Change of the human taste bud volume over time
Introduction
Fungiform papillae (fPap) are located at the anterior part of the tongue and bear the peripheral taste organs, the taste buds. Taste buds are epithelial structures within the epithelium that resemble an unopened calyx of a rose [1]. They consist of about 50–120 epithelial cells [2] and have a diameter of between 25 and 50 μm [1]. Each taste bud usually has a single opening on the upper surface of the fPap, the taste pore. The area of the taste pore varies between 135 and 225 μm2 [3]. It has been shown that over half of the fPap bear no taste buds [4], [5], [6] and are also referred to as non-gustatory fPap. The numbers of taste buds per gustatory fPap range from 0 to 512 taste buds/cm2 on the tongue tip and from 0 to 86 taste buds/cm2 in the mid-region of the tongue. Single fPap on the tongue tip bear 0–22 taste buds with 0–9 taste buds in the mid-region [1].
Using video microscopy, the taste pores as indicators of taste buds were counted in living animals [7] and in human subjects [1], [8], [9]. In animal experiments, it has been shown that the number of pores on individual papillae changed by about 40% over a 9-week period and then in the following weeks by about 5% per week [7]. Although a constant turnover of taste buds has been assumed in animals [7], no longitudinal study has been carried out in human subjects monitoring individual taste pores/taste buds and calculating the volume of the taste buds over time.
Confocal laser scanning microscopy (LSM) is an in vivo method that provides quantitative data both non-invasively and rapidly [10]. Ophthalmology is the major application field of in vivo LSM [11]. In recent years, confocal microscopy has been used for visualisation of epithelia outside the field of ophthalmology, e.g. the oral cavity [12], [13], [14] and larynx [15], [16]. LSM allows the clinician to visualize epithelia with high-depth resolution. This technique provides cellular information within the fPap and thus makes it ideal for examining taste buds. In earlier studies, it has been demonstrated that the taste bud structure is easy to identify [13], [17]. Recently, the basic principle of volumetry of the human taste bud of fungiform papillae has been shown using in vivo LSM [18].
The specific aim of this study is to measure the taste volume in healthy human subjects in vivo over a 10-week period and to demonstrate morphological changes of the peripheral taste organs. It is important to state that always the same fPap with its taste buds were measured in the observation period.
Section snippets
Subjects
The volumetry was performed once a week on 18 taste buds in four fPap in two healthy volunteers (two men, age 23 and 38 years) over a 10-week period. The selected fPap were defined as reference papillae and are characterized by a typical shape of the papilla or by a characteristic arrangement of the taste buds as described later on. The key step of this investigation is the volumetry of these reference papillae.
The subjects were screened for taste sensitivity using taste strips [19] and
Results
Confocal photomicrography of four different fPap is presented in Fig. 1, Fig. 3, Fig. 5, Fig. 7 (Fig. 1: six taste buds in a butterfly-shaped fPap, Fig. 3: four taste buds in a T-shaped arrangement, Fig. 5: five taste buds in an X-shaped arrangement, and Fig. 7: embryo-shaped fPap with three taste buds). The fPap investigated were 230–480 μm in diameter. The taste buds were 21.8–64.7 μm in diameter and 33.1–50.5 μm in height. The diameter of the taste pore reveals a high variation among the
Discussion
To our knowledge, this is the first in vivo study measuring the volume of human taste buds in healthy subjects over a 2.5-month period using confocal microscopy. The results of this exploratory study indicated that (i) the taste bud volume changes over a 10-week period, (ii) the interval between two volume maxima within the 10-week period is 3–5 weeks, and (iii) the diameter of the fPap does not correlate with either the volume of a single taste bud or with the volume of all taste buds in the
Conclusions
The key step of the method and procedure described here is that the volumes of the taste buds always of the same fPaps, defined as reference papilla were measured in vivo. Results of this in vivo study measuring the volume of human taste buds in healthy subjects over a 10-week period using confocal microscopy indicated that the taste bud volume of single fPaps changed over a 10-week period. The volumes of some taste buds increase or decrease, whereas the volumes of other taste buds remain
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