Odor-evoked field potentials as indicators of sublethal neurotoxicity in juvenile coho salmon (Oncorhynchus kisutch) exposed to copper, chlorpyrifos, or esfenvalerate

Abstract

The sublethal effects of three different pesticides (a metal, organophosphate, and pyrethroid) on juvenile coho salmon (Oncorhynchus kisutch) were evaluated using paired electrophysiological recordings from the olfactory epithelium and the olfactory bulb. Animals were exposed to copper (5–20 µg·L–1), chlorpyrifos (0.625–2.5 µg·L–1), or esfenvalerate (0.05–0.20 µg·L–1) for 7 days. Sublethal neurotoxicity was examined by recording odor-evoked field potentials from the sensory epithelium and olfactory forebrain using two natural odorants (taurocholic acid or L-serine). Copper and chlorpyrifos decreased the amplitudes of the epithelial and bulbar responses to both odorants in a concentration-dependent manner. Benchmark concentrations for a 20% loss of sensory function were 4.4 µg·L–1 for copper and 0.72 µg·L–1 for chlorpyrifos. Esfenvalerate did not affect the amplitude of odor-evoked field potentials. However, in the olfactory bulbs of coho exposed to 0.2 µg esfenvalerate·L–1, L-serine evoked distinct and irregular bursts of postsynaptic activity in the olfactory bulb, possibly indicating sublethal excitotoxicity to central networks. Collectively, these data indicate that periodic, non-point source contamination of salmon habitats with current-use pesticides could interfere with olfactory function and, by extension, olfactory-mediated behaviors that are important for the survival and migration of salmonids.

Effect of Acute Copper Sulfate Exposure on Olfactory Responses to Amino Acids and Pheromones in Goldfish (Carassius auratus)

“…However, this inhibition is transient, and recovery is seen after one hour. Longer exposure, hours to days, does not affect olfaction (24,25), as responses recover completely within one day. Thus, the EOG can be used to establish sublethal thresholds of toxicants that are apparently ineffective over short-term exposure.…”

Olfactory inhibition and recovery in chum salmon (Oncorhynchus keta) following copper exposure

“…Short-term exposures to dissolved copper (on the order of minutes to hours) and at relatively low concentrations (1-20 µg·L -1 ) can inhibit the electrical properties of olfactory receptor neurons in salmon (Baldwin et al 2003;Sandahl et al 2004). Copper targets several sites of the olfactory neuron, and depending on the conditions of exposure, inhibitory effects can be either reversible or irreversible (Moran et al 1992;Julliard et al 1996;Hansen et al 1999).…”

“…The EOG has been useful in studying the effects of contaminants on primary sensory neurons of the olfactory system, particularly in fish (Baatrup et al 1990;Jarrard et al 2004;Sandahl et al 2004). Heavy metals, for example, can inhibit the electrical properties of olfactory neurons, presumably by blocking ligand-gated and (or) voltage-gated ion channels.…”

“…Toxins can target a number of sites along the agonist-transduction-messengerelectrical signaling pathway, ultimately resulting in inhibitory, excitatory, or distorted responses reaching the olfactory bulb (Horning and Trombley 2001;Sandahl et al 2004). Along with ion channels as initial targets of heavy metals, odorant-binding GPCRs are also susceptible sites.…”

Ecological Risk Assessment for Chlorpyrifos in Terrestrial and Aquatic Systems in the United States

“…Much of the research on effects of CPY and other pesticides on behavior has focused on migratory species of salmon because of their societal importance and the need for migratory species to be able to sense chemicals in water to successfully navigate to breeding waters. Exposure of the olfactory epithelium of Coho salmon ( Oncorhynchus kisutch ) to 0.7 μg CPY L −1 caused a 20% loss of sensory function as measured by neurophysiological response to salmonid bile salt and l -serine (Sandahl et al 2004 ). Since these studies were conducted in the laboratory, the changes in sensory function were not evaluated at the level of the whole-animal.…”