Serotonin depletion inhibits feeding in carnivorous leeches (Haemopis)

The effect of reserpine on the serotonin content of the central nervous system and the feeding behavior of the carnivorous leech Haemopis marmorata was investigated. Leeches were hand-fed to satiation by presentation of pieces of chicken liver held in forceps for three meals at 4-day intervals prior to and 1 week following three consecutive injections of 100 μg reserpine in the crop. A group matched by weight and preinjection food intake was injected with the vehicle in a blind experimental design. Histochemical and chemical determinations showed that reserpine effectively depleted the serotonin content of the animal's central nervous system. Furthermore, the food intake of reserpine-treated animals was significantly less than that of the sham-injected group. However, the depleted animals continued to ingest approximately 40% of the amount consumed during the preinjection period. These results show that reserpine successfully depleted the serotonin in the carnivorous leech H. marmorata and decreased the food intake of this leech species. They suggest that feeding behavior in Haemopis is partially but not exclusively dependent on serotonin and that, in contrast to the sanguivorous leeches, additional factors may be necessary for its regulation.