Circadian regulation of melatonin in the retina of Xenopus laevis: limitation by serotonin availability. J Neurochem 1990 Feb;54(2):716-9
Date
02/01/1990Pubmed ID
2299362DOI
10.1111/j.1471-4159.1990.tb01932.xScopus ID
2-s2.0-0025019987 (requires institutional sign-in at Scopus site) 89 CitationsAbstract
Treatments expected to increase retinal serotonin levels were found to stimulate melatonin production by cultured eyecups from Xenopus laevis. The monoamine oxidase inhibitor pargyline (100 microM) caused a sixfold increase in melatonin release, and the serotonin precursor 5-hydroxy-L-tryptophan (100 microM) caused a 70-fold increase. Both acted synergistically with eserine, an inhibitor of melatonin deacetylation in the retina. The effect of 5-hydroxytryptophan was dose dependent, with effects increasing from 1 to 100 microM. Increasing the tryptophan level in the culture medium had no effect on melatonin release. These results indicate that the rate-limiting step in retinal melatonin synthesis is 5-hydroxylation of tryptophan. Melatonin released from individual eyecups in superfusion culture in constant darkness with and without added 5-hydroxy-L-tryptophan was monitored over a 5-day period. Control eyecups released low levels of melatonin, with circadian rhythmicity persisting for 1-3 days. With 5-hydroxy-L-tryptophan added, melatonin levels were elevated 10-20-fold at all times, and rhythmicity was apparent for as long as five cycles. This provides a model system for studies of the circadian clock in the eye.
Author List
Cahill GM, Besharse JCAuthor
Joseph C. Besharse PhD, MA Emeritus Professor in the Cell Biology Neurobiology and Anatomy department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
5-HydroxytryptophanAnimals
Biological Availability
Circadian Rhythm
Culture Techniques
Dose-Response Relationship, Drug
Melatonin
Pargyline
Radioimmunoassay
Retina
Serotonin
Tryptophan Hydroxylase
Xenopus laevis
