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Tryptophan hydroxylase is expressed by photoreceptors in Xenopus laevis retina. Vis Neurosci 1995 Jul-Aug;12(4):663-70 PMID: 8527368

Pubmed ID



Serotonin has important roles, both as a neurotransmitter and as a precursor for melatonin synthesis. In the vertebrate retina, the role and the localization of serotonin have been controversial. Studies examining serotonin immunoreactivity and uptake of radiolabeled serotonin have localized serotonin to inner retinal neurons, particularly populations of amacrine cells, and have proposed that these cells are the sites of serotonin synthesis. However, other reports identify other cells, such as bipolars and photoreceptors, as serotonergic neurons. Tryptophan hydroxylase (TPH), the rate-limiting enzyme in the serotonin synthetic pathway, was recently cloned from Xenopus laevis retina, providing a specific probe for localization of serotonin synthesis. Here we demonstrate that the majority of retinal mRNA encoding TPH is present in photoreceptor cells in Xenopus laevis retina. These cells also contain TPH enzyme activity. Therefore, in addition to being the site of melatonin synthesis, the photoreceptor cells also synthesize serotonin, providing a supply of the substrate needed for the production of melatonin.

Author List

Green CB, Cahill GM, Besharse JC


Joseph C. Besharse PhD Director, Professor in the Ophthalmology and Visual Sciences department at Medical College of Wisconsin


2-s2.0-0029328558   35 Citations

MESH terms used to index this publication - Major topics in bold

DNA Probes
In Situ Hybridization
Microscopy, Confocal
Photoreceptor Cells
RNA, Messenger
Tryptophan Hydroxylase
Xenopus laevis
jenkins-FCD Prod-353 9ccd8489072cb19f5b9f808bb23ed672c582f41e