Figure 4. | Recognition of familiar food activates feeding via an endocrine serotonin signal in Caenorhabditis elegans

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Recognition of familiar food activates feeding via an endocrine serotonin signal in Caenorhabditis elegans

Figure 4.

Figure 4.
Download figureOpen in new tabDownload powerpointFigure 4. Recognition of familiar food increases feeding response by activating serotonin signaling via SER-7. SER-4 and MOD-1 are putative inhibitory receptors.

(A)–(B) Familiarity of food does not alter the feeding rates in tph-1(mg280). (C)–(D) Exogenous serotonin treatment selectively increases feeding rates of wild type worms on novel food to the level of the worms on familiar food. The average values of the feeding rates presented in (C) are 197.7 ± 4.6, 174.3 ± 5.8, 191.2 ± 4.9 and 190.7 ± 3.4 in order. The average values of the feeding rates presented in (D) are 189.0 ± 7.9, 158.4 ± 9.2, 184.2 ± 3.3 and 181.2 ± 4.6 in order. (E)–(F) ser-7(tm1325) is defective in increasing feeding response to familiar food compared to novel food. Familiarity of food does not alter the feeding rates in ser-4(ok512); mod-1(ok103); ser-7(tm1325). The average values of the feeding rates presented in (E) are 189.7 ± 2.6, 225.5 ± 3.6, 238.3 ± 2.1 and 231.3 ± 3.4 in order. The average values of the feeding rates presented in (F) are 178.8 ± 5.5, 188.4 ± 4.2, 196.3 ± 3.2 and 191.9 ± 3.1 in order. (G) Serotonin controls feeding positively via SER-7 and negatively via SER-4 and MOD-1. The feeding rate of the ser-4; mod-1; ser-7 triple null mutant is not altered by serotonin treatment. These assays were conducted on 3- to 5-hr-old L1 larvae, which pumped much more slowly than the adults used in other measurements. The average values of the feeding rates presented in (G) are 29.1 ± 4.0, 73.6 ± 3.3, 29.8 ± 4.2, 12.2 ± 1.8, 42.7 ± 11.3, 26.3 ± 4.3, 45.9 ± 8.0 and 86.8 ± 11.5 in order. (H) Serotonin signaling via SER-7 that activates the feeding response is more active on familiar food than novel food. The y axis indicates the difference in the feeding rates between wild-type and ser-7(tm1325) animals. Each value corresponds to the difference in the feeding rates between wild-type and the ser-7 null mutant presented in Figure 7A and B. Data shown as mean ± SEM, n.s., not significant (p≥0.05), *p<0.05, **p<0.01, ***p<0.001; for Figure 4A and B, unpaired t-test and Mann–Whitney U test (two-tailed), for Figure 4C–G, one-way ANOVA, post hoc Tukey test and for Figure 4H, Student's t test (two-tailed; see ‘Detailed data analysis’ in ‘Materials and methods’). The number of animals tested (n ≥ 3 independent assays per each group) is shown in parentheses or at the bottom of each bar.

DOI: http://dx.doi.org/10.7554/eLife.00329.006