Effects of continuous exposure to light on behavioral dopaminergic supersensitivity.
BACKGROUND
This study examines the effects of long-term continuous exposure to light on dopaminergic supersensitivity induced by repeated treatment with haloperidol in rats.


METHODS
Spontaneous general activity in an open-field (SGA) and stereotyped behavior induced by apomorphine (SB-APO) or amphetamine (SB-AMP) were used as experimental parameters. Rats were allocated to four groups in each experiment: 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 radioimmunoassay in saline-treated rats kept under a LD or LL cycle.


RESULTS
All the behavioral parameters used showed the development of central dopaminergic supersensitivity in rats kept under both cycles. Continuous exposure to light enhanced SGA and SB-AMP in both saline- and haloperidol-treated rats, but did not modify SB-APO. Animals kept under the LL cycle presented 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" rats. This effect seems to be mediated by a presynaptic mechanism possibly involving corticosterone actions.
Abílio
V C
VC
Departamento de Farmacologia, Escola Paulista de Medicina/UNIFESP, Săo Paulo, Brazil.
Freitas
F M
FM
Dolnikoff
M S
MS
Castrucci
A M
AM
Frussa-Filho
R
R
D000818:Animals; D014150:Antipsychotic Agents / Q000009:adverse effects*; D001058:Apomorphine / Q000009:adverse effects*; D001522:Behavior, Animal / Q000187:drug effects; D003345:Corticosterone / Q000097:blood / Q000378:metabolism; D003913:Dextroamphetamine / Q000009:adverse effects*; D015259:Dopamine Agents / Q000009:adverse effects*; D018491:Dopamine Agonists / Q000009:adverse effects*; D004342:Drug Hypersensitivity / Q000209:etiology*; D006220:Haloperidol / Q000009:adverse effects*; D008027:Light / Q000009:adverse effects*; D008124:Locomotion / Q000187:drug effects; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017661:Receptors, Presynaptic / Q000378:metabolism; D019956:Stereotypic Movement Disorder / Q000139:chemically induced*; D013997:Time Factors
D014150:Antipsychotic Agents; D015259:Dopamine Agents; D018491:Dopamine Agonists; D017661:Receptors, Presynaptic; D006220:Haloperidol; D001058:Apomorphine; D003913:Dextroamphetamine; D003345:Corticosterone