Scientists working with rats have found that animals who have a salt deficiency appear to shy away from activities they normally enjoy. The investigators say this finding suggests that a salt deficit--and the craving associated with it--can induce one of the key symptoms associated with depression. Experts say the idea that salt is a natural mood-elevating substance could help explain why humans are so tempted to over-ingest it, even though it's known to contribute to high blood pressure, heart...