There Is Accounting for Taste in Treatment of Depression

BRISTOL, England, Dec. 6 -- For newly diagnosed depression patients, there may be a tell-tale taste test for selecting the right antidepressant.

On the basis of their finding that serotonin and norepinephrine can alter taste thresholds, investigators here think they may have found a tasteful way to choosing the antidepressant that fits the patient.

In a study of 20 healthy adult volunteers, those who were exposed to the selective serotonin reuptake inhibitor Paxil (paroxetine) had significantly lower thresholds for sweet and bitter tastes than they normally did, wrote Lucy F. Donaldson, Ph.D., of the University of Bristol, and colleagues, in the Dec. 6 issue of Journal of Neuroscience.

Similarly, volunteers given the norepinephrine reuptake inhibitor Edronax (reboxetine) were able to detect much smaller concentrations of bitter and sour tastes than they normally could, although neither drug appeared to affect taste thresholds for salt, the investigators found.

"Because we have found that different tastes change in response to changes in the two different neurotransmitters, we hope that using a taste test in depressed people will tell us which neurotransmitter is affected in their illness," said Dr. Donaldson.

"This is very exciting," agreed co-author Jan Melichar, M.D. "Until now we have had no easy way of deciding which is the best medication for depression. As a result, we get it right about 60% to 80% of the time. It then takes up to four weeks to see whether the drug is working, or if we need to change it. However, with a taste test, we may be able to get it right first time."

Alteration of taste has been documented in patients with depression, anxiety, and panic disorder. One theory about the etiology of depression holds that the disorder is caused by either lower levels of circulating monoamine neurotransmitters (such as serotonin, norepinephrine, and dopamine) or a reduction in the sensitivity of monoamine receptors, or both, the authors noted.

"Many antidepressants modulate monoamine function, and their use is associated with dysgeusia," they wrote. "This modulation of monoamine function may have an impact on taste perception, and this may be the basis for altered taste in affective disorders."

To see whether they could detect a link between mood, taste, and levels of the neurotransmitters, the investigators enrolled 20 healthy volunteers (12 men and 8 women) from the ages of 19 to 47. One of the volunteers completed only part of the study.

The volunteers were tested for depression with the Beck Depression Inventory and for anxiety with the Spielberger State and Trait Inventory at each of three visits, and were then tested for taste recognition thresholds -- that is, their ability to sense sweet, salty, sour, and bitter tastes in various dilutions.

They were then given either 20 mg of Paxil, 4 mg of Edronax, or a placebo, and were tested again two hours after taking the drug. The volunteers were told what taste they would be given, but not the concentration or whether they would be expected to recognize the taste.

The authors found that boosting serotonin levels via the use of Paxil resulted in a 27% reduction in the taste threshold for sucrose, and a 53% reduction in the taste threshold for quinine (bitter).

In contrast, elevated norepinephrine levels, courtesy of Edronax, resulted in a 39% reduction in the taste threshold for quinine, and a 22% reduction in the recognition threshold for sour.

There were no effects on taste from the placebo.

To determine whether mood and taste sensitivity might be related, the authors looked at baseline thresholds and scores on the anxiety and depression scales.

Although depression scores were low in the group and anxiety scores were within the clinically normal range, they did detect an association between Spielberger Trait scores (general anxiety levels) and both bitter and salt taste thresholds among participants with high-normal anxiety.

Among the participants with the highest levels of anxiety, the taste thresholds were higher, meaning that their sensitivity for bitter and salt (but not sweet or sour) tastes was blunted, the authors wrote.

"Our findings show that taste, previously thought to be principally genetically determined with little day-to-day variability, can be extremely plastic and is profoundly affected by modulation of the 5-HT [serotonin] and/or noradrenergic systems in normal healthy individuals," Dr. Donaldson and colleagues wrote.

"Our results reinforce previously reported findings of taste disturbances in patients with affective disorders, in that taste threshold is directly related to anxiety level, again in a normal healthy population where response bias is likely to be less of a problem than in an ill population," they continued. "These results support an important and basic role for 5-HT and NA in taste function and may explain why anxious and depressed individuals exhibit diminished appetite."