Angioarchitectural form, functional distributive pattern and classification of the filiform papillae on the crossbred Japanese cat tongue anterodorsal surface in scanning electron microscopic specimens

ANNALS OF ANATOMY

Angioarchitectural form, functional distributive pattern and classification of the filiform papillae on the crossbred Japanese cat tongue anterodorsal surface in scanning electron microscopic specimens Koei Ojima, Fusako Mitsuhashi, Masanori Nasu and Yuji Suzuki Dental Research Institute, School of Dentistry at Tokyo, The Nippon Dental University, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan t

Summary. The purpose of this study was to undertake a three-dimensional comparative observation of the angioarchitectural form, functional distributive pattern and classification of the filiform papillae (FiP) as they appear on the entire dorsal surface of the front of the Japanese cat tongue using microvascular cast specimens (MVCS). By means of the corrosive resin casting technique, the MVSC of the FiP of the cat tongue were prepared and examined in detail under the scanning electron microscope (SEM). On the frontal half of the anterodorsal surface of the anterior tongue, types I-V of the f i P are arranged in the form of a A with the point in the direction of the apex and in an oblique line running from the antero-central to both postero-peripheral regions. In the rear half of the anterodorsal surface of the anterior part of the tongue, types I-V of the FiP are arranged in the form of a V with the point in the direction of the root and in an oblique line running from both antero-pefipheral regions to the postero-median region or towards the pharynx on the anterior centro-dorsal surface of the tongue. The FiE arranged in an oblique line running fron the central to the apical part of both the periphery and the pharyngeal region of the cat tongue, can be classified into five types (Types I-V) according to the shape and size of the main process (MP), numbers of the accessory processes (AP) and regional position of the lozenge arrangement. FiP Types I-III consisted of an MP which contained a large spoon-shaped and concave network process, and the AP contained a bundle of spin-like processes arranged radially at the anterior basal margin of the MP. FiP Types IV and V consisted only of MP. Correspondence to: K. Ojima Ann Anat (2000) 182:47-52 © Urban & Fischer Verlag

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It was conjectured that the lozenge arrangement of the A and V form FiPs, classified into five types (Types I-V) from the frontal portion of the anterodorsal surface toward the pharynx on the front of the tongue, play a functionally assistant role in the mastication of food and sucking of liquid, including milk.

Key words: Cat - Tongue - Filiform papillae - SEM Microvascular cast specimen

Introduction The fine structural and three-dimensional histological observations of the FiP on the cat tongue dorsal surface have been made by SEM (Boshell et al. 1982; Chamoro et al. 1987; Iwasaki et al. 1987a, b; Iwasaki 1990, 1992, 1993; Kobayashi et al. 1988; Kobayashi and Iwasaki 1988 and Kobayashi 1992). Recently, with the SEM, a microvascular structural study of the filiform papillae (Ojima and Lowe 1995c), functional and morphological observation of the microvascular structure of the filiform and fungiform papillae in the cat tongue (Ojima et al. 1996 c), angioarchitectural comparison of the filiform papillae of the cat and rabbit by scanning electron microscopic specimens (Ojima et al. 1996d), the functional distributive role of the filiform, fungiform and conical papillae seen in microvascular cast specimens of the cat tongue centro-dorsal surface (Ojima et al. 1998) have been reported. Little is known, however, of studies on the comparative observation of the relationship between the functional distributive role and classification of the FiP under at high magnification. 0940-9602/2000/182/1-47 $12.00•0

This study deals with the relationships b e t w e e n the angioarchitectural form, functional distributive p a t t e r n and classification of the FiR and the fine m o r p h o l o g i c a l S E M o b s e r v a t i o n at high magnification of the FiP from a comp a r a t i v e m o r p h o l o g i c a l p o i n t of view.

r a n g e d in g e o m e t r i c a l l y o r d e r e d fashion in the form of a A in an oblique line from the a n t e r o - c e n t r a l zone to the p o s t e r o - p e r i p h e r a l zone. O b s e r v a t i o n s of the C zone show the types of FiP arr a n g e d in a g e o m e t r i c a l l y o r d e r e d fashion in the form of a V in two directions, to the p o s t e r o - c e n t r a l zone and the p h a r y n x (Fig. 2).

Materials and methods J

Tongues from 60 crossbred Japanese domestic cats, Fel& catus domestica, were used in the present study. Cats of both sexes (20 females and 40 males) were obtained from a commercial supplier. All were adults of unknown age. Each cat weighed between 2.5 and 5.0 kg. They were anaesthethized with an overdose of Nembutal solution® (Pentobarbital sodium injection) by intraperitoneal injection and killed. Their tongues were immediately removed and both lingual arteries were cannulated and prepared for macroscopical, stereomicroscopical and SEM observation. For general SEM observation: each tongue surface was rinsed with 0.9% physiological saline solution or Ringer's solution at 35-37 °C, and after cannnlation with an injection needle (27 G) connected to a silicone-tube. Vascular perfusion of the inside of blood vessels with 0.9% physiological saline solution or Ringer's solution was continued until all the blood in the jugular veins had been replaced by the solution. 0.5% glutaraldehyde solution in phosphate buffer (pH 7.4) was then injected into both lingual arteries in order to fix the vessels and their tributaries. Both lingual arteries were filled with synthetic resin (Mercox ® CL-2R 5, CL-2B 5, CL-2C 5, Dainippon Ink Chemicals, Tokyo, Japan) under manual pressure. The injected specimens of the tongue were fixed for 0.5 hr at room temperature and incubated for 0.5 hr at 55 °C. The specimens were then polymerized completely, immersed in 20% KOH or NaOH solution for over 3 hr at room temperature until the soft tissues of the tongue had been dissolved away by these solutions. The finest macerated vascular samples were carefully washed 2-3 times with warm and tap water at 45-55 °C and gently dried for 2-3 days at 55 °C in an incubator. The MVCS of the whole tongue were mounted on specimen stubs, sputter-coated with platinum and then examined with a S-4000 scanning electron microscope (Hitachi, Tokyo, Japan) at an accelerating voltage of 5-10 kV.

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Fig. 1. A schematic diagram showing the distribution of the various kinds of lingual papillae on the entire dorsal surface of the cat tongue. The A zone is the apical portion, the B zone is the frontal half portion, and the C zone is the rear half portion of the central-dorsal surface on the anterior part of the tongue. The D zone is the posterior portion of the anterior part of the tongue. The E zone is the postero-dorsal portion of the posterior part of the tongue. The square insets F 1 and F 2 in the B zone of this diagram correspond to Figs. 3 and 4. From the central portion of B and C zones to the apex portion, the peripheral portion in both directions and to the posterior portion, types I - V of the FiP (filiform papillae) and types I-IV of the FuP (fungiform papillae) are arranged in a geometrically ordered and comparatively symmetrical fashion. The square insets of B and C zones in this diagram correspond to Fig. 2. On the posterior third of the centro-dorsal surface (the D and E zones), ScoP (small conical papillae) are arranged regularly from the central portion to the posterior portion (pharynx). LCoP (large conical papillae) are arranged in oblique lines geometrically and symmetrically from both peripheral portions to the central portion. The CvP (circumvallate papillae) are symmetrically arranged in the form II (parallel lines) or V (oblique lines) on both left and right sides on the postero-dorsal surface. Indication mark : • = type I of FiR (D = type II, ~) = type III, @ = t y p e I V , o = t y p e V , and @ = t y p e I of FuR ~ = t y p e I I , ( ~ = t y p e l I I , *=type IV, : - : = S C o R . ' . = L C o R O = C v R * = zone of non-lingual papillae.

