- Male dominance status regulates odor-evoked processing in the forebrain of a cichlid fish
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- An ecotoxicological view on neurotoxicity assessment | Environmental Sciences Europe | Full Text
Log out of Readcube. Click on an option below to access. Log out of ReadCube. Electroreception in marine fishes occurs across a variety of taxa and is best understood in the chondrichthyans sharks, skates, rays, and chimaeras. We briefly describe the history and discovery of electroreception in marine Chondrichthyes, the current understanding of the passive mode, the morphological adaptations of receptors across phylogeny and habitat, the physiological function of the peripheral and central nervous system components, and the behaviours mediated by electroreception.
Additionally, whole genome sequencing, genetic screening and molecular studies promise to yield new insights into the evolution, distribution, and function of electroreceptors across different environments. This review complements that of electroreception in freshwater fishes in this special issue, which provides a comprehensive state of knowledge regarding the evolution of electroreception.
We conclude that despite our improved understanding of passive electroreception, several outstanding gaps remain which limits our full comprehension of this sensory modality. Of particular concern is how electroreceptive fishes will respond and adapt to a marine environment that is being increasingly altered by anthropogenic electric and magnetic fields. Volume 95 , Issue 1. The full text of this article hosted at iucr.
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Male dominance status regulates odor-evoked processing in the forebrain of a cichlid fish
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View access options below. You previously purchased this article through ReadCube. Institutional Login. Log in to Wiley Online Library. Thus, their impairment can have severe impact on fitness and survival of an animal. Environmental contaminants such as pharmaceuticals, pesticides and heavy metals have been shown to interfere with the sensory structures of different species including humans and fish, thereby creating deficiencies in sensation and behaviour.
Behavioural output is an increasingly measured, ecologically relevant and very sensitive endpoint. To localize specific sensory impairments within the nervous system using behaviour is, however, challenging because behaviour is the integrated output of multisensory, neuroendocrine and neuromuscular signals, and tests are often not specific enough e. While all of them have their advantages and drawbacks, there is no recommendation as to which one is the best. Rather, tests have to be tailored to the study purpose and a multidisciplinary integrated approach is necessary to fully understand neurotoxicity mechanisms [ 2 ].
In fish, the olfactory system is particularly vulnerable to neurotoxic contaminants because of the direct contact of olfactory sensory neurons with the surrounding water. Reduced or absent ability to smell hyposmia or anosmia have been shown to occur upon exposure to metals, pesticides and other contaminants like, e. The classical method to assess olfactory impairment is by electro-olfactography [ ].
An ecotoxicological view on neurotoxicity assessment | Environmental Sciences Europe | Full Text
It assesses electrophysiological changes in olfactory sensory neurons by extracellular recordings. Notably, while the zebrafish olfactory system offers several experimental advantages to study sensory neurobiology in general and olfactory neurotoxicity in particular, there are a number of profound differences that might render translation of results from such studies to other species. Among the major advantages of the zebrafish model are i identified ecologically relevant classes of natural odours such as amino acids and bile acids [ , ]; ii cultivation of the adult zebrafish head ex vivo without anaesthesia, allowing neurophysiological measurements in the intact brain [ ]; iii comparably small brain size that provides access to larger fractions of neurons by multiphoton microscopy [ ]—a fact particularly true for the zebrafish olfactory system, which contains relatively few neurons and glomeruli [ ]; and iv large detailed data at both the single neuron and population level that allows realistic mathematical simulations of circuit function [ ].
Moreover, at first glance, the zebrafish olfactory system contains molecular and cellular constituents that appear similar in organization to the rodent olfactory system, thus, providing an attractive vertebrate model system to investigate the mechanisms underlying olfactory system development and function. Both express distinct types of chemosensory receptors, project to different brain regions and likely mediate different behaviours [ ].
The mouse has become the most widely used model system in olfactory research based on established protocols for genetic manipulation. An important distinction between the olfactory systems in fish and mice is stimulus delivery. While the fish olfactory organs are exposed to pollutants and xenobiotics that are dissolved in water, rodent noses constantly sample volatile air-borne chemicals at minute concentrations.
