The effect of intra-amygdalar leptin administration on anxiety, depression and learning behaviors in rats

Leptin is released by adipose tissue. Leptin can cross the blood–brain barrier and bind to receptors on neurons in brain areas to exert its biological function when released into circulation. This study aimed to determine the influences of intra-amygdalar administration of high and low doses of leptin on anxiety, depression, learning behaviors of rats. In the experimental protocol I, intra-amygdalar injection of high and low doses of leptin (0.1 and 1 μg/ kg) and saline were administered 30 min before the behavioral tests. Then, the animals were exposed to open field, elevated plus maze, Porsolt and Morris water maze tests for measuring of behaviors. In experimental protocol 2, the cerebrospinal fluids of all groups of experimental protocol 1 were collected by microdialysis method and then were analyzed by HPLC. The effect of the low dose of leptin was significant on the open field. The effect of the high and low dose of leptin was significant on the elevated plus maze test. The effect of the low dose of leptin was significant on mobility in the center of the Porsolt. A high dose of leptin group had spent less time around the platform than controls in the Morris water maze test. HPLC analysis showed that the amount of serotonin and glutamate in the amygdala region increased after low dose leptin administration. Intra-amygdalar injection of low doses of leptin may decrease anxiety and depression-like behavior in rats by increasing serotonin and glutamate levels in the amygdala.