Tactile sensory function in the forearm of the monotreme Tachyglossus aculeatus

David A. Mahns, Gordon T. Coleman, Ken W. Ashwell, Mark Rowe

    Research output: Contribution to journalArticle

    8 Citations (Scopus)

    Abstract

    Peripheral tactile neural mechanisms in the forepaw of the echidna (Tachyglossus aculeatus, from the order Monotremata) were investigated to establish the extent of correspondence or divergence that has emerged over the widely different evolutionary paths taken by monotreme and placental mammals. Electrophysiological recordings were made in anesthetized echidnas from 29 single tactile sensory nerve fibers isolated in fine strands of the median or ulnar nerves of the forearm. Controlled tactile stimuli were applied to the forepaw glabrous skin to classify fibers, initially, into two broad divisions, according to their responses to static skin displacement. One displayed slowly adapting (SA) response properties, and the other showed a selective sensitivity to the dynamic components of the skin displacement. The SA class was made up of low-threshold SA fibers and other less sensitive SA fibers, and the purely dynamically sensitive tactile fibers could be subdivided according to vibrotactile sensitivity and receptive field characteristics into a rapidly adapting (RA) class, sensitive to low-frequency (50-Hz) vibration, that resembled a corresponding RA class in placental species, and another class, sensitive to a broader range of vibrotactile frequencies (50-300 Hz), that may represent a monotreme equivalent of the Pacinian corpuscle (PC)-related fiber class of placental mammals. The differential tactile sensitivity of the three principal fiber classes and their individual coding characteristics, determined by quantitative stimulus-response analysis, indicate, first, that this triad of fiber classes can subserve high-acuity tactile signalling from the echidna footpad and, second, that peripheral tactile sensory mechanisms are highly conserved across evolutionarily divergent mammalian orders.
    Original languageEnglish
    Number of pages13
    JournalJournal of comparative neurology
    DOIs
    Publication statusPublished - 2003

    Keywords

    • evolution and sensory nerve function
    • mechanosensitive fibers
    • sensory nerves
    • tactile nerve fibers

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