Characterization of muscles associated with the articular membrane in the dorsal surface of the crayfish abdomen

The anatomy, physiology, and biochemistry of the dorsal membrane muscle (DM A) and the superficial extensor muscle accessory head (SEAcc) in the abdome n of the crayfish, Procambarus clarkii and lobster, Homarus americanus, are reported. These muscles have not been previously characterized physiologic ally or biochemically. The anatomy was originally described by Pilgrim and Wiersma (1963. J Morph 113:453-587). The arrangement of these muscles varie s depending on the abdominal segment. The function of the dorsal membrane m uscle is to retract the thin articulating membrane joining the cuticular se gments so that the dorsal membrane does not evert during extension of the a bdomen. Consequently, the articular membrane does not protrude, and thus po tential damage to the membrane is minimized. Examination of nerve terminal morphology revealed strings of varicosities, usually only associated with t onic terminals. The electrophysiological data indicate that there are at le ast four tonic excitatory and one inhibitory motor neuron innervating these muscles. Facilitation indices and fatigue-resistance indicate physiologica lly the tonic nature of innervation. Anti-GABA antibodies demonstrate the a natomical presence of an inhibitor motor neuron. The SDS electrophoretic an alysis of myofibrillar proteins and Western blots of key protein isoforms f or these muscles in crayfish and lobsters also indicate that the DMA and SE Acc muscles are tonic phenotype. J. Exp. Zool. 287:353-377, 2000. (C) 2000 Wiley-Liss, Inc.