title: EphA4 expression promotes network activity and spine maturation in cortical neuronal cultures.
abstract: BACKGROUND
  Neurons form specific connections with targets via synapses and patterns of synaptic connectivity dictate neural function. During development, intrinsic neuronal specification and environmental factors guide both initial formation of synapses and strength of resulting connections. Once synapses form, non-evoked, spontaneous activity serves to modulate connections, strengthening some and eliminating others. Molecules that mediate intercellular communication are particularly important in synaptic refinement. Here, we characterize the influences of EphA4, a transmembrane signaling molecule, on neural connectivity.
  
  
  RESULTS
  Using multi-electrode array analysis on in vitro cultures, we confirmed that cortical neurons mature and generate spontaneous circuit activity as cells differentiate, with activity growing both stronger and more patterned over time. When EphA4 was over-expressed in a subset of neurons in these cultures, network activity was enhanced: bursts were longer and were composed of more spikes than in control-transfected cultures. To characterize the cellular basis of this effect, dendritic spines, the major excitatory input site on neurons, were examined on transfected neurons in vitro. Strikingly, while spine number and density were similar between conditions, cortical neurons with elevated levels of EphA4 had significantly more mature spines, fewer immature spines, and elevated colocalization with a mature synaptic marker.
  
  
  CONCLUSIONS
  These results demonstrate that experimental elevation of EphA4 promotes network activity in vitro, supporting spine maturation, producing more functional synaptic pairings, and promoting more active circuitry.
authors.affiliation: Department of Biology, Georgetown University, Washington DC 20057, USA.
authors.forename: Meredith A
authors.initials: MA
authors.lastname: Clifford
authors.forename: Jessleen K
authors.initials: JK
authors.lastname: Kanwal
authors.forename: Rhonda
authors.initials: R
authors.lastname: Dzakpasu
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Donoghue
mesh_terms: D000200:Action Potentials / Q000235:genetics; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology*; D002522:Chlorocebus aethiops; D049229:Dendritic Spines / Q000502:physiology*; D004594:Electrophysiology; D018274:Electroporation / Q000379:methods; D004622:Embryo, Mammalian; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000235:genetics; D051379:Mice; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000166:cytology*; D036122:Receptor, EphA4 / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection / Q000379:methods
chemical_list: D049452:Green Fluorescent Proteins; D036122:Receptor, EphA4