Animal models: Sugar addiction model (Colantuoni et al., 2001); animals given sweet glucose solution with full access or intermittent access. Overtime intermittent access to glucose causes binge like behaviour.
In these animals, cross-sensitisation studies show that their dopamine system is sensitised with animals having intermittent glucose access followed by an injection of amphetamine, measuring locomotor responses intermittent animals showed a greater response to amphetamine (Avena and Hoebel, 2003).
Long term exposure to cafeteria diet (Johnson and Kenny, 2010) Rats get access to high fat/sugar foods in as much quantity as they want, measuring the willingness of animals to do work to get brain stimulation, if they press the lever more they are requiring more reward to maintain response. Extended access to cafeteria diet, the animals are require greater stimulation to maintain behaviour, suggesting they are experiencing a reduction in their sensitivity to reward