Behavioral and Neurological Changes Associated with Sucrose Bingeing
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The behavioural and neurological effects of excessive sucrose intake overlap with those of abused drugs, suggesting that sucrose bingeing should be categorized with addictive disorders. Behaviorally, a primary characteristic of drug addiction is compulsive responding, manifested as an inability to inhibit drug intake despite negative consequences. We examined whether excessive sucrose self-administration produces these behavioural patterns using a validated rat model of sucrose bingeing (Avena et al., 2008) and investigated potential neurophysiological correlates with brain slice electrophysiology. Rats (n = 8-16 per group) received 12 or 24 hour access to a 10% sucrose solution and food, while control groups received food only or a 0.1% saccharin solution with food, each day for 28 days. Sucrose/saccharin/food consumption and weight were recorded daily. Compulsive responding for sucrose was assessed one or 28 days after the final self-administration session using a conditioned suppression paradigm. Persistent responding in the presence of a cue (tone) predicting a negative outcome (0.5 mA footshock) was used as a measure of compulsive responding. Only rats given 12-hour access to sucrose developed a binge pattern of intake, in which solution consumption increased dramatically during the first hour of each session. This group also developed compulsive responding for sucrose, exhibiting a reduced conditioned suppression effect following both one day and 28 days of abstinence. At a neural level, there was a switch in direction (from reduction to enhancement) in dopaminergic (DA) modulation of GABA synaptic transmission in the oval bed nucleus of the stria terminalis (ovBNST) of rats that developed a binge pattern of sucrose intake. This switch was similar to that recently observed in rats displaying enhanced motivation to self-administer cocaine. Therefore, excessive intermittent sucrose consumption produces compulsive responding and this shift from controlled to compulsive intake may involve the same neural mechanisms that underlie excessive cocaine self-administration.