Role Of Tissue Plasminogen Activator In Visual Cortical Plasticity Of Developing Rat Visual Cortex

Objective1.To investigate the co-expression relationships among tissue plasminogen activator (tPA), paralbumin (PV) and perineuronal nets (PNs) in the visual cortex of Long Evans rat during postnatal development of plasticity.2.Although it has been recognized that ocular dominance(OD) plasticity of adult rats can be restored through brief dark exposure(DE),the definite molecular changes behind this phenomenon are still obscure.Tissue plasminogen activator(tPA) plays a crucial role in visual system involved with a multifactorial event in which glutamic acid decarboxylase 67(GAD67) and perineuronal nets(PNs) both participate.Here,we focused on the expression and distribution of tPA^ GAD67 and PNs in adult rats exposured in dark as well as the variation of tPA activity.Methods1.According to postnatalage, rats (n= 15) were divided into 3 weeks (outset of critical period),4 weeks (peak),5 weeks (later stage),7 weeks (termination of critical period), and 9 weeks (adult) groups. The co-expression of tPA, NeuN, DAPI and tPA, PV, PNs were both detected by immunofluorescence histochemistry.2.we analyzed expression of tPA>. GAD67 and PNs in adult rats exposured in dark with immunofluorescence histochemistry, protein expression of tPA and GAD67 with western-blotting and tPA activity with chromogenic product assay.Control groups are adult rats in normal rearing(NR) condition.Results1.The density of tPA+PNs-containing cells had a significant up-regulation at PW4, then remarkably decreased at PW9, both of tPA+PV and PV+PNs-positive cells’densities peaked at PW3 but reduced at PW5 rapidly, then increased significantly along with the end of critical period (CP);2.The maximum and minimum rate of both tPA+PV/tPA and PV+PNs/PNs appeared in PW3 and PW5, respectively; The density of tPA+PV+PNs-containing cells peaked at the most active time of CP neuro-plasticity.3.Our studies show that density of tPA-positive cells in DE group increased significiantly than NR rats,on the contrary,GAD67-stained cells and PNs-stained cells both exerted a remarkable decline in comparison with matched group;the consequence of western-blotting assay were roughly consistent with fluorescence immunohistochemistry which showed accrued tPA expression accompanied with attenuated GAD67.Besides,tPA performed stronger activity due to tremendous changes in visual inputs.Conclusion1.Our present results suggest that the variation of PV-positive cells wrapped by PNs in developing visual cortex may reveal the structure foundation of PNs’participating in the termination of CP;2.The enrichment of tPA+PV+PNs-containing cells we found in this study,indicates a significant correlation between tPA+PV+PNs-containing neurons and neuro-plasticity’s enhancement in CP;3. Potentiating action of tPA in visual cortex of rats may be response to DE in molecular level,the resulting consequence of both quantitative and qualitative changes of tPA involve with the degradation of PNs,which induces a decrease of GABA levels,ultimately results in reactivation OD plasticity.