Price Theodore J, Hargreaves Kenneth M, Cervero Fernando
McGill University, Departments of Anesthesia and Dentistry and McGill Centre for Research on Pain, 3655 Prom Sir William Osler, Montreal, QC, Canada H3G 1Y6.
Brain Res. 2006 Sep 27;1112(1):146-58. doi: 10.1016/j.brainres.2006.07.012. Epub 2006 Aug 10.
Primary afferent neurons maintain depolarizing responses to GABA into adulthood. The molecular basis for this GABAergic response appears to be the Na+K+2Cl- cotransporter NKCC1 that contributes to the maintenance of a high intracellular chloride concentration. Recently, a role for NKCC1 has been proposed in nociceptive processing which makes it timely to gain a better understanding of the distribution of NKCC1 in sensory ganglia. Here, we describe that, in the rat, NKCC1 mRNA is predominately expressed by small and medium diameter dorsal root (DRG) and trigeminal (TG) ganglion neurons. The colocalization of NKCC1 mRNA with sensory neuron population markers was assessed. In the DRG, many NKCC1 mRNA-expressing neurons colocalized peripherin (57.0+/-2.5%), calcitonin-gene-related peptide (CGRP, 39.2+/-4.4%) or TRPV1 immunoreactivity (50.0+/-1.9%) whereas only 8.7+/-1.2% were co-labeled with a marker for large diameter afferents (N52). Similarly, in the TG, NKCC1 mRNA-expressing neurons frequently colocalized peripherin (50.0+/-3.0%), CGRP (35.4+/-2.6%) or TRPV1 immunoreactivity (44.7+/-1.2%) while 14.8+/-1.3% were co-labeled with the N52 antibody. NKCC1 mRNA was also detected in satellite glial (SGCs) in both the DRG and TG. Colocalization of NKCC1 protein with the SGC marker NG2 confirmed the phenotype of these NKCC1-expressing glial cells. In contrast to in situ hybridization experiments, we did not observe NKCC1 immunoreactivity in primary afferent somata. These findings suggest that NKCC1 is expressed in anatomically appropriate cells in order to modulate GABAergic responses in nociceptive neurons. Moreover, these results suggest the possibility of a functional role of NKCC1 in the glial cells closely apposed to primary sensory afferents.
初级传入神经元在成年后仍对γ-氨基丁酸（GABA）保持去极化反应。这种GABA能反应的分子基础似乎是钠钾氯共转运体NKCC1，它有助于维持细胞内高氯离子浓度。最近，有人提出NKCC1在伤害性感受处理中发挥作用，这使得更好地了解NKCC1在感觉神经节中的分布变得很及时。在这里，我们描述了在大鼠中，NKCC1 mRNA主要由中小直径的背根神经节（DRG）和三叉神经节（TG）神经元表达。评估了NKCC1 mRNA与感觉神经元群体标记物的共定位情况。在DRG中，许多表达NKCC1 mRNA的神经元与外周蛋白（57.0±2.5%）、降钙素基因相关肽（CGRP，39.2±4.4%）或TRPV1免疫反应性（50.0±1.9%）共定位，而只有8.7±1.2%与大直径传入神经标记物（N52）共标记。同样，在TG中，表达NKCC1 mRNA的神经元经常与外周蛋白（50.0±3.0%）、CGRP（35.4±2.6%）或TRPV1免疫反应性（44.7±1.2%）共定位，而14.8±1.3%与N52抗体共标记。在DRG和TG的卫星神经胶质细胞（SGCs）中也检测到了NKCC1 mRNA。NKCC1蛋白与SGC标记物NG2的共定位证实了这些表达NKCC1的神经胶质细胞表型。与原位杂交实验不同，我们在初级传入神经元胞体中未观察到NKCC1免疫反应性。这些发现表明，NKCC1在解剖学上合适的细胞中表达，以调节伤害性感受神经元中的GABA能反应。此外，这些结果提示了NKCC1在与初级感觉传入神经紧密相邻的神经胶质细胞中发挥功能作用的可能性。
