Ultrastructural synaptic features differ between alpha- and gamma-motoneurons innervating the tibialis anterior muscle in the rat

Ronaldo M. Ichiyama, Jonas Broman, V. Reggie Edgerton, Leif A. Havton

Research output: Contribution to journalArticlepeer-review

24 Citations (SciVal)

Abstract

We investigated the synaptology of retrogradely labeled spinal motoneurons after injection of horseradish peroxidase into the tibialis anterior (TA) muscle of adult rat. In total, 32 TA motoneurons were investigated in the electron microscope and demonstrated a bimodal size distribution with cell diameter peaks at 40 mu m and 20 mu m, likely representing alpha- and gamma-motoneurons, respectively. Both alpha- and gamma-motoneurons were apposed by S- and F-type synaptic boutons, whereas only alpha-motoneurons demonstrated inputs by the large M- and C-type boutons. The proportion of cell body membrane covered by synaptic inputs was surprisingly indistinguishable between alpha-motoneurons (72.2%) and gamma-motoneurons (63.5%). The ratio between the number of F- and S-type boutons in apposition with the motoneuron cell body (F/S ratio) and the ratio between the soma membrane coverage provided by F- and S-type boutons were both significantly higher in alpha- than in gamma-motoneurons. When comparing our data with previous findings in other species, we conclude that rat TA alpha-motoneurons are similar to cat and primate alpha-motoneurons with regard to synaptic terminal morphology, frequency, and distribution. However, rat gamma-motoneurons show a markedly higher total synaptic coverage and frequency than cat gamma-motoneurons, although both species exhibit appositions made by the same synaptic types and similar ratios between inhibitory and excitatory inputs.
Original languageEnglish
Pages (from-to)306-315
JournalJournal of Comparative Neurology
Volume499
Issue number2
DOIs
Publication statusPublished - 2006

Subject classification (UKÄ)

  • Neurology

Keywords

  • spinal cord
  • horseradish peroxidase
  • electron microscopy
  • labeling
  • retrograde

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