Extending the analysis of zebrafish behavioral endophenotypes for modeling psychiatric disorders: Fear conditioning to conspecific alarm response.

Anxiety, trauma- and stressor-related disorders are severe psychiatric conditions that affect human population worldwide. Given their genetic tractability, evolutionarily conserved neurotransmitter systems, and extensive behavioral repertoire, zebrafish have become an emergent model organism in translational neuroscience. Here, we investigate whether a single exposure to conspecific alarm substance (CAS) produces fear conditioning in zebrafish using a conditioned place aversion (CPA) paradigm, as well as the persistence of aversive responses at different time intervals. While CAS elicited freezing and erratic movements at conditioning phase, zebrafish showed a robust avoidance for the CAS-paired compartment and increased risk assessment up to 7 days postconditioning. Additionally, we observed the existence of two behavioral phenotypes (high- and low-avoider fish) that present different fear-like responses at conditioning phase and evasion of the conditioning side at postconditioning trials. Collectively, we show a prolonged conditioned place aversion in zebrafish after a single CAS conditioning session, reinforcing the use of fear conditioning protocols as valuable strategies for modeling psychiatric disorders-related phenotypes in zebrafish.

Integrating ontogenetic shift, growth and mortality to determine a species' ecological role from isotopic signatures.

Understanding species linkages and energy transfer is a basic goal underlying any attempt at ecosystem analysis. Although the first food-web studies were based on gut contents of captured specimens, the assessment of stable isotopes, mainly δ13C and δ15N, has become a standard methodology for wide-range analyses in the last 30 years. Stable isotopes provide information on the trophic level of species, food-web length, and origin of organic matter ingested by consumers. In this study, we analyzed the ontogenetic variability of δ13C and δ15N obtained from samples of three Neotropical fish species: silver sardine (Lycengraulis grossidens, n=46), white lambari (Cyanocharax alburnus, n= 26), and the red-tail lambari (Astyanax fasciatus, n=23) in Pinguela Lagoon, southern Brazil. We developed a new metric, called the Weighted Isotopic Signature (φ 15N or φ 13C, ‰), that incorporates ontogenetic variability, body growth, and natural mortality into a single number.

Subchronic atrazine exposure changes defensive behaviour profile and disrupts brain acetylcholinesterase activity of zebrafish.

Animal behaviour is the interaction between environment and an individual organism, which also can be influenced by its neighbours. Variations in environmental conditions, as those caused by contaminants, may lead to neurochemical impairments altering the pattern of the behavioural repertoire of the species. Atrazine (ATZ) is an herbicide widely used in agriculture that is frequently detected in surface water, affecting non-target species. The zebrafish is a valuable model organism to assess behavioural and neurochemical effects of different contaminants since it presents a robust behavioural repertoire and also all major neurotransmitter systems described for mammalian species. The goal of this study was to evaluate the effects of subchronic ATZ exposure in defensive behaviours of zebrafish (shoaling, thigmotaxis, and depth preference) using the split depth tank. Furthermore, to investigate a putative role of cholinergic signalling on ATZ-mediated effects, we tested whether this herbicide alters acetylcholinesterase (AChE) activity in brain and muscle preparations. Fish were exposed to ATZ for 14days and the following groups were tested: control (0.2% acetone) and ATZ (10 and 1000µg/L). The behaviour of four animals in the same tank was recorded for 6min and biological samples were prepared. Our results showed that 1000µg/L ATZ significantly increased the inter-fish distance, as well as the nearest and farthest neighbour distances. This group also presented an increase in the shoal area with decreased social interaction. No significant differences were detected for the number of animals in the shallow area, latency to enter the shallow and time spent in shallow and deep areas of the apparatus, but the ATZ 1000 group spent significantly more time near the walls. Although ATZ did not affect muscular AChE, it significantly reduced AChE activity in brain. Exposure to 10µg/L ATZ did not affect behaviour or AChE activity. These data suggest that ATZ impairs defensive behaviours of zebrafish, which could be related to its action on brain cholinergic neurotransmission. Moreover, the use of the split depth tank could be an alternative strategy to assess group behaviour and depth preference after exposure to chemical compounds.