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Rate modification in the heartbeat central pattern generator of the medicinal leech

Summary

  1. 1.

    Intracellular recordings from neurons in partially dissected leeches and isolated nerve cords were used to study the effects of temperature, sensory stimulation and locomotory activity on the output of the central pattern generator that drives heartbeat.

  2. 2.

    The rate of motor burst production by the heartbeat oscillator changes on gradual heating or cooling with a Q10 averaging around 2.4. Abrupt cooling of isolated nerve cords can induce additional changes in heart rate that are associated with ‘paradoxical’ firing of motor neurons.

  3. 3.

    Heart rate was accelerated when mechanical stimuli were applied to the body wall of partially dissected preparations or when restrained preparations spontaneously initiated movements. For instance, marked acceleration of heart rate occurred when preparations exhibited body movements and motor neuron activity characteristic of swimming in intact animals. Activation of the motor program for swimming in isolated nerve cords led to acceleration of heartbeat oscillator cycling. Accelerations of heart rate associated with swimming are therefore mediated at least partially through central interactions.

  4. 4.

    Individual identified neurons were tested for their influence on the cycle rate of the heartbeat oscillator in isolated nerve cords. Activity of individual mechanosensory neurons was found to accelerate heart rate. Touch mechanosensory neurons were also found to influence the heartbeat oscillator through a rapidly adapting inhibitory pathway. Activity of individual motorneurons generally did not affect heart rate. Some interneurons and neuroeffector cells known to cause motor activation (e.g. swim initiating interneurons, serotonergic Retzius cells) can also produce acceleration of heart rate.

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Arbas, E.A., Calabrese, R.L. Rate modification in the heartbeat central pattern generator of the medicinal leech. J. Comp. Physiol. 155, 783–794 (1984). https://doi.org/10.1007/BF00611595

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Keywords

  • Heart Rate
  • Motor Neuron
  • Central Pattern Generator
  • Motor Program
  • Cycle Rate