Iwata K, Kanda K, Tsuboi Y, Kitajima K, Sumino R
Department of Physiology, School of Dentistry, Nihon University, Tokyo, Japan.
Brain Res. 1995 Apr 24;678(1-2):127-39. doi: 10.1016/0006-8993(95)00176-q.
In order to elucidate the effect of aging on nociceptive neurons in the central nervous system, c-fos was used as a marker of excitability of neurons in the medullary dorsal horn (MDH) and the first spinal segment (C1) following noxious stimulation of the lateral face of young and aged rats. The distribution of c-fos-positive cells was dense in the superficial laminae and sparse in the deep laminae of the MDH and C1 in both young and aged animals following subcutaneous injection of formalin into the lateral face, whereas few c-fos-positive cells were labeled after saline injection. The distribution of c-fos-positive cells in the superficial laminae of the aged rats was found to be denser and more rostro-caudally expanded compared to that in the young rats. C-fos-positive cells were distributed more rostro-caudally in aged than in young rats. There was no difference between young and aged rats in the distribution of c-fos-positive cells in the deep laminae. Substance P (SP), 5-HT and calcitonin gene-related peptide-like immunoreactive (CGRP-LI) fibers and varicosities showed similar distribution density in the MDH and C1. Furthermore, many 5-HT-LI aberrant fibers and varicosities were observed in the MDH and C1 of the aged rats. The SP-LI and CGRP-LI cells in the trigeminal ganglion of aged rats were larger than those of young rats. These findings suggest that a deficit of the descending 5-HT inhibitory system produces the increment of c-fos-positive cells in the MDH and C1 of aged rats, resulting in the recruitment of a larger number of neurons in the superficial laminae of the MDH and C1 for conveying nociceptive sensory information to the central nervous system.
为了阐明衰老对中枢神经系统伤害性神经元的影响，在对年轻和老年大鼠的侧面进行伤害性刺激后，使用c-fos作为延髓背角（MDH）和第一脊髓节段（C1）中神经元兴奋性的标志物。在年轻和老年动物的侧面皮下注射福尔马林后，MDH和C1的浅层中c-fos阳性细胞分布密集，深层中稀疏，而注射生理盐水后几乎没有标记到c-fos阳性细胞。与年轻大鼠相比，老年大鼠浅层中c-fos阳性细胞的分布更密集，且在头尾方向上扩展得更多。老年大鼠中c-fos阳性细胞在头尾方向上的分布比年轻大鼠更广泛。年轻和老年大鼠深层中c-fos阳性细胞的分布没有差异。P物质（SP）、5-羟色胺（5-HT）和降钙素基因相关肽样免疫反应性（CGRP-LI）纤维及膨体在MDH和C1中的分布密度相似。此外，在老年大鼠的MDH和C1中观察到许多5-HT-LI异常纤维和膨体。老年大鼠三叉神经节中的SP-LI和CGRP-LI细胞比年轻大鼠的大。这些发现表明，下行5-HT抑制系统的缺陷导致老年大鼠MDH和C1中c-fos阳性细胞增加，从而导致MDH和C1浅层中有更多神经元被募集来将伤害性感觉信息传递到中枢神经系统。
