Bright artificial light produces subsensitivity to clonidine.

The authors used a thermoregulation paradigm to test the hypothesis that chronic treatment with bright artificial light produces subsensitivity to the hypothermic effects of clonidine, an alpha 2-agonist. One week of treatment produced blunting of the hypothermic response to clonidine (p less than 0.00001). These findings are consistent with previous reports that somatic treatments for depression produce subsensitivity of the alpha 2-receptor.