The impact of a neonicotinoid pesticide on neural functions underlying learning and memory

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Neonicotinoids are pesticides used worldwide and humans are ubiquitously exposed to them. They are selective for invertebrate nicotinic acetylcholine receptors (nAchRs) with a low affinity for mammalian ones, a trait that has contributed to their widespread use and assumed safety in mammals. However, an increasing body of evidence in vertebrates indicates developmental and adult exposure to neonicotinoids negatively affects a broad range of physiological processes including immune, reproductive, and metabolic systems. However, relatively little is known about the mechanisms by which neonicotinoid exposure alters learning and memory or perturbs neurophysiological signaling pathways. Learning and memory are fundamental cognitive functions regulated in large part by the hippocampus and striatum of the brain. This is done, in part, through activation of two forms of nAchRs; α2ß4 and α7. The objective of this proposal is to test the global hypothesis that neonicotinoid exposure, gestationally or in adulthood, impairs performance on spatial and procedural memory tasks by perturbing expression of α2ß4 or α7 receptor expression and acetylcholine release. To address this hypothesis, we will treat adult mice, or pregnant dams, with vehicle, or the environmentally relevant doses of 5.7 mg/kg/day and 0.5 mg/kg/day of imidacloprid. Imidacloprid is the most commonly used neonicotinoid and it has been detected in samples from children and adults. Adult and gestationally exposed mice will be tested for spatial memory and reward learning memory (Aim 1). Following behavioral testing, brains from these animals will be isolated and the protein and mRNA expression of α2ß4 or α7 nAchRs and their subunits will be quantified (Aim 2). Lastly, in adult exposed animals, we will use a virus-mediated fluorescent acetylcholine sensor and fiber photometry to measure acetylcholine release targeting the hippocampus while a freely moving animal is engaged in a spatial working task (Aim 3). We predict males will be more sensitive to neonicotinoids than females and thus have a significantly disrupted performance on memory tasks and have a larger increase in nAchR expression in the brain. We also predict that adult exposure will have a larger effect on nAchR expression compared to gestational exposure. Finally, we predict that imidacloprid exposed animals will have a reduction in acetylcholine release in response to a memory task. The results of this novel and comprehensive study will provide a critical identification of possible mechanisms underlying the impact of neonicotinoids on learning and memory.