct populations could be distinguished: the Carioca High- and Low-conditioned Freezing rats, CHF, and CLF, respectively. Later studies identified strong anxiety-like behaviors in the CHF line, while indications of impulsivity and hyperactivity were prominent in the CLF animals. The present review details the physiological and pharmacological-related findings obtained from these lines. The results discussed here point towards a dysfunctional fear circuitry in CHF rats, including alterations in key brain structures and the serotoninergic system. Moreover, data from these animals highlight important alterations in the stress-processing machinery and its associated systems, such as energy metabolism and antioxidative defense. Finally, evidence of an alteration in the dopaminergic pathway in CLF rats is also debated. Thus, accumulating data gathered over the years, place the Carioca lines as significant animal models for the study of psychiatric disorders, especially fear-related ones like anxiety.

The association between the renin-angiotensin system and the hypothalamic-pituitary-adrenal axis in anxiety disorders: A systematic review of animal studies

Anxiety is characterized as the emotional response in anticipation of a future threat. This hypervigilant state comprehends a cascade of neuroendocrine and physiological processes, involving the renin-angiotensin system (RAS) and hypothalamic-pituitary-adrenal axis (HPA). Excessive and chronic anxiety may ultimately lead to the development of anxiety disorders. This systematic review aimed to investigate experimental studies using animal models that explored the relationship between RAS and the HPA axis in anxiety disorders. A systematic search was conducted in MEDLINE/PubMed, Embase and Web of Science, and was performed according to PRISMA guidelines. The inclusion criteria was mainly the mention of RAS, HPA axis, and an anxiety disorder in the same study. Quality of studies was evaluated according to the table of risk of bias from SYRCLE. From 12 eligible studies, 7 were included. Research in rats and mice shows that the overactivation of the RAS and HPA axis triggers several neuroendocrine reactions, mainly mediated by AT1 receptors, which promote anxiety-like behaviors and positive feedback for its hyperactivation. On the contrary, the administration of antihypertensive drugs, such as angiotensin AT1 receptor blocker, propitiated the regulation of the RAS and HPA axis, maintaining homeostasis even amid aversive situations. Assessment of risk of bias revealed a pronounced unclear to high risk in several categories, which thus jeopardize the comparability and reproducibility of the results. Nonetheless, the preclinical evidence indicates that the hyperactivation of both RAS and HPA axis during stress exerts deleterious consequences, inducing anxiogenic responses. Moreover, the compiled results show that the modulation of both systems by the administration of AT1 receptor blockers produce anxiolytic effects in animal models and may constitute a new venue for the treatment of anxiety-like disorders.

Behavioral effects of chronic stress in Carioca high- and low-conditioned freezing rats

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.

Alcohol intake in Carioca High- and Low-conditioned Freezing rats

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.