Histological changes in the mouse submandibular gland subjected to parasympathetic nerve block or ischemia: Comparison between chorda tympani resection and trophic vessel transection

Abstract

The purpose of this study was to determine the effect of disorders of parasympathetic innervation or trophic vessels on the parenchymal tissue of the submandibular gland. ICR mice underwent resection of the chorda tympani nerve or transection of the trophic vessels. After treatment, the submandibular glands were removed at intervals and processed for examination using light and electron microscopy. 1. From 1 week after nerve resection, the submandibular gland parenchymal tissue showed expanded blood vessels, infiltration of wandering cells and growth of connective tissue fibers, etc. Degeneration of the acinar cells extended from the periphery of the gland proper toward the inside, and by 3–4 weeks degeneration was evident over a wide area of the gland. Striated duct and granular convoluted tubule (GCT) cells showed slight damage. At 8 weeks, GCT cells and at 10 weeks acinar and intercalated duct-like cells had begun to increase in number. At 20 weeks, the glandular tissue showed almost normal parenchyma. 2. From 3 weeks after nerve resection, the submandibular gland proper showed a marked decrease in weight, but returned to approximately 70% of the original weight by 20 weeks. 3. At 1 hour after trophic vessel transection, acinar, striated duct and GCT cells showed vacuolation of the cytoplasm in addition to nuclear atrophy. At 9 hours, growth of connective tissue in the capsule and phagocytosis of collapsed cells by wandering cells were observed. At 18 hours, almost all parenchymal cells inside the gland proper had degenerated, and at 72 hours the gland proper finally disappeared. 4. Electron microscopy and TUNEL staining showed that critical injury of the parasympathetic nerve induced necrocytosis in the acinar and GCT cells, whereas serious damage to the trophic vessels caused an apoptosis-like cell death in these cells.