Stimuli In Zebrafish Research Articles

Short telomeres drive pessimistic judgement bias in zebrafish.

The role of telomerase reverse transcriptase has been widely investigated in the contexts of ageing and age-related diseases. Interestingly, decreased telomerase activities (and accelerated telomere shortening) have also been reported in patients with emotion-related disorders, opening the possibility for subjective appraisal of stressful stimuli playing a key role in stress-driven telomere shortening. In fact, patients showing a pessimistic judgement bias have shorter telomeres. However, in humans the evidence for this is correlational and the causal directionality between pessimism and telomere shortening has not been established experimentally yet. We have developed and validated a judgement bias experimental paradigm to measure subjective evaluations of ambiguous stimuli in zebrafish. This behavioural assay allows classification of individuals in an optimistic-pessimistic dimension (i.e. from individuals that consistently evaluate ambiguous stimuli as negative to others that perceive them as positive). Using this behavioural paradigm we found that telomerase-deficient zebrafish (tert-/-) were more pessimistic in response to ambiguous stimuli than wild-type zebrafish. The fact that individuals with constitutive shorter telomeres have pessimistic behaviours demonstrates for the first time in a vertebrate model a genetic basis of judgement bias.

Acute Citalopram administration modulates anxiety in response to the context associated with a robotic stimulus in zebrafish

BackgroundAnxiety represents one of the most urgent health challenges in Western Countries, where it is associated with major medical and societal costs. A common therapeutic approach is the use of selective serotonin reuptake inhibitors, such as Citalopram. However, this treatment of choice is characterized by incomplete efficacy and potential side effects. Preclinical research is needed to detail the mechanisms underlying therapeutic efficacy of available treatments. MethodsZebrafish, a rapidly emerging model species, constitutes an excellent candidate for high-throughput studies in behavioral pharmacology. Here, we present a robotics-based experimental paradigm to investigate the effects of acute Citalopram administration on conditioned place aversion. We trained adult subjects in a three-partitioned tank, consisting of one central and two lateral compartments: the latter were associated either with a fear eliciting robotic stimulus or with an empty environment. Following training, we implemented an automated three-dimensional tracking system to assess the spatial association and detail individual phenotype in a stimulus-free test session. ResultsWe observed a linear dose-response profile with respect to geotaxis, with increasing Citalopram concentrations reducing the tendency to swim near the bottom of the tank. Although control subjects failed to exhibit the predicted conditioned aversion, we found preliminary evidence that Citalopram may affect sexes differentially, with male subjects showing increased conditioned aversion at low Citalopram concentration. ConclusionsExperimental paradigms based on robotics and three-dimensional tracking can contribute methodological advancements in zebrafish behavioral psychopharmacology.

Response to change in the number of visual stimuli in zebrafish:A behavioural and molecular study

Evidence has shown that a variety of vertebrates, including fish, can discriminate collections of visual items on the basis of their numerousness using an evolutionarily conserved system for approximating numerical magnitude (the so-called Approximate Number System, ANS). Here we combine a habituation/dishabituation behavioural task with molecular biology assays to start investigating the neural bases of the ANS in zebrafish. Separate groups of zebrafish underwent a habituation phase with a set of 3 or 9 small red dots, associated with a food reward. The dots changed in size, position and density from trial to trial but maintained their numerousness, and the overall areas of the stimuli was kept constant. During the subsequent dishabituation test, zebrafish faced a change (i) in number (from 3 to 9 or vice versa with the same overall surface), or (ii) in shape (with the same overall surface and number), or (iii) in size (with the same shape and number). A control group of zebrafish was shown the same stimuli as during the habituation. RT-qPCR revealed that the telencephalon and thalamus were characterized by the most consistent modulation of the expression of the immediate early genes c-fos and egr-1 upon change in numerousness; in contrast, the retina and optic tectum responded mainly to changes in stimulus size.

Functional Profiles of Visual-, Auditory-, and Water Flow-Responsive Neurons in the Zebrafish Tectum

The tectum has long been known as a hub of visual processing, and recent studies have elucidated many of the circuit-level mechanisms by which tectal neurons filter visual information. Here, we use population-scale imaging of tectal neurons expressing a genetically encoded calcium indicator to characterize tectal responses to non-visual stimuli in zebrafish. We identify ensembles of neurons responsive to stimuli for each of three sensory modalities: vision, audition, and water flow sensation. These ensembles display consistently represented response profiles to our stimuli, and each has a preferred stimulus and salient feature to which it is most responsive. Each sensory modality drives a unique spatial profile of activity in the tectal neuropil, suggesting that the neuropil's laminar structure functionally subserves multiple modalities. The positions of the responsive neurons in the periventricular layer are also distinct across modalities, and very few neurons are responsive to multiple modalities. The cells contributing to each ensemble are highly variable from trial to trial, but ensembles contain "cores" of reliably responsive cells, suggesting a mechanism whereby they could maintain consistency in reporting salient stimulus features while retaining flexibility to report on similar stimuli. Finally, we find that co-presentation of auditory or water flow stimuli suppress visual responses in the tectum.

A microfluidic device to study neuronal and motor responses to acute chemical stimuli in zebrafish.

Zebrafish larva is a unique model for whole-brain functional imaging and to study sensory-motor integration in the vertebrate brain. To take full advantage of this system, one needs to design sensory environments that can mimic the complex spatiotemporal stimulus patterns experienced by the animal in natural conditions. We report on a novel open-ended microfluidic device that delivers pulses of chemical stimuli to agarose-restrained larvae with near-millisecond switching rate and unprecedented spatial and concentration accuracy and reproducibility. In combination with two-photon calcium imaging and recordings of tail movements, we found that stimuli of opposite hedonic values induced different circuit activity patterns. Moreover, by precisely controlling the duration of the stimulus (50–500 ms), we found that the probability of generating a gustatory-induced behavior is encoded by the number of neurons activated. This device may open new ways to dissect the neural-circuit principles underlying chemosensory perception.

Cardiac response to startle stimuli in larval zebrafish: sympathetic and parasympathetic components

Central regulation of cardiac output via the sympathetic and parasympathetic branches of the autonomic nervous system allows the organism to respond to environmental changes. Sudden onset stimuli, startle stimuli, are useful probes to study central regulatory responses to the environment. In mammals, startle stimuli induce a transient bradycardia that habituates with repeated stimulation. Repeated presentation of the stimulus results in tachycardia. In this study, we investigate the behavioral regulation of heart rate in response to sudden stimuli in the zebrafish. Larval zebrafish show a stereotyped heart rate response to mild electrical shock. Naïve fish show a significant increase in interbeat interval that resolves in the 2 s following stimulation. This transient bradycardia decreases on repeated exposure to the stimulus. Following repeated stimulation, the fish become tachycardic within 1 min of stimulation. Both the transient bradycardia and following tachycardia responses are blocked with administration of the ganglionic blocker hexamethonium, demonstrating that these responses are mediated centrally. The transient bradycardia is blocked by the muscarinic antagonist atropine, suggesting that this response is mediated by the parasympathetic system, while the following tachycardia is specifically blocked by the beta-adrenergic antagonist propranolol, suggesting that this response is mediated by the sympathetic nervous system. Together, these results demonstrate that at the larval stage, zebrafish actively regulate cardiac output to changes in their environment using both the parasympathetic and sympathetic branches of the autonomic nervous system, a behavioral response that is markedly similar to that observed in mammals to similar sudden onset stimuli.