Effects of copper sulfate exposure on the nervous system of the Hirudo verbana leech

Copper is a significant environmental contaminant resulting from electronic waste and pesticide use. It is also a micronutrient that is essential for life because it is an enzyme cofactor. However, excess exposure to this heavy metal can lead to adverse physiologic effects. Prior studies have demonstrated neurotoxic effects of copper exposure on arthropods, mollusks, amphibians, and mammals, via mechanisms ranging from oxidative stress to changes in neurotransmitter levels. We focused on toxic effects of copper exposure on the nervous system of the Hirudo verbana leech, hypothesizing that copper exposure leads to neurobehavioral changes associated with structural changes to and proteomic changes within nerve ganglia. After exposing leeches to graded concentrations of copper sulfate, we performed neurobehavioral testing to measure their ability to ingest liver and record their movements in a 3-D printed pool. We dissected out nerve ganglia and examined them with light microscopy following hematoxylin and eosin staining. We also extracted, identified, and quantified proteins from the nerve ganglia using high performance liquid chromatography-mass spectrometry. We found that copper exposure was associated with neurobehavioral changes including food avoidance, diminished dark-seeking behavior, and decreased motility. Furthermore, we found histopathologic changes and proteomic alterations within nerve ganglia of copper-exposed leeches. These findings contribute to our understanding of potential mechanisms for nervous system damage with copper exposure. The results are concerning as they indicate that copper accumulation in the environment has tangible neurological consequences for exposed organisms.