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 ventral horn express the muscarinic m2 acetylcholine receptor. Motoneurons were retrogradely labelled in adult rats by intramuscular injection of Fluorogold and examined with confocal microscopy for evidence of immunoreactivity for the receptor. The cells were also double-labelled for choline acetyltransferase to determine if they were contacted by cholinergic axons. Almost all large motoneurons (diameters greater than 35 microm) displayed intense immunoreactivity for the receptor which was evenly distributed along the plasma membrane. Small cells were immunonegative for the receptor or weakly labelled. As large cells probably correspond to alpha-motoneurons and receive many cholinergic contacts, it is concluded that acetylcholine can influence this type of motoneuron by acting through the m2 receptor. Copyright 1999 Elsevier Science B.V.