Differential expression of the muscarinic m2 acetylcholine receptor by small and large motoneurons of the rat spinal cord

The purpose of this study was to determine if motoneurons in the spinal ven tral horn express the muscarinic m2 acetylcholine receptor. Motoneurons wer e retro,retrogradely labelled in adult rats by intramuscular injection of F luorogold and examined with confocal microscopy for evidence of immunoreact ivity for the receptor. The cells were also double-labelled for choline ace tyltransferase to determine if they were contacted by cholinergic axons. Al most all large motoneurons (diameters greater than 35 mu m) displayed inten se immunoreactivity for the receptor which was evenly distributed along the plasma membrane. Small cells were immunonegative for the receptor or weakl y labelled. As large cells probably correspond to alpha-motoneurons and rec eive many cholinergic, contacts, it is concluded that acetylcholine can inf luence this type of motoneuron by acting through the m2 receptor. (C) 1999 Elsevier Science B.V.