Fig. 2.

Mu-opioid stimulation alters the hedonic impact of sucrose at cortical sites. Functional maps show hedonic effects of DAMGO microinjections at each cortical site on taste reactivity (“liking” reactions) elicited by sucrose taste. Each symbol placement indicates an individual rat’s microinjection site (symbol size reflects the DAMGO Fos plume). Symbol colors reflect the within-subject behavioral change in hedonic reactions induced by DAMGO microinjection, shown as percentage change from vehicle control levels measured in the same rat (hedonic enhancements: yellow–orange–red; suppressions: blue). Mu-receptor stimulation effects by DAMGO microinjection in the OFC enhanced hedonic “liking”, depending on the anatomical subregion of the OFC (rostromedial versus caudolateral OFC: χ² = 4.967, P = 0.026). At rostromedial sites, DAMGO stimulation enhanced hedonic “liking” reactions to sucrose by 200–300% [χ² = 15.826, P < 0.001; DAMGO: Z = −2.983, P = 0.003, r = −0.81, CI (2, 12); n = 13]. DAMGO microinjections in the caudolateral OFC and rostral 2/3 of insula oppositely suppressed hedonic reactions [χ² = 17.659, P < 0.001; DAMGO: Z = −3.673, P < 0.001, r = 0.65, CI (−9, −2); n = 26]. DAMGO microinjections in the far-caudal insula enhanced hedonic reactions compared with vehicle baseline [vehicle: χ² = 9.75, P < 0.008; DAMGO: Z = −2.524, P = 0.012, r = 0.63, CI (1, 11); n = 11] and compared with DAMGO at rostral/mid sites in the insula (χ² = 34.320, P < 0.0001). No other cortical site altered hedonic reactions (gray; n = 42). Functional insula zones are based on Kosar et al. (51) (square), Cechetto and Saper (28) (circle), and Peng et al. (45) (triangle).