CENTRAL CONTROL BY CIRCUMVENTRICULAR ORGANS OF SALIVARY SECRETION

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The number of people who claim oral dryness increases recently. Although this is due to the increase of elderly persons and stress and a change of life style, the underlying mechanisms are not well-known. The saliva is made by the blood and the secretion is easily influenced by osmolarity and volume of body fluid and by the autonomic nervous system. This study was designed to investigate how the subfornical organ (SFO), which is a center of body fluid balance and cardiovascular regulation, is involved in salivary secretion. Rats were used for in vivo and in vitro experiments. In the in vivo experiments, a change of drinking and parotid saliva was measured by intracerebroventricular injection hypertonic saline and sucrose. We found the induction of drinking and the reduction of salivary secretion were larger by the hypertonic saline than by the sucrose. These results indicate that the salivary secretion is affected by central detection of osmolarity and sodium ions. In vitro experiments, we found the existence of sodium ion sensing receptors in the SFO and the activation of SFO neurons by a certain concentration of sodium ions. Further, we found the existence of acetylcholine muscarinic and nicotinic receptors in the SFO and the involvement of them in the body fluid balance.