Background: The growth of parotid glands is inhibited by liquid diet intake
during growing period, while that of submandibular glands is not affected. This
study examined how liquid diet intake affects nerve growth in the parotid and
submandibular glands of growing rats, because nerves are closely involved in the
maintenance of salivary gland structure.
Materials and methods: Male Wistar rats were weaned at 21 days of age. Then,
rats were fed a pellet diet and a liquid diet in the control group and experimental
group, respectively. At 0, 2, 4, or 8 weeks, they were euthanised by isoflurane
overdose, and parotid and submandibular glands were removed. The frozen
sections were made and immuno-stained with anti-protein gene product 9.5
(PGP 9.5) antibody (general nerve marker), anti-tyrosine hydroxylase (TH) antibody
(sympathetic nerve marker), or anti-neuronal nitric oxide synthase (nNOS) antibody
(parasympathetic nerve marker).
Results: In control parotid glands, scattered punctate or short linear patterns of
PGP 9.5-positive sites were observed at week 0. After 2 weeks, PGP 9.5-positive
sites, some of which were arranged in long linear patterns, increased in number.
There were some TH-positive sites at week 0. After 2 weeks, there were increasing
numbers of TH-positive sites, often in long linear patterns. At week 0, there were
very few nNOS-positive sites, and nNOS immunoreactivity increased over time. After
week 4, they demonstrated linear patterns. In the experimental parotid glands,
there were fewer PGP 9.5- and nNOS-positive sites than in control parotid glands
at each time point, although TH immunoreactivity was similar between two groups
at each time point. In control submandibular glands, few punctate exhibited
PGP 9.5-positive site were observed at week 0. At week 4, PGP 9.5 immunoreaction
increased and showed linear patterns. TH-positive sites demonstrated punctate
or short linear patterns at week 0, and thereafter TH immunoreactivity increased
and were arranged in long linear patterns. There were few nNOS-positive sites
at week 0, and they gradually increased after week 4. The immunoreactivities of
all antibodies in the experimental submandibular glands were similar to those in
the control at each time point.
Conclusions: Parasympathetic nerve growth in rat parotid glands was inhibited by
liquid diet intake during the growth period, while liquid diet intake did not affect
parasympathetic nerve growth nor sympathetic nerve growth in rat submandibular
glands.