title: Large cholinergic nerve terminals on subsets of motoneurons and their relation to muscarinic receptor type 2.
abstract: The cholinergic C-bouton is a large nerve terminal found exclusively apposing motoneuron cell somata and proximal dendrites. The origin and function of the C-bouton is not known. An antiserum against the vesicular acetylcholine transporter was used to identify large cholinergic nerve terminals putatively of the C-type in close apposition to motoneuron cell somata. This type of nerve terminal was present in the rat spinal cord ventral horn, but only in some cranial motor nuclei. Fluoro-Gold tracing showed that subsets of spinal motoneuron cell somata were contacted by different numbers of putative C-boutons. Thus, motoneurons innervating an intrinsic foot muscle were contacted by about half the number of cholinergic terminals found on motoneurons of the predominantly fast-twitch gastrocnemius muscle. Slow-twitch soleus motoneurons showed an intermediate innervation. There was a strong correlation between the presence of putative C-boutons and muscarinic receptor 2 (m2)-like immunoreactivity (-LI) within a motor nucleus. By using confocal laser microscopy, the m2-LI appeared to be confined to the motoneuron cell membrane and strongly enriched beneath the C-type nerve terminal. Thus, our results suggested a differential distribution of large cholinergic C-boutons, depending on motoneuron type, and that the presence of this nerve terminal type is associated with m2-LI in the postsynaptic membrane.
authors.affiliation: Department of Neuroscience, The Retzius Laboratory, Karolinska Institutet, SE-171 77 Stockholm, Sweden. johan.hellstrom@neuro.ki.se
authors.forename: Johan
authors.initials: J
authors.lastname: Hellström
authors.forename: Alexandre L R
authors.initials: AL
authors.lastname: Oliveira
authors.forename: Björn
authors.initials: B
authors.lastname: Meister
authors.forename: Staffan
authors.initials: S
authors.lastname: Cullheim
mesh_terms: D000344:Afferent Pathways / Q000737:chemistry; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis*; D002799:Cholinergic Fibers / Q000737:chemistry*; D005260:Female; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D026901:Membrane Transport Proteins; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000737:chemistry*; D018482:Muscle, Skeletal / Q000294:innervation; D017729:Presynaptic Terminals / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000032:analysis*; D013116:Spinal Cord / Q000737:chemistry*; D013266:Stilbamidines; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D026901:Membrane Transport Proteins; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; C493461:Slc18a3 protein, rat; D013266:Stilbamidines; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins