SUPPLEMENTARY MATERIAL Yale University: Science Education Outreach Program

I.C) Taste Buds: The PROP Method

1. What is PROP?
PROP (6-n-propylthiouracil) is a medication used to treat Grave's Disease (hyperthyroidism). PROP is designed to reduce the thyroid's ability to produce hormones. People taking this medication might take 50 mg (3-4 tablets each) daily. Each PROP paper contains about 1.6 mg PROP. Follow the procedure below for preparing PROP papers.

2. Staining Fungiform Papillae
The bumps on the anterior surface of the tongue are papillae. The most numerous are the filiform papillae but these have no taste function. The fungiform papillae look like tiny button mushrooms (hence their name). The fungiform papillae are the most densely distributed on the tip of the tongue and thin out as you move toward the center of the tongue. The fungiform papillae are the structures that contain taste buds. Although supertasters tend to have more taste buds on each papillae than nontasters, what really makes them supertasters is that they have many more fungiform papillae. Counting fungiform papillae requires only a magnifying glass, a flashlight, blue food coloring and Q-tips.

Swab the blue food coloring on the front of the tongue (cover the tip and about 1/2 inch back). Have the subject move the tongue around in the mouth and swallow. This distributes the dye. Swallowing the dye is not hazardous. You will see pink circles emerge from the blue background. The pink circles are the fungiform papillae. The fungiform papillae appear pink because they do not stain as well as the filiform papillae.

For a complete description of the method used in the laboratory see: Bartoshuk, L.M., Duffy, V.B., Miller, I.J., PTC/PROP tasting : Anatomy, psychophysics, and sex effects. Physiology and Behavior (1994) 56:1165-1171

3. A simple classroom experiment.
This is an experiment that could be done in a science lab or classroom as well as used for research. You need a template that can be placed on tongues in a consistent manner. For example, you can use a paper punch to punch a hole in a 1 inch square of wax paper or you can use the reinforcements sold for notebook paper. Either of these wil give you a hole about 6-7 mm in diameter. Place the template on the tongue so that the hole is in a standard position (see sketch below).

Swab blue food coloring on the tongue. Using a flashlight and a magnifying glass, count the number of fungiform papillae. The sketch below shows examples of a supertaster and a nontaster.

The circles correspond approximately to the hole produced by a typical paper punch or to the hole inside a notebook paper reinforcer.

In the laboratory, we can look at the stained tongue under a microscope. We see small blue dots on most of the fungiform papillae. These are taste pores, the conduits to tast buds. In size, the taste pores are to the fungiform papillae as a sesame seed is to a hamburger bun.

4. Preparing PROP papers
Source of PROP (6-n-propylthiouracil) (pharmaceutical grade):

Pfaltz-Bauer
172 E. Aurora St.
Waterbury, CT 06708 (203-574-0075)

The PROP papers are made on filter paper (Whatman #1). Heat tap water to near boiling and then add 5 grams PROP to 500ml water. The aim is to make a saturated solution. (As the solution cools, crystals will precipitate out of solution.) Dip the pieces of filter paper in the PROP solution so that they are completely soaked. We use small pieces of filter paper (3 cm circles) and allow them to dry individually on sheets of aluminum foil. The PROP crystallizes into the filter paper. Thuse the paper is a convenient way to deliver a few crystals of PROP to a subject.

To taste the paper, put the whole piece in your mouth and let it get well moistened with saliva. The bitter taste may build slowly or may be perceived immediately. When the bitter taste is at a maximum, the bitterness can be rated on a scale (see item 5).

This procedure was kindly provided by:

Linda M. Bartoshuk
Yale University School of Medicine
Department of Surgery
333 Cedar St.
New Haven, CT 06520-8041