Expression of muscarinic m2 receptor mRNA in dorsal root ganglia of neonatal rat

The expression of mRNA coding for m2 subtype of muscarinic cholinergic rece ptors was assessed in dorsal root ganglia (DRG) of 15-day post-natal rats. Northern blot analysis on total RNA using a mixture of two different oligon ucleotide probes, indicated the presence of a single prominent band of appr oximately 6.5 kb in rat DRG; a band of the same size was observed both in b rainstem and cortex taken as positive controls. Analysis by RT-PCR of the m RNA coding for a region of the third cytoplasmic loop of m2 receptor showed a single signal both in rat DRG and hippocampus. In situ hybridization was then used to identify the neuronal subpopulations expressing the mRNA for M-2. The transcripts were preferentially localized in medium-small neurons of the ganglion as well as in satellite cells surrounding the neuron cell b ody. Large neurons were usually negative. Finally, competition binding expe riments, performed in the presence of [H-3]-quinuclidinyl benzilate (QNB) a nd methoctramine (a selective competitor for M-2 receptors), demonstrated t he presence of M-2 receptor protein (K-i = 100 nM), as previously observed in chick DRG. The preferential localization of M-2 in medium-small neurons of the ganglion suggests the involvement of this receptor subtype in the tr ansduction of nociceptive stimuli. (C) 1999 Published by Elsevier Science B .V. All rights reserved.