Mechanistic and Behavioral Effects of Nicotine Exposure in Planarians: A Simple Model for Addiction Neuroscience

Planarians (Dugesia spp., Schmidtea mediterranea) have emerged as an accessible yet powerful invertebrate model for studying the neurobehavioral and molecular mechanisms of addictive drug exposure. Despite possessing a primitive, simple central nervous system, planarians exhibit nicotine-induced behavioral, neurochemical, and pharmacological responses that parallel vertebrate addiction phenotypes, including tolerance, withdrawal, and conditioned place preference. These conserved features arise from functional cholinergic, dopaminergic, serotonergic, and opioid signaling systems that regulate motility and reinforcement-like behaviors. This review synthesizes current literature on nicotine exposure in planarians, detailing behavioral assays, receptor-level mechanisms, cross-system interactions, and methodological limitations. We argue that planarians provide a uniquely integrative and accessible model for exploring molecular and behavioral-level impacts of nicotine, offering both translational and conceptual insights into dependence mechanisms.