Gap junctions on hippocampal mossy fiber axons demonstrated by thin-section electron microscopy and freeze–fracture replica immunogold labeling

Gap junctions have been postulated to exist between the axons of excitatory cortical neurons based on electrophysiological, modeling, and dye-coupling data. Here, we provide ultrastructural evidence for axoaxonic gap junctions in dentate granule cells. Using combined confocal laser scanning microscopy, thin-section transmission electron microscopy, and grid-mapped freeze–fracture replica immunogold labeling, 10 close appositions revealing axoaxonic gap junctions (≈30–70 nm in diameter) were found between pairs of mossy fiber axons (≈100–200 nm in diameter) in the stratum lucidum of the CA3b field of the rat ventral hippocampus, and one axonal gap junction (≈100 connexons) was found on a mossy fiber axon in the CA3c field of the rat dorsal hippocampus. Immunogold labeling with two sizes of gold beads revealed that connexin36 was present in that axonal gap junction. These ultrastructural data support computer modeling and in vitro electrophysiological data suggesting that axoaxonic gap junctions play an important role in the generation of very fast (>70 Hz) network oscillations and in the hypersynchronous electrical activity of epilepsy.

[1]  R. Dermietzel,et al.  Localization of the pannexin1 protein at postsynaptic sites in the cerebral cortex and hippocampus , 2007, Neuroscience.

[2]  S. Massey,et al.  Coupling between A-Type Horizontal Cells Is Mediated by Connexin 50 Gap Junctions in the Rabbit Retina , 2006, The Journal of Neuroscience.

[3]  N. Kamasawa,et al.  Abundance and ultrastructural diversity of neuronal gap junctions in the OFF and ON sublaminae of the inner plexiform layer of rat and mouse retina , 2006, Neuroscience.

[4]  Miles A Whittington,et al.  A beta2-frequency (20–30 Hz) oscillation in nonsynaptic networks of somatosensory cortex , 2006, Proceedings of the National Academy of Sciences.

[5]  N. Kamasawa,et al.  Association of connexin36 and zonula occludens-1 with zonula occludens-2 and the transcription factor zonula occludens-1-associated nucleic acid-binding protein at neuronal gap junctions in rodent retina , 2006, Neuroscience.

[6]  Roger J. Thompson,et al.  Ischemia Opens Neuronal Gap Junction Hemichannels , 2006, Science.

[7]  W. Singer,et al.  Gap Junctions among Dendrites of Cortical GABAergic Neurons Establish a Dense and Widespread Intercolumnar Network , 2006, The Journal of Neuroscience.

[8]  H. Monyer,et al.  Pannexin1 and Pannexin2 expression in the developing and mature rat brain. , 2005, Brain research. Molecular brain research.

[9]  D. Restrepo,et al.  Ultrastructural localization of connexins (Cx36, Cx43, Cx45), glutamate receptors and aquaporin-4 in rodent olfactory mucosa, olfactory nerve and olfactory bulb , 2005, Journal of neurocytology.

[10]  F. Dudek,et al.  Update on connexins and gap junctions in neurons and glia in the mammalian nervous system , 2004, Brain Research Reviews.

[11]  Uwe Heinemann,et al.  Stimulus and Potassium-Induced Epileptiform Activity in the Human Dentate Gyrus from Patients with and without Hippocampal Sclerosis , 2004, The Journal of Neuroscience.

[12]  B. Connors,et al.  Electrical synapses in the mammalian brain. , 2004, Annual review of neuroscience.

[13]  Timm Schubert,et al.  Functional expression of connexin57 in horizontal cells of the mouse retina , 2004, The European journal of neuroscience.

[14]  N. Kamasawa,et al.  Neuronal connexin36 association with zonula occludens‐1 protein (ZO‐1) in mouse brain and interaction with the first PDZ domain of ZO‐1 , 2004, The European journal of neuroscience.

[15]  F. Dudek,et al.  High-resolution proteomic mapping in the vertebrate central nervous system: Close proximity of connexin35 to NMDA glutamate receptor clusters and co-localization of connexin36 with immunoreactivity for zonula occludens protein-1 (ZO-1) , 2004, Journal of neurocytology.

[16]  Hannah Monyer,et al.  Pannexins, a family of gap junction proteins expressed in brain , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[17]  Fiona E. N. LeBeau,et al.  GABA-enhanced collective behavior in neuronal axons underlies persistent gamma-frequency oscillations , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[18]  N. Kamasawa,et al.  Connexin35 Mediates Electrical Transmission at Mixed Synapses on Mauthner Cells , 2003, The Journal of Neuroscience.

[19]  K. Willecke,et al.  Spatiotemporal transcription of connexin45 during brain development results in neuronal expression in adult mice , 2003, Neuroscience.

[20]  Kenneth D Harris,et al.  Selective Impairment of Hippocampal Gamma Oscillations in Connexin-36 Knock-Out Mouse In Vivo , 2003, The Journal of Neuroscience.

