Ranson R N, Santer R M, Watson A H D
Cardiff School of Biosciences, Biomedical Sciences Buildings, Cardiff University, Cardiff, UK.
Exp Gerontol. 2007 Jun;42(6):506-16. doi: 10.1016/j.exger.2007.01.006. Epub 2007 Jan 30.
The immunocytochemical localisation of vesicular glutamate transporters, VGLUT1 and VGLUT2, was employed to identify putative glutamatergic axon terminals innervating pelvic motoneurons. VGLUT1 terminals were sparsely distributed within lumbosacral spinal motoneuron pools, including the dorsolateral nucleus, retrodorsolateral nucleus and spinal nucleus of the bulbospongiosus. This was in marked contrast to VGLUT2 which was expressed in a robust innervation of these areas. Retrograde tracing was used to reveal motoneurons innervating the levator ani (LA) muscle. On these neurons, associations with VGLUT2 immunoreactive terminals were abundant while those with VGLUT1 were rare. Ultrastructural investigations revealed that VGLUT2 immunoreactive terminals made asymmetric synaptic contacts with dendrites of retrogradely labelled LA motoneurons. Quantification of VGLUT2 immunoreactive boutons in close association with these dendrites was carried out in young and aged animals using light microscopy. This revealed a significant decline in the numbers of VGLUT2 immunoreactive boutons on the more distal dendrites of motoneurons in aged rats. VGLUT2 boutons were reduced by approximately 21% from 11.25+/-0.5 per 35-mum length of dendrite in young rats to 8.89+/-0.5 in aged animals. This decline in glutamatergic input may reduce the excitability of LA motoneurons and consequently decrease the capacity of the rat to induce reflexive erections.
运用囊泡谷氨酸转运体VGLUT1和VGLUT2的免疫细胞化学定位来鉴定支配盆部运动神经元的假定谷氨酸能轴突终末。VGLUT1终末稀疏分布于腰骶部脊髓运动神经元池内，包括背外侧核、背外侧后核和球海绵体肌脊髓核。这与VGLUT2形成显著对比，VGLUT2在这些区域有丰富的神经支配。逆行示踪用于揭示支配提肛肌（LA）的运动神经元。在这些神经元上，与VGLUT2免疫反应性终末的联系丰富，而与VGLUT1的联系很少。超微结构研究显示，VGLUT2免疫反应性终末与逆行标记的LA运动神经元的树突形成不对称突触联系。使用光学显微镜对年轻和老年动物中与这些树突紧密相关的VGLUT2免疫反应性终扣进行定量分析。结果显示，老年大鼠运动神经元更远端树突上的VGLUT2免疫反应性终扣数量显著减少。VGLUT2终扣从年轻大鼠每35μm树突长度11.25±0.5个减少到老年动物的8.89±0.5个，减少了约21%。谷氨酸能输入的这种减少可能会降低LA运动神经元的兴奋性，从而降低大鼠诱发反射性勃起的能力。
