Elsevier

Physiology & Behavior

Volume 67, Issue 5, November 1999, Pages 635-641
Physiology & Behavior

Articles
Postingestive Chemosensation and Feeding by Leeches

https://doi.org/10.1016/S0031-9384(99)00121-3Get rights and content

Abstract

Distinct chemical cues acting on chemosensory structures on the dorsal lip of bloodsucking leeches activate the entire complement of appetitive and ingestive feeding behaviors. However, it is not known whether the maintenance of ingestion depends on continuous stimulation of these peripheral chemosensors. Leeches of the species Hirudo medicinalis and Macrobdella decora were fed for 2 min on an artificial blood solution containing 150 mM NaCl/1 mM arginine before switching the feeding solution to various experimental mixtures. Leeches did not start to feed on, but continued to ingest solutions in which equiosmolar KCl or lysine substituted for NaCl or arginine, respectively, until sated. In contrast, they rejected water and dropped off the feeding apparatus within 30 s of the exchange. Leeches also detached from the feeding tube when quinine, denatonium, or caffeine were added to the NaCl/arginine solution during an ongoing feeding bout. The duration of ingestion following the switch correlated inversely with the concentration of the drugs (0.1–10 mM). Superfusion of the dorsal lip with high concentrations of the bitter chemicals, while feeding was in progress, had no effect on the duration of ingestion. However, injections of the bitter substances directly into the gut, during a feeding bout, abruptly stopped ingestion. The results suggest that while leeches continue to sample their food once ingestion has begun, secondary chemosensory mechanisms situated downstream from the dorsal lip may be involved in the maintenance of ingestion and the rapid postingestive rejection of noxious foods.

Section snippets

Materials and methods

Leeches 2–3 g (Hirudo medicinalis, Leeches USA (Westbury Long Island, NY) and Macrobdella decora, St. Croix Biological (Stillwater, MN) were kept in artificial pond water in an incubator maintained at 19°C and starved for 3–6 months. Experiments were conducted between August 1997–December 1998 at room temperature (22–25°C) on 100–120 leeches of each species. The experimenters handled all the supplies and animals used in this study with gloves to avoid contamination with chemical stimuli from

Exchange of Feeding Solutions Experiments

In the first series of experiments, we tested whether the leeches detected any change in the chemical composition of the fluid they were ingesting. To this end, we switched the feeding solution from the control 150 mM NaCl/1 mM arginine to distilled water and scored the duration of continued ingestion following the exchange. As shown in Fig. 2A, the animals dropped off the feeding apparatus within 30 s (28 ± 5 s, mean ± SEM, n = 5) after the water reached their mouth. Removing the arginine from

Discussion

The results of this study show that the bloodsucking leeches, Hirudo medicinalis and Macrobdella decora, respond to changes in the composition of a meal during ingestion indicating that continuous “tasting” occurs during the consummatory phase. However, although the animals can detect a change, they continue to ingest some of the modified solutions that they normally would reject during the appetitive phase. For instance, leeches will probe and attach to tubes filled with NaCl alone, but they

Acknowledgements

We are grateful to Mr. Baldwin Hurns and Mr. Oscar Rodriguez (Mount Vernon High School) for their participation in some of the early experiments, and to Liz Perruccio for helpful discussion of the results. We also thank Ms. Joanne Abrahams for help with the illustrations. This work was supported by NSF Grant # IBN 9723137 to A. L. K.

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