The effects of endogenous and exogenous nitric oxide on gut motility in zebrafish Danio rerio embryos and larvae.
2006
SUMMARY 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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