| Neuronal regeneration of injured peripheral nerve is a sequential repairing process including regrowth of injured axons, as well as myelination, restoration of synaptic connections, and recovery of physiological functions. Neuronal regeneration in mammals is limited to the peripheral nervous system (PNS), and neurons in the central nervous system (CNS) is nearly absent in the ability of regeneration. To restore damaged neuronal functions both in PNS and in CNS, the underlying mechamism of regeneration in the injured peripheral nerve must be understood. Schwann cells are myelinating cells in PNS, it expresses PDGF-βreceptor under the stimulation of PDGF-BB, accompanying the proliferation of the cells. Many kinds of neurotrophic factors are synthesized in schwann cells, in addition they could keep alive after the axon transection. Indicating their crucially important roles in axonal regrowth. However, the delicate mechanism of keeping alive and promoting neuronal regeneration is still unknown. PDGF is a growth regulatory molecule with diverse functions that play critical roles in the physiological and pathological processes such as development of embryogenesis, neuronal development and tumorigenesis. The roles of PDGF in embryogenesis and CNS have been widely demonstrated in recent years with the development and application of gene knock-out technology. However, the role of PDGF in PNS is seldom reported. The present study detected the expression of PDGF in differerent segments of injured sciatic nerve and different time from the first day to the 28th days in PNS injury by applying two rat PNS injury model: crush injury and cut injury. The purpose is to elucidate the functional role of PDGF in regeneration of PNS. The results were as follows: 1,Northern blot hybridyzation: The expression of PDGF-B mRNA in both injured sciatic nerves were increased in different segments and different time course comparing to the normal control groups. Expression of all the PDGF-B transcripts was significantly increased in all samples except for day 3 after crush injury, and peaking at day 7 in cut (250±94.5pg/g) and day 28 in crush (173±89.7pg/g). In both types of injury, the expression of PDGF-B mRNA were most abundant in the D1 segments among those examined from three sites of the nerve. The expression of PDGF-B mRNA increased from day 3, and remained at high level (340pg/g) throughout the study in the cut model. In the crush model, its expression increased from day 3, and reach the peak at day 7(240pg/g). The expression in D2 segments reached a peak value on day 3 and day 28 in the crush (194±67.8pg/g) and cut (185±52.2pg/g) models respectively. 2,Immunohistochemistry: The expression of PDGF-B protein were examined by immunohistochemistry using monoclonal antibody PGF-007. In control sciatic nerve, certain amount of specific immunoreactive products for PDGF-B were localized in the axon, the cytoplasm of ensheathing Schwann cells and in the myelin sheath. Soon after nerve injury, primarily on day 1, intense immunoreactivity was frequently localized in the swollen axons within the P1 segment in both injury models. After day 3 of crush injury, enhanced expression of PDGF-B was detected in the regrowing axons compared with control. These enhanced reactions in regenerating axons were restored to normal levels on day 28. 3,The expression of PDGF-B in Schwann cells: in both injury models, many Schwann cells in the distal segments proliferated on and after day 3. The intense immunoreactive products were associated with the swollen cytoplasm of Schwann cells after injury. They were most frequent in distal segments on day 7. In the crush model, this intense Schwann cells-associated immunoreactivity decreased afterward in accordance with axonal recovery but remained at normal levels in the distal segments on day 28. In the cut model, reactivity decreased, many Schawann cells were only faintly labeled in the distal segments on day 28. 4,Immunohistochemical characterization of PDGF-B in cr...
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