Synaptic and cellular organization of layer 1 of the developing rat somatosensory cortex

Layer 1 of the neocortex is sparsely populated with neurons and heavily innervated by fibers from lower layers and proximal and distal brain regions. Understanding the potential functions of this layer requires a comprehensive understanding of its cellular and synaptic organization. We therefore performed a quantitative study of the microcircuitry of neocortical layer 1 (L1) in the somatosensory cortex in juvenile rats (P13–P16) using multi-neuron patch-clamp and 3D morphology reconstructions. Expert-based subjective classification of the morphologies of the recorded L1 neurons suggest 6 morphological classes: (1) the Neurogliaform cells with dense axonal arborizations (NGC-DA) and with sparse arborizations (NGC-SA), (2) the Horizontal Axon Cell (HAC), (3) those with descending axonal collaterals (DAC), (4) the large axon cell (LAC), and (5) the small axon cell (SAC). Objective, supervised and unsupervised cluster analyses confirmed DAC, HAC, LAC and NGC as distinct morphological classes. The neurons were also classified into 5 electrophysiological types based on the Petilla convention; classical non-adapting (cNAC), burst non-adapting (bNAC), classical adapting (cAC), classical stuttering (cSTUT), and classical irregular spiking (cIR). The most common electrophysiological type of neuron was the cNAC type (40%) and the most common morpho-electrical type was the NGC-DA—cNAC. Paired patch-clamp recordings revealed that the neurons were connected via GABAergic inhibitory synaptic connections with a 7.9% connection probability and via gap junctions with a 5.2% connection probability. Most synaptic connections were mediated by both GABAA and GABAB receptors (62.6%). A smaller fraction of synaptic connections were mediated exclusively by GABAA (15.4%) or GABAB (21.8%) receptors. Morphological 3D reconstruction of synaptic connected pairs of L1 neurons revealed multi-synapse connections with an average of 9 putative synapses per connection. These putative synapses were widely distributed with 39% on somata and 61% on dendrites. We also discuss the functional implications of this L1 cellular and synaptic organization in neocortical information processing.

[1]  Hiroaki Igarashi,et al.  Thalamocortical projection from the ventral posteromedial nucleus sends its collaterals to layer I of the primary somatosensory cortex in rat , 2004, Neuroscience Letters.

[2]  P. Somogyi,et al.  Synapses, axonal and dendritic patterns of GABA-immunoreactive neurons in human cerebral cortex. , 1990, Brain : a journal of neurology.

[3]  A. Thomson,et al.  Functional Maps of Neocortical Local Circuitry , 2007, Front. Neurosci..

[4]  Y. Kawaguchi,et al.  Parvalbumin, somatostatin and cholecystokinin as chemical markers for specific GABAergic interneuron types in the rat frontal cortex , 2002, Journal of neurocytology.

[5]  B. Sakmann,et al.  Dendritic mechanisms underlying the coupling of the dendritic with the axonal action potential initiation zone of adult rat layer 5 pyramidal neurons , 2001, The Journal of physiology.

[6]  A. Keller,et al.  Intrinsic circuitry and physiological properties of pyramidal neurons in rat barrel cortex , 1997, Experimental Brain Research.

[7]  A. Guidotti,et al.  Reelin secretion from glutamatergic neurons in culture is independent from neurotransmitter regulation. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[8]  Y. Kubota,et al.  Three classes of GABAergic interneurons in neocortex and neostriatum. , 1994, The Japanese journal of physiology.

[9]  Matthew E. Larkum,et al.  The GABAB1b Isoform Mediates Long-Lasting Inhibition of Dendritic Ca2+ Spikes in Layer 5 Somatosensory Pyramidal Neurons , 2006, Neuron.

[10]  J. Zhu,et al.  Rapid Arrival and Integration of Ascending Sensory Information in Layer 1 Nonpyramidal Neurons and Tuft Dendrites of Layer 5 Pyramidal Neurons of the Neocortex , 2004, The Journal of Neuroscience.

