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First published online January 19, 2006
Journal of Experimental Biology 209, 493-503 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02030

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Functions of the subesophageal ganglion in the medicinal leech revealed by ablation of neuromeres in embryos

Andrea Cornford¹, William B. Kristan, III^1,2, Sierra Malnove¹, William B. Kristan, Jr¹ and Kathleen A. French^1,*

¹ Division of Biological Sciences, Neurobiology Section, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357, USA
² Department of Biological Sciences, California State University, San Marcos, San Marcos, CA 92096, USA

View larger version (111K): [in a new window]   Fig. 1. Structure of subesophageal ganglion (SubEG) from embryonic and juvenile leeches. (A) SubEG and first midbody ganglion from a juvenile leech. Surrounding tissue was removed to reveal the structure, and connections with the supraesophageal ganglion were severed. (B) SubEG in embryo at 47% of embryonic development (% ED; Reynolds et al., 1998b), which is about the stage at which we performed surgeries. The ganglionic precursors to each of the neuromeres are still separate at this stage. (C) The head of an embryo at 50% ED (ventral view) following ablation of presumptive neuromeres 1 and 2. (D) SubEG of juvenile leech in which neuromeres 1 and 2 were ablated at 50% ED.

View larger version (26K): [in a new window]   Fig. 2. Effects of surgery on spontaneous behaviour. (A) All spontaneous behaviours observed, divided into experimental groups. See Materials and methods for a description of the surgical treatments and Table 1 for descriptions of the behaviours. The control group (N=40) included both intact leeches and sham-operated controls; we found no differences between the two groups. Nerve cut, N=9. Ablated some or all of the SubEG, N=33. In Figs 2, 3, 4, 5, 6, * indicates locomotory behaviours, which are discussed in Fig. 7. (B) Distribution of behaviours along the CCA1 behaviour score axis. The behaviours that lie furthest to the left or right along this axis most strongly distinguished among treatment groups. Behaviours located in the centre of the axis were seen in all groups. (C) Distributions of individual CCA1 scores in the three experimental groups. Individual scores within each group were binned and arrayed along the CCA1 axis. Crawling and probing distinctively characterized the control group, whereas swimming and incomplete crawling (ic) characterized leeches with ablations.

View larger version (29K): [in a new window]   Fig. 3. Behaviours elicited in control animals by touching three locations on the body. (A) Distribution of behaviours elicited by touching the anterior, the midbody or the posterior of the leech (N=22). The most common response varied with touch location: shortening at the anterior, local bending in the midbody, and crawling at the posterior. (B) Distribution of behaviours along the CCA1 behaviour score axis. (C) Distribution of individual CCA1 scores. The distribution of behavioural responses elicited by touch at the anterior are farthest from the distribution of behaviours elicited by touch at the posterior; the distribution of responses to midbody stimulation lies between the other two. See Table 1 for a description of the behaviours.

View larger version (26K): [in a new window]   Fig. 4. Effects of surgery on behaviours elicited by touching the anterior of the body. (A) Behaviours elicited in the three experimental groups by anterior stimulation. Shortening was the most common response in all three groups. Control, N=22; nerve cuts, N=9; neuromeres ablated, N=10. (B) CCA1 behaviour scores. (C) Individual CCA1 scores of leeches in each experimental group. The distribution of scores for `control' leeches and the distribution for `ablated' leeches are farthest apart, and the distribution of scores for `cut' leeches lies between the two. See Table 1 for a description of the behaviours.

View larger version (26K): [in a new window]   Fig. 5. Effects of surgery on behaviours elicited by touching the midbody. (A) Behaviours elicited in the three experimental groups by midbody stimulation. Local bending was the most common response in all three groups. Control, N=22; nerve cuts, N=9; neuromeres ablated, N=10. (B) CCA1 behaviour scores. (C) Individual CCA1 scores of leeches in each experimental group. The distributions of scores for `control' leeches and for `ablated' leeches are farthest apart; the distribution of scores for `cut' leeches lies between the other two. See Table 1 for a description of the behaviours.

View larger version (26K): [in a new window]   Fig. 6. Effects of surgery on behaviours elicited by touching the posterior. (A) Behaviours elicited in the three experimental groups by posterior stimulation. Locomotory behaviours (indicated by *) were the most common behaviours elicited by posterior touch. Control, N=22; nerve cuts, N=9; neuromeres ablated, N=10. (B) CCA1 behaviour scores. (C) Individual CCA1 scores of leeches in each experimental group. The distribution of scores for `control' leeches and `ablated' leeches are farthest apart, and the distribution of scores for `cut' leeches lies between the other two. See Table 1 for a description of the behaviours.

View larger version (37K): [in a new window]   Fig. 7. Effect of surgical treatments on locomotory behaviours. (A) Percentage of the three locomotory behaviours produced spontaneously by leeches in the five experimental groups. Control, N=46; cut, N=9; missing 1, 2, N=10; missing 1, 2, 3, N=10; missing, 1, 2, 3, 4, N=9. (B) Locomotion elicited by moderate touch to the posterior dorsal body. Control, N=46; cut, N=9; missing, 1, 2, N=10; missing, 1, 2, 3, N=11; missing, 1, 2, 3, 4, N=10. Locomotion was much less common in animals with ablations than in controls or animals with nerve cuts (Fig. 6A). Locomotion included only swimming, crawling and incomplete crawling, so the sum of the bars for each experimental condition is 100% and the percentages for the three modes of locomotion are not independent. Within each set of bars (that is, for each behaviour within each panel), conditions that are not significantly different from one another are labelled by the same letter, A, B, C, etc., and bars that are labelled by different letters are significantly different from one another (differences among surgical treatment groups were tested with a Kruskal-Wallis test, and post-hoc comparisons among groups were done using a Tukey's HSD procedure on the ranked data). Bars that are labelled with two or more letters are not significantly different from bars labelled with any of the letters. This analysis includes a total of six extra controls, and eight leeches with ablations were used in only this analysis.