Distribution of and organisation of dorsal horn neuronal cell bodies that possess the muscarinic m2 XXXX receptor.

@entity1246 @entity1877 @entity842 @entity1943 @entity4757 @entity934
Cholinergic systems in the dorsal horn are involved in antinociception but little is known about the organisation of receptors that mediate this process. In this study we examined immunocytochemical properties of dorsal horn neuronal cell bodies that express the m2 muscarinic @entity934 receptor. Tissue was examined with confocal laser scanning microscopy and quantitative analysis performed. Immunoreactive cells were found throughout the dorsal horn and in lamina X. Quantitative analysis revealed that 22% of neuronal somata in the dorsal horn possess the receptor. The greatest concentration of cells was found in deeper laminae (IV-VI) and around lamina X. A proportion of cholinergic cells (labelled with an antibody against @entity1877 acetyltransferase) were immunoreactive for the receptor (approximately, 40% of dorsal horn cells and 44% of lamina X cells). Populations of presumed inhibitory interneurons also displayed immunoreactivity for the receptor. Between 27-34% of cells immunoreactive for @entity1246 , @entity842 synthase and the @entity1943 receptor(2A) expressed the receptor but only 8% of parvalbumin-immunoreactive cells displayed receptor immunoreactivity. Cells labelled with neurotensin, which belong to a subgroup of excitatory neurons, displayed no receptor immunoreactivity. A small number @entity4757 receptor-immunoreactive cells in lamina I possessed m2 immunoreactivity but 42% of laminae III/IV @entity4757 cells possessed it. This study shows that a significant proportion of cell bodies in the dorsal horn express the muscarinic m2 @entity934 receptor. The receptor is present on some cholinergic neurons and therefore may function as an autoreceptor. It is associated with inhibitory local circuit neurons and may have a role in the modulation of specific inhibitory systems. It is also found on a proportion of projection cells that possess the @entity4757 receptor. This could be the basis of some of the antinociceptive actions of @entity934 .
