THE MUSCULAR CONTRACTIONS OF THE MIDGUT OF THE COCKROACH, DIPLOPTERA-PUNCTATA - EFFECTS OF THE INSECT NEUROPEPTIDES PROCTOLIN AND LEUCOMYOSUPPRESSIN

We have previously shown differential expression of leucomyosuppressin (LMS) mRNA in apparent endocrine cells in the anterior region of midg uts of the cockroach Diploptera punctata, using in situ hybridization. In contrast, other FMRFamide-related peptides, as revealed by immunoh istochemistry have been found most abundantly in the posterior region in both apparent endocrine cells and nerve tracts [1]. Here, we partia lly purified extracts of anterior and posterior cockroach midguts, usi ng HPLC coupled with radioimmunoassay, and found, among multiple FMRFa mide-like immunoreactive fractions, one fraction co-eluting with LMS i n both regions. The presence of a co-eluting fraction in the posterior region, in the absence of LMS mRNA positive endocrine cells suggests that LMS might therefore be present in nerve tracts running along the length of the midgut. Using a circular muscle contraction assay from d ifferent portions of midgut, we determined the effects of LMS, proctol in and a variety of other midgut peptides on contractions of the midgu t of Diploptera. Proctolin caused a sustained tonic contraction in the anterior midgut, the amplitude of which was dose-dependent. In contra st, LMS, and its relative SchistoFLRFamide, reduced the amplitude of t hese contractions. LMS and SchistoFLRFamide also inhibited spontaneous phasic contractions, which were elicited by proctolin application in only a few preparations. Other postulated midgut peptides did not indu ce or inhibit contractions, nor augment the proctolin-induced contract ions. The C-terminal truncated sequences of LMS, HVFLRFamide and VFLRF amide, were sufficient to reduce the amplitude of the proctolin-induce d contractions. This work illustrates a possible physiological role fo r LMS in Diploptera midguts, in the passage of food along the alimenta ry canal. (C) 1998 Elsevier Science B.V. All rights reserved.