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Serotonin agonists mimic the phase shifting effects of light on the melatonin rhythm in rats.

Abstract：

:The effect of serotonin agonists on the rhythmic excretion of the melatonin metabolite 6-sulphatoxymelatonin was examined in rats. The animals were maintained in 12L:12D and administered saline, quipazine (10 mg/kg), (+/-)-2-propylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene hydrobromide (8-OH-DPAT, 5 mg/kg) or buspirone (10 mg/kg), 4 h after dark (ZT16). All three drugs caused an acute, transient suppression of 6-sulphatoxymelatonin excretion and a significant delay (P < 0.01) in the onset of the nocturnal rise on the following night of 2.1 +/- 0.6, 1.4 +/- 0.7 and 1.5 +/- 0.3 h respectively while saline administration had no effect (0.4 +/- 0.2 h delay, P > 0.01). To examine the effects of the time of day of agonist administration, groups of rats were treated with quipazine (10 mg/kg) or 8-OH-DPAT (5 mg/kg) 18, 24 or 30 h after the initiation of continuous darkness (CT6, CT12 or CT18) and monitored for a further two nights. Quipazine but not 8-OH-DPAT injection at CT6 resulted in a small but significant delay in the onset of 6-sulphatoxymelatonin excretion on the following night (1.0 +/- 0.2 h and 0.3 +/- 0.2 h) while treatment with both agonists at CT12 failed to affect the onset of excretion (0.8 +/- 0.2 and 0.1 +/- 0.2 h). When quipazine (10 mg/kg) was administered at CT18, 6-sulphatoxymelatonin excretion was acutely suppressed for the rest of the night and there was a large significant delay in the onset of 6-sulphatoxymelatonin excretion (1.2 +/- 0.2 h) while a smaller delay was observed following 8-OH-DPAT administration (0.8 +/- 0.2 h). The acute suppression of 6-sulphatoxymelatonin excretion and subsequent phase delay following quipazine treatment at CT18 was also evident at doses of 1 mg/kg (1.6 +/- 0.4 h) and 3 mg/kg (1.5 +/- 0.6 h). These results show that peripheral administration of serotonin agonists active at 5HT1a/5HT7 receptors mimic the dual effects of light on melatonin production in the rat and raise the possibility that serotonin pathways are more important in mediating the effects of retinally perceived light in the rat than previously believed.

journal_name

Brain Res

journal_title

Brain research

authors

Kennaway DJ,Rowe SA,Ferguson SA

doi

10.1016/0006-8993(96)00922-5

subject

Has Abstract

pub_date

1996-10-21 00:00:00

pages

301-7

issue

1-2

eissn

0006-8993

issn

1872-6240

pii

0006-8993(96)00922-5

journal_volume

737

pub_type

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Serotonin agonists mimic the phase shifting effects of light on the melatonin rhythm in rats.