Bradley R M, Grabauskas G
Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109-1078, USA.
Ann N Y Acad Sci. 1998 Nov 30;855:467-74. doi: 10.1111/j.1749-6632.1998.tb10607.x.
The rostral nucleus of the solitary tract (rNST) plays a key role in modulating, organizing and distributing the sensory information arriving at the central nervous system from gustatory receptors. However, except for some anatomical studies of rNST synapses, the neural circuits responsible for this first stage in synaptic processing of taste information are largely unknown. Over the past few years we have used an in vitro brain slice preparation of the rNST to study synaptic processing, and it has become apparent that the rNST is a very complex neural relay. Synaptic potentials recorded in rNST neurons resulting from stimulation of afferent taste fibers are a composite of excitatory and inhibitory post synaptic potentials. Pure excitatory postsynaptic potentials (EPSP) can be isolated by using gamma-aminobutyric acid type A (GABAA) receptor blockers to eliminate the inhibitory postsynaptic potentials (IPSP). Application of glutamate ionotropic receptor blockers effectively eliminates all postsynaptic activity, indicating that glutamate is the transmitter at the first central synapse in the taste pathway. Stimulation of the afferent taste fibers originating from the anterior (chorda tympani) and posterior (glossopharyngeal) tongue results in a postsynaptic potential that is a complex sum of the two individual potentials. Thus, rNST neurons receive convergent synaptic input from the anterior and posterior tongue. The IPSP component of the synaptic potentials in rNST results from stimulation of interneurons. If these IPSPs are initiated by tetanic stimulation they undergo both short-term and long-term changes. Short-term changes result in the development of biphasic depolarizing IPSPs, and long-term changes result in potentiation of the IPSPs that can last over an hr in some neurons. This remarkable synaptic plasticity may be involved in the mechanism of learned taste behaviors. Synaptic transmission in rNST consists of excitation combined with inhibition. The inhibition does not simply depress excitation but probably serves many roles such as shaping and limiting excitation, coordinating the timing of synaptic events and participating in synaptic plasticity. Knowledge of these synaptic mechanisms is essential to understanding how the rNST processes taste information.
孤束吻侧核（rNST）在调节、组织和分配从味觉感受器传入中枢神经系统的感觉信息方面发挥着关键作用。然而，除了一些关于rNST突触的解剖学研究外，负责味觉信息突触处理第一阶段的神经回路在很大程度上仍不为人知。在过去几年中，我们使用rNST的体外脑片制备来研究突触处理，很明显rNST是一个非常复杂的神经中继站。刺激传入味觉纤维在rNST神经元中记录到的突触电位是兴奋性和抑制性突触后电位的复合体。通过使用A型γ-氨基丁酸（GABAA）受体阻滞剂消除抑制性突触后电位（IPSP），可以分离出纯兴奋性突触后电位（EPSP）。应用离子型谷氨酸受体阻滞剂可有效消除所有突触后活动，这表明谷氨酸是味觉通路中第一个中枢突触的递质。刺激源自舌尖（鼓索）和舌根（舌咽神经）的传入味觉纤维会产生一个突触后电位，它是两个单独电位的复杂总和。因此，rNST神经元接收来自舌尖和舌根的汇聚性突触输入。rNST中突触电位的IPSP成分是由中间神经元的刺激产生的。如果这些IPSP由强直刺激引发，它们会经历短期和长期变化。短期变化导致双相去极化IPSP的产生，长期变化导致IPSP增强，在某些神经元中这种增强可持续超过1小时。这种显著的突触可塑性可能参与了习得味觉行为的机制。rNST中的突触传递由兴奋与抑制相结合组成。这种抑制不仅仅是抑制兴奋，可能还发挥着许多作用，如塑造和限制兴奋、协调突触事件的时间以及参与突触可塑性。了解这些突触机制对于理解rNST如何处理味觉信息至关重要。
