title: Axon diversity of lamina I local-circuit neurons in the lumbar spinal cord.
abstract: Spinal lamina I is a key area for relaying and integrating information from nociceptive primary afferents with various other sources of inputs. Although lamina I projection neurons have been intensively studied, much less attention has been given to local-circuit neurons (LCNs), which form the majority of the lamina I neuronal population. In this work the infrared light-emitting diode oblique illumination technique was used to visualize and label LCNs, allowing reconstruction and analysis of their dendritic and extensive axonal trees. We show that the majority of lamina I neurons with locally branching axons fall into the multipolar (with ventrally protruding dendrites) and flattened (dendrites limited to lamina I) somatodendritic categories. Analysis of their axons revealed that the initial myelinated part gives rise to several unmyelinated small-diameter branches that have a high number of densely packed, large varicosities and an extensive rostrocaudal (two or three segments), mediolateral, and dorsoventral (reaching laminae III-IV) distribution. The extent of the axon and the occasional presence of long, solitary branches suggest that LCNs may also form short and long propriospinal connections. We also found that the distribution of axon varicosities and terminal field locations show substantial heterogeneity and that a substantial portion of LCNs is inhibitory. Our observations indicate that LCNs of lamina I form intersegmental as well as interlaminar connections and may govern large numbers of neurons, providing anatomical substrate for rostrocaudal "processing units" in the dorsal horn.
authors: Spinal Neuronal Networks Group, Institute of Molecular and Cell Biology-IBMC, University of Porto, 4150-180 Porto, Portugal. szucs@ibmc.up.pt
authors: Peter
authors: P
authors: Szucs
authors: Liliana L
authors: LL
authors: Luz
authors: Raquel
authors: R
authors: Pinho
authors: Paulo
authors: P
authors: Aguiar
authors: Zsófia
authors: Z
authors: Antal
authors: Sheena Y X
authors: SY
authors: Tiong
authors: Andrew J
authors: AJ
authors: Todd
authors: Boris V
authors: BV
authors: Safronov
mesh_terms: D000200:Action Potentials; D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D008239:Lysine / Q000031:analogs & derivatives / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008959:Models, Neurological; D009415:Nerve Net / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000145:classification* / Q000502:physiology* / Q000648:ultrastructure; D018377:Neurotransmitter Agents / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology*; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000378:metabolism
chemical_list: D018377:Neurotransmitter Agents; C118623:Slc32a1 protein, rat; D050599:Vesicular Glutamate Transport Protein 2; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; C013411:biocytin; D008239:Lysine
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