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- Holmberg, Anna, 1974, et al.
(författare)
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The effects of endogenous and exogenous nitric oxide on gut motility in zebrafish Danio rerio embryos and larvae
- 2006
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 209:13, s. 2472-2479
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Tidskriftsartikel (refereegranskat)abstract
- Using motion analysis, the ontogeny of the nitrergic control system in the gut was studied in vivo in zebrafish Danio rerio embryos and larvae. For the first time we show the presence of a nitrergic tonus, modulating both anterograde and retrograde contraction waves in the intestine of developing zebrafish. At 4 d.p.f. (days post fertilisation), the nitric oxide synthase (NOS) inhibitor L-NAME (three boluses of 50-100 nl, 10(-3) mol l(-1)) increased the anterograde contraction wave frequency by 0.50 +/- 0.10 cycles min(-1). Subsequent application of the NO donor sodium nitroprusside (SNP; three boluses of 50-100 nl, 10(-4) mol l(-1)) reduced the frequency of propagating anterograde waves (-0.71 +/- 0.20 cycles min(-1)). This coincided with the first appearance of an excitatory cholinergic tonus, observed in an earlier study. One day later, at 5 d.p.f., in addition to the effect on anterograde contraction waves, application of L-NAME increased (0.39 +/- 0.15 cycles min(-1)) and following SNP application reduced (-1.61 +/- 0.36 cycles min(-1)) the retrograde contraction wave frequency. In contrast, at 3 d.p.f., when no spontaneous motility is observed, application of L-NAME did not induce contraction waves in either part of the gut, indicating the lack of a functional inhibitory tonus at this early stage. Gut neurons expressing NOS-like immunoreactivity were present in the distal and middle intestine as early as 2 d.p.f., and at 1 day later in the proximal intestine. In conclusion, the present study suggests that a nitrergic inhibitory tonus develops shortly before or at the time for onset of exogenous feeding.
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- Sundqvist, Monika, 1976, et al.
(författare)
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Ontogeny of excitatory and inhibitory control of gastrointestinal motility in the African clawed frog, Xenopus laevis
- 2006
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Ingår i: American Journal of Physiology-Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 291:4
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Tidskriftsartikel (refereegranskat)abstract
- The transparent body wall of Xenopus laevis larvae during the first developmental stages allows in vivo studies of gastrointestinal tract activity. The purpose of this study was to chart the ontogeny of gut motility in Xenopus larvae and to identify the most important control systems during the first developmental stages. Coordinated descending contraction waves first occurred in the gut at Nieuwkoop and Faber stage 43 [0.8 +/- 0.1 contractions/min (cpm)] and increased to 4.9 +/- 0.1 cpm at stage 47. The cholinergic receptor agonist carbachol (5 - 10 mu M) increased contraction frequency already at stage 43, as did neurokinin A (NKA, 0.3 - 1 mu M). The muscarinic antagonist atropine (100 mu M) first affected contraction frequency at stage 45, which coincides with the onset of feeding. The tachykinin antagonist MEN-10,376 (6 mu M) blocked NKA-induced contractions but not spontaneous motility. Both sodium nitroprusside [nitric oxide (NO) donor, 1 - 10 mu M] and vasoactive intestinal peptide (VIP, 0.1 - 1 mu M) inhibited contractions from the earliest stage onward. Blocking NO synthesis using N-G-nitroL- arginine methyl ester (100 mu M) had no effect per se, but antagonized VIP evoked inhibition at stage 47. We conclude that gastrointestinal motility is well developed in the Xenopus laevis larvae before the onset of feeding. Functional muscarinic and tachykinin receptors are present already at the onset of motility, whereas a cholinergic tone develops around the onset of feeding. No endogenous tachykinin tone was found. Functional VIP receptors mediate inhibition at the onset of motility. NO seems to mediate the VIP effect at later stages.
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