title: Multiple spine boutons are formed after long-lasting LTP in the awake rat.
abstract: The formation of multiple spine boutons (MSBs) has been associated with cognitive abilities including hippocampal-dependent associative learning and memory. Data obtained from cultured hippocampal slices suggest that the long-term maintenance of synaptic plasticity requires the formation of new synaptic contacts on pre-existing synapses. This postulate however, has never been tested in the awake, freely moving animals. In the current study, we induced long-term potentiation (LTP) in the dentate gyrus (DG) of awake adult rats and performed 3-D reconstructions of electron micrographs from thin sections of both axonal boutons and dendritic spines, 24 h post-induction. The specificity of the observed changes was demonstrated by comparison with animals in which long-term depression (LTD) had been induced, or with animals in which LTP was blocked by an N-methyl-D-aspartate (NMDA) antagonist. Our data demonstrate that whilst the number of boutons remains unchanged, there is a marked increase in the number of synapses per bouton 24 h after the induction of LTP. Further, we demonstrate that this increase is specific to mushroom spines and not attributable to their division. The present investigation thus fills the gap existing between behavioural and in vitro studies on the role of MSB formation in synaptic plasticity and cognitive abilities.
authors.affiliation: Department of Life Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.
authors.forename: N I
authors.initials: NI
authors.lastname: Medvedev
authors.forename: G
authors.initials: G
authors.lastname: Dallérac
authors.forename: V I
authors.initials: VI
authors.lastname: Popov
authors.forename: J J
authors.initials: JJ
authors.lastname: Rodriguez Arellano
authors.forename: H A
authors.initials: HA
authors.lastname: Davies
authors.forename: I V
authors.initials: IV
authors.lastname: Kraev
authors.forename: V
authors.initials: V
authors.lastname: Doyère
authors.forename: M G
authors.initials: MG
authors.lastname: Stewart
mesh_terms: D000818:Animals; D001703:Biophysics; D003198:Computer Simulation; D049229:Dendritic Spines / Q000502:physiology* / Q000648:ultrastructure; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology*; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D036881:Long-Term Synaptic Depression / Q000187:drug effects / Q000502:physiology; D008297:Male; D009415:Nerve Net / Q000502:physiology / Q000648:ultrastructure; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013997:Time Factors; D014851:Wakefulness
chemical_list: D018691:Excitatory Amino Acid Antagonists; D010879:Piperazines; C050592:3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid