Fariñas I, DeFelipe J
Instituto Cajal, CSIC, Madrid, Spain.
J Comp Neurol. 1991 Feb 1;304(1):70-7. doi: 10.1002/cne.903040106.
In the present study we examined the synaptology of the axon initial segments (AISs) of three populations of retrogradely labeled pyramidal cells: callosal, corticothalamic, and ipsilateral corticocortical projecting cells. The cells were labeled by horseradish peroxidase injected into the contralateral visual cortex, the ipsilateral lateral geniculate nucleus, or area 19 of the ipsilateral hemisphere. The AISs of these cells were completely reconstructed from tracings of serial electron micrographs and the number and type of synapses ending on them determined. These data were compared with that described in the companion paper (Fariñas and DeFelipe, J Comp Neurol 1991; 304:53-69), in which the ultrastructure and synaptology of the somata of callosal and corticothalamic cells was investigated. Together, these data permit comparisons to be made between the somatic and axonic innervation of the same cells. Our results show that each population of efferent cells examined received a characteristic and rather homogeneous number (in comparison with the number of axosomatic synapses) of axoaxonic synapses: 16 to 23 for AISs of callosal cells, 22 to 28 for ipsilateral corticocortical cells, and 1 to 5 for corticothalamic cells. Since most axoaxonic synapses are likely to be GABAergic, it is concluded that each population of pyramidal cells receives a distinct GABAergic inhibitory synaptic profile.
在本研究中，我们检查了三类逆行标记的锥体细胞轴突起始段（AIS）的突触学，这三类细胞分别是胼胝体投射细胞、皮质丘脑投射细胞和同侧皮质-皮质投射细胞。通过将辣根过氧化物酶注入对侧视皮层、同侧外侧膝状体核或同侧半球的19区来标记这些细胞。从一系列电子显微镜照片的追踪图中完全重建了这些细胞的AIS，并确定了终止于其上的突触的数量和类型。将这些数据与配套论文（法里尼亚斯和德费利佩，《比较神经学杂志》1991年；304:53 - 69）中描述的数据进行了比较，该论文研究了胼胝体和皮质丘脑细胞胞体的超微结构和突触学。这些数据共同使得能够对同一细胞的胞体和轴突神经支配进行比较。我们的结果表明，所检查的每一类传出细胞都接受了数量特征明显且相当均匀的（与轴-体突触数量相比）轴-轴突触：胼胝体细胞的AIS有16至23个，同侧皮质-皮质细胞有22至28个，皮质丘脑细胞有1至5个。由于大多数轴-轴突触可能是γ-氨基丁酸能的，因此可以得出结论，每一类锥体细胞都接受了独特的γ-氨基丁酸能抑制性突触分布。
