Dihydroavermectin B1: actions on cultured neurones from the insect central nervous system.

The physiological effects of dihydroavermectin B1 on insect central neurones have been investigated using a culture system derived from the brains of embryonic cockroaches. In these neuronal cultures 60% of the cells respond to the application of gamma-aminobutyric acid (GABA) with a conductance increase; these responses are blocked by picrotoxin but not by bicuculline. Dihydroavermectin B1, a representative of a potentially new class of insecticide, also produces a slow conductance increase which is blocked by picrotoxin and inverted by the injection of chloride ions. Qualitatively similar responses are also evoked by dihydroavermectin B1 in some neurones unaffected by GABA and in neurones exposed to elevated Mg2+ concentrations to inhibit synaptic release mechanisms. In a subpopulation of neurones dihydroavermectin B1 evokes a transient, initial excitation prior to the apparent chloride conductance increase.