Facilitation of cholinergic transmission by huperzine A in toad paravertebral ganglia in vitro

Using the intracellular recording techniques of toad paravertebral ganglia (PVG), the effects of cholinesterase inhibitor huperzine A (Hup-A), an alkaloid first isolated from Huperzia serrata (Thunb) Trev in China, on the synaptic transmission were studied. In 30 PVG cells tested, no remarkable changes in membrane potential and input resistance were observed during superfusion of Hup-A 0.3 or 1 mumol.L-1 for 15 min. The rate of orthodromic action potential evoked by preganglionic stimulation was increased by Hup-A 0.3 or 1 mumol.L-1 (n = 12, P < 0.05), and much faster, stronger, and longer in action at 50 or 100 mumol.L-1 (n = 11). The amplitude and duration of exogenous acetylcholine-, but not carbachol-, induced depolarization were increased (P < 0.05). It is concluded that Hup-A is a selective and potent cholinesterase inhibitor, by which action it facilitates the cholinergic transmission of PVG neurons