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First published online March 2, 2007
Journal of Experimental Biology 210, 1084-1091 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.000935

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TTX-sensitive and TTX-insensitive control of spontaneous gut motility in the developing zebrafish (Danio rerio) larvae

Anna Holmberg¹, Catharina Olsson^1,* and Grant W. Hennig²

¹ Department of Zoophysiology, Göteborg University, SE 405 30 Göteborg, Sweden
² Department of Physiology and Cell Biology, University of Nevada, Reno, USA

View larger version (38K): [in this window] [in a new window]   Fig. 1. Spatiotemporal maps (STMap) of the luminal flow were constructed from unfed larvae at 4 and 7 d.p.f. (A) A box was drawn around the area of interest, covering most of the gut (900 µm). PI, proximal intestine (intestinal bulb); MI, middle intestine; DI, distal intestine. (B) STMaps, over the area within the box in A, were created based on changes in gut opacity as the gut content was propelled in a retrograde or anterograde direction. Individual contractions are identified as darker bands, travelling in either direction over time (downwards in map, 3.8 min). In this STMap, six anterograde contractions waves are present. Velocity (v, the slope of the line), interval between consecutive contractions (t), distance (d) travelled by the contractions and the total time of activity were calculated. Asterisks indicate the region where the contraction waves originated.

View larger version (48K): [in this window] [in a new window]   Fig. 2. Spatiotemporal maps (STMap; 900 µm) showing the effect of NaCl (A; 3.6 min) and tetrodotoxin (TTX; B; 3.8 min) on anterograde contraction waves at 7 d.p.f. (A) Anterograde gut activity was unaffected by 0.9% NaCl in comparison with the control period (ctrl). (B) TTX decreased the frequency and distance of anterograde contraction waves in comparison with the control period (ctrl).

View larger version (12K): [in this window] [in a new window]   Fig. 3. The effects of tetrodotoxin (TTX; black bars) compared with the control period (white bars) on frequency (A), interval (B), distance (C) or velocity (D) of anterograde contraction waves at 4 and 7 d.p.f. Values are means ± s.e.m.; for N, see Table 2). Neurons do not seem to be necessary for the initiation and progress of anterograde contraction waves before the first feeding as TTX did not affect either of the parameters at 4 d.p.f. At 7 d.p.f., however, after the theoretical time for onset of feeding, TTX reduced frequency and distance (A,C), whereas interval and velocity were unaffected (B,D). Distance (C) increased while velocity (D) decreased when comparing 4 and 7 d.p.f. larvae. *P<0.05.

View larger version (55K): [in this window] [in a new window]   Fig. 4. Whole-mount zebrafish larvae labelled with antibodies against Hu (human neuronal protein) and acetylated tubulin (AcT). (A) Whole larva at 7 d.p.f. The asterisk indicates the region of the gut where both retrograde and anterograde contraction waves originate. (B) At 4 d.p.f. (before onset of exogenous feeding) the distal part of the intestine (DI) is already densely innervated by nerve fibres as well as nerve cell bodies. (C) The number of Hu-positive nerve cell bodies showed a marked decrease between the middle intestine and the posterior part of the intestinal bulb (proximal intestine) compared to the more anterior part of the bulb at the stages investigated. PI, proximal intestine; MI, middle intestine; DI, distal intestine.