Carisa L. Bergner

Understanding behavioral and physiological phenotypes of stress and anxiety in zebrafish

The zebrafish (Danio rerio) is emerging as a promising model organism for experimental studies of stress and anxiety. Here we further validate zebrafish models of stress by analyzing how environmental and pharmacological manipulations affect their behavioral and physiological phenotypes. Experimental manipulations included exposure to alarm pheromone, chronic exposure to fluoxetine, acute exposure to caffeine, as well as acute and chronic exposure to ethanol. Acute (but not chronic) alarm pheromone and acute caffeine produced robust anxiogenic effects, including reduced exploration, increased erratic movements and freezing behavior in zebrafish tested in the novel tank diving test. In contrast, ethanol and fluoxetine had robust anxiolytic effects, including increased exploration and reduced erratic movements. The behavior of several zebrafish strains was also quantified to ascertain differences in their behavioral profiles, revealing high-anxiety (leopard, albino) and low-anxiety (wild type) strains. We also used LocoScan (CleverSys Inc.) video-tracking tool to quantify anxiety-related behaviors in zebrafish, and dissect anxiety-related phenotypes from locomotor activity. Finally, we developed a simple and effective method of measuring zebrafish physiological stress responses (based on a human salivary cortisol assay), and showed that alterations in whole-body cortisol levels in zebrafish parallel behavioral indices of anxiety. Collectively, our results confirm zebrafish as a valid, reliable, and high-throughput model of stress and affective disorders.

Modeling withdrawal syndrome in zebrafish

The zebrafish (Danio rerio) is rapidly becoming a popular model species in behavioral neuroscience research. Zebrafish behavior is robustly affected by environmental and pharmacological manipulations, and can be examined using exploration-based paradigms, paralleled by analysis of endocrine (cortisol) stress responses. Discontinuation of various psychotropic drugs evokes withdrawal in both humans and rodents, characterized by increased anxiety. Sensitivity of zebrafish to drugs of abuse has been recently reported in the literature. Here we examine the effects of ethanol, diazepam, morphine and caffeine withdrawal on zebrafish behavior. Overall, discontinuation of ethanol, diazepam and morphine produced anxiogenic-like behavioral or endocrine responses, demonstrating the utility of zebrafish in translational research of withdrawal syndrome.

Experimental Models of Anxiety for Drug Discovery and Brain Research

Animal models have been vital to recent advances in experimental neuroscience, including the modeling of common human brain disorders such as anxiety, depression, and schizophrenia. As mice express robust anxiety-like behaviors when exposed to stressors (e.g., novelty, bright light, or social confrontation), these phenotypes have clear utility in testing the effects of psychotropic drugs. Of specific interest is the extent to which mouse models can be used for the screening of new anxiolytic drugs and verification of their possible applications in humans. To address this problem, the present chapter will review different experimental models of mouse anxiety and discuss their utility for testing anxiolytic and anxiogenic drugs. Detailed protocols will be provided for these paradigms, and possible confounds will be addressed accordingly.

Analysis of Grooming Behavior and Its Utility in Studying Animal Stress, Anxiety, and Depression

In rodents, grooming is a complex and ethologically rich behavior, sensitive to stress and various genetic and pharmacological manipulations, all of which may alter its gross activity and patterning. Observational analysis of grooming activity and its microstructure may serve as a useful measure of stress and anxiety in both wild and laboratory animals. Few studies have looked at grooming behavior more than cursorily, though in-depth analysis of the behavior would immensely benefit fields utilizing rodent research. Here, we present a qualitative approach to grooming activity and patterning analysis in mice, which provides insight into the effects of stress, anxiety, and depression on this behavioral domain. The method involves quantification of the transitions between different stages of grooming, the percentages of incorrect or incomplete grooming bouts, as well as the regional distribution of grooming activity. Using grooming patterning as a behavioral endpoint, this approach permits assessment of stress levels of individual animals, allows identification of grooming phenotypes in various mouse strains, and has vast implications in biological psychiatry, including psychopharmacology, genetics, neurophysiology, and experimental modeling of affective disorders.

