LOCALIZATION OF 5-HYDROXYTRYPTAMINE(1A) AND 5-HYDROXYTRYPTAMINE(7) RECEPTORS IN RABBIT OCULAR AND BRAIN-TISSUES

Serotonin is thought to play a physiological role in various tissues o f the rabbit eye, yet little is known about the relative distribution of the different serotonin receptors. Demonstration of the receptor su btypes present in the various ocular tissues is essential in order to understand the function of serotonin in the eye. Using a combination o f in situ hybridization histochemistry, in vitro receptor autoradiogra phy and polymerase chain reaction studies, rye have explored the distr ibution of the 5-hydroxytryptamine(1A) and 5-hydroxytryptamine(7) rece ptors in the rabbit eye. As these receptors have not been sequenced in the rabbit, we initially established the suitability of the oligonucl eotide probes by analysis of brain tissue. The distributions of 5-hydr osytryptamine(1A) and 5-hydroxytryptamine(7) receptor messenger RNAs i n rabbit brain correlated well with those in other species, confirming the specificity of the probes for detection of the messenger RNAs in rabbit tissues. In the eye, the expression of 5-hydroxytryptamine(1A) receptors arrears to be restricted to the epithelial cell layer of the ciliary processes, although very low levels may appear in the retina. In contrast, the expression of 5-hydroxytryptamine(7) receptor messen ger RNA is more widespread with positive signals evident in the ciliar y processes, retina and iris. The results confirm the existence of 5-h ydroxytryptamine(1A) receptors in the ciliary body and their localizat ion in the ciliary epithelium supports the hypothesis that they are in volved in the secretion of aqueous humour. Unexpectedly, there was lit tle evidence to support the idea that 5-hydroxytryptamine(1A) receptor s are present in the retina and iris sphincter. However, the subsequen t finding of 5-hydroxytryptamine(7) receptor messenger RNA in the reti na and iris may explain the apparent absence of 5-hydroxytryptamine(1A ) receptors in these tissues. The presence of both 5-hydroxytryptamine (1A) and 5-hydroxytryptamine(7) receptors in the ciliary processes may account for the complex intraocular pressure response of the rabbit t o seratonin. (C) 1998 IBRO. Published by Elsevier Science Ltd.