Chen L, Hamaguchi K, Hamada S, Okado N
Department of Anatomy, University of Tsukuba, Ibaraki, Japan.
J Neural Transplant Plast. 1997 Jan-Mar;6(1):41-8. doi: 10.1155/NP.1997.41.
Previous studies in our laboratory [3,17] have demonstrated that serotonin (5-HT) appears to have a trophic-like effect in enhancing synapse formation and maintenance in both the developing and the adult central nervous system. In the present study, we focused on age-related changes in the density of the axosomatic and axodendritic synapses and the number of 5-HT-positive fibers in the chicken spinal cord, with special reference to differences between the ventral (laminae VII and IX) and the dorsal (lamina I) horn. At 1 week posthatching (P1W), a transient overproduction of synapses and 5-HT-immunoreactive fibers occurred in lamina IX; all parameters had returned to their initial levels by 1 month post-hatching (P1M). The density of synapses further decreased by about 40% between P6M and P2Y (2 years posthatching). Although the magnitude of the transient increase in lamina VII was less than that in lamina IX, the changing pattern of the synapses and the 5-HT-positive fibers was similar in both regions. In the ventral horn, thin 5-HT-positive fibers were most prominent at P1W and then decreased with development; thin 5-HT-positive fibers were still found at P6M but had almost disappeared by P2Y. By contrast, at P2Y the density of the synapses and the 5-HT-positive fibers in the dorsal horn was even higher than that of younger animals. Reduction of 5-HT levels in P2Y-old chickens by p-chlorophenylalanine (pCPA) administration decreased the synaptic density in lamina I but not in lamina IX. The results of this study demonstrate that 5-HT-mediated synaptic plasticity is markedly different in the ventral and dorsal horns of the aged chicken. In the ventral horn, synaptic plasticity reached a maximum at about P1W, remained stable in the young-adult period, and then finally disappeared in the aged chicken. Conversely, the results suggest that in the dorsal horn, 5-HT fibers continue to mediate the trophic influence on synaptic plasticity even in the old chicken.
我们实验室之前的研究[3,17]表明，血清素（5-羟色胺，5-HT）似乎在促进发育中的和成年中枢神经系统的突触形成与维持方面具有类似营养的作用。在本研究中，我们重点关注鸡脊髓中轴体和轴树突触密度以及5-HT阳性纤维数量的年龄相关变化，特别提及腹侧（VII层和IX层）和背侧（I层）角之间的差异。在孵化后1周（P1W），IX层出现了突触和5-HT免疫反应性纤维的短暂过度产生；到孵化后1个月（P1M）时，所有参数都恢复到了初始水平。在P6M和P2Y（孵化后2年）之间，突触密度进一步下降了约40%。尽管VII层的短暂增加幅度小于IX层，但两个区域中突触和5-HT阳性纤维的变化模式相似。在腹侧角，细的5-HT阳性纤维在P1W时最为突出，然后随着发育而减少；在P6M时仍可发现细的5-HT阳性纤维，但到P2Y时几乎消失。相比之下，在P2Y时，背侧角的突触和5-HT阳性纤维密度甚至高于年轻动物。通过给予对氯苯丙氨酸（pCPA）降低P2Y老龄鸡的5-HT水平，可降低I层的突触密度，但IX层不受影响。本研究结果表明，5-HT介导的突触可塑性在老龄鸡的腹侧和背侧角明显不同。在腹侧角，突触可塑性在约P1W时达到最大值，在年轻成年期保持稳定，然后在老龄鸡中最终消失。相反，结果表明，在背侧角，即使在老龄鸡中，5-HT纤维仍继续介导对突触可塑性的营养影响。
