The effects of copper, calcium, and nickel on the olfactory response of fathead minnows: from neurophysiology to behaviour

The olfactory system is essential for a fish to be successful in an ecological context, and has been demonstrated to be sensitive to a variety of toxicants. The current biotic ligand model (BLM) for copper is an acute-toxicity model based on the gill that is used to predict site-specific safe copper concentrations. Recently, work has been done to develop a BLM based on a more sensitive tissue, namely the olfactory epithelium. The work presented in this dissertation determines that a number of the assumptions of the current acute-toxicity gill-based BLM do not hold for the olfactory epithelium. Two techniques were employed for the work contained within this dissertation, a neurophysiological measure of olfactory acuity, electro-olfactography (EOG), and measurement of behavioural responses. For all experiments, fathead minnows (Pimephales promelas) and yellow perch (Perca flavescens) were used as these species are ubiquitous in waterways across Canada. Fathead minnows were exposed to low, ecologically-relevant concentrations of copper for varying exposure durations in hard and soft water. While it was determined that there was a significant of inhibition of olfactory function as measured by EOG, there was recovery, at least partially, of EOG function with increased exposure duration. It was also determined that not only does calcium have no protective effect against copper-induced olfactory dysfunction at the olfactory epithelium as it does at the gill, but calcium induces its own response. The response to calcium in fathead minnows was further investigated. Fathead minnows had a strong olfactory-dependent avoidance response to calcium. The reduction in EOG response caused by calcium was demonstrated to be due to cross-adaptation with the odourant used, namely L-arginine. Different olfactory sensory neuron (OSN) classes within the olfactory epithelium respond specifically to different odourants. Exposures of fathead minnows or yellow perch to copper demonstrated that there was a specific impairment of ciliated OSNs, while exposure to nickel resulted in impairment of microvillous OSNs. Behavioural work with fathead minnows using an anti-predator cue demonstrated that copper impairs the response to an anti-predator cue, while nickel does not. These observations demonstrate that ciliated cells are responsible for mediating response to anti-predator cue, which is the first time response to a specific chemosensory cue has been directly connected with a specific OSN class. The work presented in this dissertation represents a significant advancement in our understanding in how copper impairs the olfactory system of fish, which will aid in the construction of models and regulations to protect fish populations

Smelling salt: calcium as an odourant for fathead minnows

Sherpa Romeo green journalCalcium plays an essential role in olfactory sensory neuron function. Studies with fish have indicated that in addition to being involved in olfactory signalling, calcium is itself an odourant. In this study we used fathead minnows (Pimephales promelas) and employed two different techniques; electro-olfactography (EOG), a neurophysiological technique that measures olfactory acuity at the olfactory epithelium, and a behavioural choice assay using a trough maze. The results demonstrate that calcium and a known odourant L-arginine are cross-adaptive, that calcium induces an EOG response in a concentration-dependent manner, and that calcium induces a strong avoidance behaviour. The behavioural avoidance was also demonstrated to be olfactorydependent. Taken together, the results demonstrate that calcium is a potent odourant for fathead minnows. Being able to smell calcium may represent an ability to sense and avoid areas with significant changes in ionic strength, thereby avoiding physiological stress.Ye

Correction to: Cluster identification, selection, and description in Cluster randomized crossover trials: the PREP-IT trials

An amendment to this paper has been published and can be accessed via the original article

Dietary sodium protects fish against copper-induced olfactory impairment

Exposure to low concentrations of copper impairs olfaction in fish. To determine the transcriptional changes in the olfactory epithelium induced by copper exposure, wild yellow perch (Perca flavescens) were exposed to 20 g/L of copper for 3 and 24 h. A novel yellow perch microarray with 1000 candidate genes was used to measure differential gene transcription in the olfactory epithelium. While three hours of exposure to copper changed the transcription of only one gene, the transcriptions of 70 genes were changed after 24 h of exposure to copper. Real-time PCR was utilized to determine the effect of exposure duration on two specific genes of interest, two sub-units of Na/K-ATPase. At 24 and 48 h, Na/K-ATPase transcription was down-regulated by copper at olfactory rosettes. As copper-induced impairment of Na/K-ATPase activity in gills can be ameliorated by increased dietary sodium, rainbow trout (Oncorhynchus mykiss) were used to determine if elevated dietary sodium was also protective against copper-induced olfactory impairment. Measurement of the olfactory response of rainbow trout using electro-olfactography demonstrated that sodium was protective of copper-induced olfactory dysfunction. This work demonstrates that the transcriptions of both subunits of Na/K-ATPase in the olfactory epithelium of fish are affected by Cu exposure, and that dietary Na protects against Cu-induced olfactory dysfunction.Keywords: Olfaction Olfactory toxicity Copper Microarray Real-time PCR Electro-olfactograph

Effects of Continuous Copper Exposure and Calcium on the Olfactory Response of Fathead Minnows

The current gill-based Biotic Ligand Model (gbBLM) is an acute-toxicity model used to predict site-specific safe copper (Cu) concentrations. Recent effort to develop a chronic BLM has focused on the olfactory epithelium. To further this effort, the current study looked at the effect of varying Cu concentration and exposure duration on Cu-induced olfactory dysfunction, and whether calcium (Ca) protected against Cu-induced impairment as it does at the gill. Fathead minnows (<i>Pimephales promelas</i>) were treated with five Cu concentrations for varying exposure durations in hard and soft water. A neurophysiological technique, electro-olfactography (EOG), was employed to determine the level of olfactory dysfunction. At the low, ecologically relevant Cu concentrations tested there was significant inhibition of EOG function; however, over time there was at least a partial recovery of olfactory function, despite the continuous Cu exposure. Calcium did not appear to protect against Cu-induced olfactory dysfunction; and even alone, Ca appeared to interfere with the olfactory response to the amino acid l-arginine. Safe copper concentrations as predicted by the gbBLM, chemosensory-based BLMs, the USEPA BLM, and hardness-adjustment equations based on the exposure waters were not entirely protective against olfactory dysfunction