Fig. 1. Exposure to the active factor present in the hemolymph of early-molt stage larvae triggers a dramatic decline in anterior foregut contraction amplitude. (A) In saline, anterior foreguts isolated from nonmolting 5th instar larvae respond to a 10 ms stimulation of the severed recurrent nerve with a large amplitude contraction. Within a few minutes of exposure to the hemolymph fraction from early-molt stage larvae, however, the amplitude of the elicited contractions was markedly decreased. The response rebounded following a saline wash. The anterior foregut contractions were recorded using a movement transducer attached to the anterior esophageal constrictor muscles. (B) Summary of the results (N=6; P<0.001, paired t-test). In saline rinse we found that the average contraction amplitude recovered and surpassed the initial control levels (P<0.05, paired t-test). *Significant difference from saline value.