Long photoperiod regimen may produce antidepressant actions in the male rat.

The exposure to bright light reverts the depressive symptoms of seasonally affective disorder. Rats received tricyclic antidepressants or were submitted to two photoperiod regimens. After treatments, the rats were forced to swim or were submitted to the differential reinforcement of the low-rate 72s schedule. Two animal models designed to testing the antidepressant effects of drugs. Clomipramine, desipramine or the long photoperiod decreased immobility in rats forced to swim. In the differential reinforcement of the low-rate 72s schedule, clomipramine, desipramine or the long photoperiod increased the reinforcers obtained by the rats. It is concluded that the long photoperiod regimen may produce antidepressant effects in male Wistar rats.