Ontogeny of the gut motility control system in zebrafish Danio rerio embryos and larvae.

摘要

Using digital motion analysis, the ontogeny of the cholinergic, tachykinin and pituitary adenylate cyclase-activating polypeptide (PACAP) control systems was studied in vivo in zebrafish (Danio rerio) larvae. For the first time, it was shown that the regular propagating anterograde waves that occurred in the zebrafish larval gut before and around the onset (at 5-6 days post-fertilization; d.p.f.) of feeding were modulated by acetylcholine or atropine, PACAP and neurokinin A (NKA). When no spontaneous motility had developed at 3 d.p.f., it suggested that application of acetylcholine did not affect the gut. However, at 4 d.p.f., acetylcholine increased and atropine reduced the frequency of propagating anterograde waves. At 5 d.p.f., NKA increased and PACAP reduced the wave frequency. This suggested that both excitatory and inhibitory pathways developed at an early stage in the gut, independent of exogenous feeding. Immunohistochemistry established the presence of gut neurons expressing PACAP and NKA in the proximal part of the developing gut from the first stage investigated (2 d.p.f.) and before regular motility was observed. The whole gut was innervated at 1 (PACAP) or 2 (NKA) d.p.f. stages later. This supported physiological results that gut motility was under neuronal control during the period when regular motility patterns developed.