Ultrastructural Changes in Tissue Columns of Fundus striati (Nucleus accumbens) Surgically Isolated from all Extrastriatal Connections

摘要

Following columnar isolation of fundus striati (nucleus accumbens) tissue from all afferent and efferent connections, the ‘aspiny’ giant cells of the striatum, which are electron microscopically characterized by many axosomatic synapses, undergo severe retrograde dark degeneration. In the same experiments, a less severe penumbral degeneration of large ‘aspiny’ neurons (large type I neurons of Mori) was observed. In contrast, the somata of 90–95% of the striatal cells that fall under the category of ‘spiny type I neurons’ show only minor changes in the form of cytoplasmic swelling or pale alteration. The same bland alteration is seen in the dwarf cells, which substantiates the general opinion that they are Golgi type II nerve cells. It is concluded that the efferent fibers of the giant and large types of neurons leave the striatum and project to the substantia nigra and the pallidum, respectively. This conclusion is based on the general pattern of retrograde degeneration due to axonal lesions. The severe dark degeneration of the large and giant ‘aspiny’ neurons indicates that a great length of the axon (with axon collaterals) has been separated from the trophic center. It is therefore suggested that these neurons project to the substantia nigra. The less severe penumbral degeneration of the large ‘aspiny’ neurons is probably the expression of a more distal interruption of their axons. It is, therefore, assumed that they conduct impulses to the adjacent pallidum. The pale alteration of the small ‘spiny’ neurons represents a mere ‘irritation’, without a direct mechanical injury to their axonal processes. Consequently, the vast majority of the ‘spiny’ neurons are regarded as intrinsic striatal interneurons which do not send efferent axons beyond the boundaries of the striatum. These results seem to support the classic view that the striatum is an integrating structure consisting of many small interneurons, a few dwarf cells and a relatively small number of g