Effect Of Dendrobium Nobile Lindl. Alkaloids On The Learning And Memory Deficits Induced By Streptozotocin In Rats

Objective: To explore the effects of Dendrobium nobile Lindl.alkaloids(DNLA)on learning and memory deficits,neuronal impairment,hyperphosphorylation of Tau protein and abnormal insulin signaling pathway induced by streptozotocin(STZ)in rats.Methods: Fifty male Sprague Dawley(SD)rats were randomly divided into 5groups: Control group,Control+DNLA40 group,STZ group,STZ+DNLA20 group,and STZ+DNLA40 group.There were 10 rats in each group.After being anesthetized,STZ rats were fixed on the stereotaxic instrument,the coordinate: 0.8 mm posterior to bregma;1.5 mm lateral to sagittal suture;3.6 mm ventral.A volume of 5 μL of STZ solution(70.5 μg/μL)was injected into the bilateral ventricle by micro syringe at the rate of 1 μL/min and remained for 5 min,leading to 3 mg/kg STZ given to every STZ-rat,which was used to prepare the sporadic Alzheimer’s Disease(SAD)animal model.After the preparation of SAD animal model,DNLA-treated groups were administered with DNLA at the dose of 20 mg/kg or 40 mg/kg for consecutively 28 days,while Control and STZ rats were administered with volume-matched vehicle,instead.In the present study,the spatial learning and memory function of rats was measured by Morris water maze(MWM)from the 23 th day after bilateral intracerebroventricular streptozotocin(ICV-STZ)injection lasting for 5 days,and then the time in target quadrant and the motor ability was tested the second day of MWM.The density and morphology of hippocampal neurons were observed through HE and Nissl staining.The expression and phosphorylation levels of insulin receptor(IR),insulin receptor sudstrate-1(IRS-1),protein kinase B(Akt),glycogen synthase kinase-3β(GSK-3β)and Tau protein were detected by Western blot.The expression level of PP2A-α was also detected by Western blot.Results: From the behavioral performance of rats in MWM test,the escape lantency of STZ group rats was dramatically increased in compared with Control group rats from day4;After treated with DNLA,the escape lantency of STZ+DNLA40 group rats was dramatically increased in compared with Control group rats at day4.And the swimming speed of rats from different group was also recorded and it didn’t show significant difference in different group.From the tissue pathological slices of rats after HE and Nissl staining,the number of neurons in hippocampal CA3 region was decreased,the layer of CA3 neurons became thinner and some cells were deeply dyed with pyknotic nuclei in STZ group when compared with Control group;After treated with DNLA,the number and the layer of neurons in CA3 region were increased,and the cells deeply dyed with pyknotic nuclei were decreased in STZ+DNLA40 group when compared with STZ group;Also,the number and the layer of neurons in CA3 region were increased,and the cells deeply dyed with pyknotic nuclei were decreased in STZ+DNLA20 group when compared with STZ group.From protein immunoblotting experiment by Western Blot,the phosphorylation levels of IR at tyrosine 1361 site(p Y1361-IR)and GSK-3β at serine9 site(p-Ser9-GSK-3β)were decreased,GSK-3β at tyrosine 216 site(p Y216-GSK-3β)was not alternated;as well the phosphorylation levels of Akt at serine 473 site(p-Ser473-Akt),IRS-1 at serine 616 site(p-Ser616-IRS-1)and Tau at the sites of serine199,396,404,422 and threonine 231(p-Ser199-Tau,p-Ser396-Tau,p-Ser404-Tau,p-Ser422-Tau and p-Thr231-Tau)were significantly increased in STZ group.After treated with DNLA,the levels of p Y1361-IR and p-Ser9-GSK-3β were increased;the levels of p-Ser473-Akt,p-Ser616-IRS-1 and p-Tau were decreased in STZ+DNLA40 group when compared with STZ group.Also,the levels of p-Ser404-Tau,p-Thr231-Tau were decreased;p-Ser9-GSK-3β was increased;the level of p-Ser473-Akt was increased in STZ+DNLA40 group when compared with STZ group.However,the expression level of PP2A-α didn’t show significant difference among these groups.Conclusion: DNLA is effective on protecting against STZ-induced learning and memory deficits,neuronal impairment,and the protective effect may be associated with the restraint of Tau protein hyperphosphorylation and insulin signaling impairment in hippocampus of rat.