Abstract
Consumption of foods can be suppressed by two feeding system defense mechanisms: conditioned taste aversion (CTA) or taste avoidance learning (TAL). There is a debate in the literature about which form of intake suppression is caused by various aversive stimuli. For instance, illness-inducing stimuli like lithium chloride are the gold standard for producing CTA and external (or peripheral) painful stimuli, such as footshock, are the traditional model of TAL. The distinction between CTA and TAL, which have identical effects on intake, is based on differential effects on palatability. That is, CTA involves a decrease in both intake and palatability, whereas TAL suppresses intake without influencing palatability. We evaluated whether lactose, which causes gastrointestinal pain in adult rats, produces CTA or TAL. Using lick pattern analysis to simultaneously measure intake and palatability (i.e., lick cluster size and initial lick rate), we found that pairing saccharin with intragastric infusions of lactose suppressed both the intake and palatability of saccharin. These results support the conclusion that gastrointestinal pain produced by lactose malabsorption produces a CTA, not TAL as had previously been suggested. Furthermore, these findings encourage the view that the CTA mechanism is broadly tuned to defend against the ingestion of foods with aversive post-ingestive effects.
Highlights
The present article is concerned with the nature of the learning that occurs when ingestion of a taste stimulus is followed by the aversive internal effects caused by lactose malabsorption
Taste learning with an aversive US can be categorized as either a conditioned taste aversion (CTA; for reviews see Barker, Best & Domjan, 1977; Braveman & Bronstein, 1985; Milgram, Krames & Alloway, 1977; Reilly & Schachtman, 2009) or as taste avoidance learning
It will be evident from inspection of the figure that one CS-US pairing was sufficient for lactose malabsorption to cause a reduction in total licks, cluster size and initial lick rate
Summary
The present article is concerned with the nature of the learning that occurs when ingestion of a taste stimulus (conditioned stimulus; CS) is followed by the aversive internal effects (unconditioned stimulus; US) caused by lactose malabsorption. Both types of learning cause a reduction in the amount consumed of the taste CS. CTA involves a conditioned downshift in the palatability of the CS; no change in palatability occurs in TAL. One method of assessing taste palatability in non-human animals involves detailed analysis of the patterns of licks that occur during voluntary consumption (e.g., Davis, 1989; Davis & Smith, 1992; Dwyer, 2012). Lick pattern analysis has confirmed that lithium chloride, the quintessential laboratory US used to induce CTAs, causes a reduction in both intake and palatability (e.g., Arthurs, Lin, Amodeo & Reilly, 2012; Baird, St John & Nguyen, 2005; Dwyer, Boakes, & Hayward, 2008; Kent, Cross-Mellor, Kavaliers & Ossenkopp, 2002)
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