title: A Differential and Timed Contribution of Identified Hippocampal Synapses to Associative Learning in Mice.
abstract: Although it is generally assumed that the hippocampus is involved in associative learning, the specific contribution of the different synapses present in its intrinsic circuit or comprising its afferents and efferents is poorly defined. We studied here activity-dependent changes in synaptic strength of 9 hippocampal synapses (corresponding to the intrinsic hippocampal circuitry and to its main inputs and outputs) during the acquisition of a trace eyeblink conditioning in behaving mice. The timing and intensity of synaptic changes across the acquisition process was determined. The evolution of these timed changes in synaptic strength indicated that their functional organization did not coincide with their sequential distribution according to anatomical criteria and connectivity. Furthermore, we explored the functional relevance of the extrinsic and intrinsic afferents to CA3 and CA1 pyramidal neurons, and evaluated the distinct input patterns to the intrinsic hippocampal circuit. Results confirm that the acquisition of a classical eyeblink conditioning is a multisynaptic process in which the contribution of each synaptic contact is different in strength, and takes place at different moments across learning. Thus, the precise and timed activation of multiple hippocampal synaptic contacts during classical eyeblink conditioning evokes a specific, dynamic map of functional synaptic states in that circuit.
authors.affiliation: Division of Neurosciences, Pablo de Olavide University, Seville 41013, Spain.
authors.forename: Agnès
authors.initials: A
authors.lastname: Gruart
authors.affiliation: Division of Neurosciences, Pablo de Olavide University, Seville 41013, Spain.
authors.forename: Raudel
authors.initials: R
authors.lastname: Sánchez-Campusano
authors.affiliation: Division of Neurosciences, Pablo de Olavide University, Seville 41013, Spain.
authors.forename: Azahara
authors.initials: A
authors.lastname: Fernández-Guizán
authors.affiliation: Division of Neurosciences, Pablo de Olavide University, Seville 41013, Spain.
authors.forename: José M
authors.initials: JM
authors.lastname: Delgado-García
mesh_terms: D000818:Animals; D001245:Association Learning / Q000502:physiology*; D001767:Blinking / Q000502:physiology; D003214:Conditioning, Classical; D004558:Electric Stimulation; D004576:Electromyography; D019706:Excitatory Postsynaptic Potentials; D007839:Functional Laterality; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D017966:Pyramidal Cells / Q000502:physiology*; D018709:Statistics, Nonparametric; D013569:Synapses / Q000502:physiology*; D013997:Time Factors
keywords: LTP; associative learning; behaving mice; hippocampal networks; learning-dependent synaptic plasticity