Dj. Kennaway et al., Serotonin, excitatory amino acids and the photic control of melatonin rhythms and SCN c-FOS in the rat, BRAIN RES, 897(1-2), 2001, pp. 36-43
There is a growing acceptance that serotonergic pathways to the suprachiasm
atic nucleus play an important role in the mediation and modulation of ligh
t entrainment of rhythms. In this study administration of the 5-HT2A/2C ago
nist (+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane (DOI, 0.5 mg/kg) a
t mid dark caused a phase shift in the onset of the urinary excretion of 6-
sulphatoxymelatonin in rats that was sustained for at least 8 days and was
blocked by the specific 5-HT2C antagonist SB-242084. Administration of DOI
(2 mg/kg) across the night resulted in the appearance of c-FOS in the nucle
us of cells in the suprachiasmatic nucleus during subjective darkness, but
did not cause induction at the time of expected lights on (CT0). By contras
t light exposure induced c-fos throughout the night including CT0. Administ
ration of the NMDA receptor antagonist MR-801 (3 mg/kg) prior to light puls
es had no effect on c-fos in the first part of the night, but towards the e
xpected time of lights on, became progressively more potent, such that by C
T0, light induction of c-fos was almost completely inhibited. These results
provide further evidence that serotonin plays a role in the mediation of l
ight effects on rhythms in the rat. (C) 2001 Elsevier Science B.V. All righ
ts reserved.