title: Rapid hippocampal network adaptation to recurring synchronous activity--a role for calcineurin.
abstract: Neuronal networks are thought to gradually adapt to altered neuronal activity over many hours and days. For instance, when activity is increased by suppressing synaptic inhibition, excitatory synaptic transmission is reduced. The underlying compensatory cellular and molecular mechanisms are thought to contribute in important ways to maintaining normal network operations. Seizures, due to their massive and highly synchronised discharging, probably challenge the adaptive properties of neurons, especially when seizures are frequent and intense - a condition common in early childhood. In the experiments reported here, we used rat and mice hippocampal slice cultures to explore the effects that recurring seizure-like activity has on the developing hippocampus. We found that developing networks adapted rapidly to recurring synchronised activity in that the duration of seizure-like events was reduced by 42% after 4 h of activity. At the same time, the frequency of spontaneous excitatory postsynaptic currents in pyramidal cells, the expression of biochemical biomarkers for glutamatergic synapses and the branching of pyramidal cell dendrites were all dramatically reduced. Experiments also showed that the reduction in N-methyl-D-aspartate receptor subunits and postsynaptic density protein 95 expression were N-methyl-D-aspartate receptor-dependent. To explore calcium signaling mechanisms in network adaptation, we tested inhibitors of calcineurin, a protein phosphatase known to play roles in synaptic plasticity and activity-dependent dendrite remodeling. We found that FK506 was able to prevent all of the electrophysiological, biochemical, and anatomical changes produced by synchronised network activity. Our results show that hippocampal pyramidal cells and their networks adapt rapidly to intense synchronised activity and that calcineurin play an important role in the underlying processes.
authors.affiliation: The Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA; The Cain Foundation Laboratories, The Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, 1250 Moursund Street, Suite 1225, Houston, TX, 77030, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Casanova
authors.forename: M
authors.initials: M
authors.lastname: Nishimura
authors.forename: J
authors.initials: J
authors.lastname: Le
authors.forename: T T
authors.initials: TT
authors.lastname: Lam
authors.forename: J W
authors.initials: JW
authors.lastname: Swann
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D056547:CA1 Region, Hippocampal / Q000166:cytology / Q000378:metabolism / Q000502:physiology* / Q000503:physiopathology; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D020013:Calcium Signaling; D000076122:Disks Large Homolog 4 Protein; D019706:Excitatory Postsynaptic Potentials; D051528:Guanylate Kinases / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009415:Nerve Net / Q000254:growth & development / Q000502:physiology*; D017966:Pyramidal Cells / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism; D012640:Seizures / Q000378:metabolism / Q000503:physiopathology; D013569:Synapses / Q000378:metabolism / Q000502:physiology; D016559:Tacrolimus / Q000494:pharmacology
chemical_list: D065095:Calcineurin Inhibitors; D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D016194:Receptors, N-Methyl-D-Aspartate; D051528:Guanylate Kinases; D019703:Calcineurin; D016559:Tacrolimus
keywords: dendrite; development; epilepsy; memory; mice; rat