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Interneurons involved in abdominal posture in crayfish: Structure, function and command fiber responses

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  1. 1.

    An intracellular search was undertaken in an effort to locate and characterize the elements involved in command-driven positional behavior in the isolated abdominal nerve cord of the crayfish,Procambarus clarkii. Small bundles containing flexion or extension-evoking command fibers were isolated in the anterior connectives; these bundles are considered here to be equivalent to identified command fibers. A microelectrode filled with Lucifer Yellow CH was used to find elements within the fourth abdominal ganglion that showed synaptic responses to either flexion or extension command fibers; and these elements were further characterized by current and dye injections.

  2. 2.

    The interneurons thus encountered have been classified primarily by the form of motor output they evoked when strongly depolarized, and secondarily by their morphologies. We present data in this paper from 12 types of flexion-evoking cells, 4 types of extension-evoking cells and one inhibitory type that we term ‘flexion-antagonistic’.

  3. 3.

    With the exception of this latter group, many of the interneurons evoked a fully or nearly fully organized motor output. That is, flexion-evoking interneurons activated the flexor motoneurons and the peripheral inhibitor to the extensor muscles, and usually inhibited much of the activity in the extensor motoneurons. Conversely, the extension-evoking interneurons activated the extensor motoneurons and the peripheral inhibitor to the flexor muscles and usually inhibited the flexor motoneurons. The flexion-antagonists inhibited the flexor motoneurons and the peripheral inhibitor to the extensor muscles, but did not activate any motoneurons.

  4. 4.

    Because of the search strategy used, the majority of the cells that were studied showed synaptic connections to one or more of the three flexion and one extension command fiber bundle stimulated. Both apparently monosynaptic and polysynaptic connections were evident, but very few inhibitory connections were found. Thus, while flexion-evoking interneurons were in general depolarized by the flexion CFs, they were not hyperpolarized by the extension CF. Furthermore, we have demonstrated that several flexion-evoking interneurons share inputs from more than one flexion CF, whereas others have inputs from only one of three flexion CFs. Finally, at least two interneurons were found (type 5 and 6) that were apparently independent of the command neurons used in this study.

  5. 5.

    Six of the flexion-evoking types were seen to have their somata within ganglion 4 and all had axonal processes extending either anteriorly or posteriorly. The remaining 6 flexor interneurons were seen only as an axonal process running through ganglion 4. We cannot determine from the present data their origins or the extent of their axons in the nerve cord. In several preparations, both forms of flexion-evoking cells were seen to produce motor output in the ganglia adjacent to G4, suggesting that these cells may be either command neurons or driver interneurons. Different experimental approaches will be required to resolve this question.

  6. 6.

    While we cannot at this point propose the organization of CF-driven postural behavior, we have encountered several potentially important elements involved in the control of abdominal flexion. The motor output appears to be achieved by a combination of direct synaptic connections from the CF to the motoneurons and through connections with several other interneurons acting in parallel. A combination of these connections may provide for the strong reciprocity between flexor and extensor motoneurons, since individual driver cells are not always capable of this reciprocal output. Finally, redundancy of driver cells is indicated since we have not been able to identify any critical elements that, when functionally removed by hyperpolarization, eliminate a significant portion of the CF driven motor output.

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CF :

command fiber

CF stim :

electrical stimulation of a command fiber

G4 :

abdominal ganglion 4

LR2G4 :

left second (abdominal extensor) root of ganglion 4

RR3sG5 :

right third superficial (flexion) root of ganglion 5


slow (postural) flexor motoneuron


slow (postural) extensor motoneuron

uE :

microelectrode recording

uE depol :

Injection of depolarizing current through the recording microelectrode

uE hyper :

injection of hyperpolarizing current

Cf stim/uEhyper :

simultaneous command fiber stimulation and current injection


  1. Bentley D, Konishi M (1978) Neural control of behavior. Annu Rev Neurosci 1:35–39

  2. Davis WJ (1977) The command neuron. In: Hoyle G (ed) Identified neurons and behavior of arthropods. Plenum Press, New York London, pp 293–306

  3. Eckert RO (1961) Reflex relationships of the abdominal stretch receptors of the crayfish. II. Stretch receptor involvement during the swimming reflex. J Cell Comp Physiol 57:163–176

  4. Evoy WH, Kennedy D (1967) The central nervous organization underlying control of antagonistic muscles in the crayfish. I. Types of command fibers. J Exp Zool 165:223–238

  5. Goodman CS, Pearson KG, Heitler WJ (1979) Variability of identified neurons in grasshoppers. Comp Biochem Physiol [A] 64:455–462

  6. Harreveld A van (1936) A physiological solution for freshwater crustaceans. Proc Soc Exp Biol 34:428–432

  7. Kennedy D, Davis WJ (1977) Organization of invertebrate motor systems. In: Geiger SR, Kandel ER, Brookhart JM, Mountcastle VB (eds) Handbook of physiology, vol 1/2. Am Physiol Soc, Bethesda, Maryland, pp 1023–1087

  8. Kovac M (1974a) Abdominal movements during backward walking in crayfish. I. Properties of the motor program. J Comp Physiol 95:61–78

  9. Kovac M (1974b) Abdominal movements during backward walking in crayfish. II. The neuronal basis. J Comp Physiol 95:79–94

  10. Kupfermann I, Weiss KR (1978) The command neuron concept. Beh Brain Sci 1:3–39

  11. Larimer JL (1976) Command interneurons and locomotor behavior in crustaceans. In: Herman RM, Grillner S, Stein PSG, Stuart DG (eds) Neural control of locomotion. Plenum, New York, pp 293–326

  12. Larimer JL, Gordon WH (1977) Circumesophageal interneurons and behavior in crayfish. In: Hoyle G (ed) Identified neurons and behavior of arthropods. Plenum Press, New York London, pp 243–258

  13. Larimer JL, Kennedy D (1969) The central nervous control of complex movements in the uropods of crayfish. J Exp Biol 51:135–150

  14. Miall RC, Larimer JL (1982) Abdominal posture motoneurons in crayfish: Structure and synaptic connections with extension and flexion evoking interneurons. J Exp Zool (in press)

  15. Page CH, Sokolove PG (1972) Crayfish muscle receptor organ: Role in regulation of postural flexion. Science 175:647–650

  16. Stewart WW (1978) Functional connections between cells as revealed by dye-coupling with a highly fluorescent naphthalimide tracer. Cell 14:741–759

  17. Thompson CS, Page CH (1981) Interneuronal control of postural motoneurons in the lobster abdomen. J Neurobiol 12:87–91

  18. Wiersma CAG, Hughes GM (1961) On the functional anatomy of neuronal units in the abdominal cord of the crayfish,Procambarus clarkii (Girard). J Comp Neurol 116:209–228

  19. Wiersma CAG, Ikeda K (1964) Interneurons commanding swimmeret movements in the crayfish,Procambarus clarkii (Girard). Comp Biochem Physiol 12:509–525

  20. Williams BJ, Larimer JL (1981) Neural pathways of reflex-evoked behaviors and command systems in the abdomen of the crayfish. J Comp Physiol 143:27–42

  21. Wine JJ (1975) Crayfish neurons with electrogenic cell bodies: correlations with function and dendritic properties. Brain Res 85:92–98

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Christopher Miall, R., Larimer, J.L. Interneurons involved in abdominal posture in crayfish: Structure, function and command fiber responses. J. Comp. Physiol. 148, 159–173 (1982). https://doi.org/10.1007/BF00619123

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  • Nerve Cord
  • Extensor Muscle
  • Motor Output
  • Lucifer Yellow
  • Command Neuron