Disruption of Drug Effects (Dopamine, Nicotine, Pilocarpine, κ-Opioid) in Planarians by UV Light

Based on previous work, it has been hypothesized that the energetics of ultraviolet (UV) light disrupts effects induced by receptor-binding ligands. If this hypothesis is true, then UV light should (i) disrupt a broad variety of endpoints and (ii) disrupt effects produced by ligands that bind to diverse receptor types. This was tested directly in the present study by using ligands selective for four different receptors (one ionotropic, three metabotropic) and three different behavioral endpoints. The selective dopamine D2 receptor antagonist (–)sulpiride (0.1 uM) dose-relatedly decreased spontaneous locomotor velocity, the selective nicotinic acetylcholine receptor agonist nicotine (1, 3, 5 mM) and the selective muscarinic acetylcholine receptor agonist pilocarpine (20, 30, 50 mM) induced seizure-like activity, and the selective-opioid receptor agonist U-50,488H (10 uM) produced physical dependence (manifested as abstinence-induced withdrawal) in planarian models. Each of these diverse ligand and receptor-mediated effects were attenuated by UV light (254 nm = 7.83 × 10–19 J = 4.89 eV). These findings provide further evidence that UV light disrupts ligand-receptor mediated interactions and that UV light might provide a useful tool for examining drug-receptor interactions.