Expression of cholinergic muscarinic receptor subtypes mRNA in rat blood mononuclear cells

The cholinergic system plays a role in the neuroimmune network. White blood cells have been found to express muscarinic and nicotinic cholinergic receptors as well as acetylcholinesterase on their surface, and cholinergic agents have been shown to modulate immune functions. Although the presence of muscarinic receptors on white blood cells has been well documented by binding and functional studies, the subtype(s) of muscarinic receptor present on these cells is still unknown. We have previously shown the absence of m2 muscarinic receptor subtype mRNA in rat mononuclear cells (Costa et al., 1994). The expression of m1, m3, m4 and m5 mAChR mRNA was analyzed in this study in rat peripheral blood mononuclear cells by Northern blotting hybridization experiments and reverse transcription-polymerase chain reaction. Only mRNA of the m3 subtype was detected in rat mononuclear cells, at levels about 100 times lower than in brain. Traces of m4 subtype mRNA were found in lymphocytes, at levels about 10,000 times lower than the cerebral cortex, while m5 mRNA was undetectable.