Effects of the venom of Philanthus triangulum F. (Hym. sphecidae) and β‐ and δ‐philanthotoxin on axonal excitability and synaptic transmission in the cockroach CNS

Abstract

AbstractThis paper provides answers to the questions which of the toxins present in the venom of the wasp Philanthus triangulum may be responsible for the previously reported blockage of transmission through the sixth abdominal ganglion of the cockroach, and whether this may occur by block of synaptic transmission or by affecting axonal exitability. In current clamp experiments the crude venom induces a slight depolarization of the membrane of the giant axon from the sixth abdominal ganglion of the cockroach and a small and irreversible decrease in the amplitude of the action potential. These marginal effects are not seen with relatively high concentrations of the philanthotoxins β‐PTX and δ‐PTX. It appears that neither the crude venom nor the toxins significantly affect the excitability of the cockroach giant axon. At a concentration of 20 μg ml−1 δ‐PTX causes a slowly reversible block of synaptic transmission from the cercal nerve XI to a giant interneuron without any change in resting membrane potential, whereas β‐PTX is inactive. Iontophoretically evoked acetylcholine potentials of the giant neuron are more sensitive to δ‐PTX than excitatory postsynaptic potentials. This suggests that the toxin acts on the postsynaptic membrane.