Figure 1.

AGRP neurons are sufficient to evoke voracious food consumption in well-fed mice. (a) For light delivery, an optical fiber was implanted ~0.8 mm above the arcuate nucleus (ARC, red). (b) Experimental design. Food intake was recorded before, during and after photostimulation. The stimulus was applied repeatedly over 1 second followed by a 3 second break. Photostimulation frequency was 20 Hz with 10 ms light pulses. (c) Photostimulation in an AGRP-ChR2 mouse evoked voracious food consumption during the stimulation period (black trace) but not in a mouse without ChR2 expression (grey trace). (d) Food intake was dependent on the number of ChR2-expressing AGRP neurons. Circles represent 1 hour food intake for individual mice (n = 22). (e) Mice without ChR2 expression in AGRP neurons (n = 11) did not show a significant difference in food intake during photostimulation, whereas in mice with greater than 800 ChR2-expressing neurons (n = 16) the increase in food intake during photostimulation was significant. Circles connected by lines represent food intake for individual mice. (f) Food intake during photostimulation was significantly increased in mice with intermediate (300–700 neurons; n = 3) or high levels of ChR2 expression (>800 neurons; n = 16) relative to mice with low or no ChR2 (0–100 neurons; n = 14). Photostimulation-induced food consumption was nearly as great as the magnitude of re-feeding (n = 9) for 1 hour after 24 hours of food deprivation. n.s., not significant; ** P < 0.01; *** P < 0.001. Error bars represent s.e.m.