Study On The Protective Effect Of Extracts Of Gingko Biloba Leaves (EGb) On Learning And Memory Disorder In Diabetic Rats

Chronic diabetes mellitus can result in structural and functional lesions of multiple organsin human. Even more, it will cause diabetic neuropathy, including peripheral and centralneuropathy. In the early stage, more basic researches had been done on the peripheralneuropathy to find effective neuroprotection. Unfortunately, less attention had been paidto the central neuropathy. For this reason, it is significant to investigate the diabetic braininjury and to find the corresponding neuroprotective agents. Gingko biloba extract (EGb)is a well-defined plant extract containing two major groups of constituents, i.e.flavonoids and terpenoids. Possessing antioxidant and free radical-scanvenging activities,EGb improves blood rheology and tissue metabolism. It has markedly neuroprotectiveeffects on CNS and counteracts the cognitive deficits that follow stress or traumatic braininjury. It is viewed as a polyvalent agent with a possible therapeutic use in the treatmentof neurodengenerative diseases of multifactional origin, e.g. AD.In the present study with streptozotocin-induced diabetes in Wistar rats as objects, we haveinvestigated the protective effects of EGb on brain in morphological, functional and molecularbiology aspects.A. Morphological and functinal aspects1.Administration of STZ (55 mg.kg-1, i.p.) produced diabetic symptoms such as weight loss,polyuria, polydipsia, and hyperglycemia. After 6 months of diabetes, morphological analysis ofthe hippocampal cells by Nissl staining revealed that the neuronal cells were in the state ofraritas and disorder, accompanied by reduced neuronal density in the hippocampus.Ultrastructural analysis of the hippocampal pyramidal neurons by electronmicroscope revealedthat the cell organs of neurons were ambiguous, cell body and nervous process were obviouslyswelling, endochylema was vacuolated, rough endoplasmic reticulum and free ribosome weremarkedly decreased, chondriosome was engorged, lyzed and destructed, cellular membrane wasdisaggregated. The ultrastructural analysis also showed that the nerve fiber and nerve plexuswere ambiguous, synaptic cleft was widened, postsynaptic density (PSD) was attenuated. EGbadministration(100 mg.kg-1)could improve the above morphological changes, obviouslydiminishing synapse cleft and increasing PSD and neuronal density.2.To explore mechanisms underlying central nervous system complications in diabetes, we alsoexamined hippocampal neuronal apoptosis and the effect of EGb. Apoptosis was demonstratedafter 6 months of diabetes by electronmicroscope observation. Increased numbers ofTdT-mediated dUTP nick-end labeling (TUNEL)-positive cells were shown in the diabetichippocampus. Whereas EGb administration(100 mg.kg-1)could decrease the numbers of positiveapoptotic cells by TUNEL in diabetic hippocampus.3. After 6 months of diabetes, the activity of Na+-K+-ATPase in diabetic hippocampus wasdescended from the normal 16.07 ±3.60 ( μmolPi.mg Pr-1.h-1 ) to 10.52 ±3.02, EGbadministration 100, 50 mg.kg-1)could enhance the Na+-K+-ATPase to 15.50±2.76, ( 14.67±3.55,respectively. The data suggested that EGb could protect the functional Na+-K+ATPase ofneuronal cytolemma from diabetic injury.4. After 6 months of diabetes, diabetic rats could swim for more than 3hrs. The open filed testalso showed that the limb's movements of diabetic rats were not harmed. Accordingly, weobsvered the learning and memory potentia by Morris water maze, and behavior profiles by openfiled test. The result of open field test showed that the center detention time was prolonged,accompanied by decreased numbers of hollow-probing in diabetic rats. The result of Morriswater maze showed that the escaping latency was prolonged, and score of platform-searchingwas decreased on d5 and d8 after training. EGb administration(100, 50 mg.kg-1)could shortencenter detention time, increase numbers of hollow-probing, improve deficient escaping latencyand score of platform-searching in diabetic rats.B.Molecular biology aspectsStreptozotocin-induced diabetes was produced in another batch...