Neural network in the brainstem subserving reflex salivation

通过行为学和电生理学研究，探讨了神经网络在脑干反射性唾液分泌中的作用。在行为学研究中，分析了大鼠的唾液分泌量和鼓索(味觉传入神经)的神经反应。在电生理研究中，从脑干切片记录上唾液核(副交感神经分泌中枢)的神经活动。结果如下：1)大鼠在咀嚼食物颗粒、梳理毛发和舔食苦味物质引起的味觉排斥行为中分泌大量唾液，而在舔可接受的味液(甜味、咸味和酸味)时分泌少量唾液，2)将辣根过氧化物酶(HRP)注射到鼓索神经对上唾液神经元进行标记，HRP标记的神经元在出生后几天内呈圆形，10日龄后形成2~5个树突；3)将膜片钳记录技术应用于10日龄的上唾液神经元(四甲基罗丹明标记)，发现该神经元对乙酰胆碱敏感，其最大放电频率约为20 Hz；电刺激孤束(味觉传递中枢的一级)不能诱发上唾液神经元的棘波放电。上述行为学和电生理研究表明，唾液分泌受控于高级神经系统，如摄食中枢和臂旁核(第二级味觉传递中枢)，而不是一级味觉传递中枢(孤束核)。

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).