Technique: Parabiosis

This past week in my developmental biology class, I learned about this really cool method called "parabiosis" that scientists use to study physiology.

Parabiosis is a method that joins two animals together physically and vascularly (they are exchanging blood). This model is analogous to making Siamese twins. It allows for scientists to learn a lot about physiology.  
Berntson, Gary G., and John T. Cacioppo. Handbook of Neuroscience for the Behavioral Sciences. Hoboken, NJ: Wiley, 2009. Print.

Parabiosis was used most famously to study leptin. 
Coleman, D.L. A historical perspective on leptin. (2010). Nature Medicine, 16, 1097-1099. 
historical perspective on leptin

Using the parabiosis model, Dr. Douglas Coleman was able to predict the presence of leptin and its receptor, 25 years before they were cloned. Here is a summary of his experiment. This was taken from the article (figure 2) mentioned above.

Leptin is a lipostatic signal that is produced by the ob gene, and its receptor is produced by the db gene.

• In part A, a db/db animal is paired with a lean animal. The db/db animal is producing leptin, but not its receptor. From this we can conclude that the db/db animal is producing something (leptin) that is promoting a decreased in food intake and blood sugar. 

• In part B, a db/db animal is paired with an ob/ob animal. The ob/ob animal has leptin receptors, but is not producing leptin. From this we can conclude that leptin from the db/db animal is promoting a decreased in food intake, insulinemia, and blood sugar. 

Remember that the animals are joined by their circulatory system.

• In part C, an ob/ob animal is paired with a lean animal. The ob/ob animal has a decrease in food intake and blood sugar, while there isn't a change in the lean animal. The lean animal is able to make leptin.

• In part D, two lean animals are paired together. There isn't a noticeable change in their physiology.

Dr. Coleman and Dr. Friedman (the guy who cloned the ob and db genes 25 years after Dr. Coleman's studies) won a Lasker award for their research about leptin and its receptor. 
http://www.jci.org/articles/view/45094

Dr. Douglas Coleman  (http://www.maineahead.com/vantage-point%E2%80%93doug-coleman/)

Dr. Jeffrey Friedman (http://www.nature.com/nm/journal/v10/n2/images/nm0204-116-I1.jpg)