[21]  G. Buzsáki,et al.  Single granule cells reliably discharge targets in the hippocampal CA3 network in vivo , 2002, Nature Neuroscience.

[22]  Andreas Draguhn,et al.  Reduction of high‐frequency network oscillations (ripples) and pathological network discharges in hippocampal slices from connexin 36‐deficient mice , 2002, The Journal of physiology.

[23]  Miles A Whittington,et al.  Fast network oscillations in the rat dentate gyrus in vitro. , 2002, Journal of neurophysiology.

[24]  R. Traub,et al.  Axo-Axonal Coupling A Novel Mechanism for Ultrafast Neuronal Communication , 2001, Neuron.

[25]  Miles A. Whittington,et al.  Impaired Electrical Signaling Disrupts Gamma Frequency Oscillations in Connexin 36-Deficient Mice , 2001, Neuron.

[26]  F. Dudek,et al.  Cell-Specific Expression of Connexins and Evidence of Restricted Gap Junctional Coupling between Glial Cells and between Neurons , 2001, The Journal of Neuroscience.

[27]  W. Staines,et al.  Immunogold evidence that neuronal gap junctions in adult rat brain and spinal cord contain connexin-36 but not connexin-32 or connexin-43. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[28]  D. Henze,et al.  The multifarious hippocampal mossy fiber pathway: a review , 2000, Neuroscience.

[29]  N. Belluardo,et al.  Expression of Cx36 in mammalian neurons , 2000, Brain Research Reviews.

[30]  Roger D. Traub,et al.  A Model of High-Frequency Ripples in the Hippocampus Based on Synaptic Coupling Plus Axon–Axon Gap Junctions between Pyramidal Neurons , 2000, The Journal of Neuroscience.

[31]  R. Traub,et al.  High-frequency population oscillations are predicted to occur in hippocampal pyramidal neuronal networks interconnected by axoaxonal gap junctions , 1999, Neuroscience.

[32]  T. Yasumura,et al.  Direct immunogold labeling of connexins and aquaporin-4 in freeze-fracture replicas of liver, brain, and spinal cord: factors limiting quantitative analysis , 1999, Cell and Tissue Research.

[33]  R. Traub,et al.  Electrical coupling underlies high-frequency oscillations in the hippocampus in vitro , 1998, Nature.

[34]  F. Dudek,et al.  Grid‐mapped freeze‐fracture analysis of gap junctions in gray and white matter of adult rat central nervous system, with evidence for a “panglial syncytium” that is not coupled to neurons , 1997, The Journal of comparative neurology.

[35]  K. Fujimoto.  Freeze-fracture replica electron microscopy combined with SDS digestion for cytochemical labeling of integral membrane proteins. Application to the immunogold labeling of intercellular junctional complexes. , 1995, Journal of cell science.

[36]  T. Valiante,et al.  Coupling potentials in CA1 neurons during calcium-free-induced field burst activity , 1995, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[37]  B. McNaughton,et al.  Spatial selectivity of unit activity in the hippocampal granular layer , 1993, Hippocampus.

[38]  J. Rash,et al.  Postreplication labeling of E-leaflet molecules: membrane immunoglobulins localized in sectioned, labeled replicas examined by TEM and HVEM. , 1987, Journal of electron microscopy technique.

[39]  K. Akert.  Neuroanatomical tract-tracing methods Edited by L. Heimer and M.J. RoBards Plenum Press, New York and London, 1981. $49.50 (567 pp.) ISBN 0-306-405938 , 1982, Neuroscience Letters.

[40]  F. Dudek,et al.  Electrotonic coupling between granule cells of rat dentate gyrus: physiological and anatomical evidence. , 1982, Journal of neurophysiology.

[41]  L. Heimer,et al.  Neuroanatomical Tract-Tracing Methods , 1981, Springer US.

[42]  H. Jahnsen,et al.  Gap junctions on CA3 pyramidal cells of guinea pig hippocampus shown by freeze-fracture , 1981, Brain Research.

[43]  M. Dennis,et al.  Synaptic vesicle exocytosis captured by quick freezing and correlated with quantal transmitter release , 1979, The Journal of cell biology.

[44]  M. Santini.  Golgi Centennial Symposium: perspectives in neurobiology , 1978, Medical History.

[45]  H. Korn,et al.  Morphological correlates of electrical and other interactions through low-resistance pathways between neurons of the vertebrate central nervous system. , 1978, International review of cytology.

[46]  T. Reese,et al.  JUNCTIONS BETWEEN INTIMATELY APPOSED CELL MEMBRANES IN THE VERTEBRATE BRAIN , 1969, The Journal of cell biology.

[47]  E. Kandel,et al.  ELECTROPHYSIOLOGY OF HIPPOCAMPAL NEURONS: IV. FAST PREPOTENTIALS. , 1961, Journal of neurophysiology.