TY - JOUR T1 - Neuropeptide degradation produces functional inactivation in the crustacean nervous system JF - The Journal of Neuroscience JO - J. Neurosci. SP - 6205 LP - 6216 DO - 10.1523/JNEUROSCI.14-10-06205.1994 VL - 14 IS - 10 AU - MJ Coleman AU - PH Konstant AU - BS Rothman AU - MP Nusbaum Y1 - 1994/10/01 UR - http://www.jneurosci.org/content/14/10/6205.abstract N2 - The pentapeptide proctolin (Proct.; Arg-Tyr-Leu-Pro-Thr) is a modulatory transmitter found throughout the crustacean nervous system. No information is available in this system, however, as to how the actions of this peptide are terminated. To study this issue in the crab Cancer borealis, we incubated exogenous proctolin (10(-5) M) with either the thoracic ganglion (TG) or with conditioned saline (CS) that had been preincubated with the TG. We removed aliquots at standard time points for analysis by reverse-phase high-performance liquid chromatography (HPLC). We found that over time the proctolin peak became progressively smaller, while three novel peaks appeared and increased in size. Comigration experiments using HPLC indicated that the major novel peak was Proct. (Tyr-Leu-Pro-Thr), while one of the two minor peaks was Proct. (Leu-Pro-Thr). The other minor peak appeared to be Proct. (Arg-Tyr), based on similar HPLC retention time to synthetic Proct. The reduction in the proctolin peak and the increase in the Proct. peak was prevented by co-incubation of proctolin with any one of several aminopeptidase inhibitors (10(-4) M). Proct. and Proct. appeared to result from a diaminopeptidase-mediated cleavage of proctolin. We tested whether N-terminal cleavage functionally inactivated proctolin by coapplying proctolin (10(-8) M) and individual aminopeptidase inhibitors (10(-5) M) to the isolated stomatogastric ganglion (STG). We found that these inhibitors significantly enhanced the proctolin excitation of the pyloric rhythm. Furthermore, application of synthetic Proct. to the STG had no effect unless high concentrations (> 10(-6) M) were used, and neither Proct. nor Proct. (10(-4) M) influenced the pyloric rhythm. Our results indicate that proctolin is enzymatically degraded and thereby biologically inactivated in the crab nervous system, primarily by extracellularly located aminopeptidase activity. ER -