Dopamine-₃ receptor modulates intraocular pressure: implications for glaucoma.

The aim of the present study was to investigate the role of D₃ receptor on intraocular pressure regulation using WT and KO D₃R⁻/⁻ mice. Both mice were used with normal eye pressure or steroid-induced ocular hypertension. As measured by tonometry, the topical application of 7-OH-DPAT, a dopamine D₃-preferring receptor agonist, significantly decreased, in a dose-dependent manner, the intraocular pressure in WT mice both in an ocular normotensive group and an ocular hypertensive group. Pretreatment with U-99194A, a D₃ receptor antagonist, reverted 7-OH-DPAT induced ocular hypotension in WT mice. No change of intraocular pressure was observed after topical application of 7-OH-DPAT in KO D₃R⁻/⁻ mice. PCR analysis demonstrated the presence of all dopamine receptor genes in eye tissues obtained from WT mice, and the lack of D₃R mRNAs in KO mice. The present study identified the D₃R subtype as the most important receptor of the dopaminergic system to modulate intraocular pressure with relevant implications for glaucoma that represents one of the most crippling optic neuropathies.