Disgust
Animal research

With respect to studies using rats, prior research of signs of a conditioned disgust response have been experimentally verified by Grill and Norgren (1978) who developed a systematic test to assess palatability. The Taste Reactivity (TR) test has thus become a standard tool in measuring disgust response. When given a stimulus intraorally which had been previously paired with a nausea -inducing substance, rats will show conditioned disgust reactions. "Gaping" in rats is the most dominant conditioned disgust reaction and the muscles used in this response mimic those used in species capable of vomiting. Studies have shown that treatments that reduced serotonin availability or that activate the endocannabinoid system can interfere with the expression of a conditioned disgust reaction in rats. These researchers showed that as nausea produced conditioned disgust reactions, by administering the rats with an antinausea treatment they could prevent toxin-induced conditioned disgust reactions. Furthermore, in looking at the different disgust and vomiting reactions between rats and shrews the authors showed that these reactions (particularly vomiting) play a crucial role in the associative processes that govern food selection across species.

In discussing specific neural locations of disgust, research has shown that forebrain mechanisms are necessary for rats to acquire conditioned disgust for a specific emetic (vomit-inducing) substance (such as lithium chloride). Other studies have shown that lesions to the area postrema and the parabrachial nucleus of the pons but not the nucleus of the solitary tract prevented conditioned disgust. Moreover, lesions of the dorsal and medial raphe nuclei (depleting forebrain serotonin) prevented the establishment of lithium chloride-induced conditioned disgust.
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