Visual Prey Capture in Larval Zebrafish Is Controlled by Identified Reticulospinal Neurons Downstream of the Tectum

The effect of MeL ablation, and combined MeL and tectum ablation, on prey capture. A, Projection of a confocal image stack (35 images at 2 μm steps taken through the dorsal surface in a living larva) showing retrograde labeling of RS neurons, including the MeLc and MeLr neurons (arrowhead and asterisk, respectively). The box inside the outline of a larva at the top left indicates the general position of labeled reticulospinal cells. The dendritic projection of the right MeLr neuron is clearly visible, innervating the ventromedial tectum. The M cell is labeled for reference (M). B, A time sequence of nMLF neurons during laser ablation of MeLc. The location of the targeted MeLc neuron and the neighboring MeLr neuron are marked with an arrowhead and asterisk, respectively, as in A. Frames 1-6 are taken at 1 s intervals, and the seventh frame is taken at 25 s after the onset of lasing. The plot shows the fluorescence intensity (on a 256 level grayscale, indicated by the gradient along the y-axis) of the targeted MeLc neuron, as well as for the neighboring MeLr. Loss of fluorescence signal is specific to the targeted MeLc neuron and, after sufficient laser exposure, permanent. C, Prey capture performance in groups with bilateral MeLc and MeLr ablations (Bilateral MeL) or unilateral ablation of these neurons in combination with unilateral tectum ablation on the same (Ipsilateral MeL + Tectum) or opposite (Contralateral MeL + Tectum) sides. Bilateral nMLF ablation and contralateral nMLF plus tectum ablation significantly impaired prey capture performance relative to controls. The ipsilateral nMLF plus tectum ablation group was not significantly different from controls but was numerically intermediate between controls and the crossed ablation group at every sampling point. D, Prey capture performance in a bilateral MeLc and MeLr ablated group (a separate group from that presented in C) and control ablated group in which an equal number of identified RS neurons from within hindbrain rhombomeres 4-6 were ablated. The control ablated group captured significantly more paramecia than the bilateral MeLc and MeLr group across the 5 h assay period and was indistinguishable from the unablated group in C.