Characterizing Hedonic Responses to Flavors Paired with Internal Pain and Nausea through the Taste Reactivity Test in Rats.

Feeding behavior is a complex experience that involves not only sensory (i.e., visual, odor, taste, or texture) but also affective or emotional aspects (i.e., pleasure, palatability, or hedonic value) of foods. As such, behavioral tests that assess the hedonic impact of foods are necessary to fully understand the factors involved in ingestive behavior. In this protocol, we use the taste reactivity (TR) test to characterize the hedonic responses of rats to flavors paired with either lithium chloride-induced nausea or internal pain produced by hypertonic NaCl, two treatments that reduce voluntary consumption. This application of the TR test demonstrates how emetic and non-emetic (somatic pain in particular) treatments produce dissociable patterns of hedonic reactions to fluids: only emetic treatments result in the production of aversive orofacial responses, reflecting conditioned nausea, whereas somatic pain produces immobility, reflecting conditioned fear. Other methods, such as the microstructural analysis of licking behavior, do not reliably distinguish conditioned nausea and fear, a key advantage of the more selective TR procedure. This protocol also contains guidance for adaptation to other species and designs.