Quantitative analysis of synaptic connections in the fronto-corticostriatal system

为了了解大鼠额叶皮层GABA能回路的特征，我们研究了(1)GABA细胞亚型的突触连接模式，(2)胆碱能对GABA能突触电流的影响，以及(3)GABA细胞亚型在皮质同步活动中的放电模式。(1) FS细胞支配体细胞和树突棘以及轴。生长抑素Martinotti细胞支配树突轴，而棘头和棘柄同时接受其他兴奋输入。轴突末梢的突触连接面积随着突触后树突或棘的周长呈线性增加。马蒂诺蒂细胞轴突的连接面积随着树突周长或突触后棘头表面积的增加而线性增加。(2)甲胆碱和毒蕈碱均引起皮层细胞突触后抑制性电流调节两种时间上不同的模式：强直性和周期性增加。抑制性电流频率持续增加，周期性增加表现为抑制性突触后电流的节律性爆发。在邻近的细胞中，这些活动作为一个整体是同步的，但脉冲中的单个抑制事件并不总是在时间上联系在一起，这表明几个突触前中间神经元是同步去极化的。(3)通过体外降低细胞外Mg^<2+>，我们诱导了NMDA受体依赖的自发活性。在一系列自发的去极化移动之后，出现了长爆发。由初始放电和快速跑样电位组成的长爆发。在同步活动的每个阶段，皮层神经元类型表现出不同的放电模式。皮层神经元的放电模式不仅取决于同步输入的强度和时间模式，还与具有特定生理、化学和形态特征的神经元亚型密切相关。少

To understand the characteristics of the GABAergic circuit in the rat frontal cortex, we investigated (1) the synaptic connection patterns of GABA cell subtypes, (2) cholinergic effects on the GABAergic synaptic currents, and (3) firing patterns of GABA cell subtypes during the cortical synchronized activities.(1) FS cells innervated somata and dendritic spines as well as shafts. Somatostatin Martinotti cells innervated the dendritic shafts, and the heads and stalks of spines receiving other excitatory inputs simultaneously. The synaptic junctional area of axon terminals from FS cells linearly increased along with the circumference of postsynaptic dendrites or spines. The junctional area of axons from Martinotti cells linearly increased with the dendritic circumference or the surface area of the postsynaptic spine heads.(2) Both carbachol and muscarine caused two temporally different patterns of inhibitory postsynaptic current modulation in cortical cells : tonic and periodic increase … More of GABA-A receptor-mediated currents. The tonic pattern features continuous increase of inhibitory current frequency, while the periodic increase manifests itself as a rhythmic burst of inhibitory postsynaptic current. In nearby cells these are synchronized as a whole but individual inhibitory events within the bursts are not always temporally linked, suggesting synchronized depolarization of several presynaptic interneurons.(3) By lowering extracellular Mg^<2+> in vitro, we induced NMDA receptor-dependent spontaneous activities. After a series of spontaneous depolarization shifts, the long bursts occurred. The long burst composed of initial discharges and fast run-like potentials. At each phase of the synchronized activities, cortical neuron types exhibited distinct firing patterns. The firing patterns of cortical neurons are not only determined by the strength and temporal pattern of synchronized inputs, but also strongly dependent on the neuronal subtype with specific physiological, chemical and morphological characteristics. Less