Neural network in the brainstem subserving reflex salivation

点击翻译按钮获取中文摘要

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).