Effects Of Metaldehyde And Acetaldehyde On Specific Membrane Currents In Neurons Of The Pond Snail Lymnaea-Stagnalis

Bath application of metaldehyde or acetaldehyde led to tonic depolarization and bursting activity in identified neurones in the isolated central nervous system of Lymnaea stagnalis. This activity was sometimes accompanied by paroxysmal depolarizing shifts in membrane potential. Those neurones which possessed type 2 action potentials showed marked spike broadening in response to metaldehyde, but little increase in action potential duration in the presence of acetaldehyde. Under voltage clamp, metaldehyde caused a reduction in the delayed rectifier and A-currents, both of which are outward potassium currents. Acetaldehyde also reduced the delayed rectifier but had no effect on the A-current. In type 2 neurones, voltage-dependent calcium current appeared to increase in the presence of metaldehyde, but was decreased by acetaldehyde. The action of metaldehyde and acetaldehyde on firing activity, as well as their differential effects on action potential duration, may be partly explained by alterations in these specific membrane currents.