Disinhibition caused by the molluscicide N-trityl morpholine (Frescon) in the nervous system of a freshwater snail

Abstract

When applied to the isolated nervous system of Lymnaea stagnalis, Frescon (Shell Chemicals) produces spontaneous, summated “bursts” of synaptic potentials, affecting nearly all the cells in synchrony. Experiments with chloride-free salines containing acetate, propionate, sulfate, nitrate, or bromide ions showed that reversal of chloride inhibitory postsynaptic potentials can produce “bursts” of the same form as those induced by Frescon. The Frescon “bursts” are preceded by a progressive change in the reversal potential of spontaneous inhibitory postsynaptic potentials, presumably also resulting from a reduction in the chloride gradient across the cell membrane. It is thus proposed that Frescon acts to alter neuronal intracellular chloride levels, giving rise to a state of “disinhibition” in which the fine balance between excitatory and inhibitory processes is upset.