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Roles for inhibition: studies on networks controlling swimming in young frog tadpoles

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Abstract

The hatchling frog tadpole provides a simple preparation where the fundamental roles for inhibition in the central nervous networks controlling behaviour can be examined. Antibody staining reveals the distribution of at least ten different populations of glycinergic and GABAergic neurons in the CNS. Single neuron recording and marker injections have been used to study the roles and anatomy of three types of inhibitory neuron in the swimming behaviour of the tadpole. Spinal commissural interneurons control alternation of the two sides by producing glycinergic reciprocal inhibition. By interacting with the special membrane properties of excitatory interneurons they also contribute to rhythm generation through post-inhibitory rebound. Spinal ascending interneurons produce recurrent glycinergic inhibition of sensory pathways that gates reflex responses during swimming. In addition their inhibition also limits firing in CPG neurons during swimming. Midhindbrain reticulospinal neurons are excited by pressure to the head and produce powerful GABAergic inhibition that stops swimming when the tadpole swims into solid objects. They may also produce tonic inhibition while the tadpole is at rest that reduces spontaneous swimming and responsiveness of the tadpole, keeping it still so it is not noticed by predators.

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Abbreviations

aIN:

Ascending interneuron

cIN:

Commissural interneuron

CPG:

Central pattern generator

dIN:

Descending interneuron

dla:

Dorsolateral ascending interneuron

dlc:

Dorsolateral commissural interneuron

K–A:

Kolmer–Agduhr cell

mhr:

Midhindbrain reticulospinal interneuron

mn:

Motoneuron

PIR:

Post-inhibitory rebound

RB:

Rohon–Beard neuron

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Acknowledgments

We would like to thank firstly our colleagues past and present for making the work reported here possible and providing a stimulating and friendly environment and secondly, the Wellcome Trust and MRC for many years of financial support.

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Authors and Affiliations

  1. School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK

    Alan Roberts, Wen-Chang Li & S. R. Soffe

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  1. Alan Roberts
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  2. Wen-Chang Li
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  3. S. R. Soffe
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Correspondence to Alan Roberts.

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Roberts, A., Li, WC. & Soffe, S.R. Roles for inhibition: studies on networks controlling swimming in young frog tadpoles. J Comp Physiol A 194, 185–193 (2008). https://doi.org/10.1007/s00359-007-0273-3

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  • DOI: https://doi.org/10.1007/s00359-007-0273-3

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