Fenótipos envolvidos em comorbidades associadas às crises convulsivas: abordagens experimentais utilizando o peixe-zebra como organismo modelo

Abstract

Epilepsy is a neurological disease characterized by recurrent seizures that affects the cerebral homeostasis. This disease can generate negative consequences for the patient, such as behavioral and cognitive changes. Aggressiveness, anxiety, cognitive impairment, social isolation, and stress are examples of psychiatric comorbidities associated with epilepsy. Although this correlation has been well described in the literature, suggesting shared underlying mechanisms, it is necessary to characterize novel alternative model organisms to investigate the evolutionarily conserved bases associated with seizure-related comorbidities. The zebrafish (Danio rerio) is a model organism widely used in behavioral neuroscience, because this species shows conserved physiological features, well-characterized neurotransmitters, and a fully sequenced genome with a high degree of homology when compared to human genes. Here, we aimed to characterize the use of zebrafish models to study seizure-related comorbidities. In the first study, animals were exposed to pentylenetetrazole PTZ (10 mM) for 20 min to analyze the aggressive behavior in the mirror-induced aggression test at different time intervals (1h, 3h, 6h, 24h, 48h and 72h). In the second study, animals were exposed to PTZ in the same conditions and the effects on the exploratory pattern (novel tank diving test), anxiety-like behavior (light-dark test), memory consolidation (inhibitory avoidance test), shoaling behavior, and on whole-body cortisol levels were analyzed 24 h after the exposure. In the third study, to verify whether stress influences seizures behavioral responses, animals were acutely exposed to an intense stressor (conspecific alarm substance) for 5 min. The latency of animals to reach the clonic-like seizure behavior (score 4) induced by PTZ (7.5 mM), as well as the effects of conspecific alarm substance on the aversive behavior and whole-body cortisol levels were verified in stressed and non-stressed fish. Briefly, we verified that PTZ increased aggressive behavior, modified the exploratory pattern by disrupting the habituation to novelty, increased anxiety-like behavior, induced social isolation, and impaired memory consolidation. Furthermore, stress increased the susceptibility to seizures in zebrafish and we observed positive correlations between anxiety-like phenotypes and seizure-related behaviors. Overall, our results suggest that the zebrafish is an emerging model organism to investigate neuropsychiatric disorders that parallel those observed in epilepsy, serving as a potential tool to investigate the evolutionarily conserved mechanisms of seizures in vertebrates as well as to unravel future neuroprotective strategies.