突触前GABA_B受体的激活对大鼠内侧膝状体突触传递的调节作用

发布时间：2018-09-04 21:07

【摘要】：内侧膝状体(MGB)是中枢听觉系统中重要的中继核团,它接受来自下丘及其他皮层下听觉核团的上行纤维投射,同时,它也接受来自皮层的下行纤维投射。代谢型G蛋白偶联的GABAB受体与离子型GABAA受体和GABAC受体类似,在中枢神经系统中作为抑制性受体发挥作用。突触后GABAB受体的激活可以引起内向整流K+通道(GIRK或Kir3)的开放,增加钾离子电导,从而去极化神经元,而突触前GABAB受体的激活可以抑制N型或者P/Q型电压门控Ca2+通道,引起突触前诱发的神经递质释放减少。已有研究利用形态学方法证明,在MGB部位存在有GABAB受体,而突触后的GABAB受体也已经被电生理方法所证实。但在MGB是否有功能性的突触前GABAB受体存在?对于传入到MGB的上行和下行通路,突触前GABAB受体对突触传递的调节是否有区别?对于兴奋性和抑制性突触传递,突触前GABAB受体的激活对它们的调节是否一致?内源性GABA释放是否能激活突触前GABAB受体从而调节突触传递?这种调节是否受到发育的调节?本论文运用脑片膜片钳技术试图回答以上提出的问题。本研究中,在下丘臂(BIC)和上丘脑辐射(STR)分别放置了双极刺激电极,以激活到达MGB的上行和下行传入纤维；在浴液中分别加入犬尿酸和木防已苦毒素以分别记录抑制性突触后电流(IPSCs)和兴奋性突触后电流(EPSCs)。为了研究突触前GABAB受体的功能,电极内液中运用了含铯离子的成分,并加入了QX-314以阻断突触后的GABAB受体的作用。主要的研究结果如下： (1) GABAB受体激动剂baclofen能够压抑IPSCs和EPSCs,这种作用是可逆的,并且是浓度依赖性的。GABAB受体的拮抗剂CGP35348可以逆转由baclofen引起的这种压抑,证明了这种作用是通过激活GABAB受体引起的。(2)baclofen显著地增加了IPSCs和EPSCs的双脉冲比值(PPR, paired-pulse ratio),证明baclofen对IPSCs和EPSCs的抑制作用有突触前的机制参与。(3)研究发现刺激上行通路得到的突触后电流和刺激下行通路得到的突触后电流被压抑的程度没有显著性区别,而baclofen在这两个通路上对EPSCs的压抑要强于对IPSCs的压抑。(4)baclofen可以压抑反复刺激诱发的EPSC和IPSC的幅度,并且减缓了或者反转了它们的幅度随刺激下降的趋势。此外,baclofen还显著地增加了IPSC和EPSC归一化的反应。(5)GABAB受体拮抗剂CGP55845可以提高年幼大鼠(P8-10)而非青少年大鼠(P15-18)的IPSC PPR,提示内源性释放的GABA能够激活突触前的GABAB受体,并且这种作用是受到发育调节的。以上研究结果为MGB存在功能性的突触前GABAB受体提供了电生理证据,并且提示突触前GABAB受体的功能可能受到了发育的调节。
[Abstract]:The medial geniculate (MGB) is an important relay nucleus in the central auditory system. It receives the ascending fiber projection from the inferior colliculus and other subcortical auditory nuclei, and at the same time, it also receives the descending fiber projection from the cortex. Metabolic G protein-coupled GABAB receptors are similar to ionic GABAA receptors and GABAC receptors and act as inhibitory receptors in the central nervous system. The activation of postsynaptic GABAB receptor can induce the opening of inward rectifier K channel (GIRK or Kir3), increase potassium ion conductance, thereby depolarization neurons. The activation of presynaptic GABAB receptor can inhibit the N type or P / Q type voltage-gated Ca2 channel. Reduced release of neurotransmitters caused by presynaptic stimulation. Morphological studies have demonstrated the presence of GABAB receptors in the MGB site and postsynaptic GABAB receptors have been confirmed by electrophysiological methods. But is there a functional presynaptic GABAB receptor in MGB? Is there a difference between the regulation of presynaptic GABAB receptors on synaptic transmission in the upstream and descending pathways from afferent to MGB? For excitatory and inhibitory synaptic transmission, is the activation of presynaptic GABAB receptors consistent with their regulation? Does endogenous GABA release activate presynaptic GABAB receptors to regulate synaptic transmission? Is this regulation regulated by development? In this paper, the patch-clamp technique is used to answer the above questions. In this study, bipolar stimulation electrodes were placed in the lower colliculus arm (BIC) and the hypothalamic irradiated (STR) to activate the ascending and descending afferent fibers to MGB. To record inhibitory postsynaptic current (IPSCs) and excitatory postsynaptic current (EPSCs).) by adding canine uric acid and pentachloropicrin to bath fluid, respectively. In order to study the function of presynaptic GABAB receptor, caesium ion was used in the solution of the electrode and QX-314 was added to block the postsynaptic GABAB receptor. The main results are as follows: (1) the inhibitory effect of GABAB receptor agonist baclofen on IPSCs and EPSCs, is reversible, and CGP35348, the antagonist of .GAAB receptor, can reverse the inhibition induced by baclofen. (2) baclofen significantly increased the double pulse ratio of IPSCs and EPSCs (PPR, paired-pulse ratio), proved that baclofen inhibited IPSCs and EPSCs by presynaptic mechanism. (3) it was found that the stimulation of uplink pathway was successful. There was no significant difference in the degree to which postsynaptic currents were suppressed from those resulting from stimulation of the downlink. The inhibition of EPSCs by baclofen on these two pathways was stronger than that on IPSCs. (4) baclofen could inhibit the amplitude of EPSC and IPSC induced by repeated stimuli and slow down or reverse their amplitude with the decrease of stimuli. In addition, baclofen significantly increased the normalized response of IPSC and EPSC. (5) CGP55845, a GABAB receptor antagonist, increased IPSC PPR, in young rats (P8-10) and not in adolescent rats (P15-18), suggesting that endogenous GABA could activate pre-synaptic GABAB receptors. And this action is regulated by development. These results provide electrophysiological evidence for the existence of functional presynaptic GABAB receptors in MGB and suggest that the function of presynaptic GABAB receptors may be regulated by development.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2011
【分类号】：R338

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