Summary
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1.
We have investigated functional roles of serotonin (5-hydroxytryptamine, 5-HT) in the feeding behavior of the medicinal leech,Hirudo medicinalis. Bathing intact leeches in serotonin (3×10−5 mol/l, 20 min) significantly alters three components of their feeding behavior. Leeches exposed to serotonin initiate swimming toward a vibrating point with a shorter latency, bite a warm surface more frequently, and ingest more blood than control animals.
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2.
Thermal stimulation of the prostomium evokes pharyngeal peristalsis, jaw movements and an obvious salivation by semidissected preparations. The application of serotonin (10−8 to 10−6 mol/l) directly activates and increases the rates of pharyngeal peristalsis and salivary secretion in these preparations. Serotonin also produces jaw movements and a constriction of the crop when centrally applied.
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3.
Vibrational stimuli, which evoke the swimming phase of feeding behavior, synaptically excite Retzius cells within segmental ganglia. Thermal stimuli, which evoke the biting phase, synaptically excite 5-HT-containing neurons within the subesophageal ganglia. Intracellular stimulation of identified 5-HT-containing neurons produces pharyngeal peristalsis reliably and enhances salivation.
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4.
Pharmacological lesions of particular 5-HT neurons abolishes feeding behavior. However, a brief exposure to exogenous 5-HT restores biting behavior. Well-fed leeches do not normally bite, but a brief bath in 5-HT will evoke biting behavior by them as well.
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5.
Serotonin is localized to a limited population of identifiable neurons in the C.N.S., and plays a pivotal and mandatory role in organizing the feeding behavior of the medicinal leech.
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Abbreviations
- E :
-
extra interneuron
- g :
-
ganglion
- 5-HT :
-
5-hydroxytryptamine
- LL :
-
large lateral cell
- SubEG :
-
subesophageal ganglion
- RZ :
-
Retzius cell
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Lent, C.M., Dickinson, M.H. Serotonin integrates the feeding behavior of the medicinal leech. J. Comp. Physiol. 154, 457–471 (1984). https://doi.org/10.1007/BF00610161
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DOI: https://doi.org/10.1007/BF00610161