Cellular proliferation in the nasal septal cartilage of juvenile minipigs

Abstract

The growth of the nasal septal cartilage is believed to be a driving force of midfacial growth. Cellular proliferation is an important contributor to growth of the cartilage, but this factor has been rarely investigated. The current study was undertaken to assess the proliferation and cellular density in the septal cartilage of fast-growing juvenile minipigs. Six minipigs averaging 4.4 ± 1 months old were injected with 5'-bromo-2'-deoxyuridine (BrdU), a thymidine analog, 24 h before death. The septal cartilage was sectioned in the coronal plane and reacted for BrdU. The proliferative index (number of BrdU-positive chondrocytes/total number of chondrocytes) and cellular density (number of cells mm(-2) ) of various locations of the septum were measured and compared in order to determine overall proliferation rate and whether regional variations in proliferative activity and cellular density are present. To provide a time perspective to the problem of midfacial growth, the lengths of the nasal bone and the palate were measured in a collection of 61 dry skulls of minipigs aged 1-8 months. Results showed that the septal chondrocytes were proliferating at a surprisingly high rate (~21%). The proliferative index was higher in the ventral and middle compared with the dorsal locations, and in the central cartilage compared with the perichondrium. No difference in proliferative index was found between the anterior and posterior parts of the septum. Cellular density was higher in the perichondrium than in the central cartilage. Within the central cartilage there was a trend for higher cellular density anteriorly. In conclusion, the rapidly growing midface of juvenile minipigs is associated with a high rate of septal proliferation, especially in the ventral half of the cartilage.

Keywords: 5′-bromo-2′-deoxyuridine; cellular proliferation; midfacial growth; minipigs; nasal cartilage.

Fig. 1

Medial view of a sagittal section illustrating the position of the blocks, and the anterior and posterior portions of the septal cartilage. The entire shaded area is cartilaginous, but the lightly shaded ventral section is contained within the bony vomerine groove. E, perpendicular plate of the ethmoid bone; F, frontal bone; M, maxillary bone; N, nasal bone; NFS, nasofrontal suture; PM, premaxillary bone; PM-MS, premaxillary-maxillary suture; PS, presphenoid bone; SC, septal cartilage; SC/VG, vomerine groove housing the ventral part of the septal cartilage; V, vomer.

Fig. 2

Coronal section through the snout at a level corresponding to block 3 in Fig. 1, illustrating the locations used to measure the proliferative index and cellular areal density. Cartilage locations: D, dorsal; M, middle; T, parietotectal; V, ventral. Perichondrial locations: PD, perichondrial dorsal; PL, perichondrial lateral; PV, perichondrial ventral.

Fig. 3

Left: positive staining of the nasal epithelial cells used as positive control (A) and positively stained nasal cartilage chondrocytes (C). Right: negative control showing absence of staining in nasal epithelial cells (B) and nasal cartilage chondrocytes (D).

Fig. 4

(A) Overall proliferative index for each block (mean and standard deviation, n = 6). No pattern of variation is apparent. (B) Proliferative index of septal locations (mean and standard deviation, n = 6). The proliferative index of the parietotectal cartilage was lower than the averages for central cartilage and perichondrium. Within the central cartilage and the perichondrium, the proliferative index of the dorsal location was lower than those of the middle and ventral locations.

Fig. 5

(A and B) The middle cartilage location in the anterior (A, block 2) and posterior (B, block 8) portions of the septum of animal 402. The cells in the posterior portion appear larger than those in the anterior portion. (C) The anterior tip of the septal cartilage of animal 402 (block 0). Decalcified bone of the os rostri is seen just above the heavily labeled chondrocytes in the upper (dorsal) part of the slide. Scale bars: 200 μm.

Fig. 6

Scatter plots of midline lengths of the nasal bone (triangles) and the hard palate (squares) against minipig age in weeks (n = 25 males, open symbols; and 35 females, solid symbols). Growth of both elements is generally linear (Pearson's correlation coefficient, R = 0.87–0.97) and there is no difference between the sexes in this age range. The shaded area between 16 and 22 weeks of age represents the age span of the BrdU sample.