[11]  Bert Sakmann,et al.  The extracellular patch clamp: A method for resolving currents through individual open channels in biological membranes , 1978, Pflügers Archiv.

[12]  C. Ribak,et al.  Aspinous and sparsely-spinous stellate neurons in the visual cortex of rats contain glutamic acid decarboxylase , 1978, Journal of neurocytology.

[13]  J. Hablitz,et al.  GABAB receptor-mediated heterosynaptic depression of excitatory synaptic transmission in rat frontal neocortex , 2003, Brain Research.

[14]  Christian Wozny,et al.  Specificity of Synaptic Connectivity between Layer 1 Inhibitory Interneurons and Layer 2/3 Pyramidal Neurons in the Rat Neocortex , 2011, Cerebral cortex.

[15]  B. Sakmann,et al.  A new cellular mechanism for coupling inputs arriving at different cortical layers , 1999, Nature.

[16]  T. Woolsey,et al.  The structural organization of layer IV in the somatosensory region (S I) of mouse cerebral cortex , 1970 .

[17]  A. Pestronk.  Histology of the Nervous System of Man and Vertebrates , 1997, Neurology.

[18]  R. Yuste,et al.  Comparison Between Supervised and Unsupervised Classifications of Neuronal Cell Types: A Case Study , 2010, Developmental neurobiology.

[19]  Thomas K. Berger,et al.  A synaptic organizing principle for cortical neuronal groups , 2011, Proceedings of the National Academy of Sciences.

[20]  Omar J. Ahmed,et al.  Thalamic Control of Layer 1 Circuits in Prefrontal Cortex , 2012, The Journal of Neuroscience.

[21]  S. Anderson,et al.  The origin and specification of cortical interneurons , 2006, Nature Reviews Neuroscience.

[22]  Jascha D. Swisher,et al.  Multiscale Pattern Analysis of Orientation-Selective Activity in the Primary Visual Cortex , 2010, The Journal of Neuroscience.

[23]  Y. Kawaguchi.  Physiological subgroups of nonpyramidal cells with specific morphological characteristics in layer II/III of rat frontal cortex , 1995, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[24]  V. Mountcastle.  Modality and topographic properties of single neurons of cat's somatic sensory cortex. , 1957, Journal of neurophysiology.

[25]  Miguel Marín-Padilla,et al.  Cajal–Retzius cells and the development of the neocortex , 1998, Trends in Neurosciences.

[26]  G. Tamás,et al.  Identified Sources and Targets of Slow Inhibition in the Neocortex , 2003, Science.

[27]  T. Sejnowski,et al.  G protein activation kinetics and spillover of gamma-aminobutyric acid may account for differences between inhibitory responses in the hippocampus and thalamus. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[28]  S. Hestrin,et al.  Morphology and Physiology of Cortical Neurons in Layer I , 1996, The Journal of Neuroscience.

[29]  H. Markram,et al.  Anatomical, physiological, molecular and circuit properties of nest basket cells in the developing somatosensory cortex. , 2002, Cerebral cortex.

[30]  C. Petersen,et al.  Membrane Potential Dynamics of GABAergic Neurons in the Barrel Cortex of Behaving Mice , 2010, Neuron.

[31]  Andreas T. Schaefer,et al.  Coincidence detection in pyramidal neurons is tuned by their dendritic branching pattern. , 2003, Journal of neurophysiology.

[32]  Demian Battaglia,et al.  Classification of NPY-Expressing Neocortical Interneurons , 2009, The Journal of Neuroscience.

[33]  T. M. Marin-Padilla,et al.  Origin, prenatal development and structural organization of layer I of the human cerebral (motor) cortex , 1982, Anatomy and Embryology.

[34]  A. Destexhe,et al.  Dual intracellular recordings and computational models of slow inhibitory postsynaptic potentials in rat neocortical and hippocampal slices , 1999, Neuroscience.

[35]  Heng Tao Shen,et al.  Principal Component Analysis , 2009, Encyclopedia of Biometrics.

