Proceedings of The Physiological Society

Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, PC324a

Poster Communications

The ability of humans to discriminate binary taste mixtures is reduced by noradrenaline reuptake inhibition and alpha-2 adrenoceptor agonism

S. James1, M. Skelly1, I. Annett1, J. K. Melichar1, L. F. Donaldson1

1. Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.

Serotonin (5HT) and noradrenaline (NA) reuptake inhibitors increase taste sensitivity in healthy humans (1). Both 5HT and NA are hypothesised to have paracrine effects in taste buds (2,3), for example 5HT released from Type III taste cells (sour, salt) inhibits Type II taste cells (sweet, bitter, umami). The functions of paracrine actions of 5-HT and NA in the taste bud are not understood. This study investigated whether modulation of 5HT and NA altered taste contrast of Type III (salt) and Type II (sweet) taste cell modalities in healthy young adults. Ethical approval for the study was given by the University of Bristol Faculty of Medical and Veterinary Sciences Ethics committee. Healthy subjects (n=10, age range 20-22yrs, female:male 7:3) gave informed consent for inclusion in the study. Taste contrast was measured by determining the participant's ability to rank 8 mixtures of increasing NaCl (0-0.6%) and constant sucrose (2%) solution (R index (4)). This task was performed before, and 1 and 2 hours after double-blind administration of placebo (lactose), serotonin specific reuptake inhibitor (paroxetine; 20mg), noradrenaline reuptake inhibitor (NARI; reboxetine, 4mg), or α-2 adrenoceptor agonist (lofexidine, 200μg). The cumulative R index for each participant was calculated, and linear regression analysis used to compare cumulative R index before and after drug administration (elevation of regression lines compared using ANCOVA). Stress, affect and anxiety were assessed using standard questionnaires, and participants divided into two groups on median scores for comparison of taste discrimination. Participants were less able to correctly rank salt/sucrose mixtures compared to salt alone. After 1 hour, the ability of participants to discriminate salt in a salt/sweet mixture was only reduced by NARI (p=0.0016). After 2 hours, only the α-2 agonist reduced discrimination (p=0.0087). Less anxious participants performed better in the discrimination task than more anxious participants (p=0.02). Affective measures did not change with drug showing that reduced discrimination after drug administration is not due to an acute drug-induced mood change. Our findings suggest that NA acts to reduce the ability of healthy individuals to discriminate between Type II and III taste modalities, possibly through alpha-2 adrenoceptors. Furthermore, these findings suggest that reduced taste contrast may contribute to taste disturbance in anxiety.

Where applicable, experiments conform with Society ethical requirements