Effects of continuous exposure to light on behavioral dopaminergic supersensitivity

Background: This study examines the effects of long-term continuous exposur e to light on dopaminergic supersensitivity induced by repented treatment w ith haloperidol in rats, Methods: Spontaneous general activity in an open-field (SGA) and stereotype d behavior induced by apomorphine (SB-APO) or amphetamine (SB-AMP) were use d as experimental parameters. Rats were allocated to four groups in each ex periment: saline-treated animals kept under a 12-hour light/dark cycle (LD) or 24-hour light/light cycle (LL), and 2 mg/kg haloperidol-treated animals kept under the above cycles. Plasma corticosterone concentration was also measured by radioimunoassay in saline-treated mts kept under a LD or LL cyc le. Results: All the behavioral parameters used showed the development of centr al dopaminergic supersensitivity in rats kept under both cycles. Continuous exposure to light enhanced SGA and SB-AMP in both saline- and haloperidol- treated mts, but did not modify SB-APO. Animals kept under the LL cycle pre sented an increased plasma corticosterone concentration. Conclusions: Our results suggest that continuous exposure to light leads to an increase in dopaminergic function in both normal and "supersensitive" r ats. This effect seems to be mediated by a presynaptic mechanism possibly i nvolving corticosterone actions. (C) 1999 Society of Biological Psychiatry.