Results The t h r e e - d i m e n s i o n a l c o m p a r a t i v e o b s e r v a t i o n of the angioarchitectural form, functional distributive p a t t e r n and classification in M V C S of the FiP on the whole dorsal surface of the crossbred J a p a n e s e d o m e s t i c cat tongue w e r e investigated u n d e r the SEM. The S E M m i c r o p h o t o g r a p h s of the whole dorsal surface of the tongue were d i v i d e d into five zones: the A zone (the apical portion), the B zone (the frontal half) and the C zone (the r e a r half) of the anterior p a r t of the tongue, the D zone (the frontal half) and E zone (the r e a r half) of the p o s t e r i o r p a r t of the cat tongue in this study (Fig. 1). O b s e r v a t i o n of the B zone shows the types of FiP at48

Fig. 2. Upper view of the composite photograph of a scanning electron micrograph of an MVCS (microvascular cast specimen) of the frontal portion corresponding to the square inset of B and C zones in Fig. 1 on the anterior part of the tongue. Types I - V of the FiP arranged in an oblique line running fron the antero-central portion to the posterior periphery of the both sides in geometrically ordered fashion in the form of a A. On the other hand, the FiPs arranged in an oblique line running from both the peripheral portions to the centro-dorsal portion in geometrical fashion in the form of a V. The A and V form the lozenge zone.

Fig. 3. Upper view of the composite photograph of scanning electron microphotographs of MVCS corresponding to the square inset F 1 in the B zone in Fig. 1. The spoon-like concave network structure consisting of the ascending and descending capillary branches of the MP on types I-III of the FiP is arranged on the oblique line running from the central to the peripheral part facing in the anterior direction, and the top of the MP on the FiP is inclined in the posterior direction. Indication mark : • = type I of FiP, O = type II, (~) = type III, @ ; type IV, o = type V. The arrow in the upper left corner in Figs. 1-3 indicates the anterior (apical) direction of the tongue. Bar = 500 gm 49

Fig. 4. Upper view of the composite photograph of the scanning electron micrograph of the MVCS corresponds to the square inset F 2 in the B zone in Fig. 1. The FiPs arranged on the oblique line geometrically and consisting of the spoon-like concave microvascular network structure of the MP of the FiP face in the anterior direction and the AP surrounding the basal part of the MP radially are seen.

Fig. 5. Frontal views of high magnification of Types I-III of the FiP with an MP and the APs, and Types IV and V respectively. Type II were smaller than type I, but larger than type III, and type III were smaller than type II. Type I had 6-8 pairs AR Type II had 5-7 pairs AP and type III had 4-5 pairs AP respectively.

Observation of F 1 (Fig. 3) and F 2 a r e a s (Fig. 4) in the B zone, as described in a previous report, shows that there are five types of FiP (types I - V ) (Ojima and Lowe 1995 c) on the anterior half of the dorsal surface of the front part of the cat tongue. The FiP were classified into five types I - V according to the size, shape, number of their processes, and their regional relationships arranged in an oblique line running from the central to the apical parts, both the peripheral part and the pharynx. These processes were of two kinds: the main process (MP) and the accessory processes (AP). The MP included large, middle and small processes of types I - I I I respectively, but there were no types IV or V. The AP consisted of many pairs of processes of types I-III. The groups of characteristic types I - I I I were arranged in a regular geometrical pattern from the central

to the peripheral portion of the anterior part of the tongue (Fig. 3-4). Types I - I I I FiPs contained a single MP which originated in a spoon-like concave microvascular network structure, pointed and inclined in the posterior direction. Furthermore, many pairs of APs extended from the anterior basal margin, formed a fence-like circle and radiated out in the anterior direction (Fig. 5: I-III). Types IV and V FiPs did not contain an AP. Type IV were comparatively long cylinder-like processes (Fig. 5:IV) and type V were short, rod-like or ring-like processes (Fig. 5: I-V). Type I (I) FiP was designated the large process type, type II (II) the middle process type, type III (III) the small process type, type IV (IV) the cylinder-like type and type V (V) the ring-like type (Fig. 5: I-V). 511

