Ethanol and Knockouts… Mice, that is

One of the articles we focused on was a review on the signaling caused by ethanol (commonly known as alcohol). Ethanol has various cellular effects that result in dependence, preference, and seeking behaviors. One of the main pathways is where ethanol stimulates the synthesis of the second messenger cAMP through activating the enzyme adenylyl cyclase. Formation of cAMP is also reinforced by inhibiting ENT1, which leads to the accumulation of adenosine outside of the cell.
Another mechanism of ethanol reward reinforcement is the activation or inhibition of NMDA receptors. NMDA is a glutamate receptor that is important in the reward pathway. Ethanol binds to a complex, Fyn, that regulates NMDAR activity.Fyn dissociates from the receptor. NMDARs are also affected by a molecule called DARP-32, which when phosphorylated, keeps NMDARs active. DARP-32 receives a phosphate from an enzyme called PKA which is regulated by cAMP. With ethanol, there is more cAMP which increases the active DARP-32. These mechanisms encourage reward signaling.
Many pathways are characterized using knockout mice. Knockout can also refer to transgenic or genetically modified. A specific gene has been interrupted in mice (also yeast, bacteria, plants. . . just about anything), by a piece of DNA. The genetic expression of the mouse will be affected; hopefully the absence of a protein product will tell researchers what that gene is used to produce.
Knockout mice were used in many of the cited studies in the ethanol paper. For instance, mice without the ENT1 gene showed lower responses to ethanol. The ethanol didn’t affect them as much, indicating ethanol interacts with the ENT1 receptor. One important transgenic mouse was the Fyn kinase deficient mice. These guys (or girls) did not produce any Fyn product. The results showed that NMDA receptors were not phosphorylated. Based on this, the conclusion is that Fyn is the enzyme that acts on the NMDA receptor.
Transgenic organisms can be used to study gene sequences that are known but the function remains unknown. They are a useful tool for elucidating the signaling pathways, not only in the nervous system, but the rest of body as well. A drawback of transgenic mice is that there is a possibility the cells are somehow compensating for the lost gene product. The organism is a messy system, but taking it step-by-step, one knockout at a time, we may be able to figure out the mechanisms that drive life.