Role of α_2-adrenoreceptor on the excitability of trigeminal root ganglion neurons : Patch-clamp and Single-cell RT-PCR analysis

本研究采用穿孔补片湿法观察α_2-肾上腺素受体激动剂对大鼠尾根神经节（TRG）神经元兴奋性的影响，并探讨TRG神经元表达α_2-肾上腺素受体mRNA的情况。在含量钳模式下，测试膜电位为-57.4±1.2 mV（n=26）。大多数神经元（71%）在可乐定（5-50μM）作用下呈浓度依赖性超极化。这种反应与细胞输入电阻的增加有关。此外，可乐定减少了去极化电流脉冲引起的重复放电。α_2-肾上腺素能激动剂uk14304 （10-20μM）也能引起TRG神经元的超极化。碘唑嗪（α_2-肾上腺素受体拮抗剂）可阻断多尼定和uk14,304诱导的亢进。在电压阻尼下，donidine （1-50μM）可逆地降低了超极化和时间相关的阳离子电流。以uk13304 （10 ~ 20μ m）为模拟剂，以咪唑嗪为拮抗剂。细胞外Cs^+ (2mM)或特定阻断剂ZD7288 （20μM）阻断超极化激活的阳离子电流。结果表明，超极化激活阳离子电流的可乐定敏感组分的反转电位为-46mV。单细胞逆转录-聚合酶链反应分析证实α_<2A>和α_<2C>肾上腺素受体mRNA表达。上述结果表明，α_2-肾上腺素受体的激活可使TRG神经元发生超极化，其抑制作用与抑制超极化激活的阳离子电流有关。我们的研究结果表明，在没有神经损伤的情况下，α_2-肾上腺素受体的激活可能在TRG神经元胞体和初级传入端水平上抑制三叉神经系统中伤害感觉的传递。

The aim of the study was to mauiine the effects of α_2-adrerioreceptar agonists on the excitability of teigeminalroot ganglion (TRG) neurons using the perforated-patch damp technique, and to deternine wither these neurons express mRNA for α_2-adrenoreceptors. In cunent-clamp mode, the testing membrane potential was -57.4 ± 1.2 mV(n=26). Most neurons (71%) were hyperpolarized by clonidine (5-50μM) in a concentration-dependent manner. The response was associated with an increase of cell input resistance. In addition, clonidine reduced the repetitive firing evoked by depolarizing current pulses. An α_2-adrenergic agonist UK14,304 (10-20μM) also hyperpolarized TRG neurons. The donidine- and UK14, 304- induced hyperpdarizatian was blocked by idazoxan (α_2-adrenoreoeptor antagonist). In voltage-damp, donidine (1-50μM) reversibly reduced the hyperpolarization- and -time dependent cationic current. The effect was mimicked by UK13,304 (10-20μM), and antagonized by idazoxan. Hyperpoiarization-activated cationic current was blocked by extracelluar Cs^+ (2mM) or a specific blocker, ZD7288 (20μM). Analysis of taii-cinrcnts revealed that a reversal potential of the clonidine sensitive component of hyperpolarization-activated cationic current was -46mV. Single cell reverse transcription-polymerase chain reaction analysis demonstrated the expression of mRNA for α_<2A> and α_<2C> adrenoreceptors.These results demonstrate that activation of α_2-adrenoreceptors can hyperpolarize TRG neurons, and that the in hibitory effect is associated with inhibition of hyperpolarization-activated cationic current. Our results suggest that activation of α_2-adrenoreceptors in the absence of nerve injury may have an inhibitory effect on nociceptive transmission in the trigeminal system at the level of both TRG neuronal cell bodies and primary afferent terminals.