Speculation

• Parts of genes, known as alleles, may be responsible for depression. Not much is known about how these genes work, so mice are being genetically altered to contain the alleles thought to play a role in depression.
  
  

Result

• The most promising strain of mice is those without the gene nicknamed TREK-1 in Nice, France. TREK-1 makes a protein that is thought to interfere with normal brain chemistry. Altered brain chemistry has been linked to depression.
  
  

Test

• Mice are tested for depression by being made to swim. The theory is that depressed mice soon quit swimming while "happy" mice keep on swimming.