title: P boutons in lamina IX of the rodent spinal cord express high levels of glutamic acid decarboxylase-65 and originate from cells in deep medial dorsal horn.
abstract: Presynaptic inhibition of primary muscle spindle (group Ia) afferent terminals in motor nuclei of the spinal cord plays an important role in regulating motor output and is produced by a population of GABAergic axon terminals known as P boutons. Despite extensive investigation, the cells that mediate this control have not yet been identified. In this work, we use immunocytochemistry with confocal microscopy and EM to demonstrate that P boutons can be distinguished from other GABAergic terminals in the ventral horn of rat and mouse spinal cord by their high level of the glutamic acid decarboxylase (GAD) 65 isoform of GAD. By carrying out retrograde labeling from lamina IX in mice that express green fluorescent protein under the control of the GAD65 promoter, we provide evidence that the cells of origin of the P boutons are located in the medial part of laminae V and VI. Our results suggest that P boutons represent the major output of these cells within the ventral horn and are consistent with the view that presynaptic inhibition of proprioceptive afferents is mediated by specific populations of interneurons. They also provide a means of identifying P boutons that will be important in studies of the organization of presynaptic control of Ia afferents.
authors.affiliation: Spinal Cord Group, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
authors.forename: D I
authors.initials: DI
authors.lastname: Hughes
authors.forename: M
authors.initials: M
authors.lastname: Mackie
authors.forename: G G
authors.initials: GG
authors.lastname: Nagy
authors.forename: J S
authors.initials: JS
authors.lastname: Riddell
authors.forename: D J
authors.initials: DJ
authors.lastname: Maxwell
authors.forename: G
authors.initials: G
authors.lastname: Szabó
authors.forename: F
authors.initials: F
authors.lastname: Erdélyi
authors.forename: G
authors.initials: G
authors.lastname: Veress
authors.forename: P
authors.initials: P
authors.lastname: Szucs
authors.forename: M
authors.initials: M
authors.lastname: Antal
authors.forename: A J
authors.initials: AJ
authors.lastname: Todd
mesh_terms: D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D017930:Genes, Reporter; D005968:Glutamate Decarboxylase / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D051379:Mice; D020671:Posterior Horn Cells / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000201:enzymology* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D049452:Green Fluorescent Proteins; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2