Figure 4. LH^LEPR neurons mediate appetitive learning via projections to VTA circuitry.

(A) Viral injection/implant schematics and Pavlovian training and extinction protocols.

(B) Activation or inhibition of LH^VGAT neurons disrupts appropriate responding. LH^VGAT:GFP mice learned to discriminate CS⁺ from CS⁻. Activation of LH^VGAT disrupted conditioning, as did inhibition of LH^VGAT neurons. **p = 0.0021.

(C) Intact sucrose pellet collection across LH^VGAT groups.

(D) Discrimination between CS⁺ and CS⁻ was intact during the extinction test without optogenetic manipulation.

(E) Activation or inhibition of LH^LEPR neurons disrupts appropriate responding. LH^LEPR:GFP mice learned to discriminate CS⁺ from CS⁻. Activation of LH^VGAT disrupted conditioning, as did inhibition of LH^VGAT neurons. ***p = 0.0007.

(F) Intact sucrose pellet collection across LH^LEPR groups.

(G) Discrimination between CS⁺ and CS⁻ was intact during the extinction test without optogenetic manipulation.

(H) Activation or inhibition of the LH^VGAT→VTA pathway attenuates Pavlovian learning. LH^VGAT:GFP→VTA mice learned to discriminate CS⁺ from CS⁻. Activation of the pathway in LH^VGAT:ChR2→VTA mice or inhibition of the pathway in LH^VGAT:ArchT→VTA mice disrupted discrimination. *p = 0.017.

(I) Retrieval of sucrose pellets was comparable across groups.

(J) Discrimination between CS⁺ and CS⁻ was intact during the extinction test without optogenetic manipulation.

(K) Inhibition of the LH^LEPR→VTA pathway enhances Pavlovian learning. LH^LEPR:GFP→VTA mice learned to discriminate the CS⁺ and CS⁻ (*p = 0.0063). While discrimination was not apparent in LH^LEPR:ChR2→VTA mice, LH^LEPR:ArchT→VTA mice displayed discrimination between cues in block 3 (*p = 0.0047).

(L) Retrieval of sucrose pellets was comparable across groups.

(M) Extinction test performance was significantly affected by LH^LEPR→VTA pathway manipulation during training (group × CS interaction, p = 0.017). Within-group discrimination of the CS⁺ and CS⁻ was abolished in LH^LEPR:ChR2→VTA mice (p > 0.99), but was increased in LH^LEPR:ArchT→VTA mice (p = 0.0032) as compared to controls (p = 0.27).

Data represented as means ± SEMs; n = 5–8 mice/group.

See also Table S1 for full statistics and Figure S3.