title: Increased threshold for spike-timing-dependent plasticity is caused by unreliable calcium signaling in mice lacking fragile X gene FMR1.
abstract: Fragile X syndrome, caused by a mutation in the Fmr1 gene, is characterized by mental retardation. Several studies reported the absence of long-term potentiation (LTP) at neocortical synapses in Fmr1 knockout (FMR1-KO) mice, but underlying cellular mechanisms are unknown. We find that in the prefrontal cortex (PFC) of FMR1-KO mice, spike-timing-dependent LTP (tLTP) is not so much absent, but rather, the threshold for tLTP induction is increased. Calcium signaling in dendrites and spines is compromised. First, dendrites and spines more often fail to show calcium transients. Second, the activity of L-type calcium channels is absent in spines. tLTP could be restored by improving reliability and amplitude of calcium signaling by increasing neuronal activity. In FMR1-KO mice that were raised in enriched environments, tLTP was restored to WT levels. Our results show that mechanisms for synaptic plasticity are in place in the FMR1-KO mouse PFC, but require stronger neuronal activity to be triggered.
authors.affiliation: Department of Experimental Neurophysiology, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Rhiannon M
authors.initials: RM
authors.lastname: Meredith
authors.forename: Carl D
authors.initials: CD
authors.lastname: Holmgren
authors.forename: Meredith
authors.initials: M
authors.lastname: Weidum
authors.forename: Nail
authors.initials: N
authors.lastname: Burnashev
authors.forename: Huibert D
authors.initials: HD
authors.lastname: Mansvelder
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D002540:Cerebral Cortex / Q000166:cytology; D049229:Dendritic Spines / Q000378:metabolism; D004558:Electric Stimulation / Q000379:methods; D004777:Environment; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009473:Neuronal Plasticity / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques / Q000379:methods; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure; D013997:Time Factors
chemical_list: D002118:Calcium; D002121:Calcium Channel Blockers; D051860:Fragile X Messenger Ribonucleoprotein 1; D009543:Nifedipine; C497684:Fmr1 protein, mouse