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Neuronal control of heartbeat in the medicinal leech

I. Generation of the vascular constriction rhythm by heart motor neurons

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Summary

The leech heartbeat consists of a constriction-dilation rhythm of two lateral heart tubes extending over the length of the body. The beats of the segmental sections of these two tubes are coordinated in such a manner that the heart tube of one body side produces a frontward peristaltic wave while the heart tube on the other body side produces nearly concerted constrictions. This rhythm is metastable, in that left and right heart tubes alternate between peristaltic and concerted constriction modes, with a given mode lasting for tens or hundreds of beat cycles.

The constriction-dilation cycles of the segmental heart tube sections are controlled by a set of rhythmically active motor neurons, the heart excitors, or HE cells. A bilateral pair of HE cells is located in all but the two frontmost and the two rearmost segmental ganglia of the ventral nerve cord. Each HE cell innervates via excitatory synapses the circular muscle fibers in the wall of the ipsilateral heart tube section. The activity cycle of the HE cells consists of an active phase, during which they are depolarized and produce a burst of impulses, and an inactive phase during which they are repolarized by a burst of inhibitory synaptic potentials. The intersegmentally coordinated activity cycles of the HE cell set are maintained in an isolated ventral nerve cord. Hence the generation of the heart excitor rhythm does not require sensory feedback.

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Author notes

  1. Wesley J. Thompson

    Present address: Institute of Physiology, University of Oslo, Karl Johans Gate 47, Oslo, Norway

Authors and Affiliations

  1. Department of Molecular Biology, University of California, 94720, Berkeley, California, USA

    Wesley J. Thompson & Gunther S. Stent

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  1. Wesley J. Thompson
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  2. Gunther S. Stent
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Additional information

We are indepted to Amy Kelly and King-Wai Yau for advice on the use of the intracellular staining technique and to John Kretz for calling to our attention the existence of an afferent impulse burst rhythm emanating from denervated heart tube preparations. We thank Georgia Harper for excellent technical assistance. This research was supported by Grant GB 31933X from the National Science Foundation and NIH research grants GM17866 and Training Grant GM 01389 from the Institute of General Medical Sciences.

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Thompson, W.J., Stent, G.S. Neuronal control of heartbeat in the medicinal leech. J. Comp. Physiol. 111, 261–279 (1976). https://doi.org/10.1007/BF00606468

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