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Vanilloid Receptors Presynaptically Modulate Cranial Visceral Afferent Synaptic Transmission in Nucleus Tractus Solitarius

机译:香草受体在突触核中预先突触调节颅内脏传入突触传递。

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摘要

Although the central terminals of cranial visceral afferents express vanilloid receptor 1 (VR1), little is known about their functional properties at this first synapse within the nucleus tractus solitarius (NTS). Here, we examined whether VR1 modulates afferent synaptic transmission. In horizontal brainstem slices, solitary tract (ST) activation evoked EPSCs. Monosynaptic EPSCs had low synaptic jitter (SD of latency to successive shocks) averaging 84.03 ± 3.74 μsec (n = 72) and were completely blocked by the non-NMDA antagonist 2,3-dihydroxy-6-nitro-7-sulfonyl-benzo[f]quinoxaline (NBQX). Sustained exposure to the VR1 agonist capsaicin (CAP; 100 nm) blocked ST EPSCs (CAP-sensitive) in some neurons but not others (CAP-resistant). CAP-sensitive EPSCs had longer latencies than CAP-resistant EPSCs (4.65 ± 0.27 msec, n= 48 vs 3.53 ± 0.28 msec, n = 24, respectively; p = 0.011), but they had similar jitter. CAP evoked two transient responses in CAP-sensitive neurons: a rapidly developing inward current (Icap) (108.1 ± 22.9 pA;n = 21) and an increase in spontaneous synaptic activity. After 3–5 min in CAP,Icap subsided and ST EPSCs disappeared. NBQX completely blocked Icap. The VR1 antagonist capsazepine (10–20 μm) attenuated CAP responses. Anatomically, second-order NTS neurons were identified by 4-(4-dihexadecylamino)styryl)-N-methylpyridinium iodide transported from the cervical aortic depressor nerve (ADN) to stain central terminals. Neurons with fluorescent ADN contacts had CAP-sensitive EPSCs (n = 5) with latencies and jitter similar to those of unlabeled monosynaptic neurons. Thus, consistent with presynaptic VR1 localization, CAP selectively activates a subset of ST axons to release glutamate that acts on non-NMDA receptors. Because the CAP sensitivity of cranial afferents is exclusively associated with unmyelinated axons, VR1 identifies C-fiber afferent pathways within the brainstem.
机译:尽管颅内脏传入神经的中枢末端表达香草样受体1(VR1),但对孤束核(NTS)内第一个突触的功能特性知之甚少。在这里,我们检查了VR1是否调节传入突触传递。在脑干水平切片中,孤立道(ST)激活引起EPSC。单突触EPSC具有较低的突触抖动(连续电击潜伏期的SD),平均为84.03±3.74μsec(n = 72),并且被非NMDA拮抗剂2,3-二羟基-6-硝基-7-磺酰基-苯并[]完全阻断。 f]喹喔啉(NBQX)。持续暴露于VR1激动剂辣椒素(CAP; 100 nm)可阻断某些神经元的ST EPSC(CAP敏感),但不能阻断其他神经元(CAP耐药)。 CAP敏感型EPSC的等待时间长于CAP耐受型EPSC(分别为4.65±0.27毫秒,n = 48和3.53±0.28毫秒,n = 24; p = 0.011),但抖动相似。 CAP引起CAP敏感神经元的两个瞬时反应:快速发展的内向电流(Icap)(108.1±22.9 pA; n = 21)和自发突触活性增加。在CAP中3-5分钟后,Icap消退,ST EPSC消失。 NBQX完全阻止了Icap。 VR1拮抗剂辣椒素(10–20μm)减弱了CAP反应。在解剖学上,二阶NTS神经元是由从宫颈主动脉降压神经(ADN)转运至染色的中央末端的4-(4-二十六烷基氨基)苯乙烯基)-N-甲基碘化碘确定的。与荧光ADN接触的神经元具有CAP敏感的EPSC(n = 5),其潜伏期和抖动类似于未标记的单突触神经元。因此,与突触前VR1定位一致,CAP选择性激活ST轴突子集以释放作用于非NMDA受体的谷氨酸。由于颅传入神经的CAP敏感性仅与未髓鞘的轴突相关,因此VR1可以识别脑干内的C纤维传入通路。

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