Figure 7. Photoactivation of the GABAergic, but not the glutamatergic, component of the LH-VTA projection increased feeding behaviors.

(A) In order to selectively activate glutamatergic or GABAergic LH-VTA projections, VGLUT2::Cre and VGAT::Cre mice received an injection of AAV₅-DIO-ChR2-eYFP or AAV₅-DIO-eYFP into the LH and had an optic fiber implanted over the VTA. In the sucrose-seeking task, there were no significant differences in the number of port entries per cue in any epoch for LH^glut-VTA:ChR2 mice (n=7) compared to LH^glut-VTA:eYFP control mice (n=6) nor (B) in LH^GABA-VTA:ChR2 mice (n=6) compared to LH^GABA-VTA:eYFP mice (n=8). (C) There was no significant difference between LH^glut-VTA:ChR2 mice and eYFP controls in feeding behavior. (D) However, LH^GABA-VTA:ChR2 mice showed a significant increase in time spent feeding during light stimulation compared to LH^GABA-VTA:eYFP controls (2-way ANOVA revealed a group × epoch interaction, F_2,24=4.78, p=0.0178; Bonferroni post hoc analysis, **p < 0.01). (E) Neither LH^glut-VTA:ChR2 mice, (F) nor LH^GABA-VTA:ChR2 mice showed a difference in tail withdrawal latency compared to their respective controls. (G) \LH-VTA:ChR2 mice showed a significant increase in time spent gnawing during the light ON epoch compared to eYFP controls (2-way ANOVA revealed a group × epoch interaction, F_2,24=4.78, p=0.0179; Bonferroni post hoc analysis, ***p < 0.001). (H) There was no significant difference between LH^glut-VTA:ChR2 and LH^glut-VTA:eYFP controls in gnawing behavior. (I) However, LH^GABA-VTA:ChR2 animals also showed a significant increase in time spent gnawing during the light ON epoch compared to LH^GABA-VTA:eYFP controls (2-way ANOVA revealed a group × epoch interaction, F_2,24=18.91, p<0.0001; Bonferroni post hoc analysis, ****p < 0.0001). (J) The difference score for gnawing behavior between the ON and OFF epochs was significantly greater in LH^GABA-VTA:ChR2 animals in comparison with either wild-type LHVTA:ChR2 or LH^glut-VTA:ChR2 animals (1-way ANOVA, F_2,18=16.76, p<0.0001; Bonferroni post hoc analysis, ***p <0.001). (K) Frequency-response curve showing the effect of different blue light stimulation frequencies (OFF, 5 Hz, 10 Hz) on behavior in LH^GABA-VTA:ChR2 animals. See also Figure S7.