| Objective: Aging is a common and complex process,in which the function of every organ and system including central nerve system decline progressively.In the process of brain aging,olfactory dysfunction is one of the manifestations of cognition impairment.Therefore,how to delay the decline of olfactory function is crucial.A number of studies have shown that Extract of Fructus Cannabis(EFC)has the effect of improving learning and memory impairment,but whether it can improve olfactory dysfunction remains unexplored.Nerve growth factor(NGF)and brain derived growth factor(BDNF)belong to the neurotrophic factors(NTFs)family,which protect neurons andmaintain normal function of neurons.This study was designed to assess the effect of EFC on olfactory decline in D-gal-induced SD rats and to explore whether NGF and BDNF are involved in this process.Methods: 1.60 healthy male Sprague-Dawley(SD)rats were randomly divided into 5 groups.(1)The normal control group(Control group),normal saline continuous intraperitoneal injection and intragastric administration for 3 months.(2)D-galactose model group(D-galactose,D-gal),400mg/kg D-galactose solution was continuous intraperitoneal injection,and normal saline continuous intragastric administration for 3 months simultaneously.(3)Low,medium and high dose EFC intervention group(D-gal+EFC-L,D-gal+EFC-M,D-gal+EFC-H),400mg/kg D-galactose solution was administered intraperitoneally with EFC at concentrations of 400mg/kg,800mg/kg and 1200mg/kg was given intragastrically for 3 months.The daily administration time is fixed from 3:00p.m.to 5:00p.m.2.Morris water maze(MWM)test was used to evaluate the learning and memory function of rats in each experimental group.3.Olfactory identification and memory test measures the olfactory identification and memory function of rats from a behavioral assessment.4.The pathological changes of mitral cells in rat olfactory bulb were detected by hematoxylineosin staining(HE).5.Western blot(WB)was used to detect the expression levels of NGF and BDNF in rat olfactory bulb.6.Immunohistochemical(IHC)staining was used to detect the expression of NGF and BDNF in rat mitral cells.Results: 1.In the directional navigation test,there was no significant difference in the escape latency of rats in each experimental group on the first day of testing.From day 2 to day 5,the escape latency of the D-gal model group was significantly longer than that of the normal control group(P<0.05).Except for the 1200mg/kg EFC intervention group,the escape latency of the 400mg/kg and 800mg/kg EFC intervention groups was significantly shorter than that of the D-gal model group(P<0.05).On the 5th day of the test,the swimming trajectories of the D-gal model group were disorderly and irregular compared with the normal control group,and were randomly distributed in all quadrants(P<0.05).In addition to the 1200mg/kg EFC intervention group,the swimming trajectory of rats in the 400mg/kg and 800mg/kg EFC intervention groups was significantly improved compared with the D-gal model group(P<0.05)2.In the space exploration test,the frequency of rats crossing the hidden platform in the D-gal model group was significantly lower than that in the normal control group(P<0.05).Except for the 1200mg/kg EFC intervention group,the number of rats in the 400mg/kg and 800mg/kg EFC intervention groups crossing the position of the hidden platform was significantly higher than that in the D-gal model group(P<0.05).3.In the olfactory identification and memory test,the latency of D-gal model rats was significantly longer than that of normal control rats,and the correct frequency was significantly reduced(P<0.05).Except for the 1200mg/kg EFC intervention group,the latency of rats in 400 mg/kg and 800 mg/kg EFC intervention groups were significantly shorter than that in D-gal model group(P < 0.05),and the correct times were significantly increased(P< 0.05).4.The results of HE staining showed that the mitral cells in the olfactory bulb of the D-gal model group were deformed,atrophied and decreased in number compared with the normal control group(P<0.05).Compared with the D-gal model group,except for the 1200 mg/kg EFC intervention group,the morphology of the mitral cells in the olfactory bulb of the 400mg/kg and 800 mg/kg EFC intervention groups were normal and the number was significantly increased(P<0.05).5.Western blot results showed that protein expression levels of NGF and BDNF in the D-gal model group were significantly lower than those in the normal control group(P<0.05).In addition to the 1200mg/kg EFC intervention group,the protein expression levels of NGF and BDNF in the olfactory bulb of the 400mg/kg and 800mg/kg EFC intervention groups were significantly higher than those in the D-gal model group(P<0.05).6.The results of IHC showed that the protein expression levels of NGF and BDNF in the mitral cell layer of the D-gal model group were significantly lower than those in the normal control group(P<0.05).Except for the 1200mg/kg EFC intervention group,the expression levels of NGF and BDNF in the 400 mg/kg and 800mg/kg EFC intervention group were significantly higher than those in the D-gal model group(P<0.05).Conclusion: 1.Low and moderate dosage of EFC can improve the spatial learning and memory decline of D-gal-induced aging SD rats.The improvement effect of high concentration of EFC was not obvious.2.Low and moderate dosage of EFC can improve the olfactory identification and memory function decline in D-gal-induced aging SD rats.High dosage of EFC had no this effect.3.Appropriate concentration of EFC may protect neurons by up-regulation of NGF and BDNF protein expression levels in the mitral cells,thereby improving olfactory identification and memory function in aging rats. |
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