Thus, the range of potentially hazardous chemicals that water-living species like fish are naturally exposed to will be dramatically different from the repertoire of potential harmful compounds that land-living species like mice encounter and vice versa. The olfactory epithelium has extensive neurogenic and regenerative capacity in both rodents and humans that persists throughout adult life and is unmatched elsewhere in the nervous system [ ].
However, the niche signals that control the self-renewal and differentiation of these basal cells are not well understood [ ]. This regenerative capacity will strongly impact eco-neurotoxicological assays that target the olfactory system. Few neurotoxicological assays have been developed using mice. This is somewhat surprising given the large body of knowledge available, established animal care facilities, comparably short generation turnover and the large translational promise that rodent model systems offer.
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- Electroreception in marine fishes: chondrichthyans;
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Thus, it appears likely that future eco-neurotoxicology assays will utilize a pipeline that spans cell-based in vitro experiments, high-throughput behavioural assays in zebrafish and other ecologically relevant species. About chemicals are toxic to the human eye and visual system [ ].
Retinotoxic effects for organic solvents and metals have been described, not only for humans [ ] but also for fish [ , , , ], for which most literature focuses on effects of methylmercury and ethanol. Moreover, the fish retina was affected upon herbicide [ , ] and pesticide exposure [ ] and was shown to accumulate cocaine [ ].
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Electrophysiological measurements of retinal function are called electroretinograms. They record the retinal sum field potential to a visual stimulus [ ] and are applied in many species including fish [ ]. Visual behaviour tests for fish are well developed, even to the point that different visual properties like motion detection, colour detection and discrimination, object recognition and visual acuity can be tested [ ].
A popular assay is the measurement of optokinetic reflex, in which the animal is presented a moving grating which it follows with accurate eye movements. Impaired visual function results in reduced or absent eye movements [ , ]. Although both techniques are widely established in zebrafish models for human ocular diseases [ ], toxicant-induced impairments of visual function are only scarcely studied.
Instead, retinotoxic effects are mostly assessed based on rather insensitive endpoints like histology or eye size e. Hair cells are sensory cells of the vertebrate inner ear and the lateral line system of aquatic vertebrates. They transduce pressure changes in the surrounding medium into a neuronal signal as a result of deflection of their cilia, which leads to the opening of ion channels, enabling the detection of acoustic stimuli and hydrodynamic flow.
Many drugs such as aminoglycoside antibiotics, platinum-based anti-cancer drugs, anti-malarics or non-steroidal anti-inflammatory drugs are known to induce ototoxicity in humans see references in [ ] , for the most part irreversible. In fish, some of these drugs equally cause ototoxicity and damage to the lateral line [ ]. Moreover, metals such as copper, cadmium and others have been shown to cause hair cell death and deficits in behavioural responses in zebrafish [ , ] and other fish [ ]. Behavioural responses to acoustic stimuli [ , , ], responsiveness to water motion [ ] and rheotaxis counter-flow swimming [ , ] have been measured to assess hair cell function.
Moreover, vital dyes to stain hair cells have been widely used to assess the structure of lateral line hair cells in zebrafish [ ]. Another method to assess hearing abilities in fish is sound-evoked potential audiometry, which measures field potentials in response to an auditory stimulus using cutaneous electrodes [ ]. In order to assess the full neurotoxic potential of environmental pollutants, a combination of tests and the assessment of multiple sensory systems are necessary to precisely localize effects within the nervous system [ 2 , ].
Future studies should strive to increase our mechanistic understanding of chemical neurotoxicity, which would help predicting eco-neurotoxicological effects. In this respect, model organisms such as the zebrafish are very helpful, because a large variety of genetic tools and genomic resources are available and many tests are already established for the analysis of human brain disorders [ 98 ], but they are not yet fully adopted for neurotoxicity testing. Additionally, emerging neuroscience techniques such as in vivo 2-photon calcium-imaging of neuronal activity [ , , ] or optogenetics [ ] might hold underexplored opportunities for the mechanistic dissection of complex neurotoxicological processes.
Moreover, large-scale toxicity screenings using the zebrafish model has been implemented in the framework of ToxCast and Tox21 [ , , , ], but more efforts are needed to increase the specificity of tests for sensory neurotoxicity in larval zebrafish and implement them in a high-throughput manner in order to keep pace with toxicity testing of the vast number of newly registered chemicals.