| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 85 === The specific aim of this study is to analyze molecules and gene expression as-sociated with memory processing in the rat hippocampus. One way inhibitory avoidance learning task was used as behavioral paradigm. The first part of this study is to investigate the role of nitric oxide (NO) and the anatomical locus was aimed at the dentate gyrus (DG). Results indicated that intra-DG administration of a NO generator, sodium nitroprusside (SNP), at moderate doses (0.024 ug to 0.06 ug) dose-dependently enhanced retention performance in rats at twenty-four hours later. Intra-DG injection of a NO inhibitor,L-NG-monomethylarginine (L-MeArg), impaired retention performance at moderate doses. Coadministration of a NO precursor L-arginine (2.9 ug and 7.2 ug) reversed the memory-impairing effect of L-MeArg. In vitro ADP-ribosylation experiment has shown that six protein bands were labeled. The labeling intensity of these proteins decreased at doses of SNP which impaired memory retention. However, at doses of SNP which enhanced memory retention, the labeling intensity of these proteins did not change significantly. These results together suggest that hippoampal NO plays a facilitatory role in the memory process of an inhibitory avoidance learning task in rats and the facilitatory effect of SNP on memory retention may not act through the ADP-ribosylation pathway. The second part of this study is to analyze gene expression associated with memory formation. Two genes at different stages ofmemory formation were found to be related to retention performance. Three hours after inhibitory avoidance training, three cDNA fragments (A5, A6 and A7) were increased in good memory rats. Sequence analysis indicated that these three cDNAs are derived from the alternative spliced forms of integrin associatedprotein (IAP) mRNA. Quantitative reverse transcriptase-PCR (RT-PCR) analysis revealed that the mRNA level of all of the three forms from good memory rats was significantly higher than that of the poor memory rats. Further, this increase in IAP mRNA level was not due to different sensitivity to shock stimulus in individuals rats. Twenty-four hours after inhibitory avoidance training, two cDNA fragments (the upper and lower bands) were found to be differentially expressed. Good memory rats expressed the upper cDNA band only,while the poor memory rats expressed the upper and lower cDNA bands simultaneously. The two cDNA bands show 98% similarity in sequence and are homologous to the 3'' untranslated region (3''UTR) of the glial fibrillary acid protein (GFAP) cDNA. The upper cDNA represents a new GFAP mRNA isotype which has a 7-base-pair insertion in the 3''UTR. Northern blot analysis indicated that the new GFAP mRNA isotype exists in the hippocampus. Southern blot analysis suggested that the 7-base-pair insertion is derived from the genetic level. Further analyses indicated that retention performance in rats containing onlythe new GFAP mRNA isotype was significantly better than that of rats containing both the new GFAP mRNA isotype and the standard GFAP mRNA simultaneously.The above findings together suggest that different molecules and genes are involved in different stages of memory processing for the inhibitory avoidance learning task in rats. Immediately after training, moderate concentration of nitric oxide facilitates retention performance. Three hours after training, expression of IAP mRNA is related to memory formation. Twenty-four hours after training, expression of a new GFAP mRNA isotype in individuals is associated with memory retention.
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