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The function and role of two types of mechanoreceptive ‘free’ nerve endings in the head skin of amphibian embryos

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Summary

The properties of trigeminal ganglion sensory neurones innervating the head skin of lateXenopus laevis embryos have been studied using extracellular recordings. Two types of mechanosensory neurones were found:Rapid-transient detectors which responded with few impulses to rapid, local, indentation of the skin with a fine probe (10–25 μm diameter), andMovement detectors which responded with a slowly adapting discharge to even very slow distortion of the skin (5 μm· s−1) with small or large probes. Receptive fields over the whole head surface as far back as the gill rudiments were plotted for both types of neurone. The areas for the two types were similar (means of 0.015 mm2 for rapid-transient and 0.017 mm2 for movement).

Comparative observations on embryos ofRana temporaria andTriturus helveticus showed a very similar division of trigeminal sensory neurones into two types. InXenopus embryos stimuli which only excite the movement detectors were found to have inhibitory effects on behaviour. They would stop swimming and responses to other excitatory stimuli. Stimuli which excited the rapid-transient detectors normally evoked swimming. The division of the somatosensory system inXenopus embryos into two subsystems with different sensitivities and inhibitory, or excitatory effects on behaviour is discussed and related to findings in other groups of animals.

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  1. Department of Zoology, University of Bristol, BS8 1UG, Bristol, Great Britain

    Alan Roberts

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  1. Alan Roberts
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I thank the MRC for support.

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Roberts, A. The function and role of two types of mechanoreceptive ‘free’ nerve endings in the head skin of amphibian embryos. J. Comp. Physiol. 135, 341–348 (1980). https://doi.org/10.1007/BF00657650

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