Involvement of alpha 7 nicotinic acetylcholine receptors in activation of tyrosine hydroxylase and dopamine beta-hydroxylase gene expression in PC12 cells

Nicotine treatment increases intracellular free Ca2+ concentration [Ca2+](i ), stimulates catecholamine release, and elevates gene expression for the c atecholamine biosynthetic enzymes tyrosine hydroxylase (TH) and dopamine be ta-hydroxylase (DBH). However, the type of nicotinic acetylcholine receptor s (nAChRs) mediating these events is unclear. The nAChR receptor antagonist s alpha-bungarotoxin (alpha BTX) and methyllycaconitine greatly reduced the nicotine-triggered initial transient rise in [Ca2+](i) and prevented the s econd prolonged elevation of [Ca2+](i), suggesting the involvement of alpha 7 nAChRs. Two specific alpha 7 nicotinic agonists, 3-(2,4-dimethoxybenzili dene)anabaseine (DMXB) and E,E-3-(cinnamylidene)anabaseine (3-CA), were fou nd to elicit a small, delayed increase in [Ca2+](i) with kinetics and magni tude similar to the second elevation observed with nicotine. This increase was inhibited by the inositol trisphosphate receptor antagonist xestospongi n C. Exposure to 3-CA or DMXB for 6 or 24 h elevated TH and DBH mRNA levels two- to fourfold over control levels. These agonists were more effective t han nicotine alone in increasing TH and DBH gene expression and significant ly elevated [Ca2+](i) for up to 6 h. The increase in [Ca2+](i) or the eleva tion in TH mRNA by 3-CA was completely inhibited by alpha BTX. This study, for the first time, implicates stimulation of alpha 7 nAChRs in the activat ion of TH and DBH gene expression.