Muscarinic M2-receptors in rat thoracic dorsal root ganglia

The occurrence and distribution of the muscarinic M2-receptor subtype (M2R) was investigated in rat thoracic dorsal root ganglia (DRG). Messenger RNA for M2R was demonstrated by RT-PCR in total RNA from DRG. Immunoreactivity to MPR-protein was localized to 26% of sensory neurons, the majority of the m (85%) belonging to the size class of 25-40 mu m in diameter. Double-label ing (immuno)histochemistry revealed that all M2R-immunoreactive neurons bin d the lectin, I-B4, whereas they are generally devoid of substance P-immuno reactivity. These data show the presence of M2R on a subpopulation of presu mably nociceptive primary afferent neurons, thereby extending previous phar macological and electrophysiological studies that indicated a role of M2R a nd/or M4R in inhibition of calcium channel currents in rat sensory neurons (Wanke, E., Bianchi, L., Mantegazza, M., Guatteo, E., Macinelli, E. and Fer roni, A., Muscarinic regulation of Ca2+ currents in rat sensory neurons: ch annel and receptor types, dose-response relationships and cross-talk pathwa ys, (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.