Gonchar Yuri, Burkhalter Andreas
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Neurosci. 2003 Nov 26;23(34):10904-12. doi: 10.1523/JNEUROSCI.23-34-10904.2003.
Processing of visual information is performed in different cortical areas that are interconnected by feedforward (FF) and feedback (FB) pathways. Although FF and FB inputs are excitatory, their influences on pyramidal neurons also depend on the outputs of GABAergic neurons, which receive FF and FB inputs. Rat visual cortex contains at least three different families of GABAergic neurons that express parvalbumin (PV), calretinin (CR), and somatostatin (SOM) (Gonchar and Burkhalter, 1997). To examine whether pathway-specific inhibition (Shao and Burkhalter, 1996) is attributable to distinct connections with GABAergic neurons, we traced FF and FB inputs to PV, CR, and SOM neurons in layers 1-2/3 of area 17 and the secondary lateromedial area in rat visual cortex. We found that in layer 2/3 maximally 2% of FF and FB inputs go to CR and SOM neurons. This contrasts with 12-13% of FF and FB inputs onto layer 2/3 PV neurons. Unlike inputs to layer 2/3, connections to layer 1, which contains CR but lacks SOM and PV somata, are pathway-specific: 21% of FB inputs go to CR neurons, whereas FF inputs to layer 1 and its CR neurons are absent. These findings suggest that FF and FB influences on layer 2/3 pyramidal neurons mainly involve disynaptic connections via PV neurons that control the spike outputs to axons and proximal dendrites. Unlike FF input, FB input in addition makes a disynaptic link via CR neurons, which may influence the excitability of distal pyramidal cell dendrites in layer 1.
视觉信息的处理在不同的皮质区域进行，这些区域通过前馈（FF）和反馈（FB）通路相互连接。尽管FF和FB输入是兴奋性的，但它们对锥体神经元的影响也取决于γ-氨基丁酸能（GABAergic）神经元的输出，而GABAergic神经元会接收FF和FB输入。大鼠视觉皮层至少包含三种不同类型的GABAergic神经元，它们分别表达小白蛋白（PV）、钙视网膜蛋白（CR）和生长抑素（SOM）（Gonchar和Burkhalter，1997）。为了研究通路特异性抑制（Shao和Burkhalter，1996）是否归因于与GABAergic神经元的不同连接，我们追踪了大鼠视觉皮层17区第1-2/3层以及次级内外侧区中PV、CR和SOM神经元的FF和FB输入。我们发现，在第2/3层中，最多2%的FF和FB输入进入CR和SOM神经元。这与进入第2/3层PV神经元的12-13%的FF和FB输入形成对比。与第2/3层的输入不同，第1层的连接具有通路特异性，第1层含有CR但缺乏SOM和PV胞体：21%的FB输入进入CR神经元，而第1层及其CR神经元没有FF输入。这些发现表明，FF和FB对第2/3层锥体神经元的影响主要涉及通过PV神经元的双突触连接，PV神经元控制着轴突和近端树突的动作电位输出。与FF输入不同，FB输入还通过CR神经元形成双突触连接，这可能会影响第1层远端锥体细胞树突的兴奋性。
