Localization of 5-hydroxytryptamine1A and 5-hydroxytryptamine7 receptors in rabbit ocular and brain tissues

Serotonin is thought to play a physiological role in various tissues of the rabbit eye, yet little is known about the relative distribution of the different serotonin receptors. Demonstration of the receptor subtypes present in the various ocular tissues is essential in order to understand the function of serotonin in the eye. Using a combination of in situ hybridization histochemistry, in vitro receptor autoradiography and polymerase chain reaction studies, rye have explored the distribution of the 5-hydroxytryptamine(1A) and 5-hydroxytryptamine(7) receptors in the rabbit eye. As these receptors have not been sequenced in the rabbit, we initially established the suitability of the oligonucleotide probes by analysis of brain tissue. The distributions of 5-hydrosytryptamine(1A) and 5-hydroxytryptamine(7) receptor messenger RNAs in 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 messenger RNA is more widespread with positive signals evident in the ciliary processes, retina and iris. The results confirm the existence of 5-hydroxytryptamine(1A) receptors in the ciliary body and their localization in the ciliary epithelium supports the hypothesis that they are involved in the secretion of aqueous humour. Unexpectedly, there was little evidence to support the idea that 5-hydroxytryptamine(1A) receptors are present in the retina and iris sphincter. However, the subsequent finding of 5-hydroxytryptamine(7) receptor messenger RNA in the retina 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 to seratonin. (C) 1998 IBRO. Published by Elsevier Science Ltd.