Morphological heterogeneity of layer VI neurons in mouse barrel cortex

Understanding the basic neuronal building blocks of the neocortex is a necessary first step toward comprehending the composition of cortical circuits. Neocortical layer VI is the most morphologically diverse layer and plays a pivotal role in gating information to the cortex via its feedback connection to the thalamus and other ipsilateral and callosal corticocortical connections. The heterogeneity of function within this layer is presumably linked to its varied morphological composition. However, so far, very few studies have attempted to define cell classes in this layer using unbiased quantitative methodologies. Utilizing the Golgi staining technique along with the Neurolucida software, we recontructed 222 cortical neurons from layer VI of mouse barrel cortex. Morphological analyses were performed by quantifying somatic and dendritic parameters, and, by using principal component and cluster analyses, we quantitatively categorized neurons into six distinct morphological groups. Additional systematic replication on a separate population of neurons yielded similar results, demonstrating the consistency and reliability of our categorization methodology. Subsequent post hoc analyses of dendritic parameters supported our neuronal classification scheme. Characterizing neuronal elements with unbiased quantitative techniques provides a framework for better understanding structure–function relationships within neocortical circuits in general. J. Comp. Neurol. 512:726–746, 2009. © 2008 Wiley‐Liss, Inc.

[1]  S. Itohara,et al.  Impaired Cerebellar Development and Function in Mice Lacking CAPS2, a Protein Involved in Neurotrophin Release , 2007, The Journal of Neuroscience.

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

[3]  Thomas Lemberger,et al.  SRF mediates activity-induced gene expression and synaptic plasticity but not neuronal viability , 2005, Nature Neuroscience.

[4]  K. Rockland,et al.  Comparative analysis of layer-specific genes in Mammalian neocortex. , 2007, Cerebral cortex.

[5]  I. Fábregues,et al.  A Golgi study of the sixth layer of the cerebral cortex. I. The lissencephalic brain of Rodentia, Lagomorpha, Insectivora and Chiroptera. , 1986, Journal of anatomy.

[6]  T. L. Davis,et al.  Microcircuitry of cat visual cortex: Classification of neurons in layer IV of area 17, and identification of the patterns of lateral geniculate input , 1979, The Journal of comparative neurology.

[7]  E. Evarts,et al.  Relation of size and activity of motor cortex pyramidal tract neurons during skilled movements in the monkey , 1981, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[8]  P. Bailey,et al.  Organization of the cerebral cortex. , 1948, The Proceedings of the Institute of Medicine of Chicago.

[9]  C. Petersen.  The Functional Organization of the Barrel Cortex , 2007, Neuron.

[10]  J. Mendizabal-Zubiaga,et al.  The underside of the cerebral cortex: layer V/VI spiny inverted neurons , 2007, Journal of anatomy.

[11]  Rafael Yuste,et al.  Quantitative morphologic classification of layer 5 neurons from mouse primary visual cortex , 2003, The Journal of comparative neurology.

[12]  H. B. M. Uylings,et al.  The metric analysis of three-dimensional dendritic tree patterns: a methodological review , 1986, Journal of Neuroscience Methods.

[13]  G. Raivich,et al.  Connective tissue growth factor: a novel marker of layer vii neurons in the rat cerebral cortex , 2003, Neuroscience.

[14]  Henry H Yin,et al.  Disrupted motor learning and long-term synaptic plasticity in mice lacking NMDAR1 in the striatum , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[15]  I. Divac.  Cortical circuits: Synaptic organization of the cerebral cortex. Structure, function and theory by Edward L. White, Birkäuser, 1989. Sw. fr. 88.00 (xvi + 223 pages) ISBN 3 7643 3402 9 , 1990, Trends in Neurosciences.

[16]  Ian R. Wickersham,et al.  Monosynaptic Restriction of Transsynaptic Tracing from Single, Genetically Targeted Neurons , 2007, Neuron.

[17]  Ian T. Jolliffe,et al.  Discarding Variables in a Principal Component Analysis. I: Artificial Data , 1972 .

[18]  T. Kaneko,et al.  Organization and development of corticocortical associative neurons expressing the orphan nuclear receptor Nurr1 , 2003, The Journal of comparative neurology.

