Distribution of tracheal and laryngeal mucous glands in some rodents and the rabbit

We used scanning electron microscopy to count the number of mucous gland openings in the tracheae and lower portion of the larynges of the rat, guinea pig, hamster, mouse and rabbit. Cells of the airway surface epithelium were removed by protease digestion better to visualise the gland openings. The distribution of glands was further studied by conventional histology and by PAS/Alcian blue staining of whole mounts. In all rodent species, gland openings in the larynx occurred with a frequency of 1–2 per mm². Mice had no gland openings in their tracheae, and hamsters, only a handful. Rat tracheae contained 126±42 gland openings (± S.D. ; n = 6) at a frequency of ∼ 0.6 per mm² at the top of the trachea and ∼ 0.15 per mm² at the bottom. Guinea pig tracheae contained 153±90 gland openings (± S.D. ; n = 5), with 54% being in the top 40% of the trachea. In both rat and guinea pig, tracheal glands were found in the ventral aspect between the cartilaginous rings, and were absent from the dorsal membranous portion. Gland openings in most species were simple circles of ∼ 50 μm diameter. However, glands in the rat trachea generally opened obliquely into shallow (∼ 20 μm deep) oval troughs (∼ 150×75 μm), which had their long axes oriented from head to tail. In the rabbit, there was no evidence of tracheal or laryngeal glands histologically. However, the tracheal and laryngeal surfaces contained numerous pits (∼ 30 μm diameter) distributed evenly over and between cartilages at a frequency of ∼ 4 per mm². These may correspond to the 'nests' of goblet cells described by others.