Li X G, Somogyi P, Ylinen A, Buzsáki G
Center for Molecular and Behavioral Neuroscience, Rutgers, State University of New Jersey, Newark 07102.
J Comp Neurol. 1994 Jan 8;339(2):181-208. doi: 10.1002/cne.903390204.
The intrahippocampal distribution of axon collaterals of individual CA3 pyramidal cells was investigated in the rat. Pyramidal cells in the CA3 region of the hippocampus were physiologically characterized and filled with biocytin in anesthetized animals. Their axonal trees were reconstructed with the aid of a drawing tube. Single CA3 pyramidal cells arborized most extensively in the CA1 region, covering approximately two-thirds of the longitudinal axis of the hippocampus. The total length of axon collaterals in the CA3 region was less than in CA1 and the axon branches tended to cluster in narrow bands (200-800 microns), usually several hundred microns anterior or posterior to the cell body. The majority of the recurrent collaterals of a given neuron remained in the same subfield (CA3a, b, or c) as the parent cell. CA3a neurons innervated predominantly the basal dendrites, whereas neurons located proximal to the hilus (CA3c) terminated predominantly on the apical dendrites of both CA1 and CA3 cells. Two cells, with horizontal dendrites and numerous thorny excrescences at the CA3c-hilus transitional zone, were also labeled and projected to both CA3 and CA1 regions. All CA3 neurons projected some collaterals to the hilar region. Proximal (CA3c) neurons had numerous collaterals in the hilus proper. One CA3c pyramidal cell in the dorsal hippocampus sent an axon collaterals to the inner third of the molecular layer. CA3c pyramidal cells in the ventral hippocampus had extensive projections to the inner third of the dentate molecular layer, as well as numerous collaterals in the hilus, CA3, and CA1 areas, and several axon collaterals penetrated the subiculum. The total projected axon length of a single neuron ranged from 150 to 300 mm. On the basis of the projected axon length and bouton density (mean interbouton distance: 4.7 microns), we estimate that a single CA3 pyramidal cell can make synapses with 30,000-60,000 neurons in the ipsilateral hippocampus. The concentrated distribution of the axon collaterals ("patches") indicates that subpopulations of neurons may receive disproportionately denser innervation, whereas innervation in the rest of the target zones is rather sparse. These observations offer new insights into the physiological organization of the CA3 pyramidal cell network.
在大鼠中研究了单个CA3锥体细胞轴突侧支在海马内的分布情况。在麻醉动物中，对海马CA3区的锥体细胞进行生理特性鉴定并用生物胞素填充。借助绘图管重建其轴突树。单个CA3锥体细胞在CA1区的分支最为广泛，覆盖了海马纵轴的约三分之二。CA3区轴突侧支的总长度比CA1区短，且轴突分支倾向于聚集在狭窄带（200 - 800微米）内，通常在细胞体前方或后方几百微米处。给定神经元的大多数回返侧支与母细胞处于同一子区域（CA3a、b或c）。CA3a神经元主要支配基底树突，而位于海马门附近的神经元（CA3c）主要终止于CA1和CA3细胞的顶树突上。在CA3c - 海马门过渡区有水平树突和许多棘状赘生物的两个细胞也被标记，并投射到CA3和CA1区。所有CA3神经元都向海马门区域投射了一些侧支。近端（CA3c）神经元在海马门内有许多侧支。背侧海马中的一个CA3c锥体细胞向分子层的内三分之一发送了一条轴突侧支。腹侧海马中的CA3c锥体细胞向齿状分子层的内三分之一有广泛投射，在海马门、CA3和CA1区也有许多侧支，并且有几条轴突侧支穿透了下托。单个神经元的总投射轴突长度在150至300毫米之间。根据投射轴突长度和终扣密度（平均终扣间距：4.7微米），我们估计单个CA3锥体细胞可与同侧海马中的30,000 - 60,000个神经元形成突触。轴突侧支的集中分布（“斑块”）表明神经元亚群可能接受不成比例的密集神经支配，而目标区域其余部分的神经支配则相当稀疏。这些观察结果为CA3锥体细胞网络的生理组织提供了新的见解。
