Cholinergic currents in leg motoneurons of Carausius morosus

J Neurophysiol. 2010 May;103(5):2770-82. doi: 10.1152/jn.00963.2009. Epub 2010 Mar 17.

Abstract

We used patch-clamp recordings and fast optical Ca(2+) imaging to characterize an acetylcholine-induced current (I(ACh)) in leg motoneurons of the stick insect Carausius morosus. Our long-term goal is to better understand the synaptic and integrative properties of the leg sensory-motor system, which has served extremely successfully as a model to study basic principles of walking and locomotion on the network level. The experiments were performed under biophysically controlled conditions on freshly dissociated leg motoneurons to avoid secondary effects from the network. To allow for unequivocal identification, the leg motoneurons were backfilled with a fluorescent label through the main leg nerve prior to cell dissociation. In 87% of the motoneurons, I(ACh) consisted of a fast-desensitizing (I(ACh1)) and a slow-desensitizing component (I(ACh2)), both of which were concentration dependent, with EC(50) values of 3.7 x 10(-5) and 2.0 x 10(-5) M, respectively. Ca(2+) imaging revealed that a considerable portion of I(ACh) ( approximately 18%) is carried by Ca(2+), suggesting that I(ACh), besides mediating fast synaptic transmission, could also induce Ca(2+)-dependent processes. Using specific nicotinic and muscarinic acetylcholine receptor ligands, we showed that I(ACh) was exclusively mediated by nicotinic acetylcholine receptors. Distinct concentration-response relations of I(ACh1) and I(ACh2) for these ligands indicated that they are mediated by different types of nicotinic acetylcholine receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / metabolism
  • Animals
  • Calcium / metabolism
  • Cells, Cultured
  • Cholinergic Agonists / pharmacology
  • Cholinergic Antagonists / pharmacology
  • Extremities / physiology
  • Fluorescent Dyes
  • Insect Proteins / agonists
  • Insect Proteins / antagonists & inhibitors
  • Insect Proteins / metabolism*
  • Insecta
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Microscopy, Confocal
  • Motor Neurons / cytology
  • Motor Neurons / drug effects
  • Motor Neurons / physiology*
  • Patch-Clamp Techniques
  • Receptors, Cholinergic / metabolism*
  • Receptors, Muscarinic / metabolism
  • Receptors, Nicotinic / metabolism

Substances

  • Cholinergic Agonists
  • Cholinergic Antagonists
  • Fluorescent Dyes
  • Insect Proteins
  • Receptors, Cholinergic
  • Receptors, Muscarinic
  • Receptors, Nicotinic
  • Acetylcholine
  • Calcium