Chronic stress appears to block a gene that guards against brain atrophy associated with depression, according to a study in rats that may help guide new treatments for mood disorders.  The gene, called neuritin, appears to be responsible for keeping healthy neuron connections in certain parts of the brain, according to the study published in the Proceedings of the National Academy of Sciences.  Rats whose genes were suppressed were more anxious and depressed than those whose genes weren’t, an experiment found.  Further, activating the gene led to an antidepressant response.