Problem:

Researchers involved in clinical trials for a new anti-depressant drug, drug J, suspect that the drug may be having side effects and could be addictive. They decide to investigate the addictive properties of the drug in mice. Using a behavioral paradigm the researchers find that the drug causes dependence. They therefore compare the effects of drug J in wild-type mice with its effects in D2 dopamine receptor (D2R) knockout mice and find that D2R knockout mice are resistant and do not develop drug dependence.

Question 1: Describe the behavioral paradigm that can be used to test whether drug J is addictive.

Question 2: Why do they compare wild-type mice with D2R knockout mice?

Question 3: What can you conclude about the mechanisms of action of drug J?

Describe all the answers in detail.