Figure 1.

Schematic overview of inhibitor screen. A collection of 700 small molecule compounds was screened for nematocyte discharge inhibition in Hydra by three consecutive stages. In the initial prey capture screen, a majority of compounds lacking any inhibitory effect at 10 µM were excluded. The remaining 59 compounds were screened for their activity range in the prey capture screen, leaving 15 positive candidates with half-maximal inhibition at 50 µM or lower. Compounds inducing high toxicity (11 compounds) or paralysis (8 compounds) during long-term exposition were excluded at this stage. Toxicity was evaluated using 5 categories: 0, no visible toxic effects; 1, slightly retracted tentacles; 2, pronounced tentacle retraction; 3, complete tentacle retraction and body contraction; 4, as in 3 and animals partly dissociated; 5, animals completely dissociated and/or dead. In the last stage, 3 compounds showing full discharge inhibition for a purely mechanical stimulus and half-maximal inhibition at 5 µM or lower were selected as the most potent candidate substances.