It is widely assumed that D1 and D2 dopamine receptor-expressing striatal neurons code for discrete pathways in the basal ganglia. Combining optogenetics and electrophysiology, the authors show that this output architecture does not apply to nucleus accumbens neurons. Current thinking attributing D1/D2 selectivity to accumbens projections thus should be reconsidered. It is widely accepted that D1 dopamine receptor–expressing striatal neurons convey their information directly to the output nuclei of the basal ganglia, whereas D2-expressing neurons do so indirectly via pallidal neurons. Combining optogenetics and electrophysiology, we found that this architecture does not apply to mouse nucleus accumbens projections to the ventral pallidum. Thus, current thinking attributing D1 and D2 selectivity to accumbens projections akin to dorsal striatal pathways needs to be reconsidered.

The core subcompartment of the nucleus accumbens (NAcore) contributes significantly to behavioral responses following motivationally relevant stimuli, including drug-induced, stress-induced, and cue-induced reinstatement of cocaine seeking. Projections from NAcore that could carry information necessary to initiate reinstated cocaine seeking include outputs via the indirect pathway to the dorsolateral subcompartment of the ventral pallidum (dlVP) and through the direct pathway to the medial substantia nigra (SN). Here we used an optogenetic strategy to determine whether the dlVP or nigral projections from the NAcore are necessary for cocaine seeking initiated by a cocaine and conditioned cue combination in rats extinguished from cocaine self-administration. Rats were pretreated in the NAcore with an adeno-associated virus expressing the inhibitory opsin archaerhodopsin, and fiber-optic cannulae were implanted above the indirect pathway axon terminal field in the dlVP, or the direct pathway terminal field in the SN. Inhibiting the indirect pathway to the dlVP, but not the direct pathway to the SN, prevented cocaine-plus-cue-induced reinstatement. We also examined projections back to the NAcore from the ventral tegmental area (VTA) and dlVP. Inhibiting the dlVP to NAcore projection did not alter, while inhibiting VTA afferents abolished reinstated cocaine seeking. Localization of green fluorescent protein reporter expression and whole-cell patch electrophysiology were used to verify opsin expression. These data reveal a circuit involving activation of VTA inputs to the NAcore and NAcore projections through the indirect pathway to the dlVP as critical for cocaine-plus-cue-induced reinstatement of cocaine seeking.

Orexins are hypothalamic neuropeptides which bind to two G-protein-coupled receptors, orexin-1 (OX1R) and orexin-2 (OX2R) receptor. While a role for OX1R has been established in both ethanol reinforcement and ethanol-seeking behaviour, the role of OX2R in these behaviours is relatively less-studied. The aim of this study was to determine the role of central OX2R in ethanol-taking and ethanol-seeking behaviour. Indiana ethanol-preferring rats were trained to self-administer ethanol (10% w/v) or sucrose (0.7–1% w/v) in the presence of reward-associated cues before being implanted with indwelling guide cannulae. The selective OX2R antagonist TCS-OX2-29 was administered i.c.v. to assess its effect on operant self-administration and cue-induced reinstatement following extinction. Following i.c.v. injection TCS-OX2-29 reduced self-administration of ethanol, but not sucrose. Despite reducing ethanol self-administration, TCS-OX2-29 had no impact on cue-induced reinstatement of ethanol seeking. To determine where in the brain OX2R were acting to modulate ethanol self-administration, TCS-OX2-29 was microinjected into either the shell or core of the nucleus accumbens (NAc). Intra-NAc core, but not shell, infusions of TCS-OX2-29 decreased responding for ethanol. Importantly, the doses of TCS-OX2-029 used were non-sedating. Collectively, these findings implicate OX2R in the NAc in mediating the reinforcing effects of ethanol. This effect appears to be drug-specific as antagonism of central OX2R had no impact on sucrose self-administration. Thus, OX2R in addition to OX1R may represent a potential therapeutic target for the treatment of ethanol-use disorders. However, unlike OX1R, no impact of OX2R antagonism was observed on cue-induced reinstatement, suggesting a more prominent role for OX2R in ethanol self-administration compared to cue-conditioned ethanol-seeking.

Increased obesity rates, an evolving food supply and the overconsumption of energy dense foods has led to an increase in research exploring addictive eating behaviours. This study aimed to investigate food addiction in a sample of Australian adults using the revised Yale Food Addiction Survey (YFAS) 2.0 tool and how it is associated with dietary intake, personality traits and mental health issues. Australian adults were invited to complete an online survey that collected information including: demographics, dietary intake, depression, anxiety, stress and personality dimensions including impulsivity, sensation seeking, hopelessness and anxiety sensitivity. A total of 1344 individuals were recruited with the samples comprising 75.7% female, mean age 39.8 ± 13.1 years (range 18–91 years) and body mass index BMI 27.7 ± 9.5. Food addiction was identified in 22.2% of participants using the YFAS 2.0 tool, which classified the severity of food addiction as “mild” in 0.7% of cases, “moderate” in 2.6% and “severe” in 18.9% of cases. Predictors of severe food addiction were female gender (odds ratio (OR) 3.65 95% CI 1.86–7.11) and higher levels of soft drink OR 1.36 (1.07–1.72), confectionary consumption and anxiety sensitivity 1.16 (1.07–1.26). Overall people with “severe” (OR 13.2, 5.8–29.8) or extremely severe depressive symptoms (OR 15.6, range 7.1–34.3) had the highest odds of having severe food addiction. The only variable that reduced the odds of having severe food addiction was vegetable intake. The current study highlights that addictive food behaviours are associated with a complex pattern of poor dietary choices and a clustering with mental health issues, particularly depression.