Background: Although feeding with a liquid diet does not affect the growth of rat submandibular glands, it inhibits the growth of rat parotid glands during growth periods. In these growth-inhibited parotid glands, the growth of parasympathetic nerves is also suppressed. Meanwhile, the mature parotid glands of animals maintained on a liquid diet become morphologically and functionally atrophic, however, there is no effect of a liquid diet on mature submandibular glands. The objective of the present study was to clarify whether the nerve distribution in the mature salivary glands of rats was affected by a liquid diet.
Materials and methods: Seven-week-old male Wistar rats were used in this study. Half of the rats were kept on a pellet diet, and half were kept on a liquid diet, for 3, 7, 14, or 21 days. All rats were euthanised by isoflurane at each endpoint. Then, the parotid and submandibular glands were removed, frozen in liquid nitrogen, cryosectioned, and stained with antibodies against protein gene product 9.5 (PGP 9.5; general nerve marker), tyrosine hydroxylase (TH; sympathetic nerve marker), or neuronal nitric oxide synthase (nNOS; parasympathetic nerve marker).
Results: In parotid and submandibular glands of the pellet diet group, PGP 9.5- and TH-like immunoreactivity were seen around acini and ducts, and nNOS-like immunoreactivity was lower than PGP 9.5- and TH-like immunoreactivity. In the parotid glands of the liquid diet group, similar immunoreactivities were seen throughout the experimental period. The distribution of antibody labelling in the submandibular glands of the liquid diet group was similar to that of the pellet diet group and remained unchanged during the experimental period.
Conclusions: The present study demonstrated no regressive effects of a liquid diet on the distribution of sympathetic or parasympathetic nerves in mature parotid glands and submandibular glands. This differed from inhibitory effects on the growth of parotid glands seen during growth periods.
Keywords: parasympathetic nerves; salivary glands; soft diet; sympathetic nerves.