PROCTOLIN AND EXCITATION OF THE CRAYFISH SWIMMERET SYSTEM

The ventral nerve cord of crayfish contains axons of five pairs of exc itatory interneurons, each of which can activate the swimmeret system. Perfusion of the ventral nerve cord with the neuropeptide proctolin a lso activates the swimmeret system. The experiments reported here were conducted to test the hypothesis that one or more of these excitatory interneurons uses proctolin as a transmitter. Each of the five excita tory axons was located and stimulated separately in an individual cray fish, and similar motor activity was elicited by stimulating each of t hem. Quantitative comparison of spontaneous swimmeret motor patterns w ith activity caused by stimulating one of these excitatory axons, E(C) , or by perfusing with proctolin solutions showed that the motor patte rns produced under these three conditions were not significantly diffe rent (P > 0.05). By using a new, affinity-purified proctolin antiserum , we labeled axons in the connective tissue between the last thoracic and first abdominal ganglion and compared the positions of labeled axo ns with the previously described positions of the excitatory axons. Ab out 0.3% of the axons in these connective tissues showed proctolin-lik e immunoreactivity, but heavily labeled pairs of axons did occur bilat erally in the regions of excitatory swimmeret axons. The projections o f these labeled axons into the abdominal ganglia were traced in serial plastic sections. Labeled processes were abundant in the lateral neur opils, the loci of the swimmeret pattern-generating circuitry. From th is evidence, we propose that three of these excitatory swimmeret inter neurons use proctolin as a transmitter, but that a fourth does not. Th e evidence for the fifth axon is ambiguous. (C) 1994 Wiley-Liss, Inc.