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Heartbeat control in the medicinal leech: a model system for understanding the origin, coordination, and modulation
R L Calabrese1, F Nadim, O H Olsen
1Department of Biology, Emory University, Atlanta, Georgia 30322, USA.
Insights
Researchers detailed the leech heartbeat neuronal network, revealing how interneuron oscillators and coordinating cells create rhythmic bursts. This study enhances understanding of neural control in motor pattern generation.
Area of Science:
- Neuroscience
- Computational Biology
- Systems Biology
Background:
- The leech heartbeat is generated by a complex neuronal network.
- Understanding neural circuit function is crucial for deciphering motor pattern generation.
Purpose of the Study:
- To analyze the leech heartbeat neuronal network in detail.
- To develop a computational model of the heartbeat oscillator network.
- To investigate the role of neuropeptides and ionic currents in rhythm generation.
Main Methods:
- Detailed analysis of neuronal network architecture.
- Identification of key interneuron types (oscillator, coordinating, switch).
- Development of a conductance-based computer model.
- Exploration of ionic currents and synaptic transmission.
Main Results:
- Identified an eight-cell timing oscillator network for heartbeat.
- Demonstrated reciprocal inhibition between oscillator interneurons.
- Showcased modulation of oscillator periods by RFamide neuropeptides.
- Validated a computational model with predictive power.
Conclusions:
- The leech heartbeat network comprises interconnected oscillator and coordinating interneurons.
- Reciprocally inhibitory networks are key to rhythmic motor pattern generation.
- Computational models are valuable for understanding neural dynamics and guiding future research.
Abstract:
We have analyzed in detail the neuronal network that generates heartbeat in the leech. Reciprocally inhibitory pairs of heart interneurons form oscillators that pace the heartbeat rhythm. Other heart interneurons coordinate these oscillators. These coordinating interneurons, along with the oscillators interneurons, form an eight-cell timing oscillator network for heartbeat. Still other interneurons, along with the oscillator interneurons, inhibit heart motor neurons, sculpting their activity into rhythmic bursts. Critical switch interneurons interface between the oscillator interneurons and the other premotor interneurons to produce two alternating coordination states of the motor neurons. The periods of the oscillator interneurons are modulated by endogenous RFamide neuropeptides. We have explored the ionic currents and graded and spike-mediated synaptic transmission that promote oscillation in the oscillator interneurons and have incorporated these data into a conductance-based computer model. This model has been of considerable predictive value and has led to new insights into how reciprocally inhibitory neurons produce oscillation. We are now in a strong position to expand this model upward, to encompass the entire heartbeat network, horizontally, to elucidate the mechanisms of FMRFamide modulation, and downward, to incorporate cellular morphology. By studying the mechanisms of motor pattern formation in the leech, using modeling studies in conjunction with parallel physiological experiments, we can contribute to a deeper understanding of how rhythmic motor acts are generated, coordinated, modulated, and reconfigured at the level of networks, cells, ionic currents, and synapses.