Fig. 4
Hypothalamic projection neurons deliver inhibitory inputs to the tectum. (A) Activation of ChR2-expressing neurons in the RH using sculpted blue light (shaded blue) results in inhibitory responses (shaded red) and excitatory visual responses (green) in tectal PVL neurons. (B) A raster plot of these responses (n = 46 inhibited neurons across six larvae) shows the z-scored ∆F/F of these inhibited neurons (top), and an average trace of these neurons through the experiment is shown (bottom). (C) Similar proportions of tectal cells were excited by a short pulse of blue light in ChR2+ larvae and ChR2− controls, indicating that these are direct visual responses (green). Significantly more tectal neurons were inhibited in ChR2+ larvae vs. ChR2− controls (red) by a prolonged illumination of the RH, indicating a causative effect of hypothalamic inputs. Dots represent individual larvae and mean ± SEM is indicated, mean value is reported above each scatter plot. *p < 0.05. n = 6 experimental, n = 6 controls.