Journal of comparative physiology

, Volume 94, Issue 2, pp 121–154 | Cite as

Neuronal control of swimming in the medicinal leech

II. Identification and connections of motor neurons
  • Carol A. Ort
  • William B. KristanJr.
  • Gunther S. Stent
Article

Summary

The cell bodies and function of twelve neurons whose impulse pattern is clearly related to that of the swimming rhythm were identified in the segmental ganglion of the leech. These include excitatory and inhibitory motor neurons of the dorsal and ventral longitudinal muscles and the excitatory flattener motor neuron of the dorsoventral muscles. During swimming the membrane potential of these cells oscillates between a depolarized and a hyperpolarized phase. The activity of this ensemble of cells is sufficient to account for the contractile rhythm of the swimming animal. The following connections were found between these motor neurons. Electrotonic junctions link: (1) bilaterally homologous cells; (2) excitors of the dorsal longitudinal muscles; (3) excitors of the ventral longitudinal muscles; (4) inhibitors of both dorsal and ventral longitudinal muscles. The dorsal inhibitors project via an inhibitory pathway to the dorsal excitors, and the ventral inhibitor projects via an inhibitory pathway to the ventral excitors. The membrane potential oscillation of the excitors is at least partly attributable to the phasic inhibitory synaptic input which they receive from the inhibitors. The excitatory shortener motor neuron of the entire longitudinal musculature is maintained in an inactive state during swimming. This control is achieved by rectifying electrotonic junctions linking this neuron to the dorsal and ventral excitors. These junctions allow passage of only depolarizing current from the shortener to the dorsal and ventral excitors and of only hyperpolarizing current in the reverse direction. Furthermore, both dorsal and ventral inhibitors project via inhibitory pathways to the shortener neuron.

Keywords

Motor Neuron Inhibitory Pathway Medicinal Leech Segmental Ganglion Inhibitory Motor Neuron 

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References

  1. Bristol, C. L.: The metamerism ofNephelis. J. Morph.15, 17–72 (1898)Google Scholar
  2. Coggeshall, R. E., Fawcett, D.W.: The fine structure of the central nervous system of the leech,Hirudo medicinalis. J. Neurophysiol.27, 229–289 (1964)Google Scholar
  3. Eckert, R.: Electrical interaction of paired ganglion cells in the leech. J. gen. Physiol.46, 573–587 (1963)Google Scholar
  4. Evoy, W.H., Kennedy, D., Wilson, D.M.: Discharge patterns of neurons supplying tonic abdominal flexor muscles in the crayfish. J. exp. Biol.46, 393–411 (1967)Google Scholar
  5. Fomina, M. S., Tereshkov, O. D.: Electrical transmission between symmetrical neurons in leech ganglia. Neuroscience and Behavioral Physiol.5, 91–96 (1972)Google Scholar
  6. Gaskell, J.F.: The chromaffine system of annelids and the relation of this system to the contractile vascular system in the leech,Hirudo medinalis. Proc. roy Soc. B.205, 153–211 (1914)Google Scholar
  7. Hagiwara, S., Morita, H.: Electrotonic transmission between two nerve cells in leech ganglion. J. Neurophysiol.25, 721–731 (1962)Google Scholar
  8. Harmon, I. D.: Properties and functions of artifical neurons. Kybernetik1, 89–101 (1961)Google Scholar
  9. Kristan, W.B., Jr., Stent, G. S., Ort, C.A.: Neuronal control of swimming in the medicinal leech. I. Dynamics of the swimming rhythm. J. comp. Physiol.94, 97–119 (1974)Google Scholar
  10. Kristan, W.B., Jr., Stent, G. S., Ort, C.A.: Neuronal control of swimming in the medicinal leech. III. Impulse patterns of the motor neurons. J. comp. Physiol.94, 155–175 (1974)Google Scholar
  11. Lent, C.: Physiological characterization of motoneurons involved in swimming behavior of leeches. Amer. Zoologist, in press (1974)Google Scholar
  12. Nicholls, J.G., Baylor, D.A.: Specific modalities and receptive fields of sensory neurons in CNS of the leech. J. Neurophysiol.31, 740–756 (1968)Google Scholar
  13. Nicholls, J.G., Purves, D.: Monosynaptic chemical and electrical connections between sensory and motor cells in the central nervous system of the leech. J. Physiol. (Lond.)209, 647–667 (1970)Google Scholar
  14. Stuart, A.E.: Physiological and morphological properties of motoneurons in the central nervous system of the leech. J. Physiol. (Lond.)209, 627–647 (1970)Google Scholar
  15. Tulsi, R.S., Coggeshall, R.E.: Neuromuscular junctions on the muscle cells in the central nervous system of the leech,Hirudo medicinalis. J. comp. Neurol.14, 1–15 (1971)Google Scholar
  16. Wilson, D.M.: Central nervous mechanisms for the generation of behavior in arthropods. In: Nervous and hormonal mechanisms of integration. Symp. Soc. exp. Biol., vol. XX. p. 199–228. New York: Academic Press 1966Google Scholar

Copyright information

© Springer-Verlag 1974

Authors and Affiliations

  • Carol A. Ort
    • 1
  • William B. KristanJr.
    • 1
  • Gunther S. Stent
    • 1
  1. 1.Department of Molecular BiologyUniversity of CaliforniaBerkeleyUSA

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