Studies of presynaptic events in synaptic transmission may be facilitated through the use of specific ligands for functional components of the transmitter release mechanism and through the use of genetics. For this purpose, neurotoxins that affect neuromuscular transmission in Drosophila have been identified and purified from Plectreurys spider venom (PLTX). One class of toxins causes irreversible presynaptic block, probably by blocking calcium entry or by acting on other closely associated processes. These toxins have been highly purified and are peptides of about 7 kDa in molecular weight. They specifically block transmitter release at nanomolar concentrations and may be useful in further biochemical studies.

The cockroach Periplaneta americana responds to wind puffs by turning away, both on the ground and when flying. While on the ground, the ventral giant interneurons (ventrals) encode the wind direction and specify turn direction, whereas while flying the dorsal giant interneurons (dorsals) appear to do so. We report here on responses of these cells to controlled wind stimuli of different directions. Using improved methods of wind stimulation and of positioning the animal revealed important principles of organization not previously observed. All six cells of largest axonal diameter on each side respond preferentially to ipsilateral winds. One of these cells, previously thought to respond non-directionally (giant interneuron 2), was found to have a restricted directional response (Fig. 3). The organization of directional coding among the ventral giant interneurons is nearly identical to that among the dorsals (Fig. 2). Each group contains, on each side, one cell that responds primarily to wind from the ipsilateral front, another primarily in the ipsilateral rear, and a third responding more broadly to ipsilateral front and rear. These results are discussed in terms of the mechanisms of directional localization by the assembly of giant interneurons.

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