Can both be treated by anti-depressants or is the depression caused by hypothyroidism treated by an adjustment to thyroid medication. I'm curious about the connection.

Usually they will adjust the thyroid medication. There's a difference in what part of the brain passages are affected, and the majopr difference is cause– clinical depression is caused by an imbalance of dopamine in the brain, thyroid depression may also involve imbalance of dopamine but the imbalance is caused by the thyroid condition.