M. Fuse et I. Orchard, THE MUSCULAR CONTRACTIONS OF THE MIDGUT OF THE COCKROACH, DIPLOPTERA-PUNCTATA - EFFECTS OF THE INSECT NEUROPEPTIDES PROCTOLIN AND LEUCOMYOSUPPRESSIN, Regulatory peptides, 77(1-3), 1998, pp. 163-168
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.