title: Synaptic Conductance Estimates of the Connection Between Local Inhibitor Interneurons and Pyramidal Neurons in Layer 2/3 of a Cortical Column.
abstract: Stimulation of a principal whisker yields sparse action potential (AP) spiking in layer 2/3 (L2/3) pyramidal neurons in a cortical column of rat barrel cortex. The low AP rates in pyramidal neurons could be explained by activation of interneurons in L2/3 providing inhibition onto L2/3 pyramidal neurons. L2/3 interneurons classified as local inhibitors based on their axonal projection in the same column were reported to receive strong excitatory input from spiny neurons in L4, which are also the main source of the excitatory input to L2/3 pyramidal neurons. Here, we investigated the remaining synaptic connection in this intracolumnar microcircuit. We found strong and reliable inhibitory synaptic transmission between intracolumnar L2/3 local-inhibitor-to-L2/3 pyramidal neuron pairs [inhibitory postsynaptic potential (IPSP) amplitude -0.88 ± 0.67 mV]. On average, 6.2 ± 2 synaptic contacts were made by L2/3 local inhibitors onto L2/3 pyramidal neurons at 107 ± 64 µm path distance from the pyramidal neuron soma, thus overlapping with the distribution of synaptic contacts from L4 spiny neurons onto L2/3 pyramidal neurons (67 ± 34 µm). Finally, using compartmental simulations, we determined the synaptic conductance per synaptic contact to be 0.77 ± 0.4 nS. We conclude that the synaptic circuit from L4 to L2/3 can provide efficient shunting inhibition that is temporally and spatially aligned with the excitatory input from L4 to L2/3.
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany Current address: Department of Dermatology, University of Heidelberg, D-69120 Heidelberg, Germany.
authors.forename: Jochen H O
authors.initials: JH
authors.lastname: Hoffmann
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany Current address: Department of Neurosurgery, Technical University of Munich, 81675 Munich, Germany.
authors.forename: H S
authors.initials: HS
authors.lastname: Meyer
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany.
authors.forename: Arno C
authors.initials: AC
authors.lastname: Schmitt
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany.
authors.forename: Jakob
authors.initials: J
authors.lastname: Straehle
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany.
authors.forename: Trinh
authors.initials: T
authors.lastname: Weitbrecht
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany Current address: Cortical Column in Silico Group, Max Planck Institute of Neurobiology, D-82152 Martinsried, Germany.
authors.forename: Bert
authors.initials: B
authors.lastname: Sakmann
authors.affiliation: Department of Cell Physiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany Present address: Department of Connectomics, Max Planck Institute for Brain Research, D-60438 Frankfurt, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Helmstaedter
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003198:Computer Simulation; D004558:Electric Stimulation; D006801:Humans; D021621:Imaging, Three-Dimensional; D053444:Inhibitory Postsynaptic Potentials; D007395:Interneurons / Q000166:cytology*; D008239:Lysine / Q000031:analogs & derivatives / Q000378:metabolism; D008959:Models, Neurological; D009431:Neural Conduction / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar; D013003:Somatosensory Cortex / Q000166:cytology*; D013569:Synapses / Q000502:physiology*; D014738:Vibrissae / Q000294:innervation; D055815:Young Adult
chemical_list: C013411:biocytin; D008239:Lysine
keywords: GABAergic synapse; interneuron; modeling; sensitivity analysis; shunting inhibition