Fig. 6.

Proctolin increases the amplitude of evoked contractions to a greater extent in muscle fibers 4, 12, and 13 than muscle fibers 6 and 7. A: data from Fig. 5B are used to demonstrate how proctolin-induced increases in contraction amplitude were expressed as a function of maximal contraction. Within each trial, contraction amplitudes (expressed as % of initial contraction) were averaged during the 8- to 10-min time period for both proctolin and “no-proctolin” application trials. The averaged amplitude for the trials with no proctolin was subtracted from amplitude obtained in each of the proctolin application trials to estimate the increase in nerve-evoked contraction attributed to proctolin (a). The maximal contraction value for that preparation (b) was estimated by subtracting the averaged contraction at 15 min in control trials from the contraction elicited by a single burst of impulses at 50 Hz in the presence of the peptide. The ratio a/b was then multiplied by 100 to estimate the relative effectiveness of proctolin in each trial. This procedure estimates the modulatory effect on only the muscle fibres present and allowed a comparison between preparations with different levels of ablation by compensating for differences in total muscle mass. B: effects of cell ablation on modulation by 10⁻⁸ M proctolin were assessed by estimating the relative effectiveness as described in A. Error bars, SD. (Kruskal-Wallis, H = 123.455, P < 0.001; Dunn's post hoc, *P < 0.05).