Effect of Radiation on Sucrose Detection Thresholds of Mice.

Radiotherapy is one of the most common treatments for head and neck cancers, with an almost obligate side effect of altered taste (Conger AD. 1973. Loss and recovery of taste acuity in patients irradiated to the oral cavity. Radiat Res. 53:338-347.). In mice, targeted irradiation of the head and neck causes transient repression of proliferation of basal epithelial cells responsible for taste cell replacement, leading to a temporary depletion of taste sensory cells within taste buds, including Type II taste cells involved in detection of sweet stimuli (Nguyen HM, Reyland ME, Barlow LA. 2012. Mechanisms of taste bud cell loss after head and neck irradiation. J Neurosci. 32:3474-3484.). These findings suggest that irradiation may elevate sucrose detection thresholds, peaking at 7 days postirradiation when loss of Type II cells is greatest. To test this hypothesis, sucrose detection thresholds (concentration detected in 50% of presentations) were measured in mice for 15 days after treatment of: 1) irradiation while anesthetized, 2) anesthetic alone, or 3) saline. Mice were trained to distinguish water from several concentrations of sucrose. Mice were irradiated with one 8 Gy dose (RADSOURCE-2000 X-ray Irradiator) to the nose and mouth while under 2,2,2-tribromethanol anesthesia (Avertin). Unexpectedly, mice given anesthesia showed a small elevation in sucrose thresholds compared to saline-injected mice, but irradiated mice show significantly elevated sucrose thresholds compared to either control group, an effect that peaked at 6-8 days postirradiation. The timing of loss and recovery of sucrose sensitivity generally coincides with the reported maximal reduction and recovery of Type II taste cells (Nguyen HM, Reyland ME, Barlow LA. 2012. Mechanisms of taste bud cell loss after head and neck irradiation. J Neurosci. 32:3474-3484.). Thus, even a single dose of irradiation can significantly alter detection of carbohydrates, an important consideration for patients undergoing radiotherapy.

Electrogustometry and contact endoscopy findings in patients with head and neck malignancies treated with chemotherapy, radiotherapy, or radiochemotherapy.

This study aimed to investigate in parallel changes in gustatory function, changes in morphology of the fungiform papillae, as well as changes in the shape and density of the vessels of the tip of the tongue in patients treated with chemotherapy, radiotherapy, or radiochemotherapy. Twenty patients (7 females and 13 males; age range: 42-78 years) with head and neck malignancies (hypopharynx, larynx, oropharynx, and parotid) treated with radiochemotherapy (n = 8), chemotherapy (n = 8), or radiotherapy (n = 4) were prospectively studied. In all patients, electrogustometry and contact endoscopy were performed. Radiotherapy-treated patients exhibited higher electrogustometry thresholds and greater alterations in the morphology and vascularization of the fungiform papillae than the other two groups. Radiochemotherapy patients had less pronounced changes of the electrogustometry threshold and fungiform papillae structure compared with radiotherapy patients. Chemotherapy alone caused less severe change in both electrogustometry threshold and fungiform papillae structure than radiotherapy or radiochemotherapy. Radiotherapy alone caused greater disorders of taste-related anatomic parameters and electrogustometry thresholds compared with chemotherapy and combined radiochemotherapy.

Single bright light exposure decreases sweet taste threshold in healthy volunteers.

INTRODUCTION: Bright light exposure can alter circulating serotonin levels, and alteration of available serotonin by acute selective serotonin reuptake inhibition significantly lowers sweet but not salt taste recognition thresholds. We tested the hypothesis that bright light exposure would increase sweet but not salt taste sensitivity in healthy adults. METHODS: Fourteen healthy volunteers were exposed to bright (10,000 lux) and dim (<20 lux) light for 30 min each, in counterbalanced order. Measures of taste perception (salt and sweet) and mood were determined at baseline, and before and after each light exposure period. RESULTS: Recognition thresholds for sucrose were significantly lower after bright but not dim light exposure. Thresholds for salt were unaffected by either condition. There were no significant changes in taste acuity, intensity or pleasantness for both the taste modalities and on visual analogue scales (VASs) for mood, anxiety, sleepiness and alertness, under either light condition. CONCLUSION: Brief bright light exposure reduces sweet but not salt taste recognition thresholds in healthy humans.

Umami taste dysfunction in patients receiving radiotherapy for head and neck cancer.

Taste loss is a major cause of morbidity in patients undergoing head and neck irradiation. Previous studies have reported the alteration of the four basic tastes in patients with head and neck cancer during radiotherapy. However, only a few studies have been conducted on the effects of irradiation on the function of umami taste, a novel and basic taste recently recognized. In a prospective study, 52 patients undergoing radical head and neck irradiation were assessed for taste loss. Taste ability was measured by the taste threshold for umami quality using the whole-mouth taste method in patients before, during, and immediately after radiotherapy. Umami taste declined of the 3rd week after the start of radiotherapy and improved of the 8th week.

Gustatory impairment in patients undergoing head and neck irradiation.

OBJECTIVES: To determine whether radiation alters taste function and structure. RESEARCH DESIGN: Prospective, longitudinal study. METHODOLOGY: Testing prior to starting radiation, and 2 weeks, 2 months, and 6 months after completing radiation. RESULTS: Relative to controls, patients had lower taste identification test scores for bitter, salty, and sour tastes. Sour taste also showed a significant group-by-time interaction (P = .03). Taste pores were decreased in the irradiated group, with a significant group-by-time interaction (P = .03). CONCLUSION: Head and neck cancer patients have decreased taste function, and radiation adversely affected sour taste and taste pores.

Taste dysfunction in patients receiving radiotherapy.

