Histological characterization of rat vocal fold across different postnatal periods

To evaluate the vocal fold histological characteristics during different postnatal periods in rats, especially older rats.

Sprague-Dawley rats aged 4 days, 4 and 12 weeks, and 12 and 24 months were used for the experiment. Five larynges were obtained for each age and cut into 5-μm consecutive sections. The expression of Ki-67 was assessed using immunohistochemistry to examine cell proliferation. Elastic van Gieson staining was used to detect the collagen and elastin concentrations. The cell type was determined using multicolor immunofluorescence.

Ki-67 was not expressed in the macula flava (MF) of 12-week-, 12-month-, and 24-month-old adults. Collagen fibers in the lamina propria (LP) increased with age. The elastic fiber concentrations in the LP decreased significantly at 24 months (p < .01) but remained stable in the MF. All posterior MF cells showed strong glial fibrillary acidic protein and vimentin-positive reactions with weaker expressions of CD68 and α-smooth muscle actin (α-SMA). The myofibroblasts (α-SMA-positive) and macrophages (CD68-positive) in the LP of the 24-month-old rats were significantly the highest (p < .01).

The extracellular matrix in the LP increases with age, presenting as an increase in collagen with the loss of elastin, which may be due to myofibroblast proliferation. Moreover, the cellular properties or extracellular matrix components of the mature MF in rats are comparable to those in humans.