Experimental design to examine dopamine signalling in nucleus accumbens (A). Female (3 WT, 4 KO) and male (4 WT, 4 KO) mice, trained to receive peanut butter chips, were tethered to a fiber optic cable in their home cage. Following acclimation, dopamine responses in the nucleus accumbens to a non-food object (NFO; wood dowel, a, black), standard chow (b, tangerine), and peanut butter chip (PB, c, blue) were measured. Schematic of GRAB-DA (AAV-hSyn-DA4.3) injection site in the nucleus accumbens (B) and fiber placement [scale bar = 500 µm] (C). Average z-scored dopamine release traces aligned (time = 0) to object dropping into cage of WT and KO fed mice (D, E) or WT and KO fasted (H, I) mice. The average z-score of WT and KO ad libitum-fed mice from 0 to 30 s (F) and 30–60 s (G) in response to a non-food object (NFO), standard chow, or peanut butter chip (PB) dropped into cage. The average z-score of WT and KO fasted mice from 0 to 30 s (J) and 30–60 s (K) in response to a non-food object (NFO), standard chow, or peanut butter chip (PB) dropped into cage. Average z-score dopamine release traces aligned to first contact with peanut butter chip (PB) from fed (L) and fasted (M) WT and KO mice, with individual traces shown in a heatmap (N). The average z-score of WT and KO ad libitum-fed mice from –20–0, 0–30, and 30–60 s (O), relative to first contact. The average z-score of WT and KO fasted mice from –20–0, 0–30, and 30–60 s (P), relative to first contact. Time spent eating during the recording session (Q) and time passed between drop and contact with peanut butter (P). Data± SEM, two-way ANOVA with Tukey’s post hoc analysis (F, G, J, K, O, P, Q – main effect of fasting, p < 0.05; R); a – significant compared to WT, p < 0.05. Dashed lines at time = 0 (D, E, H, I) represent the time at which food or an object was dropped into the cage. A continuous line at time = 0 (L, M) represents the time at which mice contact PB chip. Videos 3–6 accompany this figure.