Paeoniflorin, a Major Constituent of Peony Root, Reverses Muscarinic M1-Receptor Antagonist-Induced Suppression of Long-Term Potentiation in the Rat Hippocampal Slice.

We previously reported that paeoniflorin but not albiflorin, components of peony root, produced ameliorative effects on scopolamine-induced spatial cognitive impairment in rats. In this study, we examined the effects of paeoniflorin and muscarinic receptor antagonists on long-term potentiation (LTP) of population spike recorded from the CA1 region of rat hippocampal slices. Bath applications of an M1- and M2-receptor antagonist scopolamine and a selective M1-receptor antagonist pirenzepine, at a concentration of 10 microM, significantly suppressed LTP, whereas AF-DX116, a selective M2-receptor antagonist, failed to affect it. Paeoniflorin (0.1-1 microM), which alone was ineffective on LTP induction, significantly reversed the suppressive effects of scopolamine and pirenzepine (10 microM). In contrast, albiflorin (0.1- 1 microM) had no effect on the scopolamine-induced LTP suppression. These results suggest that paeoniflorin reversal of the muscarinic M1-receptor-mediated inhibition of LTP may be implicated in the ameliorative effect of paeoniflorin on spatial cognitive impairment caused by cholinergic dysfunction.