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Updated: Jul 31, 2026
Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis
Published on: November 5, 2013
Heartbeat control in leeches. I. Constriction pattern and neural modulation of blood pressure in intact animals
Angela Wenning1, Gennady S Cymbalyuk, Ronald L Calabrese
1Department of Biology, Emory University, Atlanta, Georgia 30322, USA. awenning@biology.emory.edu
Insights
Medicinal leeches have two hearts with distinct coordination modes: peristaltic and synchronous. These modes dictate blood flow patterns and are driven by a central motor program, not solely by modulatory neurons.
Area of Science:
- Cardiovascular Physiology
- Neurobiology
- Invertebrate Zoology
Background:
- Medicinal leeches possess a closed circulatory system powered by two myogenic hearts.
- A central motor pattern governs leech heart rate and intersegmental coordination.
- Understanding the translation of motor patterns into heart contractions is crucial.
Purpose of the Study:
- To investigate how the central motor pattern dictates the diastolic and systolic activity of leech hearts.
- To characterize the distinct constriction patterns of the two hearts and their coordination modes.
- To elucidate the role of heart motor neurons and constriction patterns in driving blood circulation.
Main Methods:
- Imaging heart constriction patterns in quiescent, intact medicinal leeches.
- Simultaneous monitoring of heart motor neuron discharge and heart segment constriction in reduced preparations.
- Electrophysiological recordings, including current injections into heart modulatory neurons and intravascular pressure monitoring.
Main Results:
- Leech hearts exhibit two primary coordination modes: peristaltic (rear-to-front systole) and synchronous (near-simultaneous systole), with regular switches between them.
- Intersegmental phase relations remain constant regardless of heartbeat period.
- While modulatory neurons alter pressure, the distinct systolic pressure profiles of the two modes are determined by the constriction pattern itself.
Conclusions:
- The central motor pattern generates distinct heart constriction patterns (peristaltic and synchronous modes) that govern blood flow.
- The peristaltic heart primarily drives forward and backward blood flow along the body axis.
- The synchronous heart may play a role in segmental circulation, with its pressure profiles dictated by constriction mechanics rather than direct neural input from modulatory neurons.
Abstract:
Two tubular hearts propel blood through the closed circulatory system of the medicinal leech. The hearts are myogenic but are driven by a centrally generated motor pattern that controls heart rate and intersegmental coordination. In two consecutive papers, we address the question of how the motor pattern is translated into the pattern of diastole and systole of leech hearts. We imaged the constriction patterns of the hearts in quiescent intact animals. In one heart, systole progresses rear-to-front (peristaltic coordination mode), whereas systole occurs nearly simultaneously in the other heart (synchronous coordination mode) with regular switches between these two coordination modes. Intersegmental phase relations between heart segments do not vary with changes in the heartbeat period. The peristaltic heart drives blood forward through itself and then rearward through the other longitudinal vessels. The synchronous heart does not seem to contribute to rearward flow along the body axis and may support segmental circulation instead. Simultaneous monitoring of heart motor neuron discharge and the constriction of the corresponding heart segment in innervated, reduced preparations enabled us later to meld the constriction pattern with the fictive motor pattern described in the following paper. Current injections into one heart modulatory neuron while monitoring intravascular pressure from the corresponding heart showed that these neurons can acutely change diastolic and systolic pressure. However, they do not determine the different systolic pressure profiles associated with the two coordination modes, which appear to result from the constriction pattern.
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