Distribution and altered expression of parvalbumin in dorsal root ganglion induced by neuropathtic pain

Abstract

Objective To explore the distribution and expression changes of parvalbumin in the dorsal root ganglion (DRG) neurons in chronic constriction injury rat models. Methods Forty-two adult male SD rats, weighing 180-200 g, were randomly divided into control group, sham operation group, chronic constriction injury (CCI) 1-, 3- 5-, 7-, 14-day groups, with 6 rats in each group. The right sciatic nerves of rats in CCI groups were moderately ligated proximal to its bifurcation using 4-0 chromic gut, ligation of 4, 1 mm intervals. The sciatic nerves in sham group were only exposed and isolated but not ligated.The changes of naturopathic pain behavior in all animals were observed one day before surgery and 1,3, 5,7 and 14 days after surgery. DRG of L5 spinal nerve was removed for analysis of parvalbumin and MAP2-immunoreactive neurons in DRG in relation to chronic constriction injury. Results ( 1 ) CCI, but not sham surgery, produced significant mechanical allodynia and thermal hyperalgesia ( P ＜ 0. 05 ). The mechanical hyperalfesia was significantly decreased one day after CCI, and the thermal hyperalgesia was greatly attenuated on the 3th day after CCI. Both the thermal and mechanical hyperalgesia was decreased at the lowest level at the 7th day after surgery ( P ＜0. 01 ). (2) In normal rats, there was only a small amount of PV-IR neurons in DRG that were mostly large-and medium-sized neurons, but a few small-sized neurons.PV-IR nerve fibers constituted a network of nerve fibers around cell body of non-PV neurons. In the deep tissue of DRG, bundles of PV-positive nerve fibers traversed between PV-negative neurons. (3) PV-IR neurons in DRG had no significant changes at CCI day 1,3. MAP-2 in PV positive neurons was relatively in good condition, compared with non-PV neurons. PV-IR neurons were decreased from the 5th day after surgery, reduced more significantly until the 7th day (P ＜0. 05), and recovered at the 14th day (P ＞0. 05), compared with the control group. Conclusion The reduction of PV-IR neurons in DRG was accompanied by change of pain behavior of CCI rats, suggesting that the reduction of PV-IR neurons is in relation to peripheral noxious stimulation and the down-regulation of the PV expression in the imbalance of calcium homeostasis mechanisms, which may involve in the development and maintenance of neuropathic pain. Key words: Hyperalgesia; Dorsal root ganglion; Parvalbumin; Calcium