[19]  E. Ramón-Moliner,et al.  The Golgi-Cox Technique , 1970 .

[20]  Joshua C. Brumberg,et al.  The sensorimotor slice , 2007, Journal of Neuroscience Methods.

[21]  E M Callaway,et al.  Layer-Specific Input to Distinct Cell Types in Layer 6 of Monkey Primary Visual Cortex , 2001, The Journal of Neuroscience.

[22]  Shubhodeep Chakrabarti,et al.  Differential origin of projections from SI barrel cortex to the whisker representations in SII and MI , 2006, The Journal of comparative neurology.

[23]  J. D. del Río,et al.  Developmental history of the subplate and developing white matter in the murine neocortex. Neuronal organization and relationship with the main afferent systems at embryonic and perinatal stages. , 2000, Cerebral cortex.

[24]  Facundo Valverde,et al.  Golgi Atlas of the Postnatal Mouse Brain , 2004 .

[25]  Frederic Libersat,et al.  Mechanisms of dendritic maturation , 2004, Molecular Neurobiology.

[26]  V. Mountcastle.  Perceptual Neuroscience: The Cerebral Cortex , 1998 .

[27]  R W Guillery,et al.  The role of the thalamus in the flow of information to the cortex. , 2002, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[28]  T A Woolsey,et al.  On the “selectivity” of the Golgi‐Cox method , 1975, The Journal of comparative neurology.

[29]  F. Valverde,et al.  Development and differentiation of early generated cells of sublayer VIb in the somatosensory cortex of the rat: A correlated Golgi and autoradiographic study , 1989, The Journal of comparative neurology.

[30]  D. Simons,et al.  Morphology of Golgi‐Cox‐impregnated barrel neurons in rat SmI cortex , 1984, The Journal of comparative neurology.

[31]  L. Roux,et al.  Morphological and Physiological Characterization of Layer VI Corticofugal Neurons of Mouse Primary Visual Cortex , 2003 .

[32]  Alan Peters,et al.  Cellular components of the cerebral cortex , 1984 .

[33]  G. Snyder,et al.  A comparison of the electrophysiological properties of morphologically identified cells in layers 5B and 6 of the rat neocortex , 1992, Neuroscience.

[34]  P. Somogyi,et al.  Proximally targeted GABAergic synapses and gap junctions synchronize cortical interneurons , 2000, Nature Neuroscience.

[35]  L. Reichardt,et al.  p120 Catenin Regulates Dendritic Spine and Synapse Development through Rho-Family GTPases and Cadherins , 2006, Neuron.

[36]  J. Winer,et al.  Layer VI in cat primary auditory cortex: Golgi study and sublaminar origins of projection neurons , 1999, The Journal of comparative neurology.

[37]  D Scheibler,et al.  Monte Carlo Tests of the Accuracy of Cluster Analysis Algorithms: A Comparison of Hierarchical and Nonhierarchical Methods. , 1985, Multivariate behavioral research.

[38]  L C Katz,et al.  Local circuitry of identified projection neurons in cat visual cortex brain slices , 1987, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[39]  R. Cattell.  The Scree Test For The Number Of Factors. , 1966, Multivariate behavioral research.

[40]  Edmund M. Glaser,et al.  Analysis of thick brain sections by obverse—Reverse computer microscopy: Application of a new, high clarity Golgi—Nissl stain , 1981, Journal of Neuroscience Methods.

[41]  J. Seamans,et al.  Electrophysiological and morphological properties of layers V-VI principal pyramidal cells in rat prefrontal cortex in vitro , 1996, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[42]  J M Bower,et al.  Quantitative Golgi study of the rat cerebellar molecular layer interneurons using principal component analysis , 1998, The Journal of comparative neurology.

[43]  T. H. Brown,et al.  Morphology and ontogeny of rat perirhinal cortical neurons , 2007, The Journal of comparative neurology.

[44]  J. Rossier,et al.  Classification of fusiform neocortical interneurons based on unsupervised clustering. , 2000, Proceedings of the National Academy of Sciences of the United States of America.