A study conducted by Xin-Yun Lu, PhD and colleagues of the University of Texas Health Science Center found that Leptin when administered to the rat acts as an anti-depressant. Leptin is a hormone mainly given to people involved in weight regulation.
The research was done on chronic unpredictable stress (CUS) rats. It was found that CUS rats had decreased levels of Leptin than the control rats. Hence this led to the idea that this hormone might play a significant role in assuaging depression symptoms in man. These findings were reported in the online Proceedings of the National Academy of Sciences.
The researchers say that there is very limited source on the data related to assuaging depression in humans using Leptin. For example in two studies it was proved that reduced Leptin plasma levels were seen in depressed patient an increased levels were found in patients undergoing Leptin anti-depressant therapies.
The researchers say that their finding are very useful because currently anti-depressant therapies are not of much use to the people because many of them do not respond to it.
They said that rats are the best animal models and especially CUS rats do not eat sucrose solution, which can be compared to the inability of man to enjoy his life (depression).
CUS rats don't explore open space and give up easily in case of forced swimming test. It was found that they had lowered Leptin plasma levels and when retrained further for 30 minutes resulted in the further drop of Leptin levels. When these rats are injected with Leptin they have increased appetites for sucrose solution while the normal rats did no do so.
This study analyzed two sets of CUS rats one was administered Leptin (1mg/kg) other set was given Norpramin (desipramine), a medication used as an antidepressant in humans before the forced swimming test. It was found that 15mg/kg of Norpramin was comparable to 1.0 mg/kg of Leptin.
They also found that Intrahippocampal infusions of Leptin caused anti-depressant like effect in the forced swimming test. But on the other hand hypothalamus infusion of Leptin had no effect on forced swimming test. Then they came up with the notion that hippocampus is a brain is mediating Leptin's antidepressant-like activity.