[36]  J. Deuchars,et al.  Single axon IPSPs elicited in pyramidal cells by three classes of interneurones in slices of rat neocortex. , 1996, The Journal of physiology.

[37]  T. Woolsey,et al.  The structural organization of layer IV in the somatosensory region (SI) of mouse cerebral cortex. The description of a cortical field composed of discrete cytoarchitectonic units. , 1970, Brain research.

[38]  J. Deuchars,et al.  Synaptic interactions in neocortical local circuits: dual intracellular recordings in vitro. , 1997, Cerebral cortex.

[39]  D. Prince,et al.  Development of BK channels in neocortical pyramidal neurons. , 1996, Journal of neurophysiology.

[40]  E. P. Gardner,et al.  Petilla terminology: nomenclature of features of GABAergic interneurons of the cerebral cortex , 2008, Nature Reviews Neuroscience.

[41]  B. Sakmann,et al.  Three-dimensional axon morphologies of individual layer 5 neurons indicate cell type-specific intracortical pathways for whisker motion and touch , 2011, Proceedings of the National Academy of Sciences.

[42]  Norimitsu Suzuki,et al.  Distinctive classes of GABAergic interneurons provide layer-specific phasic inhibition in the anterior piriform cortex. , 2010, Cerebral cortex.

[43]  Maria V. Sanchez-Vives,et al.  Functional dynamics of GABAergic inhibition in the thalamus. , 1997, Science.

[44]  S. Hestrin,et al.  Synaptic Interactions of Late-Spiking Neocortical Neurons in Layer 1 , 2003, The Journal of Neuroscience.

[45]  D. Prince,et al.  Patch-clamp studies of voltage-gated currents in identified neurons of the rat cerebral cortex. , 1991, Cerebral cortex.

[46]  M. Frotscher,et al.  Subcellular Localization of Metabotropic GABAB Receptor Subunits GABAB1a/b and GABAB2 in the Rat Hippocampus , 2003, The Journal of Neuroscience.

[47]  Susana Q. Lima,et al.  Remote Control of Behavior through Genetically Targeted Photostimulation of Neurons , 2005, Cell.

[48]  Gaël Varoquaux,et al.  Scikit-learn: Machine Learning in Python , 2011, J. Mach. Learn. Res..

[49]  B. Zemelman,et al.  Selective Photostimulation of Genetically ChARGed Neurons , 2002, Neuron.

[50]  M. Larkum,et al.  The Cellular Basis of GABAB-Mediated Interhemispheric Inhibition , 2012, Science.

[51]  James R. Schott,et al.  Principles of Multivariate Analysis: A User's Perspective , 2002 .

[52]  J. Bekkers,et al.  Inhibitory neurons in the anterior piriform cortex of the mouse: Classification using molecular markers , 2010, The Journal of comparative neurology.

[53]  Ivan Soltesz,et al.  Different transmitter transients underlie presynaptic cell type specificity of GABAA,slow and GABAA,fast , 2007, Proceedings of the National Academy of Sciences.

[54]  M. Marín‐padilla.  Origin, formation, and prenatal maturation of the human cerebral cortex: an overview. , 1990, Journal of craniofacial genetics and developmental biology.

[55]  L. Cauller.  Layer I of primary sensory neocortex: where top-down converges upon bottom-up , 1995, Behavioural Brain Research.

[56]  H. Markram,et al.  Physiology and anatomy of synaptic connections between thick tufted pyramidal neurones in the developing rat neocortex. , 1997, The Journal of physiology.

[57]  A. Lieberman,et al.  Neurons in layer I of the developing occipital cortex of the rat , 1977, The Journal of comparative neurology.

[58]  K. Svoboda,et al.  Diverse Modes of Axon Elaboration in the Developing Neocortex , 2005, PLoS biology.

[59]  F. Zhou,et al.  Morphological properties of intracellularly labeled layer I neurons in rat neocortex , 1996, The Journal of comparative neurology.

[60]  F. Clascá,et al.  Thalamic input to distal apical dendrites in neocortical layer 1 is massive and highly convergent. , 2009, Cerebral cortex.

