Peripheral Nerve Injury Induces The Changes Of PSD In Spinal Cord And Hippocampus In Rats

BackgroundChronic neuropathic pain is a physically and emotionally debilitating disorder for which the treatment is still far from perfect. It is generally taught that peripheral nerve lesions may generate a syndrome comprising, in addition to spontaneous pain, tactile allodynia and thermal hyperalgesia. However, the molecular mechanisms underlying these pathophysiological processes are unclear. Synaptic transmitted function changes may play important role in peripheral nerve injury-induced spinal central mechanism in neuropathic pain. The postsynaptic density (PSD), an amorphous structure located beneath the postsynaptic membrane of synapses in the central nervous system, is believed to play a potential role in the organization of receptors and related proteins involved in synaptic signaling. Therefore, it is important to study the changes of PSD expression after peripheral nerve injury.ObjectivePSD is a specialization of the cytoskeleton at the synaptic junction. Synaptic function changes play important roles in the development of neuropathic pain. To determine the expression alterations of PSD after peripheral nerve is valuable to insight into the mechanisms that underlie the chronic neuropathic pain state and provides a potential target for development of new pain therapies.MethodsA total 50 adult Male Sprague-Dawley rats (160-200 g) were used for the studies of behavioral and CaMKⅡα, CaMKⅡβ, PSD-95, PSD-93 and its subunits expression level changes in spinal cord and hippocampus in CCI 3,7and 14days group, campared with control group and sham group. Surgery was performed in the left sciatic nerve trunk of the rats after barbiturate anesthesia based on the method of Bennet and Xie. The latency of nociceptive reaction described below was conducted in all experimental animals 2 days prior to the surgery as baseline and on postoperative days 3, 7 and 14.The development of thermal hyperalgesia and mechanical allodynia was monitored in all rats using the plantar tester based on the description by Hargreaves and von Frey hair testing. Mechanical thresholds were assessed with von Frey hairs using the up-and-down-method following the procedure described by Chaplan.The sham rats were sacrificed on postoperative 3 days. Lumbar (L_4-6) spinal dorsal horn and hippocampus and brain cortex were rapidly dissected after rats killed and immediately frozen in liquid nitrogen. Total RNA of samples was extracted with TRIzol reagent. The mRNA was reversely transcribed to cDNA. The expression level of CaMKⅡα, CaMKⅡβ, PSD-95, PSD-93 and subunits were identified by RT-PCR. The PCR products were analyzed on 1.5% agarose gel. GAPDH was used as an internal control.ResultsThe results of RT-PCR showed that CaMKⅡα, CaMKⅡβ,PSD-95 and PSD-93 expressed in dorsal spinal horn ,hippocampus and brain cortex, but the expression level of different components of PSD were distinct, especially the subunits of PSD-93.Moreover, the expression level of candidate genes are different in separate CCI groups.The expression of PSD-95, PSD-93, CaMKⅡαand the isoforms of PSD-93 are related to development of allodynia in CCI model rats.CONCLUSIONThe sciatic nerve ligation produces mechanical allidynia and thermal hyperalgesia on the injured side. We found that the PSD-95, PSD-93 and its subunits expressed differently in separate CNS regions and on different postoperation days in CCI neuropathic pain rat model. Our results suggested that PSD might play a key role in the central mechanism of chronic neuropathic pain. The present study provides a novel view of the mechanisms that underlie the chronic neuropathic pain state and a novel target for development of new pain therapies.