title: Novel interactive effects of darkness and retinoid signaling in the ability to form long-term memory following aversive operant conditioning.
abstract: The vitamin A metabolite, retinoic acid, is important for memory formation and hippocampal synaptic plasticity in vertebrate species. In our studies in the mollusc Lymnaea stagnalis, we have shown that retinoic acid plays a role in memory formation following operant conditioning of the aerial respiratory behaviour. Inhibition of either retinaldehyde dehydrogenase (RALDH) or the retinoid receptors prevents long-term memory (LTM) formation, whereas synthetic retinoid receptor agonists promote memory formation by converting intermediate-term memory (ITM) into LTM. In this study, animals were exposed to constant darkness in order to test whether light-sensitive retinoic acid would promote memory formation. However, we found that exposure to constant darkness alone (in the absence of retinoic acid) enhanced memory formation. To determine whether the memory-promoting effects of darkness could override the memory-inhibiting effects of the retinoid signaling inhibitors, we exposed snails to RALDH inhibitors or a retinoid receptor antagonist in constant darkness. We found that darkness overcame the inhibitory effects of RALDH inhibition, but did not overcome the inhibitory effects of the retinoid receptor antagonist. We also tested whether constant darkness and training affected the mRNA levels of the retinoid metabolic enzymes RALDH and Cyp26, or the mRNA levels of the retinoid receptors, but found no significant effect. Overall, these data demonstrate an interaction between environmental light conditions and the retinoid signaling pathway, which influence long-term memory formation in a mollusc.
authors: Department of Biological Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada.
authors: Cailin M
authors: CM
authors: Rothwell
authors: Department of Biological Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada.
authors: Jason
authors: J
authors: Simmons
authors: Department of Biological Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada.
authors: Grace
authors: G
authors: Peters
authors: Department of Biological Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada. Electronic address: gspencer@brocku.ca.
authors: Gaynor E
authors: GE
authors: Spencer
mesh_terms: D000080462:Acyclic Monoterpenes; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D001565:Benzoates / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology*; D003624:Darkness; D004777:Environment; D008195:Lymnaea; D057567:Memory, Long-Term / Q000187:drug effects / Q000502:physiology*; D039821:Monoterpenes / Q000494:pharmacology; D050697:Retinal Dehydrogenase / Q000037:antagonists & inhibitors; D047488:Retinoid X Receptors / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D010128:p-Aminoazobenzene / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000080462:Acyclic Monoterpenes; D001565:Benzoates; D001713:Biphenyl Compounds; D039821:Monoterpenes; D047488:Retinoid X Receptors; C438269:diazepinylbenzoic acid; C007368:C.I. Solvent Yellow 56; D010128:p-Aminoazobenzene; D050697:Retinal Dehydrogenase; C007076:citral
keywords: Aerial respiration; Invertebrate; Learning; Mollusc; Retinoic acid