Synaptic Organization of the Cerebral Cortex

Synapses are the key elements for the induction, maintenance, and termination of signal transduction as well as modulating synaptic plasticity in any given network of the brain. The term ‘synapse’ (from Greek synapsis ‘conjunction,’ from σψναπτeιν, σψν ‘together’ and απτeιν ‘to fasten’) was originally introduced in 1897 by the physiologist Charles Sherrington and later adopted by the anatomist Ramon y Cajal. Synapses in all regions of the brain are composed of nearly the same structural subelements: a presynaptic element containing synaptic vesicles, mitochondria, and a prominent density composed of a cocktail of different synaptic proteins; on the opposite site, a postsynaptic element with a huge repertoire and different combinations of neurotransmitter receptors depending on the type of synapse; and, in between, a synaptic cleft that allows neurotransmitter diffusion from one site to the other following Ca 2 + -driven release of neurotransmitter from synaptic vesicles. It is the actual composition of these subelements in a given synapse that determines their unique function. Thus, synapses are perfectly adapted to the ‘job’ they have to perform in different brain networks and those of the neocortex described here.

[1]  Steven Finkbeiner,et al.  NMDA and AMPA receptors: old channels, new tricks , 2007, Trends in Neurosciences.

[2]  Thomas Nevian,et al.  Astrocyte signaling controls spike timing–dependent depression at neocortical synapses , 2012, Nature Neuroscience.

[3]  Cragg Bg.  The development of synapses in cat visual cortex. , 1972 .

[4]  E. Gray,et al.  Axo-somatic and axo-dendritic synapses of the cerebral cortex: an electron microscope study. , 1959, Journal of anatomy.

[5]  S. Heinemann,et al.  Identification of the Kainate Receptor Subunits Underlying Modulation of Excitatory Synaptic Transmission in the CA3 Region of the Hippocampus , 2000, The Journal of Neuroscience.

[6]  P. Goldman-Rakic,et al.  Concurrent overproduction of synapses in diverse regions of the primate cerebral cortex. , 1986, Science.

[7]  C. Giaume,et al.  Gap Junction-Mediated Astrocytic Networks in the Mouse Barrel Cortex , 2008, The Journal of Neuroscience.

[8]  A. Schleicher,et al.  Transmitter receptors and functional anatomy of the cerebral cortex , 2004, Journal of anatomy.

[9]  S. Miroňov.  Spontaneous and evoked neuronal activities regulate movements of single neuronal mitochondria , 2006, Synapse.

[10]  R. Nicoll,et al.  Presynaptic Kainate Receptor Mediation of Frequency Facilitation at Hippocampal Mossy Fiber Synapses , 2001, Science.

[11]  D. Ulrich,et al.  GABAB receptors: synaptic functions and mechanisms of diversity , 2007, Current Opinion in Neurobiology.

[12]  S. Traynelis,et al.  Structural aspects of AMPA receptor activation, desensitization and deactivation , 2007, Current Opinion in Neurobiology.

[13]  Y. Geinisman,et al.  Perforated axospinous synapses with multiple, completely partitioned transmission zones: Probable structural intermediates in synaptic plasticity , 1993, Hippocampus.

[14]  C. Garner,et al.  Bassoon and Piccolo maintain synapse integrity by regulating protein ubiquitination and degradation , 2013, The EMBO journal.

[15]  Gregers Wegener,et al.  A new efficient method for synaptic vesicle quantification reveals differences between medial prefrontal cortex perforated and nonperforated synapses , 2014, The Journal of comparative neurology.

[16]  B. Cragg,et al.  The development of synapses in the visual system of the cat , 1975, The Journal of comparative neurology.

[17]  B. Cragg,et al.  Estimation of the number of synapses in a volume of nervous tissue from counts in thin sections by electron microscopy , 1974, Journal of neurocytology.

[18]  W. Betz,et al.  Synaptic vesicle pools , 2005, Nature Reviews Neuroscience.

[19]  T. Pozzan,et al.  Mitochondria as all‐round players of the calcium game , 2000, The Journal of physiology.

[20]  M. Blue,et al.  The formation and maturation of synapses in the visual cortex of the rat. I. Qualitative analysis , 1983, Journal of neurocytology.

[21]  T. Pozzan,et al.  The comeback of mitochondria to calcium signalling. , 2000, Cell calcium.

[22]  P. Rakić,et al.  Synaptogenesis in visual cortex of normal and preterm monkeys: evidence for intrinsic regulation of synaptic overproduction. , 1989, Proceedings of the National Academy of Sciences of the United States of America.

[23]  G. Dallérac,et al.  How do astrocytes shape synaptic transmission? Insights from electrophysiology , 2013, Front. Cell. Neurosci..

[24]  Hannah Monyer,et al.  Electrical synapses: a dynamic signaling system that shapes the activity of neuronal networks. , 2004, Biochimica et biophysica acta.

[25]  Michael Frotscher,et al.  Structural Determinants of Transmission at Large Hippocampal Mossy Fiber Synapses , 2007, The Journal of Neuroscience.

[26]  Z. Nusser.  AMPA amd NMDA receptors: similarities and differences in their synaptic distribution , 2000, Current Opinion in Neurobiology.

[27]  E. G. Gray,et al.  Electron Microscopy of Synaptic Contacts on Dendrite Spines of the Cerebral Cortex , 1959, Nature.

[28]  I. Greger,et al.  AMPA receptor biogenesis and trafficking , 2007, Current Opinion in Neurobiology.

[29]  E. F. Stanley.  The calcium channel and the organization of the presynaptic transmitter release face , 1997, Trends in Neurosciences.

[30]  B. Connors,et al.  Functional Properties of Electrical Synapses between Inhibitory Interneurons of Neocortical Layer 4 , 2022 .

[31]  Juan Mendizabal-Zubiaga,et al.  GABA release by hippocampal astrocytes , 2012, Front. Comput. Neurosci..

[32]  R. Olsen,et al.  GABAA receptors: Subtypes provide diversity of function and pharmacology , 2009, Neuropharmacology.

[33]  Silvio O Rizzoli,et al.  The Structural Organization of the Readily Releasable Pool of Synaptic Vesicles , 2004, Science.

[34]  T. Südhof.  The Presynaptic Active Zone , 2012, Neuron.

[35]  B. Cragg,et al.  The density of synapses and neurons in normal, mentally defective ageing human brains. , 1975, Brain : a journal of neurology.

[36]  J. Lübke,et al.  The morphology of excitatory central synapses: from structure to function , 2006, Cell and Tissue Research.

[37]  S. Mironov,et al.  ER vesicles and mitochondria move and communicate at synapses , 2006, Journal of Cell Science.

[38]  Eckart D. Gundelfinger,et al.  Molecular organization of the presynaptic active zone , 2006, Cell and Tissue Research.

[39]  Leyla deToledo-Morrell,et al.  Induction of long-term potentiation is associated with an increase in the number of axospinous synapses with segmented postsynaptic densities , 1991, Brain Research.

[40]  S. Oliet,et al.  Glial modulation of synaptic transmission: Insights from the supraoptic nucleus of the hypothalamus , 2004, Glia.