Neural network in the brainstem subserving reflex salivation

采用行为学和电生理学的方法研究了脑干中控制反射性唾液分泌的神经网络。在行为学研究中，分析了唾液分泌量和中耳索（味觉传入神经）的神经反应。在电生理研究中，记录了体外切片脑干上分泌核（副交感神经分泌中枢）的神经活动。结果表明：1)大鼠在咀嚼食物颗粒、梳理毛发和舔苦味物质引起的味觉排斥行为时分泌大量唾液，而在舔可接受的味觉溶液（甜、咸、酸物质）时分泌少量唾液；2)鼓索神经内注射马萝卜过氧化物酶（HRP）标记上涎神经元；hrp标记的神经元在出生后几天呈圆形，10天后形成2-5个树突；3)膜片钳记录技术应用于10日龄的上涎神经元（体外四甲基罗丹明标记），发现该神经元对乙酰胆碱敏感，其最大放电速率约为20Hz；电刺激孤束（味觉传递中心一阶）未引起上涎神经元的尖峰放电。上述行为学和电生理学研究表明，唾液分泌受高级神经系统的控制，如摄食中枢和臂旁核（味觉传递中枢的二级），而不是味觉传递中枢的一级（孤立核）。

Neural network in the brainstem subserving reflex salivation was investigated by behavioral and electrophysiological studies. In the behavioral study, amount of salivary secretion and neural responses of the chorda tympani (taste afferent nerve) was analyzed. In the electrophysiological study, neural activity of the superior salivatory nucleus (parasympathetic secretory center) was recorded from sliced brainstem in vitro. The following results were obtained : 1) rats secreted copious flow of saliva during chewing food pellets, grooming, and the taste rejection behavior induced by licking of bitter substance, whereas small amount of saliva was secreted during licking of acceptable taste solutions (sweet, salty, and sour substances) ; 2) the superior salivatory neurons were labeled by injection of horse radish peroxidase (HRP) into the chorda tympani nerve ; HRP-labeled neurons were round shape for few days after birth and became to have 2-5 dendrites after 10 days old ; 3) the patch-clamp recording technique was applied to the 10-day-old superior salivatory neurons (labeled by tetramethyl-rhodamine in vitro, and suggested that the neurons were sensitive to acetylcholine and that their maximal discharge rate was about 20Hz ; electrical stimulation of the solitary tract (the first order of taste relay center) did not induce spike discharges in the superior salivatory neurons. Above behavioral and electrophysiological studies suggest that salivary secretion is under control of the higher nervous system such as the feeding center and parabrachial nucleus (the second order of taste relay center) rather than the first order of taste relay center (the solitary nucleus).