| Diabetes mellitus is one of the common chronic diseases which involvemulti-system and organs in human. Increasingly incidence of diabetes has beeninfluenced human health in the recent years. Diabetes affected central nerve systemand induced cognitive impairments and the structural and physiological injury of brain,which was charactored by cognitive and behavioral defect and named diabeticencephalophathy. It is known that diabetes-associated cognitive disorder is one of thecomplications of diabetes and a risk factor of senile dementia. It is significant toinvestigate the mechanisms of diabetic cognitive defect and explore the prevention andtherapy in both medical and social area.Hippocampus is the key structure for learning and memory. It has been provedthat diabetes induced apoptosis of hippocampal neurons and the decrease of synapticplasticity, and both changes were related to unbalance of intracellular calcium levels.Transient receptor potential canonical (TRPC) channels are low-voltage sensitive and have permeability to cation including calcium. TRPC3channel can be activated byhyperglycemia and induce calcium ion inflow, further influence the stability of calciumlevel and related functions. It has been suggest that TRPC channels play a key role inmany diabetes induced pothalogic states. TRPC3has wide and high expression level inhippocampus and has very important effect on neuron survival, differatiation,migration and the formation of synapse. Together, these results strongly suggested thatTRPC3channel play important role in the diabetes induced hippocampal neuron injury.In this research, a system of studies was performed with the molecular biological,morphological and behavioral technologies in diabetic rats and cultured cells, whichinclude the relationship between TRPC3expression and neuron viability, the cellularand molecular mechanisms of hippocampal neuron injury.Methods:Male adult SD rats were randomly divided into four groups after adaptively fedfor3days: normal control group (Control), diabetic group (DM), fish oil group (FO),diabetic and fish oil group (DM+FO). Diabetes type I animal model was made bystreptozocin (STZ) injection intraperitoneal. The experimental period was5weeks,rats were fed in single cage with free access to water and food. Rats were weighedonce a week and measured blood glucose on day3, day7and day35after STZinjection. Moriss water maze test was performed5weeks after STZ injection, and theanimals were scraficed after behavoural test. ELISA method was used for detecting theperoxidant level (SOD and MDA) and inflammation (TNF-α). Morphological characterof the neurons and apoptosis were observed under light miceoscope and transmissionelectromicroscope. Expression of TRPC3and apoptotic proteins were detected bywestern-blot. Hippocampal neurons from newborn rats were cultured and stimulated byhigh glucose conditions (25mM and75mM). The index mentioned above wasinvestigated and the protective effect of DHA was onserved. Results:1. Compared to control group, the diabetic rats had significant longer escapelatency in the moriss water maze (P＜0.05) and less amount of time spent in the targetquadrant in probe trial (P＜0.05).2. Amount of apoptosis neurons occurred and apoptotic related proteins increasedin hippocampus of diabetic rats. Swelling of mitochondria and axon, widen synapticcleft and pyknotic chromatin were onserved under electromicroscope.3. Golgi staining showed that the number and the ledngth of neuronal dentritesdecreased significantly in diabetic group (P＜0.05).4. The expression of TRPC3in hippocampal neurons decreased in diabetic group(P＜0.05).5. Hyperoxidation and inflammation were observed in diabetic rats andPI3K/AKT signal pathway involved in the process of diabetes induced hippocampalneurons injury.6. Dietary administration of fish oil improved the state of hippocampal neuronsand further improved learning and memory of diabetic rats.7. Apoptosis increased in primary cultured hippocampal neurons in high glucosecondition, and Hyperoxidation and inflammation were also observed. However, wefound increased TRPC3expression in cultured neurons. DHA administration improvedthe state of neurons in high glucose condition.Conclusion:1. Diabetes impaired the spacial learning and memory of rats, and fish oil improvethe cognitive performance of diabetic rats.2. The changes of TRPC3expression influenced growth of neuronal dentrites andclosely related to neuron apoptosis.3. PI3K/AKT signal pathway involved in the peroxidation, neuron apoptosis anfinflammation of diabetic rats. 4. There were different changes of TRPC3expression in vivo and in vitro, whichimplied different modulative mechanisms of TRPC3channels. Further studies are needto investigate the effect of TRPC3and its mechanisms. |
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