Ryusuke Yoshida

Expression of alpha‐synuclein (Syn), a presynaptic neuronal protein, was immunohistochemically examined in intact rat submandibular, sublingual, and lingual glands. The submandibular gland contained abundant periductal Syn‐immunoreactive (−ir) nerve fibers. Abundant Syn‐ir varicosities were present in acini of the sublingual and serous lingual glands. By confocal laser scanning microscopy, Syn‐ir nerve fibers around smooth muscle actin (SMA)‐ir cells alone were infrequent; however, those around aquaporin‐5 (AQP5)‐ir cells alone and both SMA‐ and AQP5‐ir cells were abundant in the sublingual and serous lingual glands. SMA‐ir cells were occasionally immunoreactive for toll‐like receptor 4, a Syn receptor. Syn‐ir nerve fibers contained tyrosine hydroxylase (TH) in the submandibular gland and choline acetyltransferase (ChAT) in all examined salivary glands. In the superior cervical (SCG), submandibular, and intralingual ganglia, sympathetic and parasympathetic neurons co‐expressed Syn with TH and ChAT, respectively. SCG neurons innervating the submandibular gland contained mostly Syn. In the thoracic spinal cord, 14.7% of ChAT‐ir preganglionic sympathetic neurons co‐expressed Syn. In the superior salivatory nucleus, preganglionic parasympathetic neurons projecting to the lingual nerve co‐expressed Syn and ChAT. The present findings indicate that released Syn acts on myoepithelial cells. Syn in pre‐ and post‐ganglionic neurons may regulate neurotransmitter release and salivary volume and composition.

Fermented milk is consumed worldwide because of its nutritious and healthful qualities. Although it is somewhat sour, causing some to dislike it, few studies have examined taste aspects of its ingredients. Wild-type mice and T1R3-GFP-KO mice lacking sweet/umami receptors were tested with various taste components (sucrose, galactose, lactose, galacto-oligosaccharides, fructo-oligosaccharides, l- and d-lactic acid) using 48 h two-bottle tests and short-term lick tests. d-lactic acid levels were measured after the ingestion of d- or; l-lactic acid or water to evaluate d-lactic acidosis. In wild-type mice, for the sweet ingredients the number of licks increased in a concentration-dependent manner, but avoidance was observed at higher concentrations in 48 h two-bottle tests; the sour ingredients d- and l-lactic acid showed concentration-dependent decreases in preference in both short- and long-term tests. In 48 h two-bottle tests comparing d- and l-lactic acid, wild-type but not T1R3-GFP-KO mice showed higher drinking rates for l-lactic acid. d-lactic acidosis did not occur and thus did not contribute to this preference. These results suggest that intake in short-term lick tests varied by preference for each ingredient, whereas intake variation in long-term lick tests reflects postingestive effects. l-lactic acid may have some palatable taste in addition to sour taste.