Lactose malabsorption and taste aversion learning

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.

Conditioned taste aversion versus avoidance: A re-examination of the separate processes hypothesis

“…Yet, even the Lactose rats that continued to consume some amount of saccharin on the last trial in Experiment 2 also had smaller initial lick rates and burst sizes than their NaCl counterparts. A recent study by Arthurs et al [27] also found that pairing 0.1% saccharin with, in their case, a higher dose of lactose via intragastric infusion reduced initial lick rate and burst size. Although these altered lick patterns were not directly compared to those associated with LiCl in that study, the authors concluded that the change in these two aspects of licking indicate that Lactose conditioned an aversion to the taste CS.…”

“…The literature is now replete with examples of various types of interoceptive stimuli that effectively condition reductions in intake of the associated taste CS. This includes, in addition to the ones already mentioned, motion/vestibular disturbance, GI pain, bacterial infection, chemotherapeutic drugs, and certain drugs of abuse, among others [e.g., [8, 15, 27–33].…”

“…Although these altered lick patterns were not directly compared to those associated with LiCl in that study, the authors concluded that the change in these two aspects of licking indicate that Lactose conditioned an aversion to the taste CS. Arthurs et al [27] argue that licking microstructure is sensitive to one dimension of decreased palatability but cannot detect changes in aversive reactivity. However, the fact we saw comparable reductions on burst size and initial lick rate in Experiment 2, but did not see any change in TR in Experiment 1, not even in terms of a reduction in ingestive TR, after lactose experience suggests these taste reactivity and microstructural patterns of licking are not always in register and may, in fact, be susceptible to different factors.…”

Further characterization of the effect of the prototypical antidepressant imipramine on the microstructure of licking for sucrose

“…The burst size data, which show that this measure is either unmodified or increased (10 mg/kg imipramine, first part of the experiment), do not lend support to the possibility that the reduced ingestion might be due to a drug-induced state of malaise, which is characterised by a reduction of this measure (e.g. [ 31 , 44 ]).…”