Purpose: To determine the relative density and tissue localization of mRNAs for serotonin (5-hydroxytryptamine; 5HT) receptor subtypes in human ocular tissues and correlate with their possible functions in the eye.
Methods: Total RNA was extracted from human ocular tissues samples from multiple donors and transcribed into cDNA. An optimized reverse transcriptase polymerase chain reaction (RT-PCR) procedure was then used to amplify the signals using primers designed against human 5HT receptor cDNAs. The PCR products were analyzed by gel electrophoresis and confirmed by endonuclease digestion.
Results: Variable amounts of total RNA were extracted from different tissues with the least amount from ciliary epithelium and most amount from retina. 5HT2 receptor subtype mRNAs were the most abundant with 5HT2A and 5HT2B being the most predominant in the retina, ciliary body, ciliary epithelium, choroid, conjunctiva, and iris. Ciliary body, choroid, and conjunctiva were most enriched in 5HT3 receptor mRNA, with relatively lower levels in the iris. 5HT4 receptor mRNA was most enriched in the retina, ciliary body, choroid, conjunctiva, and somewhat detectable in the iris. 5HT5 receptor mRNA was abundant in the retina, ciliary body, and iris. 5HT6 receptor mRNA was the least abundant of all subtypes studied and could only be detected in the iris. 5HT7 receptor mRNA was enriched in the ciliary body, choroid, conjunctiva, and iris, with much lower levels in the retina and ciliary epithelium. Optic nerve tissue of 1-2 donors exhibited the presence of 5HT2B, 5HT5, and 5HT7 receptor mRNAs. Data for human trabecular meshwork cells indicated a high density of mRNAs for 5HT2A and 5HT2B, with much lower levels of 5HT2C, 5HT5, and 5HT7 receptor mRNAs.
Conclusions: Human ocular tissues differentially expressed mRNAs for the various 5HT receptor subtypes. These studies suggest a diverse range of possible physiological and pharmacological functions of 5HT receptors in these human ocular tissues.