Cobalt Chloride Treatment Used to Ablate the Lateral Line System Also Impairs the Olfactory System in Three Freshwater Fishes

Abstract

Fishes use multimodal signals during both inter- and intra-sexual displays to convey information about their sex, reproductive state, and social status. These complex behavioral displays can include visual, auditory, olfactory, tactile, and hydrodynamic signals, and the relative role of each sensory channel in these complex multi-sensory interactions is a common focus of neuroethology. The mechanosensory lateral line system of fishes detects near-body water movements and is implicated in a variety of behaviors including schooling, rheotaxis, social communication, and prey detection. Cobalt chloride is commonly used to chemically ablate lateral line neuromasts, thereby eliminating water-movement cues to test for mechanosensory-mediated behavioral functions. However, cobalt acts as a nonspecific calcium channel antagonist and could potentially disrupt function of all superficially located sensory receptor cells, including those for chemosensing. Here, we examined whether CoCl2 treatment used to ablate the lateral line system also impairs olfaction in three freshwater fishes, the African cichlid fish Astatotilapia burtoni, goldfish Carassius auratus, and the Mexican blind cavefish Astyanax mexicanus. To examine the impact of CoCl2 on the activity of peripheral receptors, we quantified DASPEI fluorescence intensity of the olfactory epithelium from fish exposed to control and CoCl2 solutions. In addition, we examined brain activation in olfactory processing regions of A. burtoni immersed in either control or cobalt solutions. All three species exposed to CoCl2 had decreased DASPEI staining of the olfactory epithelium, and in A. burtoni, cobalt treatment caused reduced neural activation in olfactory processing regions of the brain. To our knowledge this is the first empirical evidence demonstrating that the same CoCl2 treatment used to ablate the lateral line system also impairs olfactory function. These data have important implications for the use of CoCl2 in future research and suggest that previous studies using CoCl2 should be reinterpreted in the context of both impaired mechanoreception and olfaction.

Comparison of Aminoglycoside Antibiotics and Cobalt Chloride for Ablation of the Lateral Line System in Giant Danios

“…2016 ). Even at low doses (e.g., 0.1 mM), CoCl 2 might disrupt other sensory systems such as olfactory tissues and chemosensory hair cells, as reported by Butler et al . ( 2016 ) in a few teleosts.…”

“…2012 ) but not consistently used with the same species or life stage. Further, we used an established concentration of 0.1 mM for CoCl 2 because previous work has already identified the overall toxicity of this chemical ( Butler et al. 2016 ; Schwalbe et al.…”

“…2017 ). However, it also acts as a nonspecific calcium channel antagonist and could potentially disrupt other sensory systems such as chemosensory systems during prolonged periods of exposure or in high concentrations ( Janssen 2000 ; Butler et al. 2016 ; Stewart et al.…”

“…2017 ). Long exposures of CoCl 2 at high concentrations could have prolonged toxic effects even after removal from the solution ( Janssen 2000 ; Butler et al. 2016 ).…”

Neural and behavioural correlates of repeated social defeat

“…Quantification of pS6 staining was done as previously described for cfos staining 29 , 42 . Briefly, slides were visualized on a Nikon Eclipse Ni microscope, images were taken at the highest magnification that encompassed the entire brain area of interest, and borders and gridlines were applied.…”