Stochastic Ca2 Waves that Propagate Through the Neuroepithelium in Limited Distances of the Brain and Retina Imaged with GCaMP3 in Zebrafish Embryos

Ca2+-imaging and photo-manipulation of the simple gut of zebrafish larvae in vivo

Zebrafish larval gut could be considered as an excellent model to study functions of vertebrate digestive organs, by virtue of its simplicity and transparency as well as the availability of mutants. However, there has been scant investigation of the detailed behavior of muscular and enteric nervous systems to convey bolus, an aggregate of digested food. Here we visualized peristalsis using transgenic lines expressing a genetically encoded Ca²⁺ sensor in the circular smooth muscles. An intermittent Ca²⁺ signal cycle was observed at the oral side of the bolus, with Ca²⁺ waves descending and ascending from there. We also identified a regular cycle of weaker movement that occurs regardless of the presence or absence of bolus, corresponding likely to slow waves. Direct photo-stimulation of circular smooth muscles expressing ChR2 could cause local constriction of the gut, while the stimulation of a single or a few neurons could cause the local induction or arrest of gut movements. These results indicate that the larval gut of zebrafish has basic features found in adult mammals despite the small number of enteric neurons, providing a foundation for the study, at the single-cell level in vivo, in controlling the gut behaviors in vertebrates.

Munch's SCREAM: A spontaneous movement by zebrafish larvae featuring strong abduction of both pectoral fins often associated with a sudden bend

Stereotyped movement of paired pectoral fins in zebrafish larvae could be considered a simple model with which to investigate the neural basis of behavior. Using a high-speed camera, we explored the repertoire of pectoral fin movements by naturally behaving larvae at 5-6 days post-fertilization. Previously, two types of fin movements were characterized in association with locomotion: 'CRAWLing,' an alternating fin movement associated with slow swimming, and 'TUCKing,' the adduction of both fins associated with fast swimming. We here describe a third mode of fin movement, which we call 'Munch's SCREAM', in which both pectoral fins were flipped anteriorly so that they reached the skin on the sides of the head, thus covering the otic vesicles. This behavior occurred spontaneously and was often associated with a slight regression or a sudden bending and change in body orientation. It could be also induced effectively in the agarose-embedded larvae by tactile stimulation on the skin around the eye and nose, some of which are associated with struggling, in which waves of bending propagate from the tail to the head. Larvae can still CRAWL and perform the SCREAM even when their forebrain and midbrain have been removed, suggesting that the neural circuits involved in the SCREAM are present in the hindbrain and/or spinal cord.