Some effects of receptor muscle contraction on the responses of slowly adapting abdominal stretch receptors of the crayfish.

It has been known for many years that stimulation of the motor nerves to vertebrate muscle spindles leads to an increase in the frequency of discharge of the receptor afferent when the muscle is at a constant length (Matthews, 1933; Leksell, 1945; Kuffler, Hunt & Quilliam, 1951). Recently it has been found in muscle-spindle primary endings of cat and rabbit (Matthews, 1962; Emonet-Denand, Laporte & Pages, 1966) and in frog spindle afferents (Matthews & Westbury, 1965) that receptor muscle contraction may significantly change the dynamic response of the endings, i.e. their response to the rate of length change. For invertebrate stretch receptors Kuffler (1954) has demonstrated the effect of receptor muscle contraction on the responses of the fast-adapting and slowly adapting abdominal and thoracic stretch receptors of crayfish and lobsters when these are kept at a constant length. The present experiments on the slowly adapting stretch receptors of crayfish were carried out to see if receptor muscle contraction modified the responses of the receptor under dynamic as well as static conditions. A preliminary communication of some of the results has already been given (Brown, 1966).