Research reportLocalization of CaMKIIα in rat primary sensory neurons: increase in inflammation
Introduction
Ca2+/calmodulin kinase II (CaMKII) is a multifunctional enzyme that can catalyze the phosphorylation of a variety of proteins and this action contributes to long term potentiation, release of neurotransmitters, and regulation of ion channels (see Ref. [10] for review). Recently it has been shown that CaMKIIα is preferentially localized in pain-processing regions in the central nervous system such as the superficial laminae of the dorsal horn in the spinal cord and the dorsal root ganglia (DRG) [2]. Ca2+-mediated cell signaling is important in nociceptor function and the presence of CaMKIIα in DRG cells suggests that this enzyme may contribute to nociceptive signaling. Several receptors whose activation results in Ca2+ influx have been localized on nociceptors and include purinergic P2X [24], capsaicin [3], NMDA [5] and bradykinin [13] receptors. Furthermore, it has been demonstrated that P2X-mediated responses in DRG cells are enhanced by endogenous CaMKII in normal and inflamed rats [26].
Presuming that CaMKIIα has a role in the transmission of nociceptive information, the goals of the present study were to investigate the distribution of CaMKIIα in primary sensory neurons and to analyze changes that occur in the expression of CaMKIIα following inflammation. To accomplish this, numbers of DRG cells in lumbar ganglia that contain CaMKIIα were estimated using stereological methods, the mean diameter of CaMKIIα-containing DRG cells were measured, and the axonal transport of CaMKIIα into the peripheral and central processes of DRG cells were visualized. Finally, increases in CaMKIIα-containing axons in the digital nerves of rats 48 h following inflammation of the hindpaw were documented.
Section snippets
Materials and methods
All procedures were approved by the University Animal Care and Use Committee and followed guidelines for the ethical treatment of animals [28]. Male, Sprague–Dawley rats were obtained from Harlan, Indianapolis, IN, USA.
CaMKIIα-labeling in DRG
Immunostaining for CaMKIIα in the lumbar DRG resulted in diffuse, rather homogeneous staining throughout the cytoplasm of labeled cells but the nuclei were weakly stained or unstained. The density of cytoplasmic staining varied from light, medium, to dark (Fig. 1). Positively stained cells had a diameter of 27.1±5 μm (mean±S.D.) and ranged from 13.5 to 48 μm. Numerical estimates of CaMKIIα-labeled DRG cells, obtained using stereological analysis, demonstrated that 5,829±513 cells were labeled (
Discussion
These analyses demonstrate that a subpopulation of small diameter DRG cells immunostain for the enzyme CaMKIIα. Placement of a tight ligature around the sciatic nerve demonstrates that CaMKIIα is transported into the peripheral processes of DRG cells. Analysis of the lumbar dorsal roots at the electron microscopic level demonstrates that the enzyme is also transported centrally into the spinal cord. Finally, electron microscopic analysis of the digital nerves in the hindpaw demonstrates the
Acknowledgements
The author thanks Vicki Wilson for her secretarial assistance and Greg Hargett and Zhixia Ding for their expertise in immunohistochemical staining. This work was supported by NS27910, NS11255 and NS40700 to S.M.C.
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