Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078, USA.
Brain Res. 2010 Apr 30;1328:71-8. doi: 10.1016/j.brainres.2010.03.003. Epub 2010 Mar 6.
Chorda tympani (CT) and glossopharyngeal (IXth) nerves relay taste information from anterior and posterior tongue to brainstem where they synapse with second order neurons in the rostral nucleus of solitary tract (rNST). rNST neurons monosynaptically connected to afferent gustatory input were identified both by anatomical labeling and synaptic latency measures. Anterograde tracing was used to label the CT and IXth terminal fields, and neurons surrounded by fluorescent neural profiles visualized with differential interference contrast (DIC) optics in horizontal brainstem slices. Anatomically identified neurons were patch-clamped and excitatory postsynaptic currents (EPSCs) evoked by electrically stimulating the solitary tract (ST) under GABA(A) receptor blockade. Monosynaptic connections were confirmed by measures of the standard deviation of synaptic latency (jitter). rNST neurons responded to ST stimulation with either all-or-none or graded amplitude EPSCs. Most (70%) of the rNST neurons with CT input and 30% with IX input responded with all-or-none EPSCs. The remainder of the neurons with CT and IX input responded with increasing EPSC amplitudes to greater intensity stimulus shocks. EPSCs evoked in rNST neurons by increasing shock frequency to both CT and IXth nerves resulted in reduced amplitude EPSCs characteristic of frequency-dependent synaptic depression. Our results suggest that the second order rNST neurons respond to afferent input with different patterns of EPSCs that potentially influence transmission of gustatory information. Frequency-dependent synaptic depression would act as a low pass filter important in the initial processing of gustatory derived sensory messages.
鼓索神经(CT)和舌咽神经(IXth)将来自舌前和舌后的味觉信息传递到脑干,在那里它们与孤束核的第二级神经元(rNST)突触。通过解剖学标记和突触潜伏期测量,鉴定出与传入味觉输入单突触连接的 rNST 神经元。顺行追踪用于标记 CT 和 IXth 末端场,并用微分干涉对比(DIC)光学在水平脑干切片中可视化被荧光神经轮廓包围的神经元。用孤束(ST)电刺激在 GABA(A)受体阻断下,对解剖学鉴定的神经元进行膜片钳记录,并测量兴奋性突触后电流(EPSC)。通过测量突触潜伏期(抖动)的标准偏差来确认单突触连接。rNST 神经元对 ST 刺激的反应要么是全或无,要么是分级幅度 EPSC。具有 CT 输入的 rNST 神经元中的大多数(70%)和具有 IX 输入的 30%神经元表现出全或无 EPSC。具有 CT 和 IX 输入的其余神经元对更强的刺激脉冲表现出递增的 EPSC 幅度。增加 CT 和 IX 神经的刺激频率引起 rNST 神经元中的 EPSC,导致幅度减小,这是频率依赖性突触抑制的特征。我们的结果表明,第二级 rNST 神经元对传入输入的反应具有不同的 EPSC 模式,这可能影响味觉信息的传递。频率依赖性突触抑制将作为重要的低通滤波器,在味觉衍生感觉信息的初始处理中发挥作用。