BACKGROUND: Taste loss is a major cause of morbidity in patients undergoing head and neck irradiation. METHODS: In a prospective study, 51 patients undergoing radical head and neck irradiation at the Tokyo University Hospital were assessed for taste loss. Taste ability was measured by the taste threshold for the four basic tastes (sweet, sour, salt, and bitter qualities) plus another taste of "umami" quality using a filter-paper-disc method in patients before, during, and after radiotherapy (RT). RESULTS: All tastes declined on the fifth week after the start of RT and improved on the 11th week. Anatomic pathologic analyses in rats revealed that taste buds diminished completely on the sixth day after irradiation of 15 Gy in a single fraction, and the appearance of taste buds returned almost to the preirradiation state on the 28th day. CONCLUSIONS: The main cause of taste disorder resulting from RT was believed to be a disappearance of taste buds and not damage to the taste nerves.

Taste dysfunction in irradiated patients with head and neck cancer.

Taste disorders caused by radiation therapy for head and neck cancer are common. This prospective study of 40 patients with head and neck cancer assessed changes in taste sensations during radiation therapy. The relationship between the time course and the degree of taste disorder was studied. The taste recognition threshold and supra-threshold taste intensity performance for the four basic tastes were measured using the whole-mouth taste method before, during, and after radiation therapy. Bitter taste was affected most. An increase in threshold for sweet taste depended upon whether the tip of tongue was included within the radiation field. The slope of the taste intensity performance did not change during or after radiotherapy. The pattern of salivary dysfunction was different from that of taste dysfunction. The main cause of taste disorders during radiation support the hypothesis that taste dysfunction is due to damage to the taste buds in the radiation field.

Taste intensity performance in patients irradiated to the head and neck.

Decrements in taste-detection thresholds during radiotherapy and subsequent recovery in the months after therapy are well documented. However, few studies have explored suprathreshold taste intensity perception in radiation patients. This cross-sectional study compared taste function in 15 men postradiation with a group of 23 healthy, nonirradiated male volunteers. A direct-scaling procedure was used to assess taste intensity perception of the four basic taste qualities. Patients performed nearly as well as control subjects on objective measures of suprathreshold functioning. Postradiation intensity judgments of salty (sodium chloride), sweet (sucrose), and bitter (quinine sulfate) solutions were not significantly reduced. Subtle, age-related taste impairments were identified for sour perception (citric acid) postradiotherapy. Younger patients judged citric acid to be more intense than did age-appropriate control subjects, whereas older patients judged it to be less intense. Moreover, younger patients were likely to be midly dysgeusic, whereas older patients appeared to be hypogeusic for citric acid. This study provides evidence for near normal suprathreshold taste intensity perception in patients who have received head and neck irradiation.

Gustatory impairment and salivary gland pathophysiology in relation to oral cancer treatment.

Gustation and salivation were evaluated in 41 patients with oral carcinoma who were treated preoperatively with Peplomycin (PLM) or PLM + 5-FU + 60CO- radiation. Thresholds for sweet, salt, sour and bitter were originally elevated in many patients. Gustatory impairment increased especially with chemo- and radiotherapy. Recovery, however, took place within a year to almost original levels. Salivation was originally not impaired. Resting salivary flow rate (SFR) of the combined therapy group was decreased to half the initial rate, and a 20% decrease of SFR was seen in the PLM group. Corresponding to SFR, 99mTc uptake of the submandibular glands had declined, and salivary viscosity had increased. Salivary gland damage persisted during the study, and appeared irreversible. It was concluded from these results that taste impairment by oral cancer treatment is temporary, while damage to the salivary glands is permanent.

Quantitative examination of taste deficiency due to radiation therapy.

A study was carried out with a Rion TR-03 type electro-gustometer for subjective and quantitative expression of the degree of taste deficiency due to radiation therapy and the effects of treatment. The changes of the electro-gustometric threshold due to irradiation were examined in patients who were divided into three groups: those receiving irradiation of the whole oral cavity, those receiving irradiation of the posterior tongue and the soft palate and those receiving irradiation of the gustatory nervous system. In the group receiving irradiation of the whole oral cavity, the threshold showed a tendency to increase when receiving 10 Gy/5 days, and the threshold became unmeasurable when more than 40 Gy/26 days was given. In the group receiving irradiation of the posterior tongue and the soft palate, almost no change of the threshold in the anterior was observed in spite of increasing irradiation doses. In the group receiving irradiation of the gustatory nervous system, the threshold in the intact hemicephalus did not changed even after irradiation, but a change was found on the pathological side. Based on these results, the authors originated a complication scoring system and a treatment scoring system both of which are divided into five stages. An electro-gustometric examination is used in order to provide effective treatment with a preserving function something which has been strongly desired for radiation therapy of cancer.

Long-term effects of radiotherapy on taste and salivary function in man.

The long-term effects of radiotherapy on taste and salivary function were studied in 13 patients treated by radiation 1--7 years previously for tumors of the head and neck. Taste function was quantitatively evaluated using a standard forced choice, three-stimulus-drop technique for the determination of detection and recognition thresholds and a forced-scaling technique for the determination of taste intensity responsiveness. Parotid salivary function was quantitatively evaluated by determination of flow rate and protein secretion rate. Nine of the 13 patients studied (69%) had measurable taste loss; every patient who had radiotherapy including the parotid glands had measurable salivary dysfunction. Our results demonstrate that curative courses of radiotherapy for tumours of the head and neck may result in long-term changes in taste and salivary function. From the present study, the maximum tolerance doses resulting in a 50% complication rate 5 years after treatment (TD 50/5) are estimated to be 40--65 Gy for xerostomia and 50--65 Gy for taste loss. Therefore, in a standard treatment regimen for tumors of the head and neck, with curative intent, gustatory and salivary gland tissues frequently sustain maximum tolerance injury.