Time course of burn to repeated applications of capsaicin

Bitter Taste Disrupts Spatial Discrimination of Piperine-Evoked Burning Sensations: A Pilot Study

Simple Summary

The chemical senses smell, taste, and trigeminal sense enable us to interact with the environment and play an essential role in protecting us from hazardous events. It is theorized that capsaicin and piperine not only elicit burning, but also bitter sensations through bitter taste-responding gustatory receptor cells that possess special channels. Similar psychophysiological responses to capsaicin and piperine suggest that bitter taste might also disrupt the spatial discrimination to piperine-induced burning sensations. Results showed that bitter taste disrupted the spatial discrimination of piperine-evoked burning sensations, providing further evidence for a qualitative similarity between burning and bitter sensations and the usefulness of chemical irritants in spatial discrimination tasks.

Abstract

This study aimed to investigate the perceptual similarity between piperine-induced burning sensations and bitter taste using piperine-impregnated taste strips (PTS). This pilot study included 42 healthy participants. PTS of six ascending concentrations (1 mg, 5 mg, 10 mg, 15 mg, 20 mg, and 25 mg piperine/dL 96% ethanol) were presented at the anterior tongue, and participants rated perceived intensity and duration. Then, participants performed a spatial discrimination task in which they had to report which of the two strips presented to the anterior tongue contained an irritating stimulus when one strip was always a PTS while the other strip was impregnated with either a single taste quality (sweet or bitter) or a blank strip. Repeated measures one-way ANOVA revealed that burning sensations of higher concentrated PTS were perceived more intense and more prolonged compared to lower concentrated PTS. McNemar’s test showed that PTS were identified correctly significantly less often when presented with bitter strips compared to when presented with blank (p = 0.002) or sweet strips (p = 0.017). Our results showed that bitter taste disrupts the spatial discrimination of piperine-evoked burning sensations. PTS might serve as a basis for further studies on disease-specific patterns in chemosensory disorders.

Temporal interactions between oral irritants: piperine, zingerone, and capsaicin

Sequential presentation of 2 irritants may produce cross-sensitization or cross-adaptation effects upon introduction of the second irritant. In Experiment 1, subjects were given either 34 min of stimulation with zingerone, capsaicin, or piperine or one of those irritants for 23 min followed by blanks for 23 min. In Experiment 2, subjects received one irritant for 23-min irritants, followed immediately by another for 23 min (piperine --> zingerone, piperine --> capsaicin, zingerone --> piperine, or zingerone --> capsaicin). Cross-sensitization was observed for the piperine --> zingerone, zingerone --> piperine, and piperine --> capsaicin groups; cross-adaptation was observed for the zingerone --> capsaicin group. Cross-adaptation and cross-sensitization were predicted by adding the independent time courses of the respective irritants, starting the second at the offset of the first. These responses were also predicted by a mathematical model of central processing of primary afferent responses.

Tonic and phasic processes in the acute effects of alcohol

This article presents a novel method for measuring the acute effects of alcohol. One hundred twenty nonproblem drinkers aged 21-28 participated in 3 alcohol administration sessions that produced peak blood alcohol concentrations (BACs) near .09 g%. Subjective intoxication ratings were taken at multiple points across rising and falling BACs. Mathematical modeling techniques decomposed intoxication ratings into a tonic component sensitive to BAC level and a phasic component sensitive to BAC rate of change. This model provided a good fit to observed data. Tonic and phasic gain parameters showed high repeatability across sessions. The average phasic gain parameter was about 4 times larger than the average tonic gain parameter, indicating that subjective intoxication is usually more affected by BAC change than by BAC level. The associations of drinking practices with tonic and phasic gain parameters varied by gender and family history of alcoholism. Tonic-phasic modeling allows individual and group differences in the acute effects of alcohol to be studied as time-dynamic processes.

Three distinct categories of time course of pain produced by oral capsaicin

Humans vary in oral pain tolerance. Our earlier studies noted that the responses of subjects show 1 of 3 qualitative response patterns to a single oral capsaicin concentration, which we termed a tonic pattern (level detection response), a phasic pattern (change detection response), and an integrator pattern (cumulative irritation) response. These patterns were modeled quantitatively as the sum of 3 underlying processes. Two time-varying capsaicin stimulus profiles were designed from the quantitative model. In the ascending step paradigm, 30 ppm capsaicin was presented to 42 subjects for 15 minutes, followed immediately and without explanation by 300 ppm capsaicin for 25 minutes. In the descending step paradigm, 300 ppm capsaicin was presented to 36 other subjects for 24 minutes, followed by 10 ppm for 22 minutes. Subjective burn was rated at 1 minute and then at 3-minute intervals throughout the presentation. Fuzzy cluster analysis identified 3 distinct response phenotypes in each paradigm, corresponding to level detection, change detection, and cumulative irritation response patterns identified previously. Discriminant functions permitted classification of these phenotypes from the response patterns. Thus, these paradigms provide the first quantitative phenotypic description of distinct oral pain responses to a common irritant, capsaicin.

PERSPECTIVE

This study examined the time-dependent behavior of pain produced by oral application of capsaicin. Three distinct temporal response phenotypes were identified objectively: level detection, change detection, and cumulative irritation detection. These time-dependent analyses provide a new dimension to understanding individual differences in pain sensation in clinical settings.

Adaptation to capsaicin burn: effects of concentration and individual differences

Human subjects rated the time course of the burn produced by three concentrations of capsaicin applied to the tongue via filter papers. Data were fit to a dynamic model composed of a level detector, a change detector, and a double integrator. These three processes responded differently to concentration. 6-n-Propyl-2-thiouracil (PROP) taster status correlated positively with the integrator process. Although a minority of subjects showed evidence of the integrator process, any subject with an integrator process at a given concentration also showed it at any higher concentration.