| Summary: | 碩士 === 國立陽明大學 === 解剖學及細胞生物學研究所 === 101 === Background：Leptin is an adipose-derived hormone that acts on receptors in the hypothalamus where it inhibits appetite. The absence of leptin or its receptor leads to uncontrolled food intake and obesity. Some studies also revealed that the downstream molecules of leptin in the hippocampus modulate hippocampal neurogenesis, emotions and memory. We obtained an obese mouse line with an amino acid change in codon 145 of leptin (Leptin145E) from screening N-ethyl-N-nitrosourea(ENU)-mutagenized mice. Because of the following reasons we speculated that Leptin145E could be, unlike truncated and inactive Leptinob, functional and that Leptin145E/145E mice might display different behavioral and molecular features from Leptinob/ob mice：(1)Serum leptin levels are abnormally high in Leptin145E/145E mice while leptin is undetectable in Leptinob/ob mice;(2) Leptin145E/145E mice have lower body weight and higher Insulin resistance index than Leptinob/ob mice at the same age; (3) Leptin145E/145E mice did not display the depression-like behavior in the forced swim test as Leptinob/ob mice did. In order to prove our speculation we compared the downstream molecules of leptin in the hippocampus and the behaviors between Leptin145E/145E and Leptinob/ob mice.
Materials and methods: Five to six weeks old male Leptin+/+, Leptin145E/145E and Leptinob/ob C57BL/6J mice were used in this study. Elevated plus maze (EPM), the forced swim test (FST), multiple T-maze and the Conditioned freezing test were adopted to evaluate emotional and cognitive behaviors of mice. After the behavioral tests, the mice were injected with BrdU(50mg/kg) every 8 hours for three times and sacrificed 2 hours after the last injection. The right hippocampus was preserved for BrdU immunohistochemical staining and the left hippocampus was homogenized for Akt, GSK3 and β-catenin measurements with western blots. SPSS software was used for statistical analysis.
Results: Leptin145E/145E and Leptinob/ob mice both showed better one-hour, 24-hours and 2-weeks emotional memories in the conditioned freezing test and better spatial memory in the multiple T-maze test than Leptin+/+ mice. No significant difference was found in the EPM or FST among Leptin145E/145E, Leptinob/ob, and Leptin+/+ mice. The phosphorylated ratios of Akt(T308) and GSK3β(ser9) from the hippocampus and BrdU-stained area in the dentate gyrus of Leptin145E/145E and Leptinob/ob mice were all higher than that in Leptin+/+ mice, but none of the above data was significantly different between Leptin145E/145E and Leptinob/ob mice.
Conclusion: Because Leptin145E/145E and Leptinob/ob mice display similar molecular and behavioral features, our data disagree with the hypothesis that Leptin145E is functional. However, we found that leptin deficiency can lead to elevated phosphorylation of Akt(T308), GSK3β(ser9) in the hippocampus and increased neurogenesis in the dentate gyrus, which is the possible mechanism of enhanced emotional and spatial memories with Leptin145E/145E and Leptinob/ob mice.
|
|---|