Mouse Models for Studying Depression-Like States and Antidepressant Drugs

Depression is a common psychiatric disorder, with diverse symptoms and high comorbidity with other brain dysfunctions. Due to this complexity, little is known about the neural and genetic mechanisms involved in depression pathogenesis. In a large proportion of patients, current antidepressant treatments are often ineffective and/or have undesirable side effects, fueling the search for more effective drugs. Animal models mimicking various symptoms of depression are indispensable in studying the biological mechanisms of this disease. Here, we summarize several popular methods for assessing depression-like symptoms in mice and their utility in screening antidepressant drugs.

Mutant and Transgenic Zebrafish in Modeling Neurobehavioral Disorders

Zebrafish have traditionally been used as effective genetic and developmental models in biomedical research. Recently, the scope and utility of zebrafish in biomedical research has been further expanded with the implementation of new genetic techniques aimed at developing translational models of human pathogenesis. Additionally, screens measuring specific neurobehavioral and developmental phenotypes have proven to be very robust. This chapter further discusses the utility of zebrafish in biomedical research and highlights some of the genetic techniques used in the creation of transgenic and mutant strains. Behavioral phenotypes of genetically altered zebrafish are also discussed with respect to both their robust stress responses and similarity to human disorders. Specific emphasis is placed on human brain pathogenesis and neurodevelopmental abnormalities, especially as they relate to stress and anxiety spectrum disorders.

Genetic Animal Models of Depression

Depression, as part of a larger class of affective disorders, is one of the world’s most deleterious and widespread neurobehavioral diseases. However, much remains to be discovered concerning depression, due to the daunting complexity of its pathological mechanisms and etiology. Various animal models have been proposed over the years, some of which have come into widespread use, particularly in the area of pharmacological screening. By combining behavioral and physiological analyses with mutant and transgenic animal models, researchers are able to determine the role of specific genes and proteins in the pathogenesis of depression. Discussing several behavioral and transgenic/mutant rodent models, this chapter briefly summarizes the current progress in this area of psychiatric research.

The Utility of Genetically Modified Animals in Modeling OCD-Spectrum Disorders

Obsessive-compulsive disorder (OCD) inflicts uncontrollable, intrusive thoughts and ritualistic, compulsive behaviors affecting approximately 3% of the population. Clinical symptoms of OCD can be categorized as checking, hoarding, washing, or ordering. Mounting evidence suggests that OCD phenotypes can be modeled effectively, and with remarkable validity, through translational approaches in ethological animal models. Experimental models of OCD-like behavior, including nesting, marble burying, grooming, spatial alternation, and barbering allow researchers to investigate the neurobiological mechanisms responsible for this disorder. While its exact pathogenesis remains unknown, genetic factors also play a key role in OCD. Genetic animal models of OCD and related disorders are now becoming available, aiding researchers in identifying associated neural pathways and pharmacological treatments. Here, we discuss how some genetically modified animals may be used for modeling OCD-like endophenotypes.

Genetic Animal Models of Anxiety

Conditions such as generalized anxiety disorder, panic disorder, social phobia, specific phobia, obsessive-compulsive disorder, and post-traumatic stress disorder cause undue suffering and economic burden on a substantial portion of our society. The prevalence and serious debilitating effects of anxiety disorders increases the necessity for fast and efficacious understanding of the neurobiological pathways associated with these maladies. While the neural underpinnings of this spectrum may have been identified, further analysis is necessary to generate pharmacologically significant data. The development of new molecular genetics techniques applied towards the generation of specific knockout models with anxietylike phenotypes have been instrumental to our understanding of anxiety spectrum disorders due to their specificity of effected targets. This chapter will discuss the individual anxiety spectrum disorders with a focus on the animal models displaying relevant phenotypes for neurobehavioral research.