Sensorimotor function is modulated by the serotonin receptor 1d, a novel marker for gamma motor neurons

Anders Enjin, Katarina E. Leão, Sanja Mikulovic, Pierre Le Merre, Warren G. Tourtellotte, Klas Kullander*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

Gamma motor neurons (MNs), the efferent component of the fusimotor system, regulate muscle spindle sensitivity. Muscle spindle sensory feedback is required for proprioception that includes sensing the relative position of neighboring body parts and appropriately adjust the employed strength in a movement. The lack of a single and specific genetic marker has long hampered functional and developmental studies of gamma MNs. Here we show that the serotonin receptor 1d (5-ht1d) is specifically expressed by gamma MNs and proprioceptive sensory neurons. Using mice expressing GFP driven by the 5-ht1d promotor, we performed whole-cell patch-clamp recordings of 5-ht1d::GFP + and 5-ht1d::GFP - motor neurons from young mice. Hierarchal clustering analysis revealed that gamma MNs have distinct electrophysiological properties intermediate to fast-like and slow-like alpha MNs. Moreover, mice lacking 5-ht1d displayed lower monosynaptic reflex amplitudes suggesting a reduced response to sensory stimulation in motor neurons. Interestingly, adult 5-ht1d knockout mice also displayed improved coordination skills on a beam-walking task, implying that reduced activation of MNs by Ia afferents during provoked movement tasks could reduce undesired exaggerated muscle output. In summary, we show that 5-ht1d is a novel marker for gamma MNs and that the 5-ht1d receptor is important for the ability of proprioceptive circuits to receive and relay accurate sensory information in developing and mature spinal cord motor circuits.

Original languageEnglish (US)
Pages (from-to)322-332
Number of pages11
JournalMolecular and Cellular Neuroscience
Volume49
Issue number3
DOIs
StatePublished - Mar 2012

Keywords

  • 5-ht1d
  • Fusimotor system
  • Gamma motor neurons
  • Motor behavior
  • Muscle spindle
  • Proprioception
  • Serotonin
  • Spinal cord

ASJC Scopus subject areas

  • Molecular Biology
  • Cellular and Molecular Neuroscience
  • Cell Biology

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