title: Metaplastic up-regulation of LTP in the rat visual cortex by monocular visual training: requirement of task mastery, hemispheric specificity, and NMDA-GluN2B involvement.
abstract: "Metaplasticity" is defined as an alteration of synaptic plasticity properties or mechanisms by a priming event without actual changes in synaptic strength. For example, visual discrimination training of rats leads to a facilitation of the subsequent induction of long-term potentiation (LTP) between the lateral geniculate nucleus (LGN) and the primary visual cortex (V1). Here, rats received visual discrimination training in a modified water maze, with one eye occluded during training to create monocular viewing conditions; 63% of rats acquired the task under these conditions. Following training, in vivo electrophysiology was used to examine LTP of field postsynaptic potentials (fPSPs) in V1 elicited by LGN stimulation. Rats that had successfully learned the task showed significantly greater LTP in the "trained V1" (contralateral to the open, trained eye) relative to the "untrained" hemisphere. Rats that underwent training but failed to acquire the task did not show this lateralized plasticity enhancement and had similar levels of LTP in both cerebral hemispheres. Cortical application of the NMDA receptor-GluN2B subunit antagonist Ro 25-6981 (2 mM) reversed the training-induced LTP facilitation without affecting LTP in the untrained V1. Whole-cell patch clamp recordings of V1 (layers II/III) pyramidal cells in vitro demonstrated that pharmacologically isolated NMDA currents exhibit a greater sensitivity to GluN2B blockade in the trained relative to the untrained V1. Together, these experiments reveal a surprising degree of anatomical (only in the hemisphere contralateral to the trained eye) and behavioral specificity (only in rats that mastered the task) for the effect of visual training to enhance LTP in V1. Further, cortical GluN2B subunits appear to be directly involved in this metaplastic facilitation of thalamocortical plasticity, suggesting that NMDA subunit composition or functioning is, at least in part, regulated by the exposure to behaviorally significant stimuli in an animal's sensory environment.
authors.affiliation: Department of Psychology, Queen's University, Kingston, Ontario, Canada.
authors.forename: A M
authors.initials: AM
authors.lastname: Hager
authors.affiliation: Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada.
authors.forename: P J
authors.initials: PJ
authors.lastname: Gagolewicz
authors.affiliation: Department of Psychology, Queen's University, Kingston, Ontario, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Rodier
authors.affiliation: Department of Psychology, Queen's University, Kingston, Ontario, Canada.
authors.forename: M-C
authors.initials: MC
authors.lastname: Kuo
authors.affiliation: Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada; Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.
authors.forename: É C
authors.initials: ÉC
authors.lastname: Dumont
authors.affiliation: Department of Psychology, Queen's University, Kingston, Ontario, Canada; Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada. Electronic address: dringenb@queensu.ca.
authors.forename: H C
authors.initials: HC
authors.lastname: Dringenberg
mesh_terms: D000818:Animals; D004192:Discrimination, Psychological / Q000502:physiology; D004558:Electric Stimulation; D007839:Functional Laterality / Q000502:physiology; D005829:Geniculate Bodies / Q000187:drug effects / Q000502:physiology*; D017774:Long-Term Potentiation / Q000187:drug effects; D008297:Male; D018782:Maze Learning / Q000502:physiology; D010636:Phenols / Q000008:administration & dosage; D010880:Piperidines / Q000008:administration & dosage; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D014793:Visual Cortex / Q000187:drug effects / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
chemical_list: D010636:Phenols; D010880:Piperidines; D016194:Receptors, N-Methyl-D-Aspartate; C109643:Ro 25-6981
keywords: GluN2B subunits; NMDA receptor; long-term potentiation; metaplasticity; visual cortex; visual learning