Perceived Irritation during Ingestion of Capsaicin or Piperine: Comparison of Trigeminal and Non-trigeminal Areas

Abstract

The aim of this study was to investigate the perception of chemosensory irritation in the oropharyngeal region during the ingestion of irritants. In two experiments subjects sipped and swallowed small samples of an ascending concentration series of capsaicin or piperine and rated the intensity of sensations or irritation perceived at four locations: the anterior tongue, the posterior tongue, the roof of the mouth and the throat. Both experiments revealed that the responsiveness to irritation from capsaicin was significantly higher in the throat than at either the front or back of the tongue. There was no difference between irritation ratings for the throat and the roof of the mouth. Compared with capsaicin, the responsiveness to piperine was more uniform along the rostro-caudal axis; for example, irritation ratings for the throat were similar to those for the anterior tongue. These results support previous findings which indicated that the oral mucosae were not uniformly sensitive to chemical irritants, and suggest further that the throat, which is innervated by both the glossopharyngeal and vagus nerves, plays an important role in the perception of chemesthetic stimuli during ingestion.

Assessment of Upper Respiratory Tract and Ocular Irritative Effects of Volatile Chemicals in Humans

“…74,75 Although little systematic human research on vagal irritation from inhaled vapors has been conducted, recent studies examining oral exposure to liquid ibuprofen demonstrated that pharyngeal irritation can be quantified and that the pharyngeal area appears to be highly sensitive to certain chemical stimuli. 76,77 However,…”

“…Positron emission tomography (PET) is a sensitive and quantitative indirect measure of brain function that relies upon changes in relative blood flow or uptake of glucose in brain regions that are undergoing increased (or decreased) neural activity. 346 A typical PET study is initiated by injecting into the subject's blood stream water or some other substance (e.g., butanol) tagged with an unstable neutron-deficient radioactive tracer such as 15 O, 77 Kr, or 11 C. 347 The amount of accumulation of the tracer is increased in brain regions with higher blood flow Furthermore, even under the most optimal of circumstances, images with no greater than ~ 3 mm 3 of spatial resolution can be obtained. Most commonly, the resolution is, in fact, four to five times this size.…”

Trigeminal Chemesthesis

“…Chemesthetic sensitivity in the mucosae of the human face (nasal, ocular, and oral) is mediated by C and A delta fibers primarily from the trigeminal nerve, although in the case of oral chemesthesis, the glossopharyngeal and vagus nerves also contribute (see reviews in Doty and Cometto-Muñiz, 2003;Doty et al, 2004;Rentmeister-Bryant and Green, 1997). The ion-channels and receptors involved are expressed by a class of peripheral neurons called polymodal nociceptors since they can respond to chemical, thermal, and mechanical stimuli (Belmonte et al, 2004).…”

“…Ingestion of these compounds at low levels elicits a predominantly pungent or burning sensation from the oral mucosa (Keele 1962;Lawless and Stevens 1988;Rentmeister-Bryant and Green 1997) and vermilion border of the lips (Lawless 1984;Lawless and Stevens 1988), but have minor or no discernible taste qualities on their own (except for nicotine which has been described as bitter (Pfaffman 1959). Recently, oleocanthal from olive oil has been identified which elicits an irritant sensation sensed primarily from the pharynx (Beauchamp et al, 2005; Peyrot des Gachons et al, 2011).…”

“…Many, but not all, chemesthetic compounds elicit this pattern of irritation including the capsaicinoids capsaicin (Lawless 1984;Stevens and Lawless 1987;Green 1989;Prescott 1999) and piperine (Stevens and Lawless 1987;Green 1996;Rentmeister-Bryant and Green, 1997), high concentrations of acids (Green 1996;Dessirier et al, 2000b) and salts (Dessirier et al, 2001), and menthol (Cliff and Green 1994;1996).…”