Discussion It may be reasonable to think that the blood supply to the tongue is more plentiful than that to most other organs of the body (Hellekant 1971). MVCS of blood vessels inside the lingual papillae form its basic structural core. MVCS provide an ideal, practical method for studying the threedimensional angioarchitectural images of the microvascular network structure of the lingual papillae. Compared with other previous vascular perfusion methods, this novel technique offers an advantage in obtaining a fine imprint of the walls of the small blood vessels of the lingual papillae and makes it possible to differentiate between arterioles and venules in terms of shape, size and anastomosis. In the present study, the resin cast methods used in previous studies (Ojima 1995 a,b; Ojima and Lowe 1995c and Ojima et al. 1996 a-d) were modified and improved by injecting Mercox into vessels that had first been twice treated with glutaraldehyde. In this way the authors achieved better results in preserving the walls of blood vessels and preventing extravasation of the injected Mercox ®. They could thus observe MVCS under better conditions (Ojima et al. 1997 a-f; Ojima 1998). In this study the fine microvascular cast network structure of the FiP which was not reported in previous papers could be observed at high magnification under the SEM. There are many SEM studies of the FiP (Boshell et al. 1982; Iwasaki etal. 1987a, b and Ojima and Lowe 1995c) on the dorsal surface of the cat tongue. Using Etec Autoscan SEM and transmission electron microscopy it has been possible to focus on variations in the shape, size and organization of the FiP on the entire dorsal surface of the cat tongue (Boshell et al. 1982) and to classify the FiP in MVCS by means of the S E M (Ojima and Lowe 1995 c). Comparisons have been made between the functional mechanisms and morphological observations of the microvascular structure of the FiP and FuP in the cat tongue (Ojima et al. 1996c). Angioarchitectural comparison of the FiP of the cat and rabbit have been undertaken with SEM (Ojima et al. 1966 d). On the other hand, the relationships between the functional role and distribution of the microvascular cast specimens of the FiP on the anterior central dorsal surface (Ojima et al. 1997b) and on the posterior central dorsal surface of the cat tongue (Ojima et al. 1997d) have been studied. In this study, the typical geometrical distributive pattern in the A and V forms on the MVCS of the FiP was seen as a lozenge-shaped arrangement, and was similar to the microphotographs in previous SEM reports. The results suggest that the FiPs play a functional assistant role in the mastication of foods and sucking of liquids (including milk) and, on the other hand, in trans-

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porting the masticated food, liquid and milk from the anterior and antero-peripheral region to the central part and root or pharyngeal part.

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Ojima K, Takeda M, Saiki C, Matsumoto S (1996c) Functional and morphological observations on the microvascular structure of the filiform and fungiform papillae in the cat tongue. Ann Anat 178:361-364 Ojima K, Takeda M, Saiki C, Matsumoto S (1996d) Angioarchitectural comparison of the filiform papillae of the cat and rabbit by scanning electron microscopic specimens. Ann Anat 178:449--454 Ojima K, Matsumoto S, Takada M, Saiki C, Takahashi T (1997 a) Numerical variation and distributive pattern on microvascular cast specimens of vallate papillae in the crossbred Japanese cat tongue. Ann Anat 179:117-126 Ojima K, Takeda M, Saiki C, Takahashi T, Matsumoto S (1997b) A form distribution seen in microvascular cast specimens of the filifom and fungiform papillae on the anterior central dorsal surface of the cat tongue, Ann Anat 179:201-208 Ojima K, Takahashi T, Takeda M, Matsumoto S, Saiki C (1997 c) Angioarchitectural comparison of the fungiform papillae of the cat and rabbit using scanning electron microscopic specimens. Ann Anat 179:209-214

Ojima K, Takeda M, Matsumoto S, Saiki C, Takahashi T (1997 d) Functional role of V form distribution seen in microvascular cast specimens of the filiform and fungiform papillae on the posterior central dorsal surface of the cat tongue. Ann Anat 179:321-327 Ojima K, Matsumoto S, Saiki C, Takahashi T, Takeda M, Mitsuhashi F (1997 e) Angioarchitectural structure of the fungiform papillae on the antero-dorsal surface of the rabbit tongue. Ann Anat 179:329-333 Ojima K, Takeda M, Matsumoto S, Nakanishi I (1997f) An investigation into the distributive pattern, classification and functional role seen in MVCS of CoP on the posterodorsal surface of the cat tongue using SEM. Ann Anat 179: 505510 Ojima K (1998) The functional distributive role of the filiform, fungiform and conical papillae seen in microvascular cast specimens of the cat tongue centro-dorsal surface. J Nippon Dent Univ 1:20-27 Accepted June 16, 1999

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