Androgenic activation, impairment of the monoaminergic system and altered behavior in zebrafish larvae exposed to environmental concentrations of fenitrothion.

Fenitrothion is an organophosphorus insecticide usually found in aquatic ecosystems at concentrations in the range of low ng/L. In this manuscript we show that 24 h exposure to environmental concentrations of fenitrothion, from ng/L to low µg/L, altered basal locomotor activity, visual-motor response and acoustic/vibrational escape response of zebrafish larvae. Furthermore, fenitrothion and expression of gap43a, gfap, atp2b1a, and mbp exhibited a significant non-monotonic concentration-response relationship. Once determined that environmental concentrations of fenitrothion were neurotoxic for zebrafish larvae, a computational analysis identified potential protein targets of this compound. Some of the predictions, including interactions with acetylcholinesterase, monoamine-oxidases and androgen receptor (AR), were experimentally validated. Binding to AR was the most suitable candidate for molecular initiating event, as indicated by both the up-regulation of cyp19a1b and sult2st3 and the non-monotonic relationship found between fenitrothion and the observed responses. Finally, when the integrity of the monoaminergic system was evaluated, altered levels of L-DOPA, DOPAC, HVA and 5-HIAA were found, as well as a significant up-regulation of slc18a2 expression at the lowest concentrations of fenitrothion. These data strongly suggest that concentrations of fenitrothion commonly found in aquatic ecosystems present a significant environmental risk for fish communities.

Further characterization of the zebrafish model of acrylamide acute neurotoxicity: gait abnormalities and oxidative stress.

Occupational, accidental, or suicidal exposure to acrylamide (ACR) may result in a neurotoxic syndrome. Development of animal models of acrylamide neurotoxicity is necessary for increasing our mechanistic understanding of this syndrome and developing more effective therapies. A new model for acute ACR neurotoxicity has been recently developed in adult zebrafish. Whereas the results of the initial characterization were really promising, a further characterization is needed for testing the construct validity of the model. In this study, the presence of gait abnormalities has been investigated by using ZebraGait, software specifically designed to analyze the kinematics of fish swimming in a water tunnel. The results of the kinematic analyses demonstrated that the model exhibits mild-to-moderate gait abnormalities. Moreover, the model exhibited negative scototaxis, a result confirming a phenotype of anxiety comorbid with depression phenotype. Interestingly, depletion of the reduced glutathione levels was found in the brain without a concomitant increase in oxidative stress. Finally, hypolocomotion and positive geotaxis exhibited by this model were fully recovered 5 days after transferring the fish to clean fish-water. All this data support the validity of the ACR acute neurotoxicity model developed in adult zebrafish.

Using a new high-throughput video-tracking platform to assess behavioural changes in Daphnia magna exposed to neuro-active drugs.

Recent advances in imaging allow to monitor in real time the behaviour of individuals under a given stress. Light is a common stressor that alters the behaviour of fish larvae and many aquatic invertebrate species. The water flea Daphnia magna exhibits a vertical negative phototaxis, swimming against light trying to avoid fish predation. The aim of this study was to develop a high-throughput image analysis system to study changes in the vertical negative phototaxis of D. magna first reproductive adult females exposed to 0.1 and 1 µg/L of four neuro-active drugs: diazepam, fluoxetine, propranolol and carbamazepine. Experiments were conducted using a custom designed experimental chamber containing four independent arenas and infrared illumination. The apical-located visible light and the GigE camera located in front of the arenas were controlled by the Ethovision XT 11.5 sofware (Noldus Information Technology, Leesburg, VA). Total distance moved, time spent per zone (bottom vs upper zones) and distance among individuals were analyzed in dark and light conditions, and the effect of different intensities of the apical-located visible light was also investigated. Results indicated that light intensity increased the locomotor activity and low light intensities allowed to better discriminate individual responses to the studied drugs. The four tested drugs decreased the response of exposed organisms to light: individuals moved less, were closer to the bottom and at low light intensities were closer each other. At high light intensities, however, exposed individuals were less aggregated. Propranolol, carbamazepine and fluoxetine induced the most severe behavioural effects. The tested drugs at environmental relevant concentrations altered locomotor activity, geotaxis, phototaxis and aggregation in D. magna individuals in the lab. Therefore the new image analysis system presented here was proven to be sensitive and versatile enough to detect changes in diel vertical migration across light intensities and low concentration levels of neuro-active drugs.

Sensor Localization from Distance and Orientation Constraints.

The sensor localization problem can be formalized using distance and orientation constraints, typically in 3D. Local methods can be used to refine an initial location estimation, but in many cases such estimation is not available and a method able to determine all the feasible solutions from scratch is necessary. Unfortunately, existing methods able to find all the solutions in distance space can not take into account orientations, or they can only deal with one- or two-dimensional problems and their extension to 3D is troublesome. This paper presents a method that addresses these issues. The proposed approach iteratively projects the problem to decrease its dimension, then reduces the ranges of the variable distances, and back-projects the result to the original dimension, to obtain a tighter approximation of the feasible sensor locations. This paper extends previous works introducing accurate range reduction procedures which effectively integrate the orientation constraints. The mutual localization of a fleet of robots carrying sensors and the position analysis of a sensor moved by a parallel manipulator are used to validate the approach.

Exploring the energy landscapes of flexible molecular loops using higher-dimensional continuation.

The conformational space of a flexible molecular loop includes the set of conformations fulfilling the geometric loop-closure constraints and its energy landscape can be seen as a scalar field defined on this implicit set. Higher-dimensional continuation tools, recently developed in dynamical systems and also applied to robotics, provide efficient algorithms to trace out implicitly defined sets. This article describes these tools and applies them to obtain full descriptions of the energy landscapes of short molecular loops that, otherwise, can only be partially explored, mainly via sampling. Moreover, to deal with larger loops, this article exploits the higher-dimensional continuation tools to find local minima and minimum energy transition paths between them, without deviating from the loop-closure constraints. The proposed techniques are applied to previously studied molecules revealing the intricate structure of their energy landscapes.

Complete maps of molecular-loop conformational spaces.

This paper presents a numerical method to compute all possible conformations of distance-constrained molecular loops, i.e., loops where some interatomic distances are held fixed, while others can vary. The method is general (it can be applied to single or multiple intermingled loops of arbitrary topology) and complete (it isolates all solutions, even if they form positive-dimensional sets). Generality is achieved by reducing the problem to finding all embeddings of a set of points constrained by pairwise distances, which can be formulated as computing the roots of a system of Cayley-Menger determinants. Completeness is achieved by expressing these determinants in Bernstein form and using a numerical algorithm that exploits such form to bound all root locations at any desired precision. The method is readily parallelizable, and the current implementation can be run on single- or multiprocessor machines. Experiments are included that show the method's performance on rigid loops, mobile loops, and multiloop molecules. In all cases, complete maps including all possible conformations are obtained, thus allowing an exhaustive analysis and visualization of all pseudo-rotation paths between different conformations satisfying loop closure.