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Journal of Experimental Biology 163,187-208 (1992)
Published by Company of Biologists 1992

PROPRIOCEPTIVE INPUT FROM TWO BASAL JOINT STRETCH RECEPTORS TO LEG MOTONEURONES IN THE ISOLATED THORACIC GANGLION OF THE SHORE CRAB

STEWART I. HEAD ¹ and BRIAN M.H. BUSH ²

¹ Department of Physiology, University of Bristol Bristol BS1 5LS; Present address: Department of Zoology, La Trobe University, Bundoora, Melbourne, Victoria, Australia 3083
² Department of Physiology, University of Bristol Bristol BS1 5LS

The reflex effects and interactions of two proprioceptors upon motoneurones supplying the four basal leg muscles of the shore crab Carcinus maenas have been studied in a new in vitro preparation consisting of the thoracic-coxal muscle receptor organ (TCMRO) and the coxo-basal chordotonal organ (CBCO) isolated together with the whole thoracic ganglion complex to which they were still connected by their afferent nerves. Each receptor strand was stimulated mechanically, while recording intracellularly from motoneurones in the ganglion, and extracellularly from the cut motor nerves innervating the promotor and remotor muscles of the thoracic-coxal (T–C) joint and the levator and depressor muscles of the coxo-basal (C–B) joint.

Stretch of the TCMRO evoked reflex firing in several units in the promotor motor nerve, confirming previous studies. In addition to this ‘intrajoint’ reflex, however, TCMRO stretch also elicited ‘interjoint’ reflex responses in motoneurones of both the levator and depressor muscles. Similarly, stretch and release of the CBCO produced intrajoint resistance reflexes in levator and depressor motoneurones, respectively, as well as interjoint reflexes in promotor and remotor motoneurones. In general, the CBCO produced stronger reflex effects in all four motor nerves than did the TCMRO.

Intracellular recordings from individual motoneurones of all four muscles revealed that the majority of them received convergent input from both proprioceptors. The importance of such convergent input in vivo is discussed

Key words: proprioceptors, motoneurones, reflexes, crab legs, Carcinus maenas

Accepted on October 3, 1991