Fig. 3

Effect of Photobleaching KillerRed-Expressing Neurons

(A) FITC-annexin V label in a KR11 fish 3 hr after photobleaching of the left habenula, in the region marked by the white circle. Annexin V binds only to habenula afferents and not to efferents. Label is visible in axons that terminate in the contralateral habenula, but not in axons that originate from that (nonirradiated) side. One cell (arrowhead), presumably undergoing apoptosis, is labeled outside the irradiated region.

(B) Deeper focus of the same fish, showing FITC-annexin V label of the cell bodies in the side that was irradiated. Asterisks indicate sites of FITC-annexin V injection.

(C) A fish 5 hr after irradiation of the left habenula. A few cells have taken up acridine orange (arrowheads), but these are not located in the region of cells that had been expressing KillerRed (arrow).

(D) Fluorescence recovery of KillerRed after photobleaching.

(E) The effect of photobleaching KillerRed-expressing cells on the avoidance response.

(F) Mean swim speed in the probe trial for KR11 fish photobleached before conditioning, compared with nonphotobleached fish.

(G) Mean swim speed in the probe trial of photobleached KR4 and KR11 fish.

(H) Number of fish showing avoidance, as a function of trial number.

(I) Number of fish displaying a startle response.

(J) Percentage of startle displayed in the probe trial by fish that had been subjected to US during conditioning.

All micrographs are dorsal views, with anterior to the left. Fish in (A)–(D) are 3 weeks old. Scale bars represent 20 μm in (A), (B), and (D) and 50 μm in (C). The following abbreviations are used: ir, irradiated; Pr, paired. Error bars indicate SEM. ^**p < 0.001; ^*p < 0.05.