title: Endogenous cholinergic tone modulates spontaneous network level neuronal activity in primary cortical cultures grown on multi-electrode arrays.
abstract: BACKGROUND
  Cortical cultures grown long-term on multi-electrode arrays (MEAs) are frequently and extensively used as models of cortical networks in studies of neuronal firing activity, neuropharmacology, toxicology and mechanisms underlying synaptic plasticity. However, in contrast to the predominantly asynchronous neuronal firing activity exhibited by intact cortex, electrophysiological activity of mature cortical cultures is dominated by spontaneous epileptiform-like global burst events which hinders their effective use in network-level studies, particularly for neurally-controlled animat ('artificial animal') applications. Thus, the identification of culture features that can be exploited to produce neuronal activity more representative of that seen in vivo could increase the utility and relevance of studies that employ these preparations. Acetylcholine has a recognised neuromodulatory role affecting excitability, rhythmicity, plasticity and information flow in vivo although its endogenous production by cortical cultures and subsequent functional influence upon neuronal excitability remains unknown.
  
  
  RESULTS
  Consequently, using MEA electrophysiological recording supported by immunohistochemical and RT-qPCR methods, we demonstrate for the first time, the presence of intrinsic cholinergic neurons and significant, endogenous cholinergic tone in cortical cultures with a characterisation of the muscarinic and nicotinic components that underlie modulation of spontaneous neuronal activity. We found that tonic muscarinic ACh receptor (mAChR) activation affects global excitability and burst event regularity in a culture age-dependent manner whilst, in contrast, tonic nicotinic ACh receptor (nAChR) activation can modulate burst duration and the proportion of spikes occurring within bursts in a spatio-temporal fashion.
  
  
  CONCLUSIONS
  We suggest that the presence of significant endogenous cholinergic tone in cortical cultures and the comparability of its modulatory effects to those seen in intact brain tissues support emerging, exploitable commonalities between in vivo and in vitro preparations. We conclude that experimental manipulation of endogenous cholinergic tone could offer a novel opportunity to improve the use of cortical cultures for studies of network-level mechanisms in a manner that remains largely consistent with its functional role.
authors.affiliation: School of Chemistry, Food and Nutritional Sciences and Pharmacy, University of Reading, Whiteknights, Reading, Berkshire RG6 6AP, UK.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Hammond
authors.forename: Dimitris
authors.initials: D
authors.lastname: Xydas
authors.forename: Julia H
authors.initials: JH
authors.lastname: Downes
authors.forename: Giovanna
authors.initials: G
authors.lastname: Bucci
authors.forename: Victor
authors.initials: V
authors.lastname: Becerra
authors.forename: Kevin
authors.initials: K
authors.lastname: Warwick
authors.forename: Andrew
authors.initials: A
authors.lastname: Constanti
authors.forename: Slawomir J
authors.initials: SJ
authors.lastname: Nasuto
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Whalley
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology*; D018678:Cholinergic Agents / Q000378:metabolism* / Q000494:pharmacology; D004566:Electrodes; D004622:Embryo, Mammalian; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D051381:Rats; D011921:Rats, Inbred WKY; D020917:Receptor, trkA / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors
chemical_list: D018678:Cholinergic Agents; D011976:Receptors, Muscarinic; D020917:Receptor, trkA; D000109:Acetylcholine