Electrophysiological analysis of impulse formation in the salivary secretory neurons

上级唾液（SS）核含有支配下颌下和舌下唾液腺的副交感节前神经元和支配舌前部的副交感节前神经元。为了评估冲动形成的机制，我们分析了SS神经元的突触后电流。在新生Wistar大鼠的神经元周围注射荧光示踪剂标记SS神经元。注射两天后，将脑干切片，并从标记的神经元获得全细胞膜片钳记录。在记录细胞附近施加电刺激诱发全细胞突触后电流。获得了以下结果。1)在延髓外侧网状结构内，支配不同靶点的SS神经元相互混杂分布，有3-4个主树突，向背腹侧延伸约700 μ m。2)全细胞电流可被荷包牡丹碱、士的宁、CPP和CNQX所拮抗，表明突触后电流的主要成分由GABA_<A->、甘氨酸_、NMDA_和非NMDA_受体介导。3)在唾液腺SS神经元中，NMDA成分在总兴奋性突触后电流中所占的比例大于非NMDA成分，GABA_A成分大于甘氨酸成分。4)GABA_B受体激动剂巴氯芬（baclofen）可可逆地降低某些神经元抑制性突触后电流的幅度，并呈剂量依赖性。在突触后膜的输入电阻没有变化，观察巴氯芬的应用过程中。当成对电刺激（50 ms间隔）时，巴氯芬增强第一和第二突触后电流的幅度比。提示突触前GABA_B受体的存在。突触输入的这些特性可以参与确定SS神经元的激发特性。

The superior salivatory (SS) nucleus contains parasympathetic preganglionic neurons innervating the submandibular and sublingual salivary glands and those innervating the anterior part of the tongue. To evaluate mechanisms of impulse formation, we analyzed postsynaptic currents of the SS neurons. The SS neurons were labeled by injection of fluorescent tracers into the peripheral course of the neurons in neonatal Wistar rats. Two days after the injection, the brainstem was sliced and whole-cell patch-clamp recordings were obtained from the labeled neurons. The whole-cell postsynaptic currents were evoked by electrical stimulation applied near the recording cell. The following results were obtained. 1) The SS neurons innervating the different targets scattered and intermingled in the lateral reticular formation of the medulla oblongata, which have 3-4 main dendrites that extended dorso-ventrally about 700 um. 2) The whole-cell currents were antagonized by bicuculline, strychnine, CPP, and CNQX, suggesting that major components of the postsynaptic currents are mediated by GABA_<A->, glycine-, NMDA-, and non-NMDA-receptors. 3) In the SS neurons for the salivary glands, the ratio of the NMDA component to the total excitatory postsynaptic currents was larger than that of the non-NMDA component, and the GABA_A component was larger than the glycine component. 4) Bath application of baclofen, GABA_B-receptor-agonist, reversibly and dose-dependently reduced the amplitude of the inhibitory postsynaptic currents in some neurons. No changes in the input resistance of the postsynaptic membrane were observed during application of baclofen. When paired electrical stimulation (50 ms interval) was applied, the amplitude ratio of the first and second postsynaptic currents was enhanced by baclofen. These results suggest existence of presynaptic GABA_B receptors. These characteristics of the synaptic inputs may be involved in determining the firing properties of the SS neurons.