PROCTOLINS ROLE IN NEURALLY EVOKED CONTRACTIONS OF THE LOCUST OVIDUCTS

Citation
Kf. Noronha et Ab. Lange, PROCTOLINS ROLE IN NEURALLY EVOKED CONTRACTIONS OF THE LOCUST OVIDUCTS, Journal of neurobiology, 33(2), 1997, pp. 139-150
Citations number
34
Categorie Soggetti
Neurosciences
Journal title
ISSN journal
00223034
Volume
33
Issue
2
Year of publication
1997
Pages
139 - 150
Database
ISI
SICI code
0022-3034(1997)33:2<139:PRINEC>2.0.ZU;2-Y
Abstract
The effects of proctolin (RYLPT) on neurally evoked contractions of lo cust oviduct muscle were studied to examine the role of proctolin as a cotransmitter, Increasing the number of stimuli in a burst (from one to 30 stimuli) resulted in an increase in amplitude of contraction of locust oviduct muscle, Proctolin was capable of increasing the amplitu de of neurally evoked contractions at lower-stimulus regimes (one- and two-stimulus bursts) but did not do so at higher-stimulus regimes (fi ve- and 10-stimulus bursts), The effects of proctolin were dose depend ent within the one- and two-stimulus regimes, with thresholds at 10(-9 ) M and maxima at 2.5 x 10(-8) M. Addition of proctolin increased the basal tonus and size of a postcontraction relaxation of the oviduct mu scle in a dose-dependent manner during all stimulus regimes, However, the effect of proctolin on basal tonus and the postcontraction relaxat ion was much less at the higher stimulus regimes, Previously, several proctolin analogues have been tested for their ability to antagonize p roctolin-induced contractions of the oviduct muscle. Since proctolin i s proposed to be a cotransmitter rat this neuromuscular junction, one of these analogues, cycloproctolin, was used to antagonize proctolin's effects on neurally evoked contractions, In the presence of the antag onist, the maximum amplitude induced by application of proctolin was d ecreased by 22.7%, while the proctolin-induced increase in basal tonus was decreased by 45.8%, Finally, the maximum increase in the size of the postcontraction relaxation caused by proctolin was lowered by 32.0 %, The results of the present study show that exogenously applied proc tolin is an excitant of the oviduct muscle at lower, rather than highe r, stimulus regimes, and this latter inaction may be due to the corele ase of endogenous proctolin during increased neural stimulation. (C) 1 997 John Wiley & Sons, Inc.