Holmgren Carl, Harkany Tibor, Svennenfors Björn, Zilberter Yuri
Karolinska Institute, Department of Neuroscience, Retzius väg 8, B2-2, S-17177 Stockholm, Sweden.
J Physiol. 2003 Aug 15;551(Pt 1):139-53. doi: 10.1113/jphysiol.2003.044784. Epub 2003 Jun 17.
The extent to which neocortical pyramidal cells function as a local network is determined by the strength and probability of their connections. By mapping connections between pyramidal cells we show here that in a local network of about 600 pyramidal cells located within a cylindrical volume of 200 microm x 200 microm of neocortical layer 2/3, an individual pyramidal cell receives synaptic inputs from about 30 other pyramidal neurons, with the majority of EPSP amplitudes in the 0.2-1.0 mV range. The probability of connection decreased from 0.09 to 0.01 with intercell distance (over the range 25-200 microm). Within the same volume, local interneuron (fast-spiking non-accommodating interneuron, FS)-pyramidal cell connections were about 10 times more numerous, with the majority of connections being reciprocal. The probability of excitatory and inhibitory connections between pyramidal cells and FS interneurons decreased only slightly with distance, being in the range 0.5-0.75. Pyramidal cells in the local network received strong synaptic input during stimulation of afferent fibres in layers 1 and 6. Minimal-like stimulation of layer 1 or layer 6 inputs simultaneously induced postsynaptic potentials in connected pyramidal cells as well as in pyramidal-FS cell pairs. These inputs readily induced firing of pyramidal cells, although synaptically connected cells displayed different firing patterns. Unitary EPSPs in pyramidal-pyramidal cell pairs did not detectably alter cell firing. FS interneurons fire simultaneously with pyramidal cells. In pyramidal-FS cell pairs, both unitary EPSPs and IPSPs efficiently modulated cell firing patterns. We suggest that computation in the local network may proceed not only by direct pyramidal-pyramidal cell communication but also via local interneurons. With such a high degree of connectivity with surrounding pyramidal cells, local interneurons are ideally poised to both coordinate and expand the local pyramidal cell network via pyramidal-interneuron-pyramidal communication.
新皮质锥体细胞作为局部网络发挥功能的程度取决于其连接的强度和概率。通过绘制锥体细胞之间的连接图谱，我们在此表明，在新皮质第2/3层中一个直径为200微米×200微米的圆柱形体积内约600个锥体细胞组成的局部网络中，单个锥体细胞从约30个其他锥体细胞接收突触输入，大多数兴奋性突触后电位（EPSP）幅度在0.2 - 1.0毫伏范围内。连接概率随着细胞间距离（在25 - 200微米范围内）从0.09降至0.01。在相同体积内，局部中间神经元（快速放电非适应性中间神经元，FS）与锥体细胞的连接数量约多10倍，且大多数连接是相互的。锥体细胞与FS中间神经元之间兴奋性和抑制性连接的概率仅随距离略有下降，在0.5 - 0.75范围内。在刺激第1层和第6层的传入纤维时，局部网络中的锥体细胞会接收到强烈的突触输入。对第1层或第6层输入进行最小样刺激会同时在相连的锥体细胞以及锥体细胞 - FS细胞对中诱导出突触后电位。这些输入很容易诱导锥体细胞放电，尽管突触连接的细胞表现出不同的放电模式。锥体细胞 - 锥体细胞对中的单一EPSP不会明显改变细胞放电。FS中间神经元与锥体细胞同时放电。在锥体细胞 - FS细胞对中，单一EPSP和抑制性突触后电位（IPSP）都能有效调节细胞放电模式。我们认为，局部网络中的计算可能不仅通过直接的锥体细胞 - 锥体细胞通信进行，还通过局部中间神经元进行。由于与周围锥体细胞具有如此高的连接度，局部中间神经元非常适合通过锥体细胞 - 中间神经元 - 锥体细胞通信来协调和扩展局部锥体细胞网络。
