Excitation and changes in adaptation by stretch of mechanoreceptors

The observation that stretch applied to the skin has a facilitatory action on the 'spontaneous' activity of tactile receptors induced by impulses arriving via sympathetic nerve fibres to the skin or by sympathomimetic substances (Loewenstein, 1956), gave the stimulus for exploring the action of stretch alone on the touch receptor. It appeared also probable that the adequate mechanical stimulus for a tactile receptor excited the ending by stretching it; this being the case, only minute stretching of the ending occurs under physiological conditions of tactile stimulation. It seemed of interest to examine the touch receptor's behaviour over a wider range of skin stretch in the hope of throwing some light on the nature of mechanoreceptive adaptation. A preparation such as the frog's skin, providing a physical system in which two differently adapting mechanoreceptors lying side by side may be simultaneously activated, seemed well suited for this purpose. The frog's skin presents a fastadapting mechanoreceptor, namely the well-known touch receptor, and a slowly adapting ending (Fessard & Segers, 1943a, b; Maruhashi, Mizuguchi & Tasaki, 1952); the latter will be shown in the present work to have the attributes of a stretch receptor. It was found that adaptation of the touch receptor is inifluenced in a marked degree by stretch, so that the ordinarily fast-adapting touch receptor when fully stretched presents a non-adapting stationary discharge like a stretch receptor. The results seem to indicate the existence of a mechanical basis for adaptation.