title: Excitatory connections made by presynaptic cortico-cortical pyramidal cells in layer 6 of the neocortex.
abstract: Paired intracellular recordings with biocytin labelling were made in slices of adult rat somatosensory and visual cortex and in cat visual cortex to examine the properties of synaptic connections made by layer 6 pyramidal cells, to determine whether cortico-cortical pyramids more commonly provide input to other layer 6 pyramids than cortico-thalamic cells, and whether these connections exhibit paired pulse and brief train depression. Pyramidal cells with cortico-cortical like morphology were 2-4 times more likely to innervate other pyramidal cells than were cortico-thalamic like cells, but less likely to innervate inhibitory interneurons. The excitatory postsynaptic potentials elicited by presynaptic, phasically firing cortico-cortical pyramids in all classes of postsynaptic infragranular layer pyramidal cells exhibited strong, presynaptically mediated paired pulse and brief train depression. Those with larger paired pulse ratios also exhibited post-tetanic potentiation, but this was accompanied by stronger paired pulse and brief train depression. Both the firing characteristics and the outputs of cortico-cortical pyramidal cells display pronounced phasic characteristics, indicating that these cells respond most effectively to and preferentially pass on information related to novelty.
authors.affiliation: Department of Pharmacology, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, UK.
authors.forename: Audrey
authors.initials: A
authors.lastname: Mercer
authors.forename: David C
authors.initials: DC
authors.lastname: West
authors.forename: Oliver T
authors.initials: OT
authors.lastname: Morris
authors.forename: Sarah
authors.initials: S
authors.lastname: Kirchhecker
authors.forename: Jane E
authors.initials: JE
authors.lastname: Kerkhoff
authors.forename: Alex M
authors.initials: AM
authors.lastname: Thomson
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D002415:Cats; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D008239:Lysine / Q000031:analogs & derivatives; D008297:Male; D019579:Neocortex / Q000166:cytology / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology*; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D017661:Receptors, Presynaptic / Q000502:physiology*
chemical_list: D017661:Receptors, Presynaptic; C013411:biocytin; D008239:Lysine