Expression and Agonist‐Induced Down‐Regulation of mRNAs of m2‐ and m3‐Muscarinic Acetylcholine Receptors in Cultured Cerebellar Granule Cells

The regulation and expression of muscarinic acetylcholine receptor (mAChR) mRNA was studied in cultured cerebellar granule cells using Northern blot hybridization, mRNA species for m2- and m3-mAChRs but not m1- and m4-mAChRs were detected in these cells. The expression of mRNAs of both m2- and m3-mAChRs reached a maximum on the tenth day in culture but their expression patterns differed. Treatment of cerebellar granule cells after 8 days in culture with 100 microM carbachol led to differential down-regulation of the mRNA species of both mAChR subtypes present. Muscarinic receptor antagonists, atropine (1 microM) and pirenzepine (10 microM), prevented carbachol-induced m3-mAChR mRNA down-regulation observed at 8 h. However, exposure to either atropine or pirenzepine alone for 8 h led to a significant up-regulation of m3-mAChR mRNA. Thus, the mRNA species for both m2- and m3-mAChR subtypes are differentially expressed in culture and down-regulated by agonist stimulation. The loss of these mRNA species may play a role in the down-regulation of mAChR binding sites that occurs after desensitization.