PgmNr Z6191: Evaluation of the circadian biology of the neurohypophyseal hormones and their relationship with aggressive behavior in a vertebral model: Zebrafish.

Authors:
L. A. Diaz-Arias 1 ; S. A. Valencia 1 ; T. Manrique 2 ; V. Akle 1


Institutes
1) Laboratory of neuroscience and circadian rhythms, School of Medicine, Universidad de los Andes, Bogota, DC, Colombia; 2) Brain and Behavior Laboratory, Pshycology department, Universidad del Rosario, Bogota, DC, Colombia.


Abstract:

The circadian rhythm is a physiological period of about 24 hours that coordinates the activity of different biological processes such as reproduction cycles, tissue regeneration, epigenetic, metabolism and behavior. Despite the fact that many studies have shown that aggressive behaviors as well as the expression of “social neuropeptides” follow a circadian pattern in different species, the relationship between aggression and the expression of the neurohypophyseal peptides has not been studied systematically. The objective of this study is to evaluate the role of the circadian system in aggressive behaviors of zebrafish and its relationship with the hormones isotocin (IT) and vasotocine (VT). For this purpose, we used a battery of behavioral tests that consisted of: Open Field test, Mirror test and Opponent test to assess aggression in the fish at specific time points during the light cycle. In subsequent experiments, using RT-PCR and immunohistochemistry the levels of IT, VT and its receptors at different times of day will be evaluated. Also, the receptors will be blocked to establish a possible mechanism of action of these neuropeptides. Preliminary results revealed that the mirror and predator assays acquire different kind of information. While the mirror test is appropriate as a measure of aggression, the encounter with the natural predator evaluates exploratory behavior or “shyness” more effectively. In general, there is a high variability in the behavior of individual fish, probably as a result of their social hierarchy. The behavior of males and females is statistically different in the Open Field test, while that difference is not evident in the Mirror test and Opponent test. Finally, even though there is a tendency toward more aggressive behaviors during the morning hours, the differences did not reach statistical significance. However, further tests are needed to clarify whether there are circadian differences in the aggressiveness of the zebrafish and between genders. This study represents the first step in exploring the role of the endogenous clock in the manifestation of aggression and neurohypophyseal expression of hormones in the vertebrate model zebrafish.