[61]  H. Markram,et al.  Correlation maps allow neuronal electrical properties to be predicted from single-cell gene expression profiles in rat neocortex. , 2004, Cerebral cortex.

[62]  M. C. Angulo,et al.  Molecular and Physiological Diversity of Cortical Nonpyramidal Cells , 1997, The Journal of Neuroscience.

[63]  Edward M Callaway,et al.  Development of layer‐specific axonal arborizations in mouse primary somatosensory cortex , 2006, The Journal of comparative neurology.

[64]  A. Young,et al.  Transcriptional dysregulation in striatal projection- and interneurons in a mouse model of Huntington's disease: neuronal selectivity and potential neuroprotective role of HAP1. , 2005, Human molecular genetics.

[65]  R. Yuste,et al.  Involvement of Cajal-Retzius Neurons in Spontaneous Correlated Activity of Embryonic and Postnatal Layer 1 from Wild-Type and Reeler Mice , 1999, The Journal of Neuroscience.

[66]  A. Fairén,et al.  What is a Cajal-Retzius cell? A reassessment of a classical cell type based on recent observations in the developing neocortex. , 1999, Cerebral cortex.

[67]  H. Markram,et al.  Anatomical, physiological and molecular properties of Martinotti cells in the somatosensory cortex of the juvenile rat , 2004, The Journal of physiology.

[68]  Johannes J. Letzkus,et al.  A disinhibitory microcircuit for associative fear learning in the auditory cortex , 2011, Nature.

[69]  P. Somogyi,et al.  Quantitative distribution of GABA-immunoreactive neurons in the visual cortex (area 17) of the cat , 2004, Experimental Brain Research.

[70]  M. Rieu,et al.  Morphology and physiology , 2005, Experientia.

[71]  K. Quesenberry,et al.  Morphology and Physiology , 1996 .

[72]  J. H. Ward.  Hierarchical Grouping to Optimize an Objective Function , 1963 .

[73]  M. Frotscher,et al.  A role for Cajal–Retzius cells and reelin in the development of hippocampal connections , 1997, Nature.

[74]  P. Langton,et al.  Patch Clamp Recording , 2012 .

[75]  G. Meyer,et al.  Prenatal development of reelin‐immunoreactive neurons in the human neocortex , 1998, The Journal of comparative neurology.

[76]  Xiaolong Jiang,et al.  The organization of two new cortical interneuronal circuits , 2013, Nature Neuroscience.

[77]  K. Toyama,et al.  An intracellular study of neuronal organization in the visual cortex , 2004, Experimental Brain Research.

[78]  N. Spruston.  Pyramidal neurons: dendritic structure and synaptic integration , 2008, Nature Reviews Neuroscience.

[79]  Y. Kubota,et al.  GABAergic cell subtypes and their synaptic connections in rat frontal cortex. , 1997, Cerebral cortex.

[80]  J. E. Vaughn,et al.  The GABA Neurons and their axon terminals in rat corpus striatum as demonstrated by GAD immunocytochemistry , 1979, The Journal of comparative neurology.

[81]  B. Sakmann,et al.  Patch-clamp recordings from the soma and dendrites of neurons in brain slices using infrared video microscopy , 1993, Pflügers Archiv.

[82]  J. Moncho-Bogani,et al.  Expression of Calcium-Binding Proteins in Layer 1 Reelin-Immunoreactive Cells during Rat and Mouse Neocortical Development , 2014, The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society.

[83]  Wojtek J. Krzanowski,et al.  Principles of multivariate analysis : a user's perspective. oxford , 1988 .

[84]  J. L. Conel,et al.  The postnatal development of the human cerebral cortex , 1960 .

[85]  M. Marín‐Padilla.  [The development of the human cerebral cortex. A cytoarchitectonic theory]. , 1999, Revista de neurologia.

[86]  O. Paulsen,et al.  Expression and distribution of metabotropic GABA receptor subtypes GABABR1 and GABABR2 during rat neocortical development , 2002, The European